RU2423534C2 - Procedure for leaching valuable metals out of ore at presence of hydrochloric acid - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: procedure consists in following stages: ore leaching at presence of hydrochloric acid with production of soluble metal chloride in solution for leaching, addition of sulphuric acid into solution for leaching, extraction of metal sulphate from solution for leaching and regeneration of hydrochloric acid. As ore there is used oxide ore of non-ferrous metal, such as oxide zinc ore, laterite nickel ore such as saprolite or limonite, sulphide ore or titanium ore. Valuable metal is chosen from group including Zn, Cu, Ti, Al, Cr, Ni, Co, Mn, Fe, Pb, Na, K, Ca, metals of platinum group and gold. Valuable metal or less valuable metal, such as magnesium, can be metal in composition of metal sulphite. Regenerated hydrochloric acid is directed into re-circulation system into process of leaching. ^ EFFECT: raised efficiency of procedure. ^ 40 cl, 36 dwg, 5 tbl

Description

BACKGROUND OF THE INVENTION

The present invention relates to a method for treating a salt solution of chloride in which the accumulation or regeneration of hydrochloric acid occurs, and to a method for leaching metals from an ore with a chloride solution. The method is an economical and environmentally acceptable hydrometallurgical process for the extraction of valuable metals from ores or concentrates.

It is known to use relatively concentrated saline chloride solutions as a medium for leaching base metals, one of the latest options includes the Outokumpu method for the hydraulic extraction of copper, described in a number of patents, such as WO 2003/35916, WP 2003/89675 and others. It is known that chloride salt high ionic strength solutions generally provide faster and more complete leaching compared to conventional relatively dilute sulfate media. However, recovering dissolved valuable materials from such saline solutions is a laborious process and excludes standard electrolytic treatment.

For many years, studies in many institutions have focused on the use of hydrochloric acid (chloride medium) for leaching nickel from lateritic ores. First of all, mention should be made of work in this area carried out at the University. NMRice of Leeds University (see Rice, 1989). When processing both types of ore, typical silicate (serpentine) and oxide ore (limonite or lake ore), optimal kinetic parameters were observed, which testified to the possibility of using this system for leaching valuable metals, such as nickel, from a number of laterite materials .. Of particular interest is the fast kinetics (1 h) of leaching at high temperature, usually more than 80 ° C, in a 4 M hydrochloric acid solution. conceptual design (Rice and Strong, 1974) using hydrochloric acid leaching to solubilize the valuable cobalt and nickel, which were then removed by solvent extraction followed by hydrolysis and obtained as nickel hydroxide (using magnesia as a neutralizing agent), respectively. impurities such as iron and magnesium. Iron chloride is removed from the solution by extraction with a solvent and treatment in a spray firing step, whereby stable hematite and regenerated hydrochloric acid which is directed to a recirculation system in the leaching step. Similarly, magnesium chloride is treated at the spray firing stage, whereby magnesia is formed (which is used as a commercial by-product and / or used as a neutralizing agent) and hydrochloric acid is regenerated (it is returned to the recirculation system to the leaching stage).

It has been estimated that approximately 70% of the world's natural reserves of nickel are found in laterite ore. Currently, only approximately 40% of nickel produced in industry is extracted from laterite ores, and it is estimated that by 2012 this value will increase to approximately 50% (calculated by Dalvi et al., 2004). Thus, there is currently a need to develop a new process for the extraction of nickel and cobalt from laterite deposits, which are characterized by significantly lower operational characteristics and, above all, lower capital costs compared to modern technologies. Moreover, taking into account future reserves and an increase in demand for nickel by approximately 4% (depending on various factors), the need for nickel production will be 40,000-45,000 tons per year of nickel produced in the industry in order to satisfy needs (estimates by Dalvi et al. , 2004). Even if you use the additional development of new sources (stocks) of small sulfide deposits, major projects involving new ways of developing laterites (such as Goro and Ravensthrope high pressure acid leaching projects, new foundry furnaces such as Koniambo furnaces, and new hydrometallurgical sulfide methods processing, such as the Voisey's Bay method), all of these methods will not be able to satisfy needs.

Geology and Mineralogy

The cost-effectiveness of laterite processing largely depends on the quality and composition of the ore being processed. Lateritic nickel deposits include two main layers (horizons), i.e. limonite (hydrated iron oxides) surface material (low nickel and magnesium, high iron) and a deeper saprolite (magnesium hydrosilicate) material (high nickel and magnesium, low iron content). These strata are formed during erosion of the original rock, which in turn is formed from crystallized molten rock in the form of Fe-Mg-Si-O minerals. The initial rock contains Ni (~ 0 <2%) and Co, since these metals can replace Fe and Mg (the same valency and radius of ions) in the crystal lattice of these silicates. Primary serpentine minerals, Mg ₃ (Si ₂ O ₅ ) (OH) ₄ , are formed from the parent rock during serpentinization at elevated temperature and pressure (in the presence of water under the surface of the earth). This process leads to the natural enrichment of nickel (<0.5% Ni). Magnetite is also formed as a joint product in the indicated process of serpentinization, which, in addition to some initial rocks (such as olivine), is the main source of Fe during erosion. Lateritization occurs if primary serpentine (the content of which depends on the degree of serpentization) and associated residues of the original rock (primarily minerals such as olivine) undergo prolonged erosion, especially in humid tropical regions (the so-called lateritization process) on the surface of the earth or in nearby layers. In the process of lateritization, Ni and Co are concentrated 3–30 times in comparison with the initial rock. The lateritization process is dynamic, and the deep section is basically a snapshot, with the relatively recently changed rock located in the lowest layer, that is, surface water (acidified by dissolving CO ₂ and organic acids) dissolves and leaches Ni, Mg, Si, Fe (in the form of Fe ²⁺ ) and Al (to reduce mobility) as water seeps through a deep section. In the surface layers, iron is rapidly oxidized and precipitated in the form of amorphous iron (III) hydroxide, while Ni (usually 1.5% Ni) and almost all of Co are adsorbed into this structure:

* - This process is a nonequilibrium reaction, which indicates the complexity of the deposition process in nature. Fe ^{2+ is} leached and dissolved under oxidizing conditions from both types of iron oxides, such as magnetite, maghemite, etc., and Mg (Fe) silicates, such as olivine and orthopyroxene. The newly formed solid (indicated on the right) most likely includes precipitated iron hydroxide (Fe (OH) ₃ ) in the form of an intermediate phase.

Over time, the crystallinity of the material improves and the first form of goethite forms (the main component of oxide deposits) and gradually turns (from the upper layers to the lower) into the most stable natural form, that is, into hematite. Ni and Co cannot accumulate in the hematite crystal lattice in a humid oxidizing Ni-lateritic environment, and its quality decreases and the upper crust forms, the so-called ferricret (the layer that is first removed during the development of lateritic deposits). It is important to note that Ni and, above all, Co are also largely adsorbed by the minerals of Mn oxides / hydroxides (mainly formed in the form of veins or surface deposits on other minerals). The Goro field in New Caledonia and the Moa Bay field in Cuba are examples of sediments that mainly include this type of limonite zone in depth.

Many limonite deposits are formed when excess free silicon (in the composition of the initial rock) is re-deposited after it is leached from the Mg-silicate structure (serpentine, olivine, etc.) in the form of microcrystalline chalcedony quartz. Typically, these processes occur due to changes in Eh and / or pH in a deep section. Microcrystalline chalcedony quartz in most cases is recrystallized into a more crystalline phase of quartz, with the formation of free individual particles of quartz from small to large (examples of ores of this type are Ravensthorpe and Jacare silicate deposits, i.e. ores of this type are enriched using physical removal of large particles of quartz).

Under milder conditions of erosion, for example, in a drier or colder climate, or in conditions of limited groundwater movement (poor drainage), the degree of leaching decreases, and magnesium is mainly leached from the crystalline structure of serpentine and olivine. As a result, there is a simultaneous enrichment of other less mobile components of minerals, for example Fe and Si, which leads to the conversion of primary serpentine and olivine into smectic clays. Fe ^{2+ is} also less mobile than Mg ²⁺ and thus replaces Mg in the crystal structure of the newly formed smectic clay. Thus, these Mg, Fe clays vary in composition from magnesium-enriched sepiolites to iron-enriched nontronites. Clay deposits (if present) are usually located between the limonite and saprolite zones. Minerals of smectic clay also fix Ni (more than 1.5% Ni) in the crystal lattice, where nickel replaces Fe ²⁺ and Mg ^{2+ ions} in the interlayer positions. The formation of smectic clay requires access to silicon, which is present as inclusions of microcrystalline chalcedony quartz in clay. An example of such a field is Murrin deposits, which contain intermittent smectic zones in a deep section.

Regardless of the presence or absence of a smectic clay layer, residual Ni, Mg, Fe, and Si pass into solution. As the groundwater level decreases, their pH increases due to reactions with un-weathering rocky soil. Near the laterite mainland rock with a modified interface, hydrated Mg-silicate minerals (known as garnierites) are enriched with nickel (more than 20% Ni). Nickel is re-precipitated at a more alkaline pH compared to magnesium, which results in nickel enrichment of Mg silicates, resulting in the formation of so-called garnierites (nickel enriched hydrated Mg silicates). Garnierites are most common in tectonically active formations, such as New Caledonia, and are less common in cratonic regions, such as Brazil or Western Australia. The nickel content in the original rock (soil) largely determines the nickel content in the formed laterite ores. Between the mainland soil or the layer of garnierite (if present) and the layer of limonite or clay (if present) there is a transition zone containing a significantly altered magnesium-silicate material called the saprolite zone, i.e. containing phyllosilicate group minerals that are formed from primary serpentine and source rock. During erosion of a non-serpentinized source rock, microcrystalline chalcedony quartz can also form, which lies in the most permeable geological structures, such as zones of transverse shear, faults, veins and cracks. Over time, Fe and, above all, Ni (usually 2-3% Ni) replace Mg with the formation of secondary “altered” serpentines. For example,

To shift the reaction equilibrium to the right, it is necessary that the nickel concentration in the penetrating groundwater is not much higher than in the solid phase.

Nickel begins to replace magnesium, preferably in areas of weaker bonds in the structure of the serpentine, that is, in the position of OH bonds of the tetrahedral structure (the so-called layer of brucite).

And finally, as a result of uneven erosion (in the context) of the laterite horizon, as well as due to uneven development, individual ore samples, for example saprolite, may contain different amounts of other ores, for example limonite and / or clay. Thus, ore as a raw material is characterized by an extremely variable mineralogical composition and the processing characteristics associated with it.

The main sources of lateritic nickel worldwide contain limonite type ores and, to a lesser extent, saprolite type ores (Monhemius, 1987 and Elias, 2002).

Existing processes

It should again be noted that in the processing of high-quality nickel ore, the most appropriate is the cost-effectiveness of any process used. If possible, enrichment is an important stage of processing. Unfortunately, both types of ores, limonite and saprolite, are difficult to enrich, since Ni is homogeneously mixed with goethite and magnesium silicate minerals, respectively. There is a certain possibility of enrichment, but only if large barren material is present. Screening of such a large material is possible only if it is characterized by a low content of Ni, such as coarse quartz, magnesite (MgCO ₃ ) and magnesium silicate, etc.

The melting process (figure 1)

Figure 1 shows a diagram of the processing of saprolite by melting. The ore contains 20-50% free water and in the first stage it is removed by drying. The ore is then calcined to remove structured water, followed by reduction of Ni and Fe to metals in a furnace mixed with coke or coal. Mg, Si, etc. form slag, which allows you to remove molten liquid alloy Ni-Fe. Then refining (remelting) is required to remove residual S, C and Si: when lime is added, it forms CaS slag, and when oxidized with air, C is converted into gaseous CO and Si to oxide slag. If ferro-nickel is obtained, a small amount of Fe is oxidized to slag, since ferro-nickel is used for the production of stainless steel. When using the matte production method, the addition of S to the kiln under reducing conditions is required. In this case, interaction with metallic Ni occurs and (undesirable) interaction with Fe with the formation of sulfides. The specified material is then melted, while the oxides form the slag, and the sulfides form the matte. Finally, air is blown through the converter to oxidize the bulk Fe to slag.

Features of the method:

- the melting point of the slag depends on SiO ₂ / MgO and FeO;

- and ore variability in composition must be averaged to ensure the indicated quality of the target raw material (development and averaging of ore increase costs);

- economic marginal quality indicators of ore raw materials for brown field projects (brownfield - reconstruction of old enterprises) with low cost are approximately 1.7% Ni, and for brown field projects with high cost - approximately 2.1% Ni (Dalvi et al., 2004), that is, the process limits the performance of materials that can be used as target ore;

- the disadvantages of the melting process include high capital investment and energy costs, therefore, the efficiency of the process largely depends on regional energy prices;

- although Ni recovery is sufficiently high (~ 90%), the yield of Co as a by-product is either too small or completely absent, firstly, due to the low content of Co in saprolite ores and, secondly, due to low extraction (~ 50 %) (Dalvi et al., 2004).

Karon process (figure 2)

First, the ore is dried in a rotary kiln and calcined under reducing conditions (usually, fuel oil is used as a reducing agent). Ni and Co are selectively reduced at about 700 ° C. to metals (approximately 10% Fe is partially reduced). If the content of silicates in the feed is increased (due to the processing of more saprolite ore), then forsterite (amorphous Mg-silicate) recrystallizes (which is difficult to recover at 700 ° C) and Ni is captured, i.e., nickel does not leaching. Similarly, higher reduction temperatures and excessive reduction lead to an increased possibility of the formation of a refractory phase (during leaching in the ammonia-ammonium carbonate system), i.e., the process reduces to kinetics depending on the extraction of Ni and Co. After cooling, the alloy is leached in an atmosphere of air under oxidizing conditions (air) in a solution of ammonia-ammonium carbonate (pH ~ 10). Leached Ni (Co) and Fe form extremely strong amino complexes in solution. The iron (II) ion is oxidized to iron (III) and is hydrolyzed in the form of gelatinized iron hydroxide (Co is precipitated together with iron hydroxide, and a significant part is not reduced). After separation of the liquid-solid system, a certain amount of Ni and all Co are precipitated as sulfides in the presence of gaseous H ₂ S (Co is less soluble compared to Ni, but due to the high Ni: Co ratio, partial precipitation of Ni occurs). The Ni solution (not containing Co) is then evaporated with steam, whereby basic Ni carbonate (solid phase) and CO ₂ and ammonia are formed in the gaseous phase. CO ₂ and ammonia are regenerated for reuse upon absorption with water to form an ammonia-ammonium carbonate solution. The nickel carbonate cake is either used as a commercial product or is further processed using a variety of finishing methods to extract Ni from carbonates or from solution. Ni and Co are regenerated by solvent extraction, or the basic carbonate is calcined in a rotary kiln to form NiO (low purity product). In another embodiment, the cake is redissolved in a solution of ammonium sulfate to form nickel-ammonium sulfate, which is then reduced to metallic nickel in the presence of hydrogen gas (see Monhemius, 1987).

Process Features:

- although this method can be used to process a larger number of certain types of saprolites (compared with the acid leaching method at high pressure), an increased content of Mg and a silicate form increases the amount of forsterite, which leads to an increase in nickel losses

- although the main amount of reagents (ammonia and CO ₂ ) enters the recirculation system of the process, significant losses are observed (primarily due to leaching of magnesium, that is, the formation of Mg-ammonium carbonate), in addition, auxiliary reagents are required to obtain a product with a relatively high degree of purification;

- more than 60% of the total energy consumed is used in the preliminary stages of the process (drying of wet ore and reduction firing), while hydrometallurgical methods are again used at the final processing stages, that is, the process is extremely inefficient from an energy point of view;

- filtration is ineffective due to the jelly-like nature of precipitated iron hydroxide;

- low extraction yield for both processes: pyrometallurgical (formation of forsterite) and hydrometallurgical (co-precipitation of Co and blocking of leached particles due to Fe deposition) processes, the total yield of Ni is approximately 75% and Co 50%.

It should not be expected that this technology can be used to develop new projects due to the low extraction of valuable metals and the use of low quality raw materials (preferably limonite ores), in addition, these processes require high energy and reagent costs (see Dalvi and others. , 2004).

The process of acid leaching at high pressure (HPAL) (figure 3)

In metallurgy, the HPAL process is considered relatively simple, in the first stage decomposition is used at a high temperature of more than 245 ° C. The resulting suspension is neutralized with lime and decanted in countercurrent, then impurities are removed and Ni and Co are precipitated as sulfides (H ₂ S) or hydroxides (lime), or Ni and Co are directly extracted with solvent extraction (Goro scheme). Optional further purification and separation include re-dissolving (if solid is obtained by precipitation) and purification using solvent extraction or selective precipitation. Finally, the metal is regenerated by electrolysis or reduction with hydrogen, or nickel oxide is obtained using pyrohydrolysis (chlorides are used as SX or IX, unlike chlorides for the leaching process).

Features of the process:

- this method can be used for a larger number of ore types compared to the melting method due to the inclusion of the limonite method (the reserves of limonite ore are twice the reserves of saprolite ore), but the process largely depends on the content of total acid absorbers, that is, Al (from clay) and primarily Mg (<4%);

- high corrosion, especially if chlorides (salts in water) are present, corrosion resistance can be improved by using high quality Ti alloys, which leads to an increase in the cost of the process;

- high investment due to the use of pressure equipment and related structural materials;

- the cost of reagents is extremely high due to acid scavengers (Mg, Al) and the need to maintain the acid level (due to the formation of bisulfates), as well as the need to neutralize with lime (usually the addition of 250-400 kg / t of acid, where the lower limit is for the processing of limonite ore with a low Mg content);

- problems when using autoclaves in connection with the formation of scale, which leads to equipment downtime, especially when processing raw materials with a high content of Mg and Al.

Calculations (Dalvi et al., 2004) showed that the cost-effectiveness of the HPAL method is largely dependent on the quality of the raw materials, i.e., the estimated lower quality limit of raw materials for new projects is 1.3% Ni, excluding compensation due to average acid consumption (see .Ambatory project in Madagascar) or when using the nearest sources of cheap acid (for example, the sulfide melting stage).

Figure 4 illustrates the inefficiency of the HPAL process, taking into account the reagents used. It has been established that the main reason for the consumption of acid is Mg, and this disadvantage can be eliminated only by processing ore materials with a low Mg content (limonite type ore). In addition, approximately half the cost is associated with the need to replenish the level of reagents (to compensate for the formation of bisulfates at a given temperature), which are not actually used for leaching. An “additional” acid is also required to be added to neutralize after pressure leaching. The higher the density of the pulp (suspension), the less the cost of reagents affects the absolute cost (cost / pounds of Ni). However, there is a limit to the maximum pulp density due to viscosity restrictions.

Sulphate Alternative Processes

Currently, there is a tendency in industry to develop and design effective methods for atmospheric leaching (ALP), primarily in connection with reduced capital investments, as well as for the processing of both limanites and saprolites. Typically, limonite ore is leached at a high residual acid concentration, while saprolite ore (with a higher ability to neutralize) is then used to neutralize the residual acid and acid formed during the hydrolysis of Fe. The combination of HPAL and ALP processes was used to develop the so-called High Pressure Acid Leach (EPAL) process, which is currently used in the Ravensthorpe project in Western Australia. Process diagrams of ALP and EPAL are shown in FIG. 5.

The essence of the processes presented in figure 5, was patented by the company AMAX in 1970. In the AMAX method, firing is also proposed for partial reduction of saprolite ore, that is, to increase its ability to neutralize, and partial recovery of Ni occurs. In the process described in FIG. 5, it is possible to use recirculation of any unleached nickel from the residue (from which the bulk of Mg has already been removed) to the HPAL process (Monhemius, 1987).

Features of the process:

- atmospheric leaching is characterized by low kinetics, which, however, can be largely offset by low investment, that is, due to the relatively cheap processing time (compared to the HPAL process);

- even if the atmospheric leaching system is effective in removing Fe (in the process of neutralization / hydrolysis of saprolite), significant acid losses due to excessive leaching of Mg are still observed (however, these costs can be partially offset by the additional energy obtained from additional sulfur burning, and also due to additional income from the sale of nickel);

- The EPAL process is characterized by greater energy consumption and greater investment compared to the HPAL process;

- when using an atmospheric sulfate process with an open system, significant problems arise in the utilization of MgSO ₄ , primarily in connection with the ever-increasing restrictions on environmental protection (primarily when processing ore materials with a high Mg content).

In general, the EPAL process is characterized by minimal risk, since at the HPAL stage a high yield of Ni and Co extraction is provided, and at the same time, stable Fe residues are formed. The acid leach stage is characterized by minimal requirements for neutralization and at the same time, additional nickel recovery is provided. However, the main disadvantages of this method are the high investment and the problem with Mg. When using the acid leaching process in full in a sulfate medium, extremely aggressive (strong acid) leaching conditions are required to ensure a high yield of Ni and Co extraction. Such conditions, in turn, cause significant limitations for neutralization during the processing of saprolite material, which leads to significant losses of sulfates due to magnesium in solution and, possibly, in the form of jarosite in the residue. High consumption of reagents (if there are no available sources of cheap reagents) and environmental restrictions minimize the efficiency of the process. For this reason, alternative methods have been developed to solve problems with Mg. In one of these methods proposed by American Climax Inc. (previous name of the company AMAX), crystallization is used without evaporation in an autoclave at 190-250 ° С for precipitation of sulfates in the form of monohydrates. Since this process requires the use of an additional and expensive autoclave, the SURAL process was proposed (Sulzer, Switzerland, Schulz regeneration with acid leaching), which uses evaporation crystallization to obtain epsomite (MgSO ₄ · 7H ₂ O). Said sulfate is then thermally decomposed to form SO ₂ (which is converted to sulfuric acid in the acid plant and sent to the HPAL process recirculation system) and a neutralizing agent, magnesia (MgO), which is sent to the process recirculation system (see Monhemius, 1987 ) The recently patented Skye Resources atmospheric acid leach process is nearly identical to the SURAL process except that the primary leach stage is also atmospheric. In addition, the Skye process is characterized by a less hydrated form of magnesium sulfate, i.e., magnesium sulfate with two to three molecules of hydrated water is formed after the evaporation crystallization step (see Hatch Feasibility Study, 2005). SURAL / Skye processes are shown in FIG. 6.

Process Features:

- the replacement of reagent costs with energy / fuel costs is effective or ineffective depending on the region;

- crystallization of magnesium sulfate from a pure sulfate solution during evaporation requires significant energy consumption (high energy consumption during evaporation), which exceed the amount of energy to maintain a normal water balance (which is of particular importance when increasing the quality requirements of primary ore raw materials).

New Chloride Process Proposals

The atmospheric chloride-acid leach process is shown in FIG. 6 (the so-called Jaguar process, developed by Canadian nickel exploration and development company Jaguar Nickel Inc.). This process involves the step of atmospheric leaching in a hydrochloric acid solution containing a high initial level of MgCl ₂ . It is assumed that proton activity increases significantly with increasing concentration of magnesium chloride in the initial solution (studies of the HCl-MgCl ₂ -H ₂ O system are described in the article by Bates et al., (1970), as well as in the article by Jansz (1983)). Leaching can be carried out in two stages, in the first stage, Ni and Co are leached into the solution, and in the second stage, the removal of Fe is controlled. It is believed that an additional advantage of Fe hydrolysis from saline is the low activity of water in saline solutions, which leads to an acceleration of the dehydration reaction. In principle, hematite can form at atmospheric temperature; otherwise (a pure sulfate system), the use of an autoclave operated at a significantly higher temperature is required. After extraction of the valuable metals, the solution is evaporated to ensure water balance, and the resulting saline solution of magnesium chloride enters the recirculation system at the leaching stage. The discharge (from the evaporator) liquid stream is subjected to pyrohydrolysis (see the reaction in Fig. 7) and magnesium is obtained (which is partially sent to the recirculation system as an internal neutralizing agent) and gaseous HCl. HCl is then condensed and sent to a recirculation system in an atmospheric leach reactor.

