Process for producing silver concentrates from metallurgical residues

Abstract

A process for producing a silver concentrate from metallurgical residues, in particular from residues containing copper, iron, lead, silicon, silver and antimony and optionally containing elements such as arsenic and bismuth, comprising: (i) copper leaching of the metallurgical residues with a first acid solution in order to obtain a first leach solution rich in copper and iron and optionally in arsenic and a first leached sludge having a reduced copper and iron content and optionally a reduced arsenic content and being rich in lead, germanium, silver and silicon, (ii) leaching of the first leached sludge, wherein the first leached sludge is treated with a first solution of a carboxylate in order to obtain a second leached sludge lacking lead and a second leach solution rich in lead, (iii) alkaline leaching of the second leached sludge, wherein a base is added in order to form an alkaline leach solution in order to obtain a third leached sludge having a reduced silicon content and a third leach solution rich in silicon and optionally in arsenic, (iv) hydrochloