MXPA97001197A - Hydrometallurgical conversion of zinc sulfide to sulphate from minerals and concentrates containing sulfide of z - Google Patents

Abstract

In a hydrometallurgical process for converting zinc sulphide into a zinc sulphide containing mineral, the sulfide is chemically converted at elevated temperatures of ZnSO4.xH2O which crystallizes substantially in the monohydrate form as ZnSO4.H2O in a conversion solution having a High concentration of H2SO4, the improvement comprises: (i) selecting a mineral containing zinc sulphide and zinc sulphide and copper sulphide, the ore containing more than 1% by weight of copper, (ii) the sulfide mineral zinc / copper sulfide is contacted with a conversion solution comprising a concentration of sulfuric acid selected from the scale of about 45% by weight to about 70% by weight of the conversion solution and at the elevated temperature on the scale of 90 ° C less than the boiling point of the conversion solution for the selected concentration of sulfuric acid, (iii) ensuring a reduction condition in the conversion solution, by virtue of the concentration of H2SO4, temperature and maintenance of atmospheric pressure, to continuously produce enough H2S to avoid oxidation of the copper sulfide, (iv) maintain the conversion solution at the elevated temperature and scale of sulfuric acid concentration to ensure continued formation of the ZnSO4.H2O crystals until substantially all the available ZnS is chemically converted, and (v) to separate the crystals of ZnSO4.H2O and remaining solids from the mineral of the conversion solution.

Description

HYDOMETHICAL CONVERSION OF ZINC FLU SULFIDE SULFIDE FROM MINERALS AND CONCENTRATES CONTAINING SULFIDE FROM ZINC FIELD OF THE INVENTION The present invention relates to a hydronetalurgical process for the conversion of sul furo de z nc into a mineral at high temperature using high concentration of sulfuric acid.

BACKGROUND OF THE INVENTION There is a significant push to develop commercial forms of a metallurgical process to recover various types of metal from bodies of sulfur ore.

