Process for the selective production of copper sulfides and zinc sulfides from lime sludge of acidic mine drainages

Abstract

The invention relates to a process for the selective production of copper sulfides and / or zinc sulfides from a lime sludge obtained from acid mine drainage, referred to as "lime sludge," comprising copper and / or zinc, and further comprising iron, calcium and / or sulfates, and cadmium and / or aluminum. The process comprises the following steps: a) treatment of the lime sludge under agitation with a sulfuric acid solution so as to selectively dissolve all or part of the copper, and / or zinc, and cadmium and / or aluminum in an acidified liquid phase; b) separation of a solid phase comprising iron, sulfates, and / or calcium from said acidified liquid phase; and c) treatment of said acidified liquid phase to obtain the selective precipitation of copper sulfides or zinc sulfides in solid form. Figure 1

Description

Title of the invention: Process for selectively obtaining copper sulfides and zinc sulfides from liming sludge from acid mine drainage

[0001] 1 - Technical field of the invention

[0002] The invention relates to the treatment of soils consisting of liming sludge from acid mine or quarry drainage polluted by the elements copper, zinc and cadmium. It relates more particularly to a process for selectively obtaining copper sulfides or zinc sulfides. The process can make it possible to selectively obtain both copper sulfides and zinc sulfides. The invention also relates to copper sulfides and zinc sulfides recovered using the process.

[0003] 2-State of the art

[0004] Acid waters from mine drainage and mine tailings are heterogeneous effluents, but always loaded with metals and metalloids. It is estimated that 19,300 km of watercourses and 72,000 hectares of lakes and aquatic reservoirs are seriously affected by mining effluents worldwide. In addition to the economic disruption caused, Acid Mine Drainage (AMD) poses risks to human health and the environment.

[0005] Acid mine drainage can flow for very long periods of time. For example, the Montana Department of Environmental Quality in the United States validated a model that shows that acid drainage from the Golden Sunlight Mine (USA) will continue to flow for thousands of years. Another study estimated that AMD generation in the relatively small tailings dam of a closed gold-silver-copper-cobalt-zinc mine in Hokkaido, Japan, will continue for at least 1,000 years. One of the oldest documented mining regions in the world, the Rio Tinto region in Spain, has had AMD problems for about 5,000 years.

[0006] As these contaminated water flows remain difficult to control, or even impossible to stop permanently, it is necessary to implement their treatment over an indefinite period. These devices represent a significant long-term cost for society, to which is added the storage of solid waste from these treatments, which accumulates over time. Chemical neutralization consists of a mixture of DMA and alkaline materials (such as limestone, magnesia and especially lime) to precipitate the majority of heavy metals. This is the method of choice for old mines, because it is effective, easy to set up and operate, and can be adapted to the geochemical properties of the DMA, specific to each site. Worldwide, 90% of acid mine drainage is treated by liming. Although effective, this process generates bulky sludge, composed largely of gypsum (CaSO4-2H2O), which can be a source of secondary impacts if not stored under optimal conditions. Liming sludge from AMD is always rich in sulfates, because acid mine drainage always contains sulfuric acid. Liming sludge that is not from AMD may not be acidic or may be acidic due to another acid such as HCl, HNO3, etc. In addition, liming sludge from AMD is always rich in iron because the minerals that generate AMD are mainly pyrite (FeS2) and pyrrhotite (FeiJS).

[0007] In economic terms, at the French national level, approximately 1,800 mining sites (including coal mines) are managed, with the associated operational cost being close to 10 million euros per year. New sites regularly join this group of monitored structures, at which drainage is treated before discharge into the environment. In France, we have identified, following a superficial review, around forty acid drainage liming installations: 15 concern mines and around thirty quarries. The volume represented by this waste on a French scale is not known, but as an example for 3 French sites the tonnages of sludge stored on site are estimated at 150 kt, 165 kt and 550 kt.

[0008] Acid mine drainage can have a significant impact on the environment, but it can also contain valuable metals, and its treatment can then generate residues that can concentrate them. The more acidic the treated effluent, the higher the concentrations of metals, particularly Cu, Zn, Ni and Mn. DMA water also generally contains significant concentrations of Fe, Al, Mn and SO42.

[0009] Undesirable trace elements, including valuable metals, are therefore found in the sludge resulting from lime treatment and can reach significant concentrations. Analyses carried out on lime treatment sludge from 7 mines in Canada show that the metals of interest can have very high concentrations: up to 1.4% copper and 22% zinc. They are associated with other elements such as Ca, Fe, Al, Mn, SO42.

[0010] Unlike the recovery of metals directly from acid mine drainage, which has generated a wealth of scientific literature and a few rare industrial applications, the recovery of sludge from the liming of mine drainage has been little studied. This subject has taken on increasing importance in recent years due to the combined effect of society's greater sensitivity to the environment and the rising price of metals.

[0011] However, the sludge from the mining site (Cu, Pb, Zn) of Almagrera in Spain has been studied (Macias F. et al, 2017, Journal of Cleaner Production, 141, 1057-1066). This The stock of liming sludge is estimated at 40,000 t and is composed of 4.3% Zn, 2.8% Mn, 0.6% Cu and 0.044% Co. In laboratory tests, it was possible to extract approximately 90% of these metals from sludge during leaching operations carried out at a solids ratio of 1 / 20 or 1 / 40 by mass of solid to the mass of liquid, with a dilute (0.5M) solution of H2SO4. Under the conditions used, a large part of the iron also passes into solution. Indeed, up to 55% of the iron is dissolved under these conditions. The authors suggest that the selective recovery of metals such as Zn, Cu, Co, Ni and Cd would be economically interesting, and cite as an example the selective recovery of metals such as Ni, Mn, Co and Li from sulfuric acid leaching solutions of used batteries. However, as Macias et al. point out., the recovery of economically valuable metals from acid mine drainage liming sludge will be difficult to implement due to the technical difficulties linked to the presence of numerous impurities in the acid leachates from liming sludge. These leachates are very different from the leachates obtained from used batteries. Also, currently, it would not be known how to selectively extract valuable metals from liming sludge leachates.

[0012] The invention aims in particular to propose a process for selectively obtaining copper or zinc from liming sludge from acid mine drainage or acid quarry drainage, the recovered copper or zinc being in a marketable form. In the remainder of this text, the term "acid mine drainage" will be used interchangeably to refer to either acid mine drainage or acid quarry drainage.

[0013] To this end, the invention relates to a process for selectively obtaining copper sulfides and / or zinc sulfides from a liming sludge from acid mine drainage, called "liming sludge", comprising copper and / or zinc, and further comprising iron, calcium and / or sulfates, and cadmium and / or aluminum, the process comprising the following steps: (a) treatment with agitation of the liming sludge with a sulfuric acid solution so as to selectively dissolve all or part of the copper, and / or zinc and cadmium and / or aluminum in an acidified liquid phase, b) separation of a solid phase comprising iron, sulfates and / or calcium from said acidified liquid phase, then c) treatment of said acidified liquid phase to obtain the selective precipitation of copper sulfides or zinc sulfides in solid form.

[0014] This process makes it possible to separate the copper or zinc, present in the acidified liquid phase, from the other elements present in the solid phase, such as iron, calcium, sulfates and aluminum, which can themselves be used in cement works, or participate in the development of technosols on site, that is to say decontaminated and fertile soils. on-site from the treatment of soils made up of liming sludge. This is interesting in a circular economy logic and to free up storage space on site. The elements present in the solid phase can also be used in the preparation of construction materials off-site.

[0015] Copper or zinc can thus be commercially recovered, and the soil can be decontaminated by removing these polluting elements.

[0016] : Copper or zinc and cadmium and / or aluminum are selectively dissolved, that is to say that these elements are dissolved, at least in part, in the sulfuric acid solution while iron and sulfates are not, or very little. It is understood that the zinc sulfide precipitation step is advantageously distinct from the copper sulfide precipitation step.

[0017] Advantageously, the selective precipitation of copper sulfides or zinc sulfides is obtained by contacting with gaseous Na2S, NaOH or H2S. The selective precipitation is preferably carried out by contacting with Na2S which is more selective than NaOH and less dangerous than H2S.

[0018] In general, the liming sludge used contains 5 to 20% solids by mass relative to the total mass of the pulp.

[0019] Optionally, the liming sludge used in the process comprises from 0.02 to 1.40% by mass relative to the total mass of solid in the Cu sludge, preferably from 0.12 to 1.20%, more preferably approximately 1.03%, and / or 0.01 to 22.00% by mass relative to the total mass of solid in the Zn sludge, preferably from 1.00 to 17.60%, more preferably approximately 5.17%.

[0020] Advantageously, the solid phase resulting from the leaching is washed with water acidified to pH 3.0 with H2SO4 and the washing solution is recycled in the leaching step.

[0021] Advantageously, during the treatment with the sulfuric acid solution, the sulfuric acid content ranges from 100 to 450 g of sulfuric acid per kg of solid, preferably from 120 to 225 g / kg, more preferably from 150 to 200 g / kg. These quantities of sulfuric acid make it possible to extract the valuable and polluting metals Cu, Zn and Cd with a yield of at least 90%, more precisely Cu at more than 90%, Zn at more than 94% and Cd at more than 91%. Furthermore, the quantities of sulfuric acid preferably used are much lower than those used in the experiments of Macias, in which the sulfuric acid was used at a rate of 980 g of H2SO4 per kg of solid, in the experiments where it was most diluted. Therefore, reduced quantities of sulfuric acid can be used while still obtaining good yield.This process therefore has the advantage of involving a relatively small quantity of toxic reagent, while still providing good yield. These reduced quantities subsequently make it possible to selectively recover copper sulfides and zinc sulfides. In . In effect, iron, sulfates and / or calcium remain in the solid phase. In an exemplary implementation, the leaching is carried out by placing 4.2 kg of solid in a reactor of approximately 20 L. Advantageously, the leaching is carried out with stirring at approximately 300 rpm. Generally, also advantageously, the leaching is carried out at a temperature between 18 and 25°C. Generally, also advantageously, the leaching lasts approximately 6 hours. Generally, also advantageously, the leaching is carried out under atmospheric pressure.

[0022] On an industrial scale, in another mode of implementation, the leaching step will rather be carried out in a reactor of several hundred m3.

[0023] In an exemplary implementation, advantageously, the separation of step c) is carried out by filtration, for example using a 1 μm Buchner filter.

[0024] Advantageously, said liming sludge comprises copper and zinc, and - during step a) the copper and zinc are selectively dissolved - during step c) the copper sulfides are selectively precipitated and - the precipitated copper sulfides are separated from a solution comprising cadmium and / or aluminum and zinc, - said solution comprising cadmium and / or aluminium and zinc is subjected to selective precipitation of cadmium sulphides and / or aluminium oxides and / or aluminium hydroxides, - a separation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides precipitated from a solution containing zinc is carried out, then - said solution containing zinc is subjected to selective precipitation allowing the production of zinc sulfides in solid form and a liquid phase depleted in zinc.

[0025] The selective obtaining process can also make it possible to recover cadmium sulfides and / or aluminum oxy / hydroxide.

[0026] Advantageously, the precipitated copper sulfides are separated from a solution comprising cadmium and / or aluminum and zinc by filtration, for example using a 1 μm Buchner filter.

[0027] Advantageously, the precipitated copper sulfides are washed with water acidified to pH 3.5 with H2SO4 and the washing solution is recycled to undergo the leaching step.

[0028] Advantageously, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides takes place firstly by bringing the solution comprising cadmium and / or aluminum and zinc into contact with Na2 S>9H2O, then with NaOH. Advantageously, during the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides, the concentration of Na2S>9H2 O varies between 0.4 and 0.7 g / L, and the NaOH concentration varies between 2.4 and 4.8 g / L. Advantageously, NaOH is added so as to reach a pH of 4.5. Advantageously, in one example, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is carried out in a reactor of approximately 20 L. Advantageously, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is carried out with stirring at approximately 300 rpm. Advantageously, in general, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is carried out at a temperature between 18 and 25°C. Advantageously during the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides, the solution comprising cadmium and / or aluminum and zinc is brought into contact with Na2S>9H2O for 10 minutes, then NaOH is added and left to react for 20 minutes.Advantageously, in general, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is carried out under atmospheric pressure. Alternatively, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is carried out in a reactor of several hundred m3, i.e. on an industrial scale. Advantageously, the separation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides precipitated from a solution containing zinc is carried out by filtration, preferably using a 1 μm Buchner filter.

[0029] Preferably, in general, the precipitated cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides are washed with water acidified to pH 3.5 with H2SO4 and the washing solution is recycled to undergo the leaching step.

[0030] In one example, the selective precipitation allowing zinc sulfides to be obtained in solid form is carried out in a reactor of approximately 20 L. Preferably, the selective precipitation allowing zinc sulfides to be obtained in solid form is carried out with stirring at approximately 300 rpm. Advantageously, the selective precipitation allowing zinc sulfides to be obtained in solid form is carried out at a temperature generally between 18 and 25°C. Advantageously, during the selective precipitation allowing zinc sulfides to be obtained in solid form, the solution containing the zinc is brought into contact with Na2S>9H2O for approximately 0.5 hours. Advantageously, the selective precipitation allowing zinc sulfides to be obtained in solid form is carried out under atmospheric pressure. Advantageously, zinc sulfides in solid form are separated from the zinc-depleted liquid phase, preferably by filtration, for example using a 1 μm Buchner filter. Advantageously, the zinc sulfides in solid form are washed with water and the washing solution is recycled to undergo the leaching step. Under these conditions, Zn is selectively extracted from liming sludge from DMA with a yield greater than 90%. On an industrial scale, the selective precipitation allowing the production of zinc sulfides in solid form is carried out in a reactor of several hundred m3.

[0031] Advantageously, the process further comprises at least one step of recovering copper sulfides or zinc sulfides.

[0032] Advantageously, the selective precipitation of copper sulfides is obtained by bringing the acidified liquid phase into contact with Na2S>9H2O.

[0033] Preferably, the concentration of Na2S>9H2O varies between 3.2 and 6.4 g / L. The concentration of Na2S>9H2O is advantageously chosen as a function of the concentration of copper sulfides. In one example, the selective precipitation of copper sulfides is carried out in a reactor of approximately 20 L. Advantageously, the selective precipitation of copper sulfides is carried out with stirring at approximately 300 rpm. Advantageously, the selective precipitation of copper sulfides is carried out at a temperature between 18 and 25°C. Advantageously, the selective precipitation of copper sulfides is carried out for approximately 0.5 hours. Advantageously, the selective precipitation of copper sulfides is carried out under atmospheric pressure. Under these conditions, Cu is selectively extracted from liming sludge from DMA with a yield greater than 85%. On an industrial scale, the selective precipitation of copper sulfides is carried out in a reactor of several hundred m3.

[0034] Advantageously, the selective precipitation of zinc sulfides is obtained by contacting a solution containing zinc with Na2S>9H2O.

[0035] Advantageously, the selective precipitation of zinc sulfides is carried out at a pH ranging from 4.5 to 5.5.

[0036] Advantageously, the selective precipitation of copper sulfides is carried out at a pH ranging from 2.5 to 4.0.

[0037] Advantageously, the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is obtained by bringing the solution comprising cadmium and / or aluminum and zinc into contact with Na2S>9H2O then with NaOH.

[0038] Advantageously, the liming sludge contains copper, during step a) the copper is selectively dissolved, and during step c) the copper sulfides are selectively precipitated. This way, copper can be obtained in solid form, in a marketable form.

[0039] The invention also relates to copper and / or zinc sulfides obtained by implementing a process as described above.

[0040] Another object of the invention is a process for recovering copper sulfides or zinc sulfides which would be extended to sulfate-rich liming sludge and industrial effluents such as effluents from incinerators or the surface treatment industry. Brief description of the figures

[0041] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended drawing in which:

[0042] [Fig. 1] shows schematically the treatment of liming sludge including the selective production process according to the invention. Detailed description

[0043] [Fig. 1] shows the treatment of liming sludge including a particularly preferred method of selective production according to the invention. The treatment shown schematizes step a) of treatment with sulfuric acid ("leaching"). In the example shown, four steps of a liquid / solid separation are carried out, in this example by filtration. A first filtration separates a solid phase comprising iron, sulfates and / or calcium from an acidified liquid phase. It is carried out after leaching, making it possible to obtain a solid phase comprising iron, sulfates and / or calcium usable for example in cement works. A second filtration makes it possible to separate precipitated copper sulfides from a solution comprising cadmium and / or aluminum and zinc. The third filtration makes it possible to discard a solid waste consisting of a mixture of cadmium sulfides and / or aluminum oxy / hydroxide.The fourth filtration allows zinc sulfides to be selectively obtained. In the example shown, the copper sulfides are selectively precipitated, and zinc sulfides are obtained in solid form following selective precipitation. In the example shown, at each filtration step, the solid phase obtained is washed in a washing solution, prior to carrying out measurements on the solid phase, its storage and / or its use and / or its sale. At the end of the washing, a “wash water” is obtained which is advantageously recycled in the leaching step, which is represented in [Fig.l] by the different arrows directed from each filtration towards the leaching.

[0044] Example 1

[0045] The method according to the invention was implemented on acid mine drainage liming sludge, the average content of the main elements of which, expressed as a percentage by mass relative to the total mass of solids in the sludge, is presented in Table 1.

[0046] [Tables 1] Cu(%) Zn (%) Cd(%) Al (%) Ca(%) Fe(%) Si (%) S(%) 1.03 5.17 0.01 1.9 12.2 12 3.2 8.7

[0047] These values ​​for Al, Ca, Cd, Cu, Fe, Si and Zn were obtained by quadru-acid digestion followed by inductively coupled plasma-atomic emission spectrometry (ICP-AES).

[0048] The S content was measured using a LECO sulfur analyzer which allows the combustion of S, then its detection and quantification in infrared cells.

[0049] The liming sludge, which initially comes in the form of wet solids, was put into the form of pulps, i.e. a mixture of liquid and solid particles, and then subjected to a treatment with stirring by a sulfuric acid solution, hereinafter called leaching. In the sludge used, the proportion of solid could vary between 5 and 20% by mass of solid relative to the total mass of the pulp. The sulfuric acid was added in proportions varying between 120 and 200 g H2SO4 per kg of solid, using an aqueous solution of sulfuric acid (96% + / - 0.15%, Acros Organics).

[0050] This leaching step was carried out with 4.2 kg of solid in a 20 L reactor with stirring at 300 rpm, at a temperature between 18 and 25°C for a period of 6 hours, under atmospheric pressure.

[0051] Once the leaching time was reached, the contents of the reactor underwent a first liquid / solid separation carried out by filtration using a 1 μm Buchner filter. The first filtration made it possible to separate a metalliferous liquor (acidified liquid phase) from a solid residue, the filter cake, a solid phase comprising iron, sulfates and / or calcium. The content of certain elements in the liquor was then determined.

[0052] More specifically, the concentration of Cu, Zn and Al in solution was analyzed by microwave plasma atomic emission spectrometry (MP-AES) (4210 MP-AES, Agilent Technologies). The different dilutions of the samples were carried out using 1% nitric acid obtained from 65% nitric acid, Fisher Chemical. The calibration of Cu, Zn and Al was carried out using 6 standards allowing to achieve ranges of 1 to 30 mg / L for these three elements. A low point at 0.5 mg / L was also included to know if samples with concentrations lower than 1 mg / L were acceptable. The standard solutions (reference material) used were certified standards (Merck) at 1 g / L in 0.5 mol / L HNO3. The analyzed wavelengths were 396.152 nm (Al), 327.395 nm (Cu) and 481.053 nm (Zn).

[0053] The Cd concentration in solution was determined by flame atomic absorbance spectrometer (AAS) analysis (SpectrAA-220FS, Varian). The different dilutions of the samples were carried out using 1% nitric acid (Obtained at from 65% nitric acid, Fisher Chemical). The calibration of Cd was carried out using five standards allowing to achieve ranges of 0.2 to 1 mg / L. The standard solution (reference material) used was an industrial solution EU-H (EnviroMAT, SCP Science) diluted 1 / 10 with 1% nitric acid. The chosen wavelength was 228.8 nm.

[0054] Table 2 shows the average content measured in the first liquid phase, resulting from the first filtration for Zn, Al, Cu and Cd, in mg / L.

[0055] [Tables2] Zn (mg / L) Al (mg / L) Cu (mg / L) Cd (mg / L) 8700 900 1400 16

[0056] As regards the filter cake (solid phase comprising iron, sulfates and / or calcium), it was washed with water acidified to pH 3.0 with H2SO4. The washing solution was then advantageously recycled to undergo step a) of acid leaching.

[0057] The previously washed filter cake was dried in a Memmert oven at 40°C. The element content of the filter cake thus treated was analyzed by portable X-ray fluorescence (pXRF) in Miner mode (Niton XL3t 980, Thermo Fisher) for 1 minute. More precisely, capsules containing approximately 5 g of the sample to be analyzed were prepared. For each sample, two capsules were prepared and three measurements were made per capsule, with offset of the area targeted by the device. The detection limits were as follows: 15 ppm (Cu, Zn) and 10 ppm (Cd).

[0058] Table 3 shows the average content measured for certain elements, expressed as a percentage of mass relative to the total mass analyzed, in the filter cake after washing, solid phase comprising iron, sulfates and / or calcium.

[0059] [Tables3] Si (%) Al (%) Fe (%) Ca (%) SO4(%) Cu (%) Zn(%) Cd (%) 3.7 1.9 13.0 14.4 26.0 <0.1 <0.3 < 0.0009

[0060] Thus, step a) of leaching by sulfuric acid made it possible to maintain in the solid phase, or even to concentrate in this phase, elements such as Si, Fe and Ca. Al is also well represented in this solid phase, even if it is also present in the liquor (acidified liquid phase). Sulfates are also found in the solid phase. On the other hand, Cu, Zn and Cd are present in small quantities. Thus, leaching by sulfuric acid made it possible to extract Cu at more than 85%, Zn at more than 90% and Cd at more than 91% from the liming sludge. Leaching makes it possible to obtain a pulp composed of a metalliferous liquor rich in Cu, Zn, Cd and Al, the acidified liquid phase, and a solid leach residue, the solid phase comprising iron, sulfates and / or calcium.

[0061] The metalliferous liquor (acidified liquid phase) then underwent a precipitation step with Na2S>9H2O (98%, Sigma-Aldrich) at a concentration which could vary between 3.2 and 6.4 g / L depending on the concentrations of the elements to be precipitated. This precipitation step was carried out in a 20 L reactor with stirring at 300 rpm, at a temperature between 18 and 25°C for a period of 0.5 hours, under atmospheric pressure.