The concept of a system for salt leaching of laterite ore and regeneration of the main amount of acid using pyrohydrolysis of magnesium chloride was first proposed by Rice and Strong (Rice and Strong, 1974), who proposed using solvent extraction to remove FeCl ₃ from the system, then a spray annealing step to form stable hematite and for the regeneration of an equivalent amount of hydrochloric acid. The Jaguar process is claimed to include an economical approach for treating iron impurities. The method is carried out at a high initial salt concentration (MgCl ₂ solution), which allows the hydrolysis of iron with controlled acidity at 80-105 ° C. However, the economic problems of the Jaguar process become apparent due to the significant amount of energy expended when evaporating excess water from a concentrated solution of magnesium chloride before and after pyrohydrolysis, which is not comparable to the savings in the regeneration of reagents. The higher the quality of the magnesium material for leaching, the more water is spent at the pyrohydrolysis stage in absolute units, that is, 1 kg of processed ore (see Fig. 8). The Jaguar process quickly becomes ineffective in terms of water balance, since if necessary, add additional water to the system to absorb more magnesium, the specified amount is again evaporated during the pyrohydrolysis. Similar to the Jaguar process, a "negative effect" on the water balance associated with a high initial magnesium content in the ore is also observed in the Skye process, but to a lesser extent (in this case, to prevent premature crystallization of sulfate in other elements of the system), but except that added “additional” water will be distributed with relative efficiency in a multi-case evaporator / crystallizer and only hydrated water from magnesium sulfate will affect the high-temperature (expensive) water thermal decomposition. The lower the degree of hydration of the resulting magnesium sulfate, the less the magnesium content in the feed affects the degree of evaporation at the high-temperature stage of regeneration of the reagent (see Fig. 8). The steeper the dependence curve (in Fig. 8), the less the additionally extracted nickel (during the processing of high-quality saprolite ore) will increase the cost of water evaporation during high-temperature regeneration of the reagent.

Heat recovery is also a low-efficiency process and is complicated in pyrohydrolysis reactors (Steinbach and Baerhold, 2002 and Adham and Lee, 2002). Rare materials are required in this process, since hydrochloric acid condenses in the evaporator and is heated by waste heat during heat transfer. In another embodiment, if hydrochloric acid is removed in a first step, heat loss for regeneration is observed. Another important factor is that some impurities, such as calcium and sodium chlorides, do not undergo pyrohydrolysis, and the corresponding equivalent amount of chlorides needs to be replaced with expensive additional hydrochloric acid or magnesium chloride. It should also be borne in mind that the overall efficiency of the pyrohydrolysis reaction is significantly lower than 100%.

Features of the closed-loop process using pyrohydrolysis (Jaguar process):

- pyrohydrolysis is advisable at relatively low temperatures (~ 500 ° C), but heat recovery is difficult (high investment), which is relatively inefficient;

- the Jaguar process becomes uneconomical when processing laterite ores with a high magnesium content, that is, this process is intended only for processing limonite ores;

- impurities, such as calcium and sodium, are not subjected to pyrohydrolysis, and there is a need to replace an equivalent amount of chlorides with expensive additional hydrochloric acid or magnesium chloride.

The Jaguar process does not absorb significant amounts of magnesium and therefore is not competitive with widespread sulfate-based atmospheric processes such as the Skye process. More recently, a chloride process has been proposed (Myes et al., 2005), designed to exclude pyrohydrolysis, that is, to regenerate hydrochloric acid by precipitation of sulfates with sulfuric acid (the chemical reaction is shown in Fig. 9). The principle of this process is to use chemical precipitation crystallization with cheap sulfuric acid to regenerate expensive hydrochloric acid, as opposed to pyrohydrolysis. The Intec process uses the CaCl ₂ / SO ₄ conversion. The principle of this process is similar to the Jaguar process, but with the exception that only iron is removed from the liquid by-pass and Ni / Co is extracted in the presence of lime. Then, magnesium is precipitated from the resulting solution in the presence of lime to form magnesia (MgO). During all three operations, the chloride cation is mainly replaced by an equivalent amount of calcium chloride. The total amount of hydrochloric acid consumed in the system is regenerated by the addition of sulfuric acid, which leads to the precipitation of calcium sulfate (with low solubility). The regenerated hydrochloric acid is returned through a recirculation system to atmospheric leaching. Sulfuric acid and lime, in turn, can be regenerated at the stage of thermal decomposition of calcium sulfate. However, a simple thermodynamic model of the thermal decomposition reaction (using the HSC process) reveals some difficulties (see FIG. 10).

Although the concept of sulfuric acid and lime recovery is of interest, the thermal decomposition of sulfates requires a high temperature, i.e. a significant amount of energy is required. In this case, the formation of extremely refractory non-reactive type of lime is possible. In addition, an intermediate solid phase forms during thermal decomposition, which presents additional problems.

Features of the closed-loop process and using the precipitation of calcium sulfate (with the addition of sulfuric acid to regenerate hydrochloric acid) (Intec process):

- in the specified process get realizable (commercial) by-products of bassanite (CaSO ₄ · 1 / 2H ₂ O) and magnesia (MgO), however, there are difficulties in cleaning by-products of this type;

- the possibility of economical regeneration of sulfuric acid and lime by the method of thermal decomposition of calcium sulfate is unlikely, thermal decomposition reactions occur through the formation of complex intermediate products, the lime product is refractory, and the process requires a large amount of energy;

- the higher the magnesium content in the ore raw materials, the more sulfuric acid and lime are required, which leads to a decrease in efficiency in the processing of saprolite ore.

Thus, there is a need for a more efficient, economical leaching process to recover valuable metals. First of all, there is a need for a method for the accumulation or regeneration of hydrochloric acid in a chloride salt solution for leaching, and it is necessary to eliminate the need for evaporation of large quantities of water, which is required when using pyrohydrolysis. All additional reagents used must be inexpensive, and there must be the possibility of regeneration of the main reagents used in the process.

Summary of the invention

In a first embodiment of the present invention, there is provided a method for leaching a valuable metal from ore containing said valuable metal, the process comprising the steps of:

ore leaching in the presence of hydrochloric acid to form metal chloride in the leach solution,

adding sulfuric acid to the leach solution,

recovery of metal sulfate from the leach solution and

simultaneous regeneration of hydrochloric acid.

The metal sulfate is characterized by the formula MeSO ₄ · yH ₂ O, where

Me means metal, and

y is 0 or more, for example from 0 to 3, more preferably 0 or 1.

The metal source in the metal sulfate is preferably ore.

The ore is preferably an oxide or silicate metal ore, such as zinc oxide ore.

Ore may also be lateritic nickel ore, such as saprolite or limonite ore.

In another embodiment, the ore is sulfide, titanium, or aluminum ore.

Metal sulfate is precipitated from the leach solution or recovered from the leach solution by crystallization by evaporation.

The valuable metal is selected from the group consisting of Zn, Cu, Ti, Al, Cr, Ni, Co, Mn, Fe, Pb, Na, K, Ca, platinum group metals and gold.

The metal in the metal sulfate may be a valuable metal, and the method further comprises the step of decomposing the metal sulfate to recover the valuable metal.

In another embodiment, the metal in the metal sulfate is a less valuable metal, in contrast to a valuable metal such as magnesium.

The metal sulfate can be processed under conditions under which sulfur dioxide, sulfur trioxide or a mixture thereof is formed.

A valuable metal can be recovered independently of the metal salt formed by the addition of sulfuric acid.

The regenerated hydrochloric acid may be super-azeotropic acid.

An alkali metal salt solution can be used as a metal chloride solution and / or an alkali metal sulfate is used as a metal sulfate.

The regenerated hydrochloric acid can then be sent to the recirculation system in the leaching process. Hydrochloric acid for leaching ore is used in the saline solution, for example, in the form of from about 10% to about 90% saturated solution of magnesium chloride, from about 10% to about 90% saturated solution of zinc chloride, or from about 10% to about 90% saturated chloride solution of another metal. More preferably, about 25% to about 40% of a saturated solution of magnesium chloride, from about 25% to about 40% of a saturated solution of zinc chloride, or from about 25% to about 40% of a saturated solution of another metal chloride are used as the saline solution. Even more preferably, approximately 30% of a saturated solution of magnesium chloride, approximately 30% of a saturated solution of zinc chloride, or approximately 30% of a saturated solution of another metal chloride are used as the saline solution.

Metal sulfate can be used to produce metal oxide. For example, the metal sulfate is thermally decomposed to form metal oxide and sulfur dioxide, sulfur trioxide, or a mixture thereof. The metal oxide is selected from the group consisting of magnesium oxide, zinc oxide, iron oxide and alumina. Sulfur dioxide, sulfur trioxide or a mixture thereof can be used to produce sulfuric acid, which in turn is returned to the leaching process to regenerate hydrochloric acid.

A valuable metal is leached from ore at a temperature of from about room temperature to about the boiling point of a metal chloride leach solution.

One or more valuable metals, such as cobalt, nickel, platinum group metals, gold, silver and / or copper, can be selectively isolated from the solution to form a metal sulfate.

Impurities of iron and / or other residual impurities formed after the solubilization of the ore are removed from the ore, for example, by solvent extraction followed by pyrohydrolysis or hydrolysis.

The sulfuric acid concentration is at least 30%, for example approximately 98%.

In a second embodiment of the present invention, there is provided a method for leaching a valuable metal from an ore containing said valuable metal, the process comprising the steps of:

ore leaching in the presence of hydrochloric acid to form a metal chloride soluble in the leach solution,

adding sulfur dioxide to the leach solution,

recovering metal sulfate or metal sulfite from ore and

simultaneous regeneration of hydrochloric acid.

The metal sulfate or metal sulfite is characterized by the formula MeSO _x · yH ₂ O, where Me means metal, x is 3 or 4, and y is 0 or more, for example from 0 to 3, preferably 0 or 1.

The metal source of the metal sulfate or metal sulfite is preferably ore.

The method also includes the step of adding an oxidizing agent to the leach solution to oxidize ferrous ions to ferric ions.

The ore used is mainly oxide or silicate ore containing a metal, such as zinc oxide ore.

As an ore, lateritic nickel ore such as saprotil or limonite is used.

In another embodiment, sulfide, titanium or aluminum ore is used as ore.

The metal sulfate or metal sulfite is precipitated from the leach solution or regenerated from the leach solution by crystallization by evaporation.

Valuable metals are selected from the group consisting of Zn, Cu, Ti, Al, Cr, Ni, Co, Mn, Fe, Pb, Na, K, Ca, platinum group metals and gold.

The method can use a catalyst to accelerate the reaction. Suitable catalysts are copper in solution, graphite or coal.

A valuable metal is provided as a metal in the metal sulfate or metal sulfite, and the method further comprises the step of decomposing the metal sulfate or metal sulfite to recover the valuable metal.

As the metal in the metal sulfate or metal sulfite, there may be a less valuable metal such as magnesium.

The metal sulfate or metal sulfite is treated under conditions in which sulfur dioxide, sulfur trioxide or a mixture thereof is formed.

Valuable metal can be recovered independently of the metal salt formed by the addition of sulfur dioxide.

The regenerated hydrochloric acid may be super-azeotropic acid.

Magnesium can be removed from the leach solution before adding sulfur dioxide and replaced with various metal ions, such as calcium or lead. After removal of magnesium and addition of sulfur dioxide, a metal salt is formed, for example intermediate sulfite or sulfate. The intermediate sulfite or sulfate may be calcium sulfate, calcium sulfite, lead sulfate or lead sulfite.

As a metal chloride solution, an alkaline solution can be used.

As the metal sulfate or metal sulfite, alkali metal sulfate or alkali metal sulfite can be used.

Regenerated hydrochloric acid can be sent to the recirculation system in the leaching process.

The hydrochloric acid used for leaching may be included in the saline solution, for example, in the form of from about 10% to about 90% of a saturated solution of magnesium chloride, from about 10% to about 90% of a saturated solution of zinc chloride, or from about 10% to about 90% saturated chloride solution of another metal. More preferably, from about 25% to about 40% of a saturated solution of magnesium chloride, from about 25% to about 40% of a saturated solution of zinc chloride, or from about 25% to about 40% of a saturated solution of another metal chloride, are used. Even more preferably, approximately 30% of a saturated solution of magnesium chloride, approximately 30% of a saturated solution of zinc chloride, or approximately 30% of a saturated solution of another metal chloride are used as the saline solution.

Metal sulfate or metal sulfite can be used to produce metal oxide. For example, metal sulfate or metal sulfite is thermally decomposed to form metal oxide and sulfur dioxide. The metal oxide is selected from the group consisting of magnesium oxide, zinc oxide, iron oxide or alumina. Sulfur dioxide can be used to produce sulfuric acid, which in turn can be used in the leaching process to regenerate hydrochloric acid.

Intermediate sulfate or sulfite can be thermally decomposed to form metal oxide, such as calcium oxide, and sulfur dioxide, sulfur trioxide, or a mixture thereof. Sulfur dioxide, sulfur trioxide or a mixture thereof can be reused for salting out sulfates or sulfites from a solution for leaching and regeneration of hydrochloric acid.

A valuable metal is leached from ore at a temperature of from about room temperature to about the boiling point of a metal chloride leach solution.

One or more valuable metals, such as cobalt, nickel, platinum group metals, gold, silver and / or copper, are selectively removed from the solution before the formation of metal sulfate or metal sulfite.