The significant advantage of a hydrometal process over the normal f-undicion process is the significant reduction in sulfur dioxide emissions. Or even though chemistry may seem to be relatively targeted in extracting zinc from sulphide minerals, all commercial proposals known in this regard have only treated zinc concentrates containing less than 1% copper, or failed or failed. They are economically viable. It is known that some of these hydrometallurgical procedures for leaching zinc from a concentrate or a rich mineral involve the use of sulfuric acid and / or nitric acid and / or nitrate salts. As it is appreciated, although sulfuric acid is very useful for removing zinc sulphides from ore such as soluble sulphates or this metal, the resulting leaching solution has to be electrolyzed to recover the zinc since in the present there is no other economically convenient way to separate the zin sulphates from the diluted H2SO4 solution. The Patent of E.U.A. 4,710,227 describes a process for leaching zinc from zinc-containing minerals wherein the zinc is removed from the ore by one or more leaching stages. The leached material is then purified and preferably subjected to electro-gain to recover zinc from the leaching solution. Subsequent to one or more steps of lecting, the remaining solution can be evaporated to increase the acid strength until it reaches a concentration of approximately 60% to 80% H2 O4. The solubility of zinc and magnesium in this composition decreases radically to acid forces of this magnitude. As a result, a glass mass comprising mainly zinc sulfate, magnesium sulfate and manganese sulfate is precipitated. The remaining liquid is predominantly acid that can then be recycled in the process. The resulting crystal mass can be discarded or dissolved in a small amount of water. This redissolved solution of magnesium sulfate mainly, zinc sulfate and manganese sulfate can be discarded or recycled for further treatment. Alternatively, zinc can be precipitated from the solution by neutralizing it at a high pH to facilitate material discharge. The process of evaporation and thus concentration of the solution to form the crystalline RNA is, however, costly due to the significant costs of fuel and energy for the evaporation step, and the need for corrosion-resistant material used in the process of evaporation of heat transfer. In this way, the procedure is not of commercial importance, due to the associated significant costs, with recirculating the liquid phase and discarding the amount of olne gornetales in the liquids removed from the stages of eiect roganancia. In Canadian Patent No. 864,455 a process is described for treating minerals. 80% to 100% sulfuric acid by weight of the reaction solution at temperatures between 160 ° C and 250 ° C is used, causing a suspension of solids including anhydrous copper and zinc sulphates. The solids are washed with water so that the zinc sulfate and copper sulfate dissolve in solution. The zinc and copper are then recovered by electro-earning techniques. Such extremely high concentrations of sulfuric acid and extremely high temperatures result in a degradation of sulfates of zinc and copper in anhydrous sulfates with the concurrent production of O2 and a plastic form of sulfur that tends to be very sticky and thus difficult to handle. The Patents of E.U.A. 4, 071,421 and 4,440.5 (59 Sherptt Gordon describe a 1-pressure pressure system that is very effective in separating zinc from ore or concentrate.) However, the commercial aspect of the process requires that the ore or concentrate contain less than 0.5% by weight of copper and preferably less than 0.1% by weight of copper; On the contrary, significant procedural complications arise along with consequent plant shutdown and equipment emptying. In addition, none of the above procedures works well with all types of zinc sulphide that contain minerals or concentrates. For example, other prominent supplies for zinc sulphide containing ore or concentrate include zinc / zmc minerums and zinc / silicate minerals. Generally one or more aspects of the prior art processes is composed of the presence of lead minerals or silicates solu Les. With some of the prior art methods, the presence of soluble silicates forms a gelatinous hydrous silica hydrate which makes the leaching solution non-filterable. Soluble silicates are more basic than insoluble silicates. For example, the Zn-4 or-fosilicatos (the Uillemite mineral) or 2ZnO.S1O2.H2O (the mineral hernirnor? To) are soluble acids, said Zncji? 3 metasili cate is insoluble. Secondly, there are soluble orthosilicates of iron acid -Fei ^ i üt, (fayalito) and magnesium (Mg2? O_;, forstepto) while the FeS? 3 etasilicates (gruenepto) and rigS? 3 (dimosterati ) are insoluble. When the soluble silicates dissolve, they form very supersaturated solutions in quartz (c »2), but the precipitation of stable quartz crystals requires geologic time frames, and thus the gelatinous silica is formed. This gelatinous silica is an impediment to the separation of liquid solids and a serious impurity in the plant electrolytes of zi c. The examples procedures for the recovery of Zn from 7n silicate minerals are described in Canadian patent 876,034 and in Kurnar and others "Zmg Recovery from Zawar Anient Siliceous Slag" Hidromenetal? Rgia, (19B6) 15: 267-280. The U.S. Patent. from Christensen 1,937,631 discloses a process for treating zinc ores to thereby recover zinc therefrom. The procedure is aimed at the recovery of zinc in the zinc sulphate form from mixed and / or condensed lead-zinc sulphide minerals, which contain only trace amounts of copper sulphide. Chpstensen grinds the mineral in mixture with hot sulfuric acid where the solubility of zinc sulfate in the hot acid is close to the minimum. The amount of sulfuric acid used is defined in terms of acid strength of about 55% to 70%. The satisfactory procedure for recovering zinc from mixed zinc-sulphide ores as the sulphide resin converted as it forms a thin surface coating on the ore can be milled to reveal fresh zinc sulphide, which is then converted into the zinc sulfate. Ohpstensen appreciates that when treating copper containing minerals such as pyrite or chalcopyrite, a very high concentration of acid is required, 95% and more. Although Chpstensen achieves the desired conversion of zinc sulphide to zinc sulfate which is recovered as a solid, no thought is given by Chpstensen to prevent the oxidation of any copper sulphide-copper sulfate. Because copper sulfate is soluble, Chpstensen has to employ additional steps to remove the copper sulfate from the treatment solution before achieving the final addition of the desired zi c sulfate. The process according to this invention overcomes several of the problems associated with prior art processes by providing a process wherein high concentrations of sulfuric acid are used to convert zinc sulphide into sulfur-containing minerals. of zinc. The process is operated at temperatures on the scale of 90 ° C to less than the boiling point of the conversion solution to convert the zinc sulphide into a zinc sulfate crystal which forms crystals in the conversion solution. In this way, the method, in accordance with this invention, provides a novel way to achieve the separation of zinc sulfate from an H2SO treatment solution if it requires an electro-gain step.

