RU2146763C1 - Method for processing of mineral ore containing gold and silver at site of their deposition - Google Patents

Abstract

FIELD: mining industry. SUBSTANCE: method relates to oxichloride technology of lixiviation of noble metals from ores containing arsenic and mercury at site of their deposition and it can be used at heap and underground lixiviation and also in hydrometallurgy for separation gold and silver from ores and concentrates. According to method, solutions of reagents are delivered into blocks of ore body through system of injection wells, and productive solutions are withdrawn through system of withdrawing wells. Lixiviation of gold and silver is performed by stages. At first stage, delivered into block of ore body is acidiferous chlorinated solution of trivalent iron so as to prevent lixiviation of arsenic from ore and also to prevent spreading of solutions from ore block being treated. At second stage, lixiviation is carried out by delivery of chlorine solution so as value pH of productive solution is maintained at level below 3. Removed from productive solution which is produced at first stage prior to its processing is surplus chlorine down to its minimal values, thus allowing for keeping gold in solution. Absorption of separated chlorine is performed by mother liquors of sorption freed from mercury. At last stage, withdrawn are solutions containing chlorine and iron to be delivered to next ore block prepared for processing. Then, silver is lixiviated in ore block being processed by means of sulfur-containing reagents. After that, productive solutions are processed by means of sorption and cementation. Ground water involved in lixiviation process is reclaimed. At each stage of lixiviation, process is monitored through inspection wells. Application of aforesaid method improves efficiency of underground lixiviation due to increased recovery of noble metals in conditions of ecological safety of process. EFFECT: higher efficiency. 5 cl, 6 tbl

Description

 The invention relates to oxychloride technology for leaching precious metals from ores containing arsenic and mercury, at the site of their occurrence. The claimed technical solution can be used in geotechnology for heap and underground leaching of gold and silver from mineral raw materials, as well as in hydrometallurgy in the extraction of precious metals from ores and concentrates.

 A number of methods are known for extracting precious metals from ores and concentrates using solutions of cyanides, thiourea, thiosulfates, rhodanides, halogen salts in the presence of strong oxidizing agents in acidic or alkaline environments as solvents and complexing agents. Each method is characterized by its own characteristics and can be used subject to a number of conditions, which determines the variety of proposed and applied methods for the extraction of precious metals from ores and concentrates (international applications NN 85/00384, 84/00563, AS Czechoslovakia N 241214).

 Known hydrometallurgical method of leaching gold and silver in an alkaline medium (pH 8-13) with a solution containing 12% chloride and 1% sodium hypochlorite. After the cementation of gold and silver with zinc, hypochlorite is regenerated by electrolysis and the solution is returned to leach (US patent N 4342592, 1982).

 Known hydrometallurgical method for the extraction of precious metals from ores chloride-hypochlorite solution. The recommended solution contains 3% sodium chloride and 0.3% sodium hypochlorite. Extraction of metals from the solution is carried out by electrodeposition on the cathode or in other ways. The solution after adding hypochlorite is again used for leaching (US patent N 5169503, 1992).

 A known method of leaching silver at the place of ore ore, in which a chlorinated aqueous brine (a chlorinated solution of high concentration salt) having an ORP of at least 500 mV is supplied to the ore body. The extraction of silver is carried out by the method of dissolution (US patent N 3647261).

 These proposed methods have a common drawback: the additional use as cations and complexing agents of increased concentrations of phosphates, chromates, hydroxides, ammonium salts, chlorides of alkali and alkaline earth metals or mixtures thereof, which does not allow their use in underground leaching without taking measures to limit the spreading of leach solutions to prevent salinization of groundwater, especially in the case of ore in the aquifer used for drinking water supply. In addition, the presence of an increased concentration of chlorides prevents the natural self-purification of solutions when they are diluted at the end of mining due to the presence of easily moving chlorine ions in the solution. The use of special methods for cleaning contaminated groundwater from phosphorus, chromium, ammonium and chlorine ions increases the cost of producing precious metals, and in some cases makes it unprofitable.

Closest to the claimed method according to the technical essence is "Environmentally friendly method of underground leaching of precious metals, mainly gold and silver, from ores at the place of their occurrence" (RF patent N 2074958, MKI ⁶ E 21 V 43/28 op. 1997) .

 According to this method, the leaching of precious metals, mainly gold and silver, is carried out in two stages. Leaching is carried out by feeding reagent solutions to the ore blocks to be mined through a system of injection wells and pumping productive solutions through a system of pumping wells with a chlorine solution for gold leaching in the first stage, and sulfur-containing reagents for silver leaching in the second stage. Processing of productive solutions is carried out by sorption, cementation or electrolysis. Groundwater involved in the leaching process is reclaimed.