[0062] The pulp thus obtained was subjected to a second liquid / solid separation, by filtration using a 1 μm Buchner filter. The filter cake was washed with water acidified to pH 3.5 with H2SO4. The washing solution was then advantageously recycled to undergo step a) of acid leaching.

[0063] The content of certain elements in the liquor from the second filtration, a solution comprising cadmium and / or aluminum and zinc, was then determined under the same conditions as those described at the end of the leaching. Similarly, the element content of the filter cake after washing was determined under the same conditions as those described at the end of the leaching.

[0064] Table 4 shows the average measured content of the liquor from the second filtration for Zn, Al, Cu and Cd, in mg / L.

[0065] [Tables4] Zn (mg / L) Al (mg / L) Cu (mg / L) Cd (mg / L) 8700 900 <50 16

[0066] Table 5 shows the average content measured for certain elements, expressed as a percentage of mass relative to the total mass analyzed, in the filter cake after washing.

[0067] [Tables5] CaO (%) Na2O (%) sulfate (%) sulfide (%) Al(%) Cd (%) Cu(%) Zn (%) 0.7 0.8 6.9 16.4 0.4 <0.02 34.7 4.0

[0068] At the end of the Na2S precipitation step, a pulp is thus obtained composed of a metalliferous liquor rich in Zn, Cd and Al, and a solid phase concentrated in copper. More than 85% of the copper present in the liming sludge is thus extracted and more than 97% of the extracted copper is precipitated in the copper concentrate.

[0069] The metalliferous liquor resulting from the precipitation by Na2S then underwent a second precipitation step. This second precipitation step was carried out in a 20 L reactor with stirring at 300 rpm, at a temperature between 18 and 25°C, under atmospheric pressure. In this second precipitation step, the metalliferous liquor was brought into contact with Na2S>9H2O (98%, Sigma-Aldrich) at a concentration varying between 0.4 and 0.7 g / L for 10 minutes, then NaOH (98.5%, Acros Organics) was introduced into the reactor and left to react for 20 minutes, at a concentration varying between 2.4 and 4.8 g / L or up to pH 4.5.

[0070] The pulp thus obtained was subjected to a third liquid / solid separation by filtration using a 1 μm Buchner filter. The filter cake was washed with water acidified to pH 3.5 with H2SO4. The washing solution was then advantageously recycled into the acid leaching step a).

[0071] Table 6 shows the average content measured in the liquor resulting from filtration for Zn, Al, Cu and Cd, in mg / L.

[0072] [Tableauxô] Zn (mg / L) Al (mg / L) Cu (mg / L) Cd (mg / L) 8700 <5 <5 < 1

[0073] Table 7 shows the average content measured for certain elements, expressed as a percentage of mass relative to the total mass analyzed, in the filter cake after washing.

[0074] [Tables7] SiO2(%) sulfate (%) sulfide (%) A12O3(%) Cd(%) Cu (%) Zn (%) 10.6 23.6 2.7 27.2 0.26 0.29 4.6

[0075] This second precipitation step makes it possible to obtain a pulp composed of a metalliferous liquor rich in Zn and a waste of Al and Cd.

[0076] The Zn-rich metalliferous liquor from the second precipitation step then underwent a third precipitation step. In this third precipitation step, the Zn-rich metalliferous liquor was brought into contact with Na2S>9H2O (98%, Sigma-Aldrich) at a concentration varying between 10 and 21 g / L, so as to be at a pH between 4.5 and 5.5. This precipitation step was carried out in a 20 L reactor with stirring at 300 rpm, at a temperature between 18 and 25°C for a period of 0.5 hours, under atmospheric pressure.