BRIEF DESCRIPTION OF THE INVENTION In accordance with one aspect of the invention, in a hydrometallurgical process for converting zinc sulphide into a zinc sulphide containing mineral, the zinc sulfide is chemically converted at elevated temperatures to render ZnS 4. H2? which crystallizes substantially in the hydrochloride as ZnSO.H2O in a conversion solution having an alpha concentration of H2O4, the improvement comprises: - selecting a mineral containing zinc sulphide and copper sulphide, the ore containing more than 1 % by weight of copper 7 - that the zinc sulphide / copper sulfide mineral has contact with a conversion solution comprising a concentration of sulfuric acid selected from the scale of about 45% by weight to about 70% by weight weight of the conversion solution and at the elevated temperature in the range of 90 ° C below the boiling point of the conversion solution for the selected concentration of sulfuric acid; - to ensure a reduction condition in the conversion solution, by virtue of the concentration of H2 O4, temperature, and maintenance of atmospheric pressure, to continuously produce sufficient H2 S to avoid oxidation of the copper sulphide; - maintain the conversion solution at the elevated temperature and the concentration scale of the sulfuric acid to ensure continuous formation of the ZnSO crystals «.H2O until substantially all the available ZnS are virtually converted; Separate the ZnSO crystals; .H2O and the remaining solids of the mineral of the conversion solution. In accordance with another aspect of the invention, the crystals recovered from Z SO ^ .bkO can be dissolved in a solution having a low concentration of sulfuric acid wherein the low concentration of sulfuric acid can be derived from an electrolytic recovery cell. of zinc.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of experimental test results for temperature versus H2O4 concentration where the successful conversion region of zinc sulphide to zinc sulfate monohydrate is identified. The legend for the diagram is the symbol "0" which indicates less than 50% zinc extraction and "" indicates more than 50% extraction of r. ? nc.