 The disadvantage of this method is the insufficiently high extraction of gold and silver at elevated pH values from ores, especially those containing clay materials (kaolinite, montmorillonite, halloysite), which have a layered crystalline structure. A feature of such minerals is their ability to swell and decompose into tiny particles, especially in the presence of alkaline solutions, which, in turn, leads to a decrease in the filtration rate of leaching solutions, and in some cases to the termination of the filtration process. In the presence of zones of increased water conductivity at pH values of solutions of more than 3.0, it becomes practically impossible to use relatively safe inorganic colmatants, for example ferric sulfate, to reduce the water conductivity of these zones due to the hydrolysis of iron salts and the mudding of the filter zone of injection wells.

 Another disadvantage of this method is its high chlorine consumption, which is associated with the neutralization of active chlorine in the subsequent leaching of silver.

 In addition, the introduction of additional reducing agents to reduce the content of active chlorine in productive solutions and spent air airlift air increases the cost of metal mining and, with inevitable fluctuations in the leaching process, can be a source of additional environmental pollution. In addition, using this method, it is impossible to utilize the chlorine released during the leaching process and remove arsenic, mercury and other heavy metals from solutions that are satellites of recoverable noble metals.

 It should be noted that the thermodynamic basis for using an alkaline medium in the dissolution of gold is also a disadvantage of this method. Since the thermodynamic potential of oxidation of elemental gold to the Au (III) state corresponds, according to the data of D. Latimer and I. Kakovsky, 1.50 - 1.41 V (hereinafter with respect to the normal hydrogen electrode), when using slightly acidic or acidic chlorine solutions creates an environment characterized by oxidizing ability at the level of 1.36 - 1.40 V, and in an alkaline medium ORP is much lower - 0.9 V. Therefore, the use of acidic chlorine solutions provides a greater kinetic effect - the rate of the process of dissolution of gold in acid wed e exceeds that in an alkaline environment.

 The problem to which the invention is directed is to increase the efficiency of underground leaching by increasing the extraction of precious metals (gold and silver), while ensuring the environmental safety of the process.

 To achieve this goal in a method of processing mineral raw materials containing gold and silver from ores at the place of their occurrence, including stepwise leaching, which is carried out by supplying reagent solutions to the processed blocks of the ore body through a system of injection wells and pumping productive solutions through a system of pumping wells, with the supply in the first stage of a solution of chlorine for leaching gold, and in the second stage with the supply of sulfur-containing reagents for leaching silver, processing of productive according to the invention, the leaching of gold is carried out by supplying a chlorine solution so that the pH of the productive solution is maintained below 3, before processing the productive solution, excess chlorine is removed from it to the minimum values that allow gold to be retained in solution, while the absorption of excess chlorine is carried out by sorption mother liquors purified from mercury, and before leaching of silver, chlorine-iron-containing solutions are pumped out the next block prepared for testing, and at each stage of leaching, the process is monitored through observation wells.

 When processing arsenic ores before leaching gold, an acid chlorinated solution of ferric iron salts is fed into the mined block to prevent leaching of arsenic from the ore and spreading of the solutions outside the mined block.

 When the molar ratio of carbonates and sulfides in the ore is less than 8, leaching begins with the addition of a chlorinated ferric salt solution with a pH value to the processed block, which excludes the mudding of the filter zone of the injection wells.

 When observing wells record a sharp increase in the redox potential and a decrease in the pH of leaching solutions, the concentration of chlorine in the injection solutions is reduced, and to achieve optimal pH and redox potential in the productive solutions, the dependence of the parameters of the injected solution on the amount of previously leached reagent, concentration and time is used its appearance in the observation well.

 Extraction of mercury from sorption mother liquors is carried out using iron and / or iron-carbon-containing waste from metallurgical industries.

 During the reclamation of waters involved in the leaching process, the residues of sulfur-containing reagents are neutralized by supplying air and a solution of calcium hydroxide to the processed block.

 The proposed method is as follows. The ore body to be mined is opened with a system of pumping, injection and observation wells, during the drilling and construction of which they determine the material composition and the presence of zones of increased water conductivity, and begin supplying acidic chlorinated solutions in the presence of ferrous sulfate. The introduction of acid into the mining block is caused by the need to prevent the precipitation of iron hydrates and the clogging of the filter zone of the injection wells, as well as to create optimal pH values of the productive solutions. In this case, the injection wells are positioned so that the spreading area of the leach solutions during mining does not extend beyond the boundary of the block being worked out. The method uses non-oxidizing acid to reduce unproductive consumption used in the leaching of the oxidizing agent. As such an acid, hydrochloric acid with a concentration of 1-5 g / l is used.