Impurities of iron and / or other impurities resulting from the solubilization of the ore can be partially or completely removed from the leach solution, for example, by solvent extraction followed by pyrohydrolysis or hydrolysis.

The sulfuric acid concentration may be at least 30%, for example approximately 98%.

Brief Description of the Figures

Below the invention is described in more detail with reference to the accompanying drawings, which show:

figure 1 is a schematic diagram of the processing of saprolite by melting;

figure 2 is a schematic diagram of a preferred processing of limonite using the Karon process;

figure 3 is a schematic diagram of the processing of limonite (as well as smectite) using the HPAL process;

figure 4 - energy consumption and operating costs for the operation of the HPAL process;

5 is a diagram of the processes of atmospheric leaching (ALP) and HPAL-ALP (EPAL);

6 is a principle of the processes of Sural / Skye: crystallization of magnesium sulfate and regeneration of the starting reagents;

7 is a principle of the Jaguar process: primary regeneration of reagents using pyrohydrolysis of magnesium chloride;

Fig. 8 is a comparison (hypothetical) of the amount of evaporated water during the pyrohydrolysis of a solution of magnesium chloride and in the process of thermal decomposition of crystalline magnesium sulfates;

Fig.9 - the principle of the Intec process: primary regeneration of reagents using the deposition of calcium sulfate;

figure 10 - thermal decomposition of calcium sulfate, see the model of the HSC process;

11 - the principle of the method according to the present invention: the regeneration of reagents using the deposition and thermal decomposition of magnesium sulfate;

Fig - solubility of magnesium sulfate depending on changes in the amount of magnesium chloride (see AspenPlus model);

Fig - activity of hydrogen ions in a solution of 0.5 mol / kg HCl depending on the concentration of magnesium chloride and temperature;

Fig - molality of hydrogen ions in solutions: from 0 to 1 mol / kg HCl and 2.5 mol / kg MgCl ₂ and from 0 to 0.5 mol / kg H ₂ SO ₄ and 2.5 mol / kg MgSO ₄ accordingly, depending on the temperature;

Fig - thermal decomposition of magnesium sulfate, see model HSC;

Fig - crystals of magnesium sulfate precipitated from saline at different temperatures;

Fig is a schematic diagram of a method according to the invention;

Fig - scheme 1 of the method according to the invention;

Fig - scheme 2 of the method according to the invention;

Fig.20 - extraction of Nickel from saprolite samples;

Fig.21 - extraction of cobalt from saprolite samples;

Fig - profiles of the extraction of all metals from saprolite using saline solution of high concentration;

Fig.23 is the extraction of Nickel from limonite samples;

Fig - extraction of cobalt from limonite samples;

Fig - profiles of the extraction of all metals from limonite using saline solution of high concentration;

Fig - extraction of Nickel from silicate-limonite samples;

Fig.27 - extraction of cobalt from silicate-limonite samples;

Fig - profiles of the extraction of all metals from silicate limonite using high concentration saline;

Fig.29 - the effect of MgCl ₂ on the extraction of Nickel;

Fig. 30 is a photograph of typical crystals (scanning electron microscope);

Fig - reactor with oil heating, the insert shows a syringe for adding reagents;

Fig - a method of processing sulfide ore;

Fig - chloride and sulfate closed cycles in an integrated process for processing sulfide ore;

Fig - laboratory setting for non-oxidative atmospheric leaching;

Fig - kinetics of leaching in non-oxidizing conditions in the presence of HCl at 90 ° C (+ 38-75 μm);

Fig - x-ray analysis (powder x-ray) of a crystalline product.

Detailed Description of Embodiments of the Present Invention

The method of the present invention represents a new general approach to optimizing reagents and energy costs. The starting reagent, i.e. HCl, regenerate, while eliminating the need for neutralization of solutions before crystallization obtained after leaching, or the need to add fresh reagents to the system. The effectiveness of this approach increases with the use of concentrated saline solutions, which provides additional advantages: 1) the formation of a dehydrated crystalline product, i.e. reduction of energy consumption during thermal decomposition (regeneration of reagents), 2) the formation of stable dehydrated products of Fe hydrolysis (such as hematite) at ambient temperature, 3) fast leaching kinetics due to the high activity of protons, and 4) leaching and extraction of important by-products (e.g. Pb , Ag).

The method of the present invention is designed to leach one or more valuable metals in a solution containing hydrochloric acid, from which the valuable metal is recovered (regenerated) in the form of solid sulfate or sulfite, and hydrochloric acid is simultaneously regenerated in the solution.

Valuable metal is leached from a metal-containing material, which is a sulfide or non-sulfide material. For example, the material may be metal oxide ore, such as zinc oxide ore, lateritic nickel ore, such as saprolite or limonite ore, sulfide ore, aluminum ore, or titanium ore. First, the valuable metal forms soluble metal chloride, then solid sulfate or sulfite is formed.

Valuable metals are preferably selected from the group consisting of Zn, Cu, Ti, Al, Cr, Ni, Co, Mn, Fe, Pb, Na, K, Ca, platinum group metals and gold.

The metal chloride solution may be an alkaline solution, and / or the metal sulfate is an alkali metal sulfate.

Sulfuric acid, usually at a concentration of at least 30% (for example, approximately 98%) or sulfur dioxide, is added to a solution containing leached valuable metal, whereby solid metal sulfate or metal sulfite is obtained, which is then recovered. In this case, a relatively cheap reagent (sulfuric acid or sulfur dioxide) is used to regenerate an expensive reagent (hydrochloric acid), which leads to significant cost savings.

Solid metal sulfate or solid metal sulfite is usually characterized by the formula:

MeSO _x yH ₂ O,

where Me means metal,

x is 3 or 4, and

y is 0 or more, for example from 0 to 3, and more preferably 0 or 1.

The solution containing hydrochloric acid is usually a saline solution (i.e., a chloride solution), such as from about 10% to about 90% of a saturated solution of magnesium chloride, from about 10% to about 90% of a saturated solution of zinc chloride, or from about 10% to approximately 90% saturated solution of another metal chloride. More preferably, about 25% to about 40% of a saturated solution of magnesium chloride, about 25% to about 40% of a saturated solution of zinc chloride, or from about 25% to about 40% of a saturated solution of another metal chloride are used as the saline solution. Even more preferably, a 30% saturated solution of magnesium chloride, 30% saturated solution of zinc chloride, or a solution of another metal or alkali metal chloride is used as the saline solution. The content of the metal or alkali metal in the saline solution is usually selected depending on the acid scavengers present in the leach solution, and their concentrations in most cases are selected so as to provide a significant difference in the solubility of chlorides and sulfates.

The metal that forms the cation in the chloride composition and which is the main component of the saline solution (leaching medium) is preferably selected from the main cations that absorb acid and are present in the ore to be leached.

The concentration of metal chloride is usually selected taking into account the following objectives:

positive effect on the leaching process, as described, for example, for the Jaguar process,

ensuring leaching of the metal from the ore, not exceeding the solubility of the metal chloride under leaching conditions (in another embodiment, water is added to prevent loss of chloride in the solid phase),

accelerated deposition of the corresponding sulfate or sulfite - i.e. the metal concentration is excessive in relation to the solubility of sulfate or sulfite,

the effect on the degree of hydration of the precipitated sulfate or sulfite, so that the degree of hydration of the salts obtained is lower compared to the possible degree of hydration of salts obtained from a neutral solution of sulfate or sulfite, and

Do not exceed the solubility limits required at other stages of the process. In this case, different operating temperatures are required at various stages of the process (in another embodiment, in order not to exceed the solubility limits, water is added at certain stages of the process).

The initial concentration of hydrochloric acid is chosen in such a way as to ensure a high degree of leaching of the metal and at the same time meet the requirements of acid absorption by the ore. It was found that leaching at a final pH of 0.5 or less leads to an increase in the yield of metal recovery to more than 80%. However, this value depends on the nature of the ore, and it will be apparent to those skilled in the art that a satisfactory leaching rate can be achieved by using other materials at high final pH values, in contrast to those studied in the present invention.

Sulfuric acid or sulfur dioxide is usually added to the solution in sufficient quantity so that the strength of the regenerated hydrochloric acid exceeds the concentration of the azeotrope, which is determined by the solubility of the metal chloride or alkali metal chloride, compared with the strength of hydrochloric acid, which is formed after precipitation in the form of sulfate or sulfite. The saline solution is characterized by a low initial concentration, which is added to the additional concentration of metal chloride during the leaching process. Preferably, the amount of added sulfuric acid or sulfur dioxide in said solution should slightly exceed the amount required to compensate for the concentration of acid-salt solution to the original value. In other words, the initial minor concentration of metal chloride should not be reduced during crystallization of the corresponding sulfate or sulfite. In another embodiment, the solution after leaching is separated into fractions and only one of them is used to precipitate sulfate or sulfite, while the precipitation depends on the solubility, while the initial level of chloride does not change in the remaining untreated fractions.

The process also includes a crystallization step to produce crystals of metal sulfate or metal sulfite with a low content of hydrated water. In another embodiment, to reduce the cost of these reagents for carrying out the specified chemical crystallization using crystallization with evaporation (within or with a slight excess of the standard water balance). This option becomes possible due to the simultaneous influence of the initial salt concentration in the solution on the degree of salt deposition during evaporation of water. Moreover, co-precipitation of Ni within the crystalline structure of a magnesium salt usually prevails upon crystallization at low temperatures. The tendency of Ni to co-crystallize significantly decreases when chemical crystallization is carried out at a temperature close to the boiling point of the solution at atmospheric pressure.

Such salts used as commercial products are thermally decomposed to form metal oxide, which is also used as a commercial product, as well as sulfur dioxide, sulfur trioxide or a mixture thereof, and / or they are redissolved in a sulfate solution and then subjected to electrolysis.

One or more valuable metals, such as cobalt, nickel, platinum group metals, gold, silver and / or copper, are selectively removed from the solution before the metal sulfate or sulfite formation step.

Iron and / or other residual impurities resulting from the solubilization of the ore are partially or completely removed from the leach solution, for example, using solvent extraction followed by pyrohydrolysis or hydrolysis.

The metal in the metal sulfate or metal sulfite may be a valuable metal, and the method includes the step of decomposing the metal sulfate to recover the valuable metal.

In another embodiment, the metal in the metal sulfate or metal sulfite is less valuable, such as magnesium, and the valuable metal is independently extracted from the metal salt formed by the addition of sulfuric acid or sulfur dioxide.

The metal sulfate or sulfite can be processed to release sulfur dioxide.

The method is not necessarily limited to temperature ranges, provided that the solubility of the metal sulfate or metal sulfite is significantly lower than the solubility of the corresponding chloride. Nevertheless, leaching is generally carried out at a temperature from room temperature to the boiling point of the solution, and the crystallization stage of sulfate or sulfite is usually carried out at a temperature at which the difference in solubility is maximal.

Before sulfur dioxide is added, magnesium is optionally removed from the leach solution and replaced with a cation of another metal, such as calcium, lead or barium. After magnesium is removed, the metal salt formed by the addition of sulfur dioxide is an intermediate sulfite or sulfate, such as calcium sulfate, calcium sulfite, lead sulfate, lead sulfite, barium sulfate or barium sulfite. Intermediate sulfate or sulfite is thermally decomposed to form metal oxide such as calcium oxide and sulfur dioxide. Sulfur dioxide is reused for salting out sulfate or sulfite from a solution for leaching and regeneration of hydrochloric acid.

Particular embodiments of the present invention may have the following features:

the concentration of hydrochloric acid is compensated in a non-ferrous metal chloride salt solution,

the leaching process is carried out in a chloride medium by adding gaseous sulfur dioxide or sulfuric acid,

a metal, such as zinc or magnesium, is recovered from a salt chloride solution in the form of a salt with a small amount of hydrated water, which is subjected to thermal decomposition, re-dissolution in a sulfate solution and electrolysis directly from the resulting solution, or in the form of commercial products, in the form of sulfate or sulfite , or after thermal decomposition to oxide.

The present invention will be described in detail below in the form of several non-limiting examples.

Sulfide-free ores

In a first embodiment, the present invention provides a method for leaching magnesium, as well as at least some valuable nickel and cobalt from sulfide-free ores, such as lateritic ores, limonite, oxide ores and / or silicate saprolites, in a hydrochloric acid feed medium. The main leaching agent is the hydroxonium ion, which is formed in the presence of chlorides, the presence of which is associated with the presence of intrinsic impurities, primarily magnesium chloride.