DESCRIPTION OF THE PREFERRED MODALITY The process of this invention is particularly suitable in the treatment of zinc sulphide metal ores that contain copper sulfides and possibly also lead sulphides or silicates. The procedure allows the zinc to be preerencially recovered without the recovery of copper, thorium or silicate interferences in the ore. The mineral can be a finely divided concentrated form, a finely divided rich mineral, or a combination of the two, and in this way the term mineral must mean any of these alternatives. Examples of such minerals that have mineral commonly include calcopyrim, chalcocite, bornite, tetrahedpto, sphalepto, galena, molibendite, pyrite, pyrrhotite, and arsenopypt. The mineral is a particle form and is preferably ground so that 75% of the finer particles pass to 275 mesh; that is, in the scale of 50 microns or less. This ensures a finely divided material in which the reagents used in the process of this invention react. Most sources of copper and zinc ore typically include chalcopyrite, sphalepto, boron, pyrite, galena and mixtures thereof. In a preferred aspect of the invention the objective is to recover zinc in the form of zinc sulfate crystals of nonohi drafo. It is also appreciated that said minerals may include precious metals such as rhodium, palm, silver, and gold. In general, these constituents are in quantities and can not guarantee recovery. It has been found that these precious metals do not present a problem with respect to processing conversion conditions. Ideally, small amounts of Pb, Cd, As, and Sb are commonly found in these minerals. It has also been discovered that the presence of iron in the ore does not present any processing problems and although most of the iron sulphide minerals are not reacted, the iron in the form of marmalite (Zn, Fe) S or pirrot to (Fe? -? S) is converted to crystalline ferrous sulfate (FeS0_v) and can be separated from zinc sulfate rnonohydrate in subsequent processing steps familiar to those versified in the art. The zi nc conversion process of the present invention involves the production of zinc sulfate crystals of rnonohydrate from the fraction of zinc sulphide in the ore. Sulfuric acid sufficiently concentrated at a sufficiently high temperature is used to produce hydrogen sulphide and to convert all available zinc sulfide. The preferred application is in the separation of zinc from copper containing minerals and in particular-minerals containing more than 0.5% by weight and generally more than 1% by weight of copper. As noted previously, such minerals are not commercially treatable by the herptt pressure leaching process of US Pat. 4,071,421 and 4,440,569, while at the same time they do not decompose or convert into any sulfuric ore. This lack of reaction with the copper sulphides is due to the presence of the H2 of reduction of the preferential zinc sulphide conversion reaction. The presence of H2 ensures a reduction condition in the conversion solution which in turn prevents oxidation of copper sulphide to copper sulfate. Although the chemistry in the prior art leaching process is well known to involve the use of sulfuric acid, it is not completely understood. Said reaction generally proceeds as follows: (1) ZnS + H2S0 <; (aq) < > ZnS0 (aq) »• H2 (g) The reaction proceeds under ordinary conditions, that is to say at room temperature and at low concentrations of H2 O4; for example sulfuric acid of a molar (98 g of H2 SO4 per liter of leaching solution). While it has been known that the reaction equilibrium moves to the right with increasing concentration and acid temperature, i.e., the concentration of zinc sulfate which increases and partial pressure of hydrogen sulfide it has been found that the reaction is over ( and not only to a balance) when the acid concentration is high enough to exit (precipitate) a minor hydrate-zinc sulfate and when the temperature is high enough to produce a hydrogen sulfide pressure in excess of the ambient pressure in the reactor to ensure at all times during the treatment that the reduction condition is maintained in the conversion solution to maintain the copper in the form of copper sulphide. Under these conditions, where the reaction ends (unlike reaching equilibrium) the salt produced from zinc sulfate is ZnSO.H2? through the entire H2SO4 concentration scale of this invention. Therefore it is believed that the conversion of zinc proceeds in the following manner at high concentrations of H2 O * and at high temperatures; (2) ZnS + H2SO4 + H2O < > Zn? 4.H2? • »H2 (y) Such has been found to increase concentration and At the acid temperature, a point is reached where the zinc sulphate produced in its monohydrate form crystallizes out of the solution and surprisingly any copper sulphide is not converted, nor does the copper sulfate come out of the solution. Therefore, it has been discovered that exi li e The concentration of minimum sulfuric acid and a minimum temperature at which the equilibrium of the above reaction exceeds the point where the partial pressure of the hydrogen sulfide is an atmosphere and the solution is saturated with zinc sulfate. Above this minimum concentration and temperature values, • > (• enough hydrogen sulfide gas is produced and boils and the zinc sulfate crystals of monohydrate form until all the zinc sulphide substantially available in the ore is converted to zinc sulfate. say that all the zinc sulphide of the ore that is available for conversion by the H2SO4 solution is converted into the basis of a commercially viable reactor residence time and commercially viable degree of grinding- and squeezing to an ore particle size. It has also been determined that operating at extremely high concentrations and acid temperatures, such as with the procedure of the aforementioned Canadian Patent 864,455, is not acceptable because the zinc and copper remain in the solution as anhydrous sulfate and unacceptable amounts of plastic sulfide and SO2 are produced instead of the desired H2S that tested the reduction condition Theoretical minimum theoretical sulfate concentrations and minimum temper- ature can be calculated empirically when using the recorded data, the theoretical data as applied to the equilibrium of equation (1) in a commercial recovery environment are not available, but can be provided from the measured data recorded - LT Rornankiw and P.L. DeBruyn, "Kinetics of Dissolution of Zinc Sulfide in Sulfurin Acid" (Kinetics of Dissolution of Zinc Sulphide in Sulfuric Acid), in Procedures for Unity in Hydroallergy, (eds. Uadsworth and Davis), Editorial Gordon & Breach Science Publishers, N.Y (1964), pp. 45-65. It is important to understand, however, that these measured data were made in precipitates of synthetic zinc sulphide, and that natural zi c sulphides are up to 20 K per more stable mole. Data from Bard, Parsons, and Jordan "Standard Potentials m Aqueous solution" (Normal potentials in aqueous solution) published by the International Union of Pure and Applied Chemistry (Marcel DoH > -er, New York and Base, 1985), pp. 252-253 give the following temperature values for the zinc sulphide phases: Phase H ° 298 (KDYMole) G ° 298 (Kj / Mole) ZnS, esfalepto -206.0 -201.3 ZnS, wurtzite -192.6 -185 ZnS, Precipitated -185-181 Theoretical calculations in Zn precipitated would indicate that not even 20% by weight of sulfuric acid at 130 ° C and a minimum of 35% by weight of sulfuric acid at 70 ° C would perform said conversion. These theoretical calculations are based on the solubility data of zinc sulfate in sulfuric acid. Based on the analysis of these data, it would appear that at sulphate concentrations of about 20% by weight and at a temperature of about 130 ° C, or about 35% by weight of sulfuric acid at a temperature of 70 ° 0, it becomes The zinc sulphide in zinc sulfate monoxide which supposedly had to be crystallized and discharged into the conversion solution, however, quite surprisingly, at these lower H2O concentrations, no zinc sulfate monohydrate was formed. Any zinc sulfate formed in the solution was not sufficient to saturate the acid conversion solution, so that no zinc sulfate onohydrate crystal appeared in the conversion solution of said lower concentration. It would seem that these theoretical calculations were not precise with respect to what was found to be required in terms of the minimum concentration of sulfuric acid and minimum temperatures to achieve the production of the zinc sulphate rnonohydrate that would crystallize in the conversion solution. This differences, due to the odometric calculations, they seem to have been somewhat oblique since the reaction was not as favorable as the theoretical data would indicate. The natural mineral is much more stable and in this way less apt to be converted in comparison with the materials reacted with sulfuric acid in which the theoretical calculations were based. Zinc sulfide was made synthetically, where the material contained less than 0.006% iron and was of a size on the scale of 0.1 to 0.3 microns. On the other hand, the actual minerals to be treated in accordance with this procedure, can be of the types indicated above and in particular brownish that contains approximately 5% to 10% of iron and which has a particle size of 50 microns or more. The higher concentrations of sulfuric acid and higher temperatures for the conversion solution were investigated to achieve the process conditions of equation (2). By means of various tests carried out in accordance with this invention and how was PG described? In the accompanying examples, it has been determined that at a temperature as low as about 90 ° C and at about 70% by weight of sulfuric acid in the conversion solution, sufficient zinc sulfate is formed leaving the solution in crystalline form as anhydrous oxide. of zinc sulfate. At a sulfuric acid concentration of about 45% by weight in the conversion solution, a temperature of about 130 ° C provides sufficient hydrochloride of its zinc oxide that crystallizes and exits from the conversion solution. In this way the process of this invention has an operable concentration of sulfuric acid and temperature over that predicted by the theoretical values. In addition, it has been found that increasing more than about 75% by weight of sulfuric acid also results in a process that is inoperable to the mind, due to the formation of plastic sulfide and SO2 instead of H2 &; and in this way the conversion of copper to copper sulfate goes to the solution. In this way the extremely high concentrations and temperatures employed in accordance with the aforementioned prior art, such as in Canadian Patent 864,455, are not applicable with respect to this invention. Figure 1 is a graph of the experimental test results that clearly indicate the region in terms of temperature versus sulfuric acid concentration where zinc extractions greater than 50% can be achieved in approximately 1 to 3 hours with the minimum generation of Sulfur, if it exists. The experimental test results are based on the conversion of minerals and mineral concentrates so that it is believed that the parameters regarding the temperature and concentration of sulfuric acid can be extolled for a commercial process to achieve the removal. preferential zinc-starting from minerals containing zinc sulphide, where other sulfides may be present including copper sulfide that is not affected by the conversion procedure and is not crystallized with zinc. This processing condition, in accordance with this invention, provides a significant advance in the hydrological treatment of minerals to remove zinc sulphides for recovery and thus provides a treated mineral that is now enriched in copper sulphide for the treatment by other procedures, such as that described in the co-pending US patent application of Applicant SN 009,844, filed on January 27, 1993. Based on the region identified in Figure 1, it is evident that, at any temperature above about 90 ° C and for a concentration of sulfuric acid selected in excess of about 60 ° C by weight, the conversion of zinc can be achieved and for temperatures up to about the boiling point of the conversion solution for weaker sulfuric acid concentrations, such as on the scale of 45% to 55%, the conversion It can also be achieved. It is also understood that the reaction rate increases with measurement if at the higher concentrations of sulfuric acid, approaching the boiling point of the conversion solution or on the scale of about 130 ° C to 140 ° C. , the preference conversion! Excellent zinc sulphide is achieved without impinging on the copper sulphides that remain in the mineral. It is also evident that the concentrations of aci or sulfuric on 80% by weight or less than 40% by weight do not produce any significantly significant result, by virtue of poor zinc extractions to less than 40% of HSO4 or by virtue of generating SO2 and plastic sulfide to more than 80% H2 SO4. Region B is indicated in Figure 1 to identify the predominant production of SO2 which is undesirable. Region A indicates the process parameters of the aforementioned Canadian patent 864.455 to Treaduell Corporation which results in the unacceptable production of O2 and the sticky sulphide deposit. Therefore in accordance with the preferred aspect of the invention, practicing any of the conditions as set forth in Figure 1, which are within the region identified as in the zinc extraction region, generates a sufficiently high yield of the monohydrate of Zinc sulphate at equilibrium so that the conversion solution becomes saturated with the form of onohi drato, so the zinc sulphate monohydrate begins to crystallize and fall out of the solution. As long as the fresh material is continuously introduced into the conversion solution and the sulfuric acid and temperature concentrations for the conversion solutions are maintained, the conversion of zinc sulphide to zinc sulfate monohydrate will continue and provide on a continuous basis salt that contains zinc sulfate rnonohydrate that can then be processed for zinc recovery. It is believed that, due to the presence of hydrogen sulphide gas which boils from the conversion solution during the conversion process, the conversion of copper ores and, in particular, copper sulphide is prevented by a much poorer balance between the ions of copper in solution, hydrogen sulfide gas and sulfuric acid. In fact, any initial copper ion present in the solution would precipitate as copper sulfide. In this way, the process provides an excellent commercial zinc-copper separation, particularly with minerals or concentrates containing more than 0.5% by weight of copper and generally in excess of 1% by weight of copper in the form of copper sulfides. It is expected that part of the iron particully in the form of (Zn, Fe) S and Feo.ßßS may react with the conversion solution. It is doubtful, however, that other types of iron, such as Fe 2 (pyrite) and FeAsS (arsenopyrite) would be attacked by the conversion solution. It is also doubted that arsenic or antimony would enter into the conversion solution. Cement, mercury, silver and gold would not enter the conversion solution. However, the magnesium and calcium minerals would be converted and would enter the conversion solution, but hardly any highly silicon mineral or quartz.