 In order to prevent the transition of arsenic into the solution during the leaching of precious metals from arsenic ores, ferric salts are introduced into the leach solution, which contribute to the precipitation of arsenic and the purification of productive solutions from it.

When the ratio of the contents in the Fe ³⁺ : As ⁵⁺ solution is more than 40, arsenic is almost completely purified from the productive solutions.

The concentration and amount of Fe ³⁺ introduced into the ore body to prevent the dissolution of arsenic, as well as to create antifiltration curtains around the perimeter of the block being worked out and colmatization of interlayers with increased permeability, is established experimentally for the ores of each deposit. In the event that a sufficient amount of Fe ³⁺ is generated in the solutions and there is no need to create anti-filtration curtains and colmatation of permeable layers, it is not supplied to the leach solutions.

 Initially, the spent block is acidified in a “passive” mode due to the spreading of acid chlorinated sulfated solutions of oxide iron supplied to the injection wells for the time necessary to fill the area to be clogged, while an antifiltration barrier is predominantly created along the external circuit of the block. At the end of the supply of the estimated amount of these solutions to the wells, they are kept in contact with the ore for a predetermined time. The contact time is determined by the properties of the ore and is established experimentally for the ores of each deposit.

 As the solutions are aged in the ore body, processes of their neutralization, hydrate formation in the range of pH 3.0 - 4.5 occur due to the hydrolysis of iron salts and the interaction of reaction products with rock-forming minerals, accompanied by precipitation and colmatization of the ore body.

 After that, pumping wells are put into operation. The non-productive solutions obtained during pumping are acidified with hydrochloric acid, chlorinated and fed into injection wells. In the absence of zones of increased water conductivity, the spreading of leach solutions beyond the limits of the processed block into the barren zone is prevented by maintaining a balance of solutions between their pumping and injection. In this case, such an amount of iron sulfate is introduced into the ore body that is sufficient to precipitate the arsenic leached from the ore.

When the molar ratio of carbonates and sulfides in the ore is less than 8, a chlorinated Fe ³⁺ solution having a pH value excluding its hydrate formation in the prefilter zone of the wells is fed into the injection wells.

 It should also be noted that during acidification and mining of an ore body having increased water conductivity, the rows of wells are located in this direction and oxide iron sulfate is fed to injection wells located in the zone of increased water conductivity. This helps to prevent the spreading of acidifying, and then leaching solutions beyond the boundaries of the mined block into the barren zone, which contributes to a more uniform study of the ore body and increases the recovery rate of precious metals.

After the specified amount of acid chloride solution of ferric salts is fed into the ore body and the anti-filtration barrier is created, the second leaching stage is started. Chlorine is used as an oxidizing agent according to GOST P 50234-92 with a volume fraction of chlorine of 99.8%. The chlorinated solution is sent to injection wells. The concentration of active chlorine is maintained in the range of 0.5 - 10 g / l, and the value of Eh of the redox potential (ORP) in the range of 1200 - 1260 mV. An increase in the concentration of active chlorine above 10 g / l is impractical, since the maximum solubility of chlorine is 9.97 g / l at an underground water temperature of 10 ^o C, and when the temperature drops below 9.6 ^o C, chlorine crystalline hydrates precipitate, which makes it impossible to supply chlorine-containing solutions into the ore body due to the cessation of their filtration, a decrease in the concentration of active chlorine below 0.5 g / l drastically increases the block working time.

 The appearance of the front of chlorinated solutions in observation wells is accompanied by a sharp drop in pH and an increase in the ORP of moving solutions. In this regard, to achieve optimal parameters of the productive solution (pH 3.0 - 2.0 and Eh 900 - 1000 mV), a new concentration of active chlorine and acid (if necessary) is calculated, supplied to the injection wells, depending on the previously leached amount , concentration and time of their appearance in observation wells, while the residual concentration of active chlorine in productive solutions should be in the range of 30 - 40 mg / l. This content is minimal and sufficient to retain gold in solution. The leaching process at a pH of the pumping solution of less than 3 prevents the premature decomposition of hypochlorous acid to chlorine ion in leaching solutions, contributes to the deep processing of the ore body and, as a result, increases the degree of gold recovery, reduces the working time and the specific consumption of chlorine for leaching. When the pH of the pumped solution is more than 3, leaching is accompanied by uncontrolled ballast formation of chlorine ions, which reduces the concentration of active chlorine in leach solutions, increases its consumption and time of ore mining.