The processing of sulfide-free materials is described in detail below on the example of nickel laterite ore. It will be apparent to those skilled in the art that other sulfide-free materials such as zinc silicates, bauxites, and the like can be processed in a similar manner. The laterite used is also an example in which a valuable metal is not a metal used in the stage of compensating the concentration of saline chloride solution. A schematic diagram of the process is shown in FIG.

The regeneration of hydrochloric acid and the extraction of magnesium, as described above, is not associated with excessive removal of water during evaporation, because magnesium is first recovered by precipitation, and not from an electrolyte solution of magnesium chloride (as in the Jaguar method). However, in another embodiment, evaporation crystallization (within or with a slight excess of the standard water balance conditions) can be used to reduce the cost of reagents at the stage of chemical crystallization. This option becomes possible due to the simultaneous effect of the initial salt solution concentration on the degree of salt deposition during evaporation of water.

After leaching, the acid concentration in the magnesium chloride salt solution is compensated by adding sulfuric acid or gaseous sulfur dioxide; as a result, magnesium sulfate or sulfite with a low degree of hydration is precipitated and hydrochloric acid is formed in the solution.

The residue after leaching of laterite is treated in the next leaching stage in order to maximize the yield of nickel and cobalt.

In the case of sulfate, the experimental data of Linke and Seidell (1965) indicate that kieserite (magnesium sulfate monohydrate) is the preferred crystallization product at elevated temperature (approximately 100 ° C), which minimizes the energy required for calcination to form magnesia ( magnesium oxide, which is partially sent to the recycling system as a neutralizing agent) and sulfur dioxide. A simplified reaction scheme is shown below:

In this way, a crystalline product is obtained with a total chloride content of less than 0.01%. It was found that the co-crystallization of Ni in the crystal structure of kieserite is reduced to a minimum when this reaction is carried out at a temperature close to the boiling point of the solution (or at elevated temperature and pressure). It is believed that using this method, it is possible to obtain magnesium oxide with a high degree of purity, which can be used as a commercial product and / or as a neutralizing agent. In another embodiment, if nickel losses are unacceptable, then nickel is removed before crystallization using chemical methods, for example, ion exchange, solvent extraction, diffusion saturation (cementation), precipitation, etc. In addition, relatively expensive hydrochloric acid is regenerated using sulfuric acid or sulfur dioxide, which are relatively cheap and affordable reagents.

The Fe ³⁺ / Fe ²⁺ pair in the salt system plays an extremely important role in the direct use of sulfur dioxide to precipitate sulfate or sulfite. In the absence of ferric ion, the ability of a solution to absorb sulfur dioxide is extremely small in solutions with a high initial salt concentration, that is, absorption in this system is ineffective. However, in the presence of ferric ions, gas is directly absorbed by the solution due to the reduction of ferric to ferrous iron. This reaction is accompanied by changes in the solution, which, in turn, lead to the preferred salting out of magnesium sulfate or magnesium sulfite.

The method of the present invention described in this context is shown in FIG. 11 and is based on the low solubility of magnesium sulfate in solution in the presence of large amounts of magnesium chloride in the initial solution. Adding sulfuric acid to a saturated leach solution (PLS) results in precipitation of sulfate while regenerating hydrochloric acid, which is returned to the recirculation system for reuse in the atmospheric leach stage. On Fig shows the estimated change in the solubility of magnesium sulfate with increasing initial chloride content using commercial software AspenPlus, designed to simulate processes.

Precipitated magnesium sulfate, in turn, undergoes thermal decomposition with the formation of magnesia (magnesium oxide) (for use as a neutralizing agent) and gaseous sulfur dioxide. Sulfur dioxide gas is converted to sulfuric acid in an acid recovery unit and reused in the sulfate chemical precipitation step.

In addition to changes in temperature and water content, an important parameter in the process scheme is the concentration of saline solution. Conversely, in a sulfate process, such as the Skye process, degrees of freedom are only temperature and water content. In this case, it is necessary to add large quantities of water to prevent unwanted crystallization in the stream, and therefore, there is a need to remove large quantities of water (per kg of processed ore) to achieve the desired level of crystallization with evaporation. The importance of this “negative” effect of water increases significantly with increasing magnesium content in the ore. In contrast, the present invention proposes a chemical crystallization step rather than an evaporation process, so that the water balance is independent of the magnesium content in the ore feed. In addition, due to the high initial salt concentration in the method of the present invention, a simultaneous effect occurs in the evaporation process, which is strictly dependent on the water balance, which leads to the precipitation of more magnesium sulfate. This effect compensates for the ineffectiveness of chemical deposition (due to undesirable solubility), while it is not necessary to significantly increase the cost of steam energy. Consequently, a system based on a mixed chloride-sulfate electrolyte increases the operational flexibility of the process compared to a simple process with a closed system using sulfate (see Skye method).

In this case, the solubility of sulfate in the system is suppressed while maintaining a high initial concentration of chloride in the system. At the same time, a high initial concentration of chloride leads to high proton activity and low water activity. On Fig shows a three-dimensional graph of the activity of protons on temperature and the concentration of magnesium chloride.

This model was developed specifically to assess the activity of individual H ⁺ ions in the HCl-MgCl ₂ -H ₂ O electrolyte system. Figure 13 shows that the activity of individual H ⁺ ions (which is an important parameter, although not the only one determining the rate of laterite destruction in order to recover Ni) increases with the addition of a starting salt such as MgCl ₂ . At 65 ° C and in the presence of 1M HCl, a ten-fold increase in such activity is observed. Unfortunately, the observed effect decreases significantly with increasing temperature. Therefore, there are two opposite effects: in order to ensure high H ⁺ activity, leaching should be carried out at a low temperature, and, on the other hand, in order to exceed the activation energy barrier at the solid / liquid interface, leaching should be carried out at a high temperature. Nevertheless, during leaching, for example, at 85 ° C, the H ⁺ activity almost doubles compared with the activity in the pure HCl-H ₂ O system. This fact is of particular interest, since a similar "aggressiveness" of protons is not realized in a pure sulfate system.

On Fig shows that when comparing two systems in an electrolyte system, hydrochloric acid / magnesium chloride, a significantly higher concentration of protons is observed in comparison with the equivalent concentration of sulfuric acid in the magnesium / sulfate system. The main reason for the observed effect is the specificity of various ions in the electrolyte: the Н ⁺ -Cl ^- bond is weak, while the Н ⁺ -SO ₄ ^2- bond is strong and "captures" most of the protons with the formation of a bisulfate complex, HSO ₄ ^- . The tendency to the formation of a bisulfate ion leads to relative weakness of sulfuric acid, primarily at high concentrations of magnesium sulfate and high temperature.

The method of the present invention is primarily intended for processing in the presence of impurities such as sodium and calcium, in contrast to the pure chloride method, for example the Jaguar method. A sufficient amount of sulfate must be present in the system of the present invention to form sodium jarosite, from which magnesium chloride is regenerated according to the following scheme:

Indeed, it is preferable to have a sufficient amount of sulfate under the conditions of the above reaction to replace the entire amount of consumed chloride in the system. If necessary, a small amount of sodium chloride is added to the system to circulate a sufficient amount of sodium ions in the iron removal step. A small amount of calcium chloride in the solution precipitates with the formation of insoluble calcium sulfate when sulfuric acid is added at the stage of chemical crystallization. Although calcium sulfate does not decompose simultaneously with magnesium sulfate, the difference can be compensated for by burning an equivalent amount of elemental sulfur. Thus, in addition to the effective treatment of the main impurities in the system, losses of chloride and sulfate are compensated by the addition of cheap reagents such as sodium chloride and elemental sulfur, respectively. For other impurities, manganese is easily removed in the presence of an excess of SO ₂ (for oxidation in the presence of SO ₂ / O ₂ to MnO ₂ ) without the need for special costs for its removal. From the point of view of environmental protection and from an economic point of view, the absence of liquid by-pass flows is important.

When calcining the precipitated magnesium product to decompose the ideal product in a fluidized bed reactor (900-1200 ° C), 1.5-4 moles of water per 1 mole of magnesium are required. This technique is described in US Pat. No. 4,096,235, which is incorporated herein by reference in its entirety. Partial rehydration of the monohydrate (to obtain a product with an optimal degree of hydration for thermal decomposition) is achieved by controlling the contact time of the crystalline precipitation product with a suitable aqueous medium. A technique for recovering sulfuric acid from sulfur dioxide generated by sulphate / sulphite calcination is known and allows the reuse of sulfuric acid if economically justified.

The main advantage of using magnesium sulfate / sulfite for decomposition to magnesium oxide is that it requires significantly lower energy consumption (compared to pyrohydrolysis of a magnesium chloride solution, as described in the Jaguar method) in connection with the removal of water, i.e. only hydrated water. In this way, high quality magnesium oxide is obtained for use as a commercial product.

Thermal decomposition of magnesium sulfate is a relatively simple process. On Fig shows a chemical model of HSC for thermal decomposition in the presence of carbon as a reducing agent. The kinetics of thermal decomposition even at 800 ° C is very fast, because precipitated magnesium sulfate forms extremely fine dispersed particles (<10 μm). On Fig shows that the deposition at low temperature (65 ° C) leads to the formation of needle-shaped particles of hexahydrate and extremely thin dispersed particles of monohydrate. Precipitation from salt solutions at higher temperatures (110 ° C) leads to the formation of only monohydrate, that is, kieserite (MgSO ₄ · H ₂ O). Thus, it can be assumed that the thermal decomposition energy in the method according to the invention is lower than the energy according to the Skye method, in which at least 2 hydrated water molecules are present in the precipitated salt. Any amount of magnesium chloride associated with small particles undergoes pyrohydrolysis with the formation of gaseous HCl, which can be sent to the recirculation system. A typical composition of precipitated sulfate (according to experimental data) includes: 17.1% Mg, <0.05% Fe, 0.1% Ni, <0.05% Co, 2% Cl, taking into account the balance of sulfates and water. The nickel content in the precipitated salt depends on temperature: its content increases with decreasing crystallization temperature.

Cheaper sources of fuel are used, such as heavy petroleum fuels (HFOs) and, above all, low-quality coal. Any amount of sulfur in the composition of coal is oxidized to form SO ₂ and, therefore, reduces the cost of adding additional reagents containing sulfur.

As mentioned above, the main advantage in the operation of the chloride system is the tendency to dehydrate the solid phase in equilibrium with saline. In addition to the formation of kieserite (monohydrate) or even an anhydrous salt during crystallization, hematite is formed during the hydrolysis of iron under atmospheric conditions. It is the preferred hydrolysis product not only from the point of view of environmental protection, but also has improved sedimentation and filtration characteristics compared to more gel-like or hydrated precipitates formed in a pure sulfate system. The observed phenomenon also leads to the formation of solid-phase cake with a lower moisture content and, consequently, to a decrease in the loss of valuable reagents in the system.

Another important factor is the tendency of nickel and cobalt to be absorbed together in the crystal structure of iron (III) hydroxide and goethite, while (similar to natural processes) hematite is practically incapable of absorbing these compounds together. The preferred precipitation of hematite from saline is primarily achieved by controlled precipitation under excessive saturation conditions by adding seed to crystallize hematite during iron hydrolysis (see Riveros and Dutrizac, 1997).

A schematic diagram of the process is shown in FIG. Using a recirculation system in a reactor at atmospheric pressure allows maximizing the contact time of hydrochloric acid and minimizing the cost of neutralizing reagents (internal recirculation loading of magnesium per 1 mass of processed ore) in the system. Only the bypass stream is neutralized for the hydrolysis of iron and then for the extraction of nickel and cobalt during precipitation during the hydrolysis. After the neutralization step, one evaporation step is used to compensate for the water balance. During chemical crystallization in the split stream of the main recirculation system, the equivalent amount of hydrochloric acid consumed + the loss from the system is regenerated. Precipitated sulfate is calcined to form gaseous SO ₂ and magnesium oxide. Gaseous SO _{2 is} converted to sulfuric acid in a sulfuric acid production unit and returned to a crystallizer, while part of the magnesium oxide is sent to a recirculation system for internal neutralization. Excess magnesium oxide obtained is used as a commercial product.

An important feature of the present invention is the relative independence of the magnesium content in the ore raw materials, as shown in Fig. 8. If a cake of monohydrate is formed at the stage of regeneration (thermal decomposition of magnesium sulfate), only a slight evaporation is required or it is completely eliminated from the system, which allows processing high-quality saprolite ores and is a significant advantage with respect to current costs in absolute terms due to the high cost of nickel.

The following is a list of all the necessary criteria that the method of the present invention satisfies.