Silicon zinc sulphide minerals presented a significant prior art processing problem, since the conversion of soluble silicates into gelatinous hydrous silicate substitutes interferes or prevents filtration to separate leached zinc from the treated or concentrated ore. The process, in accordance with this invention, overcomes this problem since when treating silicate / zinc ores at the elevated temperature and prescribed scale of sulfuric acid concentrations, the silicates are marginally hydrated so that the silicates remain solid instead of forming a gelatinous mass. Said silicate solid form then does not interfere appreciably with the process of the conversion of zinc sulphide and the fall of crystals of zinc sulfate rnonohydrate. Thus, in the removal of the crystalline zinc sulfate monoxide from the conversion solution, there may be quantities of iron, magnesium, and calcium, but these minerals may readily be separated from the zinc sulfate hydrate material. during the recovery of zinc from the crystalline material. Ideally, the recovered crystalline material, once separated from the conversion solution, can be treated with water or dilute acid solution to dissolve the zinc sulfate rnonohydrate in the form of Z S? 4.xH2 ?. The remaining constituents in the crystalline material u d n be more soluble in the mixture of dilute acid or water; in this way, by providing an additional purification of the zinc sulfate before carrying out the electro-gain or the like to remove or recover the zinc from the composition. The reaction of equation (2) is endothermic and thus requires the input of heat during the conversion that can be carried out in a continuous load or base. In a continuous base or load base, the heat can be introduced into the reactor by means of various types of heat exchange devices, although in view of the very high concentration of sulfuric acid, the preferred way of heating the reaction is by means of submerged combustion. The amount of heat needed for this endothermic reaction is much smaller than that needed to evaporate 15% sulfuric acid solution to 60 to 80% sulfuric acid, as previously described with respect to the US patent. 4,712,277. The mineral containing zinc sulphide may be in the form of a concentrate, a finely divided mineral or the like. The particle size of the finely divided ore is normally in the range of 50 microns to 100 microns.