 To prevent irrevocable losses of chlorine and air pollution before processing productive solutions, excess active chlorine is removed from them using one of the physical methods of exposure: heating, evacuation, air purging, or applying ultrasonic vibrations. The chlorine released in this case is sent for absorption to an absorber filled with plastic shavings and irrigated with mother solutions of the sorption redistribution. The resulting solutions are used for the preparation of leaching solutions, and the purified air is discharged into the atmosphere.

 The mother liquors of the sorption redistribution are subjected to treatment in order to remove mercury from them before they are fed to the absorber. This is achieved by contacting them with iron and / or iron-carbon-containing waste from metallurgical industries. With values of W: T = 100: 5 - 15 and the corresponding contact time, it is possible to reduce the mercury content to 0.01 - 0.05 mg / L. As the material containing iron, iron chips, sawdust, powder, scrap are used. The released elemental mercury is collected and disposed of. An excess of ferrous iron formed during the removal of mercury is used to absorb chlorine in the absorber. Thus, purification of the mother liquors of sorption from mercury can significantly reduce the mercury content in leaching production solutions, simplifies and facilitates the collection of released elemental mercury, and improves the environmental situation at the place of processing of mineral raw materials.

 The use of other mercury cementers, for example zinc, aluminum and others, is impractical because of their high cost, lack of simple and cheap methods for their extraction, and also because of the impossibility of their use for absorption of chlorine in the absorber.

 At the last stage of leaching, groundwater is decontaminated while silver is recovered.

 Preliminarily, in order to reduce the cost of reagents and reduce the spreading area of production solutions beyond the limits of the mined block, when ore is leached on new blocks, the industrial solutions of the processed block containing residual active chlorine and oxide iron are pumped out in the ore body, and after additional chlorination they are fed to pumping wells of the new block, while pumping unproductive solutions of the new block is not carried out, and leaching into the injection wells of the processed block solutions do not serve.

 When a new block of silver traces and / or pH values of 5.0 - 6.0 and redox potential = 400 - 500 mV appears in the injection wells, the transfer of solutions is stopped and sulfur-containing reagents capable of dissolving silver and which are deactivators are introduced into the injection wells of the processed block active chlorine. As such a reagent, sodium thiosulfate solutions are used, the concentration of which is maintained in the range of 1-5 g / l. Interacting with ore, thiosulfate leaches silver, at the same time reacts with the remains of the oxidizing agent, deactivating it.

 From the obtained thiosulfate solution, silver is extracted by known methods: sorption, cementation, or others. The completeness of silver extraction from ore is 91%.

 To extinguish acidity, destroy thiosulfates and reduce overall mineralization at the end of leaching, alternating pressure and calcium hydroxide are fed into the ore body. As a result of neutralization and the formation of precipitation, the mineralization of the waters involved in the leaching process decreases and does not exceed 1.7 - 2.5 g / l, the pH value stabilizes at 6.8 - 7.5.

 The speed of movement of groundwater through the waste block due to partial colmatation of the pore space after neutralization decreases below natural, which, with subsequent dilution by the enclosing waters, allows them to be used for economic activities.

 The proposed method was tested in laboratory conditions and in the field at the Gagarskoye deposit (Zarechny, Sverdlovsk region).

Example
At an industrial gold ore deposit, an experimental well cell was drilled according to the "envelope" scheme, including one pumping well in the center, 4 injection wells in the corners and an observation well located in the alignment of the pumping and injection wells at an equal distance between them. The distance between the pumping and injection wells is 10 m.

 For leaching gold in the first stage, solutions containing 1 g / l of active chlorine were used. The control and adjustment of the leaching process was carried out according to the results of the analysis of samples taken from the observation well. The optimal pH value of the productive solution was found during core leaching in laboratory conditions and is shown in table 1.

 Before processing the productive solution obtained on the experimental cell, an excess of chlorine was removed from it to the minimum values that allowed the gold to be retained in the solution, after which gold was extracted by sorption or cementation. Absorption of excess chlorine was carried out by sorption mother liquids purified from mercury, the purification of which was carried out using blast furnace dusts and / or zinc clinker containing,%: iron 42 and 35, carbon 16 and 20, respectively, at W: T = 100: 10.

 The results of determining the degree of extraction of mercury from mother liquors containing, for example, Hg = 6 mg / L and Eh and pH 560 mV 2.30, respectively, are shown in Table 2.

 As can be seen from table 2, the proposed metallurgical waste products are quite effective and not deficient.