[0077] The pulp thus obtained was subjected to a fourth liquid / solid separation by filtration using a 1 μm Buchner filter. The filter cake was washed with water. The washing solution was then advantageously recycled to undergo step a) of acid leaching.

[0078] Table 8 shows the average content measured in the liquor from the third filtration for Zn, Al, Cu and Cd, in mg / L.

[0079] [Tables8] Zn (mg / L) Al (mg / L) Cu (mg / L) Cd (mg / L) <5 <5 <5 < 1

[0080] Table 9 shows the average content measured for certain elements, expressed as a percentage of mass relative to the total mass analyzed, in the filter cake after washing, fourth solid phase.

[0081] [Tables9] CaO (%) Na2O (%) SiO2(%) sulfate (%) sulfide (%) Al(%) Cd(%) Cu (%) Zn(%) 0.9 14.4 1.1 11.4 0.9 0.4 0.0 <0.02 50

[0082] The third precipitation stage therefore makes it possible to obtain a pulp composed of water and a zinc concentrate. The zinc is thus extracted from the liming mud at more than 90% and is precipitated in the zinc concentrate at 90%. The remaining 10% of zinc is in the copper concentrate and in the aluminum and cadmium concentrate.

[0083] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. In particular, the conditions for implementing the method are described to correspond to an application at an experimental stage. In an application at the industrial stage, the leaching step will rather be carried out in reactors of several hundred m3 treating 50 t / h of sludge.

Claims

Claims

1. A process for selectively obtaining copper sulfides and / or zinc sulfides from a liming sludge from acid mine drainage, called "liming sludge", comprising copper and / or zinc, and further comprising iron, calcium and / or sulfates, and cadmium and / or aluminum, the process comprising the following steps: a) treatment with stirring of the liming sludge with a sulfuric acid solution so as to selectively dissolve all or part of the copper, and / or zinc and cadmium and / or aluminum in an acidified liquid phase, b) separation of a solid phase comprising iron, sulfates and / or calcium from said acidified liquid phase, then c) treatment of said acidified liquid phase to obtain the selective precipitation of copper sulfides or zinc sulfides in solid form.

2. Selective production process according to claim 1, wherein in step a), the sulfuric acid content ranges from 100 to 450 g of sulfuric acid per kg of solid, preferably from 120 to 225 g / kg, more preferably from 150 to 200 g / kg.

3. Selective production method according to claim 1, wherein: - said liming sludge comprises copper and zinc, - during step a) the copper and zinc are selectively dissolved, - during step c) the copper sulfides are selectively precipitated and - the precipitated copper sulfides are separated from a solution comprising cadmium and / or aluminum and zinc, - said solution comprising cadmium and / or aluminum and zinc is subjected to a selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides, - a separation of the precipitated cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides from a solution containing zinc is carried out, then - said solution containing zinc is subjected to a selective precipitation allowing the production of zinc sulfides in solid form and a liquid phase depleted in zinc.

4. A selective obtaining method according to any one of the preceding claims, further comprising at least one recovery step copper sulfides or zinc sulfides.

5. A selective production process according to any one of claims 1 to 4, wherein the selective precipitation of copper sulfides is obtained by contacting the acidified liquid phase with Na2S>9H

6. A selective production process according to claim 3, wherein the selective precipitation of zinc sulfides is obtained by contacting a solution containing zinc with Na2S>9H2O.

7. A selective production process according to any one of claims 1 to 6, wherein the selective precipitation of zinc sulfides is carried out at a pH ranging from 4.5 to 5.

5.

8. A selective production process according to any one of claims 1 to 7, wherein the selective precipitation of copper sulfides is carried out at a pH ranging from 2.5 to 4.

0.

9. Selective production process according to claim 3, in which the selective precipitation of cadmium sulfides and / or aluminum oxides and / or aluminum hydroxides is obtained by contacting the solution comprising cadmium and / or aluminum and zinc with Na2S>9H2O then with NaOH.

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