') It is appreciated that the procedure worked so well in the different particle sizes for the ore and ore concentrate. However, as it is understood, the finer the division in the ore, the quicker the reaction speed is when converting the available zinc sulphide and likewise, the shorter residence time to achieve more than 50% conversion of the zinc sulfide. Under optimal conditions, it is expected that conversions on the scale of 80% to 90% can be achieved with sufficiently fine ore, temperature and sulfuric acid concentration selection. The selection of the upper temperature scale is, of course, determined by the boiling point of the conversion solution for a selected concentration of sulfuric acid. It is appreciated that, as the concentration of sulfuric acid decreases, the boiling point of the conversion solution also decreases. Conversion solutions having a sulfuric acid concentration in the range of 40% to 50% by weight boil at about 120 ° C to 140 ° C, while at concentrations of sulfuric acid of 70% to 80% by weight, the conversion solution boils on the scale from 165 ° C to approximately 195 ° C. It is appreciated, however, that \ l achieve equilibrium for the reaction of equation (2), enough Hydrogen sulfide is produced which will tend to boil at temperatures below the boiling point of the conversion solution. Preferably the hydrogen sulfide is removed from the reactor so that the reaction is carried out at about atmospheric pressure. The reaction can be accelerated by improving the removal of L S from the reaction solution by applying a vacuum or using a flood gas. Smaller concentrations of sulfuric acid and / or temperature may then be possible. Nevertheless, the application of a vacuum or the addition of a flood gas to the reactor, which has a high concentration such as sulfuric acid, would dramatically increase the overall costs in the procedure and is believed to make it economically non-viable. The hydrogen sulfide gas from the reactor can be treated by various techniques to convert the hydrogen sulfide to sulfur or sulfuric acid. If it is converted to sulfuric acid, it can be used to replace the conversion solution. The various tests, how were they carried out ?! Establishing the operable region of this procedure, establish several factors that include laboratory tests and indicate that for an economic zinc extraction, the zinc must be converted by at least 50% in one hour or be submitted to the conversion solution. The amounts of sulfur generated, usually in excess of 0.5 to 1 gram based on the amounts used in the laboratory tests, pre-determine a non-economic procedure due to the excessive generation of sulfur.