Key Performance Criteria

Reduced investment over HPAL and Smelting processes:

- when operating a hydrometallurgical installation, high pressure is not required, and when operating a pyrometallurgical installation, only average temperatures are used,

- in spite of the fact that when using chloride medium special corrosion-resistant materials are required, all stages are carried out in atmospheric conditions.

Reduced energy consumption compared to the Smelting process:

- when adding a reducing agent to the system, the thermal decomposition of dehydrated magnesium sulfate (or containing a small amount of hydrated water) is achieved at a temperature of less than 800 ° C,

- the amount of energy spent at the decomposition stage at high temperature is completely spent on heating in the hydrometallurgical system using an evaporator on secondary energy sources,

- use sulfur-containing low-quality coal as a reducing agent and fuel for direct combustion in a furnace for thermal decomposition.

Reduced reagent costs compared to the HPAL process:

- during the thermal decomposition of magnesium sulfate, sulfate is regenerated (in a plant for producing sulfuric acid) and a neutralizing agent (magnesium oxide),

- the addition of additional sulfur is limited by standard losses from the closed system, which are compensated by burning additional sulfur (inexpensive reagent),

- the addition of additional chloride is limited to standard losses from the closed system, which are compensated by the addition of inexpensive chloride, such as sodium chloride,

- impurities, such as sodium and calcium, are removed at the stage of sulfate removal (sodium jarosite and calcium sulfate, respectively), i.e. no bypass flows are required.

Nickel and cobalt recovery output are comparable with HPAL process:

- higher proton activity and, therefore, a more aggressive leaching system (compared with the conditions of ore processing at atmospheric pressure in a pure sulfate system),

- despite the fact that the kinetics of the process is slower compared to the HPAL process, this disadvantage is compensated by the increase in the size of the leaching reactors in atmospheric conditions, i.e. reagent contact time becomes relatively cheap.

Liquid / solid separation and residue stability:

- iron hydrolysis products precipitated in the presence of chlorides are characterized by improved precipitation and filtration properties.

Environmental protection:

- in the chloride system at atmospheric elevated pressure, dehydrated products of iron hydrolysis are formed, such as hematite (stable under ambient conditions),

- magnesium sulfate decomposes at elevated temperatures, which meets the requirements for acid and a neutralizing agent in the internal system,

- use a closed system, i.e. there are no by-pass flows into the environment.

Increased income from the sale of nickel derived from many different types of ore:

- independence from the magnesium content allows to process simultaneously limonite and saprolite ores, which increases sales revenue.

Two schematic diagrams designed with respect to the mass / energy balance are shown in FIGS. 18 and 19. FIG. 18 is a general diagram of 1. The starting salt of the present invention is used to reduce the solubility of magnesium sulfate. Evaporation crystallization, without exceeding the normal water balance, is used to reduce costs at the stage of chemical deposition, i.e. to compensate for the inefficiency of the stage of chemical crystallization due to the formation of bisulfate. The diagram in Fig. 18 shows that it is possible to effectively eliminate the need for evaporation of water, depending on changes in the magnesium content in the ore raw materials. On Fig shows another variant of the scheme, taking into account the inefficiency of chemical crystallization in a medium with a high acid content due to the formation of bisulfate. This diagram shows the most unfavorable option in terms of regeneration of reagents.

1. The dynamic characteristic of minerals

Laterite ore samples were tested for dynamic stability. 3 ore samples were taken for further testing the effect of saline with a high initial concentration of salt and sulfur dioxide. The tests were carried out at a high concentration of solids (30%) and acid (the concentration of sulfuric acid is 2018 kg / t, hydrochloric acid - 1500 kg / t, in both cases - 41.2 kg N ⁺ / t).

For the tests used saprolite, iron and silicate ores Jacaré (Brazil). The initial composition of the components in the samples is shown in table 1.

Table 1 The initial composition of the components in the used samples Sample Ni Co Fe Mg Al Si Cr Mn Saprolite Jacaré 1.60% 0.07% 12.81% 17.43% 0.61% 17.06% 0.72% 0.24% Iron Ore Jacaré 1.14% 0.17% 42.23% 0.63% 1.25% 10.00% 2.38% 0.85% Silicate ore Jacaré 1.25% 0.22% 22.42% 2.35% 2.30% 20.92% 1.09% 0.92%

Each sample was tested under the following conditions:

1. Leaching in the presence of hydrochloric acid (1500 kg / t)

2. Leaching in the presence of sulfuric acid (2018 kg / t)

3. Leaching in the presence of hydrochloric acid in a high concentration saline solution (1500 kg / t HCl, 2 M MgCl ₂ )

4. Leaching in the presence of hydrochloric acid and SO ₂ in a high concentration saline solution (1500 kg / t HCl, 2 M MgCl ₂ , 20 kg / t SO ₂ )

The tests were carried out in a 2 L glass reactor equipped with an oil jacket through which oil from a thermostat with a certain temperature circulates. All tests were carried out at 85 ° C and in the first stage, a pulp of 300 g of ore was obtained as a 30% suspension (solid / solid + water) in water. The suspension is suspended using a steel-coated mixer with removable polypropylene blades. The acid was added in 10 portions at intervals of 1 hour. A suspension sample of 40 ml was taken at the end of each interval (to determine the yield of metal extraction). Magnesium chloride hexahydrate was added to the initial suspension, while anhydrous magnesium chloride was added in a mixture with acid to ensure a constant level of magnesium chloride during testing in a high concentration of saline. If necessary, the addition of sulfur dioxide was monitored using a Bronchorst mass flow meter.

but. Saprolite Ore Test Results

On Fig and 21 shows the extraction efficiency of Nickel and cobalt, observed when testing saprolite ore, respectively. In a chloride medium, higher extraction yields of both metals are observed, regardless of whether the high acid activity is associated with chloride ions or with the formation of a bisulfate complex in a sulfate medium. An increase in extraction efficiency of approximately 10% is observed when using the initial saline solution, as compared to leaching only in hydrochloric acid. The addition of sulfur dioxide does not affect the efficiency of nickel extraction, although it does lead to some improvement in the efficiency of cobalt extraction.

On Fig shows the profile of the extraction of all metals in saline with a high concentration. When small amounts of acid are added, nickel is selectively extracted from saprolite, then manganese and magnesium. Selectivity decreases with an increase in the amount of added acid to 26 kg H ⁺ / t; addition of acid over 26 kg H ⁺ / t does not affect the extraction profile.

b. Jacaré Iron Ore Test Results

23-25 show the results of a study of limonite ores. The results of nickel extraction are similar to those of saprolite ore. However, in the case of limonite ore, there is a significant increase in extraction efficiency in a chloride medium and a significant difference in the results of extraction with hydrochloric acid and sulfuric acid. As in the case of saprolite ore, there is a 10% increase in extraction efficiency in a salt medium and the absence of the effect of sulfur dioxide. An increase in the efficiency of Co extraction is observed when sulfur dioxide is added to the saline solution. On Fig shows a slight selectivity in saline with a high initial salt concentration. The extraction profile remains almost unchanged with the addition of acid over 26 N ⁺ / t.

at. Jacaré Silicate Ore Test Results

Nickel and cobalt extraction profiles are shown in FIGS. 26-28. The results are similar to those of iron ore.

The results of the assessment of the dynamic characteristics of minerals:

- A significant increase in the efficiency of nickel extraction is observed when sulfuric acid is replaced by hydrochloric acid in the salt system. Similar results were obtained in the case of cobalt.

- The addition of sulfur dioxide leads to an increase in efficiency only in the extraction of cobalt.

- The extraction efficiency of nickel from Jacaré silicate ore correlates with the extraction efficiency of iron, magnesium and manganese depending on the nickel content in the limonite, magnesium silicate phases and in the manganese hydroxide phase, respectively.

- The efficiency of extraction of cobalt from Jacaré silicate ore correlates only with the efficiency of extraction of manganese and does not depend on the distribution of cobalt in different phases.

2. Characterization of crystallization

Currently, there is little data on the solubility of magnesium salts in acid chloride-sulfate or chloride-sulfite water systems. Such information is necessary to determine operating conditions and the integration of various system nodes. Key options include:

- temperature

- acid concentration,

- chloride concentration and

- concentration of sulfate / sulfite.

First, a less complex two-phase sulfate-based system is selected, i.e. the system does not contain a gaseous phase. Stock solutions are prepared at a constant concentration of magnesium chloride and various concentrations of magnesium sulfate. At elevated temperature, sulfuric acid is added before the formation of a precipitate. In the resulting solution, the content of Mg ²⁺ , Cl ^- , SO ₄ ^{2 -} and free acid is determined, and the amount obtained is used to calculate the content of magnesium and sulfate compounds, while the content of Mg ²⁺ , Cl ^- , SO ₄ in the solid is determined ^2- .

Characteristic of crystals

The integrated circuit includes limitations regarding the operating conditions of the mold and the properties of the solids formed. The most important characteristics of crystals that need to be quantified are presented below:

- Particle size distribution: to obtain a fluidized bed in air, a narrow particle size distribution with a sufficiently large average size is required. Otherwise, the product is thermally decomposed in a rotary kiln.

- Crystal hydrate water: a minimum degree of hydration is required.

- Inclusion of fluid: leakage of the mother liquor must be minimized.

- Filtration ability: the ability to filter is a dependent parameter and improves if the above criteria are met.

It is assumed that the characteristics of crystals obtained on a laboratory scale (in static mode) differ from crystals obtained in a reactor in a continuous mode.

Crystals obtained on a laboratory scale (static mode) are usually finely dispersed (particles 10 μm in size form agglomerates), as shown in Fig. 30. According to the results of chemical analysis, the molar ratio of magnesium / sulfate is approximately 1 (~ 17% Mg + ~ 67% SO ₄ ), and the chloride content is less than 2%. The crystals shown in FIG. 30 are obtained at 110 ° C. by adding concentrated sulfuric acid to a solution of 6 mol / kg MgCl ₂ . The crystals obtained in this way are too small for the analysis of individual crystals (the minimum size should be 50 μm), however, the data obtained using chemical analysis and X-ray diffraction analysis (X-ray powder diffraction pattern) indicate the correspondence of the bulk of the product to kieserite (MgSO ₄ · H ₂ O) .

3. Tests in a closed loop system

Tests in a closed-loop system are used to evaluate the mutual effects of leaching and crystallization, which are the two main steps of the method of the present invention. The neutralization step is used to control the accumulation of iron and nickel in the solution for the recirculation system. Each cycle includes a sequence of stages of leaching, neutralization and crystallization using at each stage the solution obtained in the previous stage. The sequence of stages is repeated several times to achieve equilibrium.

The difference in solubility of magnesium sulfate in the leach solution compared to the crystallization solution is sufficient to distribute all the additional magnesium entering the system. The only way to remove magnesium from the system is crystallization. The difference in solubility increases due to different crystallization temperatures (110 ° C) and leaching temperatures (85 ° C).

Jacaré saprolite ore tests are conducted in a closed loop at a solid density of 10% (solid / solid + water).

Nickel extraction exceeds 90%, and the initial concentration of hydrochloric acid is maintained by sequentially adding sulfuric acid and removing magnesium sulfate in the crystallization stage. Part of the removed (diversion) solution after crystallization serves to maintain the concentration of iron and nickel in the primary cycle, however, after three cycles, the compensation of the water balance in the primary cycle becomes decisive when the process is carried out on a laboratory scale (static mode). However, the results obtained after the first three cycles (table 2) indicate that a constant concentration of the starting reagent (hydrochloric acid) can be maintained by adding sulfuric acid to precipitate magnesium sulfate.

The composition of saprolite ore:

Fe: 15%

Ni: 1.5%

Mg: 18%

The density of the leach solution: 10%.

The formation of a certain amount of crystals of magnesium sulfate is also observed upon neutralization to remove iron from the bypass stream. However, such crystals dissolve again and are sent to the recirculation system to rinse the final cake with a small amount of water.

Table 3 shows the compositions of solids formed during crystallization during the last cycle of two tests in a closed-loop system, carried out at 85 ° C and 105 ° C, respectively. In both cases, a magnesium salt is formed at a molar ratio of magnesium / sulfate close to unity. The results of X-ray diffraction analysis (see FIG. 29) indicate that the salt precipitated at elevated temperature consists mainly of kieserite (MgSO ₄ · H ₂ O).

Table 3 The composition of the solids formed in the mold Mg Fe Ni Cl SO ₄ H ₂ O * Mg: SO ₄ Mg: H ₂ O 85 ° C 16.5% 0.30% 0.22% 0.54% 64.4% 18.0% 1: 0.99 1: 1,5 110 ° C 16.4% 0.27% 0.08% 1.94% 67.0% 14.3% 1: 1,03 1: 1,2 * water content was determined by subtracting the total content of components from 100%.