The removal of excess chlorine from productive solutions before processing was carried out using known physical methods of exposure in the following degassing devices:
- countercurrent film deaerator with a nozzle made of plastic chips;
- vacuum - with a nozzle made of plastic chips, the vacuum in which was created using a vacuum pump or a water-jet ejector;
- ultrasonic intensive contact module using high frequency sound vibrations.

 The results of determining the concentration of residual chlorine in the productive solution at its initial content of 60 mg / l are shown in table 3.

 As can be seen from table 3, the degree of dechlorination of solutions in the proposed devices is quite high, while the value of the ORP in the solutions at the outlet of the apparatus was maintained in the range of values sufficient to retain gold in the solution.

 The absorption of excess chlorine released from productive solutions was carried out in a packed-type countercurrent absorber filled with polyethylene shavings and irrigated with uterine sorption solutions containing Fe (II) ions purified from mercury.

 The absorber has an additional nozzle in which air is purged from chlorine. The degree of chlorine utilization and the completeness of purification of the source chlorine gas with a chlorine content of 2 g / l in the gas to be purified are shown in Table 4.

 As can be seen from table 4, there is a fairly high efficiency and environmental friendliness of the proposed solution, which allows solving the issues of protecting the air basin and returning chlorine to the preparation of the leaching solution.

 In the second leaching stage, silver was extracted.

 Previously, before this operation, chlorine-iron-containing solutions were pumped to the next block prepared for gold leaching.

 To leach silver, a solution containing 2 g / l sodium thiosulfate was used.

 The silver recovery results are shown in table 5.

 As can be seen from table 5, leaching according to the proposed method is preferable and allows to reduce the specific consumption of the reagent by almost 2 times and, thus, reduce the total salinity of groundwater.

 At the end of leaching, the groundwater involved in the gold and silver mining process was reclaimed. Reclamation was carried out using calcium hydroxide at a rate of 2 g / l, and aerating the solutions to the pH value of the underground water of the ore body.

 The reclamation results are shown in table 6.

 Table 6 shows that pumping production solutions to a new unit before leaching silver reduces the salt content of the remaining solutions by almost half, and neutralization at the end of the process using calcium hydroxide and aeration at the stage of reclamation is accompanied by the formation of sparingly soluble iron sulfoxyhydrates, which improves the quality of groundwater.

 The method is characterized by a high degree of extraction of gold and silver, subject to environmental safety of the process.

Claims (6)

 1. A method of processing mineral raw materials containing gold and silver from ores at the place of their occurrence, including stage-by-stage leaching, which is carried out by feeding reagent solutions to the ore blocks to be mined through a system of injection wells and pumping productive solutions through a system of pumping wells, with supply to the first stage of a chlorine solution for leaching gold, and in the second stage with the supply of sulfur-containing reagents for leaching silver, the processing of productive solutions by sorption and cementation, The groundwater involved in the leaching process is utilized, characterized in that the gold leaching is carried out by supplying the solution so that the pH of the productive solution is maintained below 3, before processing the productive solution, excess chlorine is removed from it to the minimum values that allow gold to be retained in the solution, In this case, the absorption of excess chlorine is carried out by the sorption mother liquors purified from mercury, and before leaching of silver, chlorine-iron-containing solutions are pumped to the next unit prepared for mining , Wherein in each stage of leaching is performed through the process control monitoring wells.  2. The method according to claim 1, characterized in that during the processing of arsenic ores, before leaching the gold, an acid chlorinated solution of ferric iron salts is fed into the mined block to prevent leaching of arsenic from the ore and the solution spreads outside the mined block.  3. The method according to claim 1, characterized in that when the molar ratio of carbonates and sulfides in the ore is less than 8, leaching begins with the addition of a chlorinated ferric salt solution with a pH value into the processed block, excluding the clogging of the filter zone of the injection wells.  4. The method according to claim 1, characterized in that when fixing in observation wells a sharp increase in the redox potential and a decrease in the pH of the leach solutions, the concentration of chlorine in the injection solutions is reduced, and to achieve optimal pH and redox potential in productive solutions, the dependence parameters of the injected solution on the amount of the previously leached reagent, concentration and time of its appearance in the observation well.  5. The method according to claim 1, characterized in that the extraction of mercury from the mother liquors of sorption is carried out using iron and / or iron-carbon wastes from metallurgical industries.  6. The method according to claim 1, characterized in that during the reclamation of the waters involved in the leaching process, the residues of sulfur-containing reagents are neutralized by feeding air and a solution of calcium hydroxide to the processed block.

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