Experimental Tests The following laboratory scale experiments demonstrate the useful region of the process parameters involving the concentration and temperature of sulfuric acid. The experimental tests were carried out mainly in the following way. A suitable zinc sulphide mineral or concentrate was selected and finely divided at approximately 50 microns in size. The proper zinc sulphide mineral can be sphalerite or volume concentrate made from zinc copper sulfide ores. The copper in the ore may be in equal amounts compared to the weight of zinc in the ore and may be less than the iron weights in the ore. For example, the ratios of zinc, copper to iron can be 2: 2: 3. Approximately 100 grams of the mineral in 150 ml of water is placed in the reaction flask. Approximately 100% of the acid solution of the selected sulfuric acid concentration is slowly added to the mixture during mixing. The conversion solution was allowed to react with the ore for 1 to 3 hours, where the temperature of the reaction was maintained at the selected temperature. At the end of the selected reaction period, any crystalline material was filtered off the conversion solution and an analysis was carried out with respect to the amount of zinc and other components and in 9R. any other solid. The results, in terms of temperature, sulfuric acid concentration and percent conversion are set forth in Table 1. From these results, it is evident that acceptable conversions in excess of 50% and minimum sulfur production are identified.

TABLE 1 Conversion of ZnS - Effect of Acid Concentration Example # Temperature% of Zn converted Time / hours "C of bulk % Sulfuric Acid 1 70 5.0 1 100 22.5 3 30% Aci or Sul fun co 3 70 12.4 2 4 100 8.0 2 5 114 19.8 1 40% Acid Sulfuric 6 70 7.9 l 7 100 18.0 1 8 114 22.5 1 9 120 23.7 1 10 120 24.2 1 45% Aci do Sul fup co 11 70 2.0 3 12 100 23.5 l 13 127 51.2 3 14 124 76.0 1 55% Aci do Sulfun co 15 70 13.8 1 16 100 47.7 i 17 132 89.0 1 60% Sulfuric Acid 18 138 97.4 1 65% Acid Sul fupco 19 70 35.6 1 20 100 76.9 1 70% Sulfuric Acid 21 * 136 91.5 1 75% Sulfuric Acid 22 * 70 20.6 i 23 * 100 77.7 1 24 * 134 91.8 1 * Excessive quantity of sulfur produced in excess of 0.5 to 1 gram.