4. Tests with direct replacement of sulfuric acid with sulfur dioxide

The following procedure describes the use of sulfur dioxide to regenerate hydrochloric acid in a mixed chloride / sulfate system using the resulting solution to leach valuable metals from oxide or sulfide ores.

First of all, iron (3+) is required at the stage of acid regeneration for its use as a carrier / sorbent for gaseous sulfur dioxide. The bulk of the iron enters the solution in the form of Fe (3+) at the stage of ore leaching, as, for example, occurs during the leaching of oxide ores, such as nickel limonites. However, if the bulk of the iron enters the solution in the form of Fe (2+), an oxidizing agent (such as oxygen) is required to oxidize ferrous iron to ferric.

Then carry out the stage of acid regeneration, during which the absorption of sulfur dioxide is accompanied by the release of sulfuric acid in solution:

In a mixed chloride / sulfate system, the difference in solubility of chloride and sulfate is used to regenerate the equivalent of hydrochloric acid consumed during leaching. When magnesium is leached from lateritic oxide ores, the following reaction proceeds:

The following is a general reaction scheme for the acid regeneration step:

Similar reactions occur during the leaching of other metals, which can be used to develop methods for the regeneration of an equivalent amount of hydrochloric acid consumed in the leaching stage. The precipitated salt (MgSO ₄ · H ₂ O described in the previous example) is thermally decomposed to regenerate an equivalent amount of sulfur dioxide gas, thereby providing a self-sustaining process. In another embodiment, sulfur (or another cheap source of sulfur) is burned in air to form gaseous sulfur dioxide, which is used as described above, that is, there is no need to convert the gas to sulfuric acid in an expensive sulfuric acid plant.

All of the above reactions are carried out on a laboratory scale. However, at lower pH (apparently due to the continuation of the reaction), the reaction rate (6) may decrease. To accelerate the reaction (6) on an industrial scale, you can use a catalyst, such as copper ions in solution, graphite or even coal.

Nickel laterite sample provided by Jacaré, Brazil. It is established that the material contains a certain amount of magnesium, which will consume a significant amount of acid during acid leaching. Therefore, a solution of magnesium chloride is obtained at a saturation of 80% at 80 ° C. Then, other components of the saline solution were added according to the mass balance, laterite pulp was obtained in the indicated medium, and the pH of the medium was adjusted to 0.5 with the addition of hydrochloric acid. The extraction yield of nickel and magnesium from laterite is more than 80% at a contact time of 3 hours in the system. After the leaching, the saturated solution is bubbled with gaseous sulfur dioxide, and magnesium precipitation is observed at least in the amount obtained after leaching of the laterite sample. A precipitate is obtained in the form of crystalline magnesium sulfate monohydrate. At the same time, the concentration of acid in the medium is restored after leaching, providing leaching of the next sample.

Sulfate is calcined to form magnesium oxide, which is redundant in relation to the requirements for internal processes. A certain amount of the obtained magnesium oxide is used to precipitate iron, nickel and cobalt from the leaching solution in the form of two types of hydroxides - iron hydroxide and cake of nickel and cobalt hydroxides. The product containing iron is discarded, and the main product is obtained in the form of a mixture of nickel and cobalt.

The data in table 4 indicate that gaseous sulfur dioxide can, in principle, be used to replace sulfuric acid in the crystallization stage, provided that there is a sufficient amount of iron ions (3) and sufficient time is used to carry out the reaction.

Table 4 Replacing sulfuric acid with sulfur dioxide Reagents Reaction time The final amount of acid (HCl) Sulfur dioxide gas 0% + Sulfuric acid 100% 2 h 163 g / l Sulfur dioxide gas 25% + Sulfuric acid 75% 2.25 h 159 g / l Sulfur dioxide gas 50% + Sulfuric acid 50% 4,5 h 157 g / l

Based on the data obtained, the following conclusions can be drawn:

- The concentration of the starting reagent (hydrochloric acid) is kept constant in the main cycle during the precipitation of magnesium sulfate with concentrated sulfuric acid, which ensures efficient extraction of nickel during the first leaching stage.

- The solubility of magnesium sulfate in the mold is less than its solubility in the leach solution, especially at elevated temperatures and increased concentrations of magnesium chloride in the mold.

- The crystals formed during crystallization are magnesium sulfate monohydrate (kieserite) with the inclusion of a certain amount of nickel and chloride. The inclusion of chloride occurs as a result of capture of the solution with a finely divided precipitate, and the inclusion of nickel can be minimized by crystallization at elevated temperature (slightly below the boiling point of the solution at atmospheric pressure).

- Gaseous sulfur dioxide can be used to systematically replace an equivalent amount of sulfuric acid, provided that there is a sufficient amount of ferric ions to absorb gaseous sulfur dioxide.

Sulfide ores

Another embodiment of the present invention relates to the use of a solution of hydrochloric acid (chloride) for the oxidative or non-oxidative leaching of sulfide concentrates, such as zinc ores, as described below. Although the use of non-oxidative processes to extract base metals from sulfide concentrates is not new in itself (sulfate medium: SC Copper Process, Kawulka et al. (1978), chloride medium: Molleman et al. (1998)), a regeneration method acid is not known in the art. A non-oxidative method of leaching in high concentration saline solutions in combination with an integrated acid recovery step is also not known in the art. Valuable non-ferrous metals, such as zinc, are leached from sulfide concentrates in a stock solution of hydrochloric acid. Leached non-ferrous metal is obtained as a commercial product. The leaching kinetics are fast, and metals such as copper form a solid phase (such as Cu _x S) and are recovered from the tail fractions if necessary using an oxidative leaching process. An additional advantage of non-oxidizing conditions is the possibility of separating elemental sulfur using the standard Klaus process (petroleum and petrochemical industries).

The main leaching agent is the hydroxonium ion in the initial chloride medium, which is determined by the accumulation of salts, primarily non-ferrous metal salts such as zinc chloride, in the primary system of the process.

In the crystallization step, the low solubility of the non-ferrous metal sulfate or sulfite, such as zinc, in the initial chloride salt solution is used to remove the leached valuable metals from the solution. Sulfate or sulfite crystals contain a small amount of hydrated water and are suitable for thermal decomposition with the formation of oxide (for use as an internal neutralizing agent), which can be used as a commercial product or part of which can be dissolved in a solution of sulfuric acid (formed during electrolysis) and used for direct electrolysis of metal.

The regeneration of hydrochloric acid and the recovery of non-ferrous metal, such as zinc, as described above, are not associated with excessive removal of water by evaporation, because the metal is obtained from crystalline cake with a low content of water and hydrated water.

The present invention is based on a significant difference in the solubility of zinc in sulfate and chloride systems, the latter being almost 2 times higher at 100 ° C (see experimental data published by Linke and Seidell (1965)). It was also found that in a chloride medium this phenomenon is enhanced and used to significantly reduce the solubility of zinc in a chloride medium, while when sulfate or sulfite is added in the form of gaseous sulfur dioxide or in the form of sulfuric acid as intermediate reagents for entering the recirculation system , zinc sulfate or sulfite is formed and precipitated with the simultaneous regeneration of hydrochloric acid in solution. Moreover, from the obtained experimental data, it follows that gunningite (zinc sulfate monohydrate) is the preferred crystallization product in a wide temperature range (usually at about 60 ° C), which minimizes the amount of energy required for calcination to obtain zinc oxide (which partially sent to the recirculation system as an internal neutralizing agent) and sulfur dioxide regeneration. A simplified reaction scheme is shown below:

A crystalline product containing less than 0.01% of total chloride is obtained by the described procedure to illustrate the effectiveness of this technology, i.e. to obtain highly purified zinc oxide as a commercial product (a certain amount is used as an internal neutralizing agent) or to re-dissolve zinc oxide in a solution of sulfuric acid (coming after electrolysis) and direct electrolysis of zinc from the resulting solution. The relatively expensive hydrochloric acid is also regenerated using a relatively cheap and affordable reagent, i.e. gaseous sulfur dioxide or sulfuric acid. Precipitated zinc sulfate is an ideal decomposition product in a fluidized bed reactor. Partial rehydration of the monohydrate (to obtain an optimized hydrate for thermal decomposition) is carried out by monitoring the contact time of the crystalline precipitate with a suitable aqueous mother liquor. If the direct use of sulfur dioxide is technically promising, the technology for the recovery of sulfuric acid from sulfur dioxide obtained by calcining sulfur sulfate is well known and is a means of precipitating gunningite, which is experimentally feasible. In any case, no additional processing reagents are required, as sulfur dioxide is a product of the thermal decomposition stage. The main advantage of using zinc sulphate with a low content of hydrated water for decomposition to zinc oxide is a significant reduction in energy consumption compared to the pyrohydrolysis of zinc chloride solution.

Favorable leaching kinetics are achieved by processing the original crude concentrate, which allows the method of the invention to be used to leach valuable metals, such as zinc, silver and lead, from sulfide ore. The most important is the fast (less than 1 h) leaching kinetics at a temperature of 85 ° C in 4 M hydrochloric acid solutions (Fig. 35).

A schematic diagram of the process is shown in FIG. 32, in which the leaching solution of hydrochloric acid is used to solubilize valuable zinc from a sulfide material in a non-oxidative stage, and then the zinc is subsequently removed as a crystalline salt in the acid recovery step. To extract zinc sulfate with the addition of sulfuric acid, processing of a saturated solution is not required for leaching with a neutralizing agent. Sulphate is precipitated preferably in the form of a monohydrate, and not in the form of hexahydrate (as seems obvious to those skilled in the art). The main advantage is the conversion of sulfate to oxide, as however, there is a significant saving in energy consumption compared to hexahydrate. Impurities such as iron are removed by hydrolysis after neutralizing the excess acid with zinc oxide from the recirculation system obtained after calcination.

A similar result is achieved by directly adding gaseous sulfur dioxide (instead of sulfuric acid) while bubbling a saturated leach solution. The advantage of this treatment is manifested in the case of calcination of elemental sulfur or solid sulfate with the formation of sulfur dioxide compared with the use of finished commercial sulfuric acid.

This method is based on the new principle of regeneration of reagents, i.e. on the reuse of the leach agent and neutralizing agent in the recirculation system of the process.

Preliminary calculations of the mass / energy balance showed a significant advantage of this principle compared to the standard processing of sulfide ores.

The most important factors are:

- as a concentrate, you can use purified concentrate or less purified (coarse) concentrate (a higher degree of extraction of valuable metals),

- non-oxidative leaching is carried out at any desired concentration of HCl, provided that the total chloride level in the rest of the system is maintained,

- Cu is reprecipitated as Cu _x S in the leaching stage at atmospheric pressure, i.e. if necessary, copper is removed from the remainder of the waste rock, if this justifies the costs,

- Pb is leached from the system in the form of chloride complexes and precipitated in the mold in the form of sulfate. PbO formed at the stage of thermal decomposition is effectively removed from the residue obtained at the stage of re-leaching of ZnO in the form of a purified salt of PbSO ₄ ,

. Основным преимуществом данной реакции является свойство исходного солевого раствора связывать свободную воду, при этом образуются дегидратированные соли (менее 1 моля Н₂О на 1 моль цинка), что значительно снижает энергозатраты на стадии разложения по сравнению с солями, включающими большое количество гидратной воды, такими как ZnSO₄·6H₂O,- ZnSO ₄ · H ₂ O is formed in the mold when H ₂ SO ₄ is added to the chloride solution due to differences in the solubility of sulfate and chloride:

. The main advantage of this reaction is the ability of the initial salt solution to bind free water, and dehydrated salts are formed (less than 1 mol of Н ₂ О per 1 mol of zinc), which significantly reduces energy consumption at the decomposition stage compared to salts containing a large amount of hydrated water, such as ZnSO ₄ · 6H ₂ O,

- the expediency of direct use of sulfur dioxide (formed at the stage of thermal decomposition) as a starting reagent for the deposition of ZnSO ₄ · 6H ₂ O, provided that there is a sufficient amount of ferric iron for absorption of sulfur dioxide in the solution phase, has been established. In this case, before the crystallization stage, the addition of an oxidizing agent (such as atmospheric oxygen) is required to oxidize ferrous iron (obtained by non-oxidative leaching) to ferric iron,

- the above stages of crystallization and thermal decomposition include reagents in a stoichiometric ratio, and it does not require additional addition of sulfuric acid or sulfur dioxide (with the exception of the analysis of products in a specific industrial installation),

- part of the saline is diverted from the main stream (before crystallization) to limit the accumulation of iron in the original system; a proportional amount of zinc oxide (obtained at the stage of thermal decomposition) enters the recirculation system to neutralize the free acid in the waste stream containing impurities, which ensures the saturation of valuable metals (silver, nickel, cobalt, cadmium) with zinc dust before iron removal,

- hydrolysis of iron is carried out at atmospheric pressure or under reduced pressure in an autoclave, and hematite and / or goethite are obtained (presumably in the form of acaganite); Another advantage of a high concentration saline solution is the extremely low content of free water, which in turn provides dehydration of iron oxides / hydroxides and precipitation of hematite at significantly lower temperatures compared to standard sulfate systems,

- the bulk of the zinc oxide (with the exception of the bypass stream to neutralize) enters the stage of re-leaching, in which the oxide is dissolved in the presence of sulfuric acid in the anolyte coming from the electrolysis system; the acid is in a stoichiometric ratio, and the addition of additional acid or a neutralizing agent is not required (except for the analysis of products obtained in an industrial plant)

- in the whole system there is no need for a bypass stream, or it is necessary to divert only a small amount of solution, sodium sulfate accumulates to saturation and precipitates in the most concentrated part of the system,

- since there is no need for a bypass stream or it is necessary to divert only a small amount of solution, the removal of water is achieved using a multi-case evaporator,

- Fig. 33 shows chloride and sulfate closed systems in an integrated general process diagram.

Metallurgical analysis

Laboratory tests include 4 stages, i.e. leaching, crystallization, thermal decomposition and re-leaching of calcined zinc oxide. The distribution of the following elements in the system is estimated (the lower detection limit was 10 ppm): aluminum, calcium, cadmium, cobalt, chromium, copper, iron, magnesium, manganese, nickel, lead, silicon, zinc.

Test conditions are determined by the simulation of the mass / energy balance. An important difference between computer and real modeling was that computer simulations were performed using refined concentrate (approximately 50% zinc) and laboratory simulations using less refined crude concentrate (approximately 5% zinc).

Metallurgical analysis at this initial stage is carried out only for samples obtained at the stage of non-oxidative leaching at atmospheric pressure and after processing in a crystallizer. The non-oxidizing leach plant is shown in FIG. 34.

The vapor phase is absorbed in a scrubber containing iron sulfate (3), with the aim of converting all of the hydrogen sulfide H ₂ S obtained by leaching into elemental sulfur. Scrubber evacuation is more appropriate compared to the increased pressure in the leach reactor, i.e. due to the possibility of leakage of hydrogen sulfide into the environment. Air is bubbled through the leach reactor to ensure continuous removal of hydrogen sulfide from the system, i.e. To shift the reaction to the right:

On Fig shows the standard kinetics of leaching when tested at a low density of solids in the selected fraction with a specific particle size (fine particles were removed). Kinetics in the presence of 4 M hydrochloric acid turned out to be quite optimal. The presence of inhibition periods during the other two tests is a consequence of surface polarization in the anode direction, i.e. due to the presence of oxygen (during bubbling), thus, late bubbling of air through the solution must be stopped.

The main advantage of using crystallization (ZnSO ₄ · H ₂ O) in the system is that it does not need to be neutralized after leaching, i.e. leaching can be carried out at any concentration of HCl, i.e. to ensure fast kinetics. On Fig shows a typical crystallization product from saline in the presence of concentrated H ₂ SO ₄ . The main part of the product is gunningite [Zn (SO ₄ ) (Н ₂ О)], but according to X-ray diffraction analysis, a high degree of crystallinity of gypsum type is observed. At extremely high NaCl concentrations, a small amount of changoite [Na ₂ Zn (SO ₄ ) ₂ · 4H ₂ O] is also precipitated.

To prevent the influence of other elements at the crystallization stage, the concentration of the solutions is maintained below the solubility of sulfate or sulfite, which is achieved by treating the bypass stream, for example, from a saturated solution for leaching during saturation (cementation) and / or neutralization. For the indicated neutralization, part of the calcination product may be used.

The water balance of the process is maintained by evaporation to control the concentration of the saline solution, to compensate for the addition of water at various stages, such as the flow of the leach solution, rinse water, and the like.

Sulfide ore leaching

The method is described below on the example of zinc sulfide.

A concentrate obtained by flotation of sphalerite from ore from the Gamsberg deposit (South Africa) is used. The concentrate is leached in 4 N. hydrochloric acid in the presence of the starting zinc chloride in solution at 85 ° C. Leaching was completed after 15-30 minutes. The initial concentration of zinc chloride (concentrate / salt ratio) is selected so as to obtain a saturated leach solution at 80% saturation of zinc chloride. The leach solution is mixed with 98% sulfuric acid in a beaker with stirring, with the precipitation of zinc sulfate in an amount equivalent to the amount of leached zinc. The precipitate is crystalline zinc sulfate in the form of a hemihydrate, which corresponds to the calculated amount of salt. The salt is optionally calcined to produce oxide at a suitable temperature, for example 750 ° C., in air, whereby a gaseous phase is obtained containing at least 20% sulfur dioxide, suitable for use in a sulfuric acid plant or for direct reuse in the crystallization step .

Crystallization

A basic solution containing zinc, iron, sodium in the form of chlorides and sulfates is obtained at 60 ° C, then a stoichiometric amount of sulfuric acid is added to the solution. These tests are carried out with a double purpose: to determine the solubility of the main components in the solution and to determine the amount and purity of the crystals formed when sulfuric acid is added. The research results are shown in table 5.

Table 5 Solubility and Crystallization Results Sample Leach Crystalline substance Zn g / l Fe g / l Na g / l Cl g / l SO ₄ g / l Zn Fe Na Cl SO ₄ 20050324D4 288 0 0 318 167 40% 0% 0% 5% 41% 20050324D5 290 0 52 407 36 41% 0% one% 5% 45% 20050324D6 98 3.8 61 61 230 - - - - - 20050324D7 320 6.3 23 373 94 38% 2.5% 0.3% four% 46%

When testing sample 20050324D6, crystal formation was not observed due to the low initial zinc concentration. The results obtained indicate that in systems containing Zn, precipitation crystallization can be successfully used for the primary regeneration of reagents.

Obtaining a chloride solution with a high concentration of acid (super acid solution)

The chloride salt solution is mixed with sulfuric acid or sulfur dioxide to obtain a salt solution containing hydrochloric acid in an azeotropic concentration (i.e., at a concentration at which the concentration of hydrochloric acid exceeds the azeotropic concentration). This process does not require sophisticated distillation equipment or expensive reagents. Thus, a simple and cheap method of obtaining solutions with extremely high acidity is proposed for subsequent use in certain processes, such as special dissolution methods that are used in the purification of platinum group metals.

The achieved acidity of the acid, which may be lower and higher than the azeotropic concentration, is determined by the nature of the selected chloride.

Preparation of High Acid Chloride Saline

Magnesium chloride is dissolved at 100 ° C. to a concentration of approximately 42.3 g / 100 g of saturated solution. With the addition of H ₂ SO ₄ in extreme cases of complete precipitation of magnesium, approximately 50.3 g of salt in 49.7 g of water and 32.4 g of HCl with an acidity of 39% are formed as a monohydrate.

Preparation of High Acid Chloride Saline

Magnesium chloride is dissolved at 80 ° C. to a concentration of approximately 84.4 g / 100 g of saturated solution. When H ₂ SO ₄ is added, in the case of precipitation of 75% zinc, approximately 71.1 g of salt in 28.3 g of water and 33.9 g of HCl with an acidity of 54% are formed as a monohydrate.

The present invention has been described in detail using particular embodiments thereof, but those skilled in the art will appreciate that many modifications and other changes are possible without departing from the spirit and scope of the present invention within the scope of the appended claims.

Claims (40)

1. The method of leaching metal from its containing ore, in which
ore is leached in the presence of hydrochloric
acids to form soluble metal chloride in the leach solution,
sulfuric acid is added to the leach solution to form precipitated solid metal sulfate in the leach solution, in which the metal source is mainly ore,
carry out the regeneration of hydrochloric acid simultaneously with the precipitation of solid metal sulfate and remove solid metal sulfate from the solution for leaching and
a solution of regenerated hydrochloric acid with a high concentration of chloride ions and a low concentration of sulfate ions is returned to the leaching stage. 2. The method according to claim 1, in which the metal sulfate is characterized by the formula MeSO ₄ · yH ₂ O, where
Me means metal
and y is 0 or more. 3. The method according to claim 2, in which the value of y is from 0 to 3. 4. The method according to claim 2, in which y is 0. 5. The method according to claim 2, in which y is 1. 6. The method according to claim 1, in which the ore is mainly oxide or silicate ore containing a base metal. 7. The method according to claim 6, in which the ore is zinc oxide ore. 8. The method according to claim 1, wherein the ore is lateritic nickel ore. 9. The method of claim 8, wherein the laterite ore is saprolite or limonite ore. 10. The method according to claim 1, in which the ore is sulfide ore. 11. The method according to claim 1, in which the ore is titanium ore. 12. The method according to claim 1, in which the ore is aluminum ore. 13. The method according to claim 1, wherein the metal sulfate is precipitated from the leach solution. 14. The method according to claim 1, in which the metal sulfate is removed from the solution for leaching by crystallization with evaporation. 15. The method according to claim 1, in which the metal is selected from the group comprising Zn, Cu, Ti, Al, Cr, Ni, Co, Mn, Fe, Pb, Na, K, Ca, platinum group metals and gold. 16. The method according to claim 1, in which the metal in the composition of the metal sulfate is a metal leached from ore. 17. The method according to claim 1, in which additionally carry out the decomposition of metal sulfate to extract leached from the metal ore. 18. The method according to claim 1, in which the metal in the metal sulfate is a less valuable metal than the metal leached from the ore. 19. The method according to p, in which the metal in the composition of the metal sulfate is magnesium. 20. The method according to claim 1, in which the metal sulfate is processed under conditions in which sulfur dioxide or sulfur trioxide, or a mixture thereof, is formed. 21. The method according to claim 1, in which the valuable metal is recovered independently of the metal salt formed by the addition of sulfuric acid. 22. The method according to claim 1, in which the regenerated hydrochloric acid is super-azeotropic acid. 23. The method according to claim 1, in which the metal chloride solution is a solution containing an alkali metal chloride. 24. The method according to claim 1, wherein the metal sulfate is an alkali metal sulfate. 25. The method according to claim 1, in which the recycled regenerated hydrochloric acid is recycled in the leaching process. 26. The method according to claim 1, in which hydrochloric acid, designed for leaching of ore, is present in the composition of the saline solution. 27. The method according to p. 26, in which from a salt solution using from about 10% to about 90% saturated solution of magnesium chloride, from about 10% to about 90% saturated solution of zinc chloride, or from about 10% to about 90% saturated chloride solution of another metal. 28. The method according to p. 26, in which from a salt solution using from about 25% to about 40% saturated solution of magnesium chloride, from about 25% to about 40% saturated solution of zinc chloride, or from about 25% to about 40% saturated chloride solution of another metal. 29. The method according to claim 1, in which the metal sulfate is used to produce metal oxide. 30. The method according to claim 1, in which the metal sulfate is subjected to thermal decomposition to obtain metal oxide and sulfur dioxide, sulfur trioxide or mixtures thereof. 31. The method according to clause 29, in which the metal oxide is selected from the group comprising magnesium oxide, zinc oxide, iron oxide and alumina. 32. The method of claim 30, wherein the metal oxide is selected from the group consisting of magnesium oxide, zinc oxide, iron oxide, and alumina. 33. The method according to clause 30, in which sulfur dioxide, sulfur trioxide or a mixture thereof is used to produce sulfuric acid, which in turn is returned to the leaching process for the regeneration of hydrochloric acid. 34. The method according to claim 1, in which the metal is leached from ore at a temperature of from about room temperature to about the boiling point of a metal chloride solution for leaching. 35. The method according to claim 1, in which one or more leached from ore metals are selectively removed from the solution before the stage of formation of metal sulfate. 36. The method according to clause 35, in which the selectively removed metal is cobalt, nickel, platinum group metals, gold, silver and / or copper. 37. The method according to claim 1, in which impurities of iron and / or other residual impurities generated after solubilization of the ore are partially or completely removed from the leach solution. 38. The method according to clause 37, in which impurities of iron and / or other residual impurities are removed by solvent extraction followed by pyrohydrolysis. 39. The method according to § 38, in which impurities of iron and / or other residual impurities are removed by hydrolysis. 40. The method according to claim 1, in which the concentration of sulfuric acid is at least 30%.

Images