In accordance with these experimental results, the process parameters for an economically viable process have been defined which surprisingly and not repeated success provide a system for recovering zinc from zinc sulphide minerals, which may include copper sulphide, whereby the resulting material It can be solubilized to provide a solution from which zinc can be electro-grafted. When the ore includes copper sulphides, the process provides ore now enriched in copper sulphide that can be processed to recover copper from it. Although the preferred embodiments of the invention are described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims (1)

NOVELTY OF THE INVENTION CLAIMS

1- In a hydro-neurological procedure to convert zinc sulfate into a mineral containing zinc sulphide, said zinc sulphide being chemically converted at elevated temperatures to 7nS? 4. H2? which crystallizes substantially in the form of rnonohydrate as ZnS? 4.H2O in a conversion solution having a high concentration of H2SO4, the improvement comprising: 1) selecting a mineral containing zinc sulphide and copper sulphide, said mineral Containing more than 1% by weight of copper; 11) that said zinc sulphide / copper sulfide mineral makes contact with a conversion solution comprising a concentration of sulfuric acid selected from the scale of about 45% by weight to about 70% by weight of said solution of conversion and at said elevated temperature in the range of 90 ° C to less than the boiling point of said conversion solution for said selected concentration of sulfuric acid; 1 1 1) to ensure a reduction condition in the conversion solution, by virtue of the concentration of H2SO4, temperature, and maintenance of atmo- pheal pressure, to continuously produce sufficient H2S to prevent oxidation of the copper sulphide; iv) maintaining said conversion solution at said elevated temperature and said concentration scale of said sulfuric acid to ensure continued formation of said crystals of ZnS? 4.H2? until substantially all the available ZnS is chemically converted; and v) separating said crystals of ZnS? 4.H2O and remaining solids of said mineral from said conversion solution. 2. A process of conformity with claim 1, further characterized in that said concentration of sulphonic acid is in the range of 50% by weight to 65% by weight of said conversion solution. 3. A process according to claim 1, further characterized in that the sulfuric acid and heat are added as necessary to said mixture during said chemical conversion of said zinc sulphide to ensure said continued formation of said crystals. 4. A method according to claim 1, further characterized in that it comprises dissolving said crystals to separate in the hydrated form of ZnS? 4. H2? from said remaining solids of said mi ne al. 5. A process according to claim 4, further characterized in that said crystals are dissolved in a solution having a low concentration of sulfuric acid. 6. A process according to claim 5, further characterized in that said solution of low concentration of sulfuric acid is removed from the solution. electrolyte from The zinc recovery electrolytic cell. 7. A process according to any of the rei indications 1 to 6, further characterized because said mineral is finely divided. 8. A process according to any of claims 1 to 6, further characterized in that said mineral is a concentrate. RESUME OF THE IHVEHTION In a hydrometallurgical process to convert zinc sulphide into a mineral containing zinc sulphide, the zinc sulphide being chemically converted at elevated ZnS temperatures? . H2? which crystallizes substantially in the monohydrate form as ZnS? 4.H2? in a conversion solution having a high concentration of H2O4, the improvement comprises: (1) selecting a mineral containing zinc sulphide and copper sulfide, the ore containing more than 1% by weight of copper; (11) that the zinc sulphide / copper sulfide mineral makes contact with a conversion solution comprising a concentration of sulfuric acid selected from the scale of about 45% by weight to about 70% by weight of the solution of conversion and at elevated temperature on the scale of 90 ° C below the boiling point of the conversion solution for the selected concentration of sulfuric acid; (m) ensure- a condition of reduction in the conversion solution, by virtue of the concentration of H2SO4, temperature, and maintenance of atmospheric pressure, to continuously produce sufficient H2S to avoid oxidation of the copper sulfide; (iv) maintain the conversion solution at the elevated temperature and the sulfuric acid concentration scale to ensure continued formation of the crystals of ZnS? 4.H2O until all the available ZnS are chemically converted; and (v) separating the crystals of ZnS? 4.H2O and remaining solids from the mineral of the conversion solution. BSB / cgt * P97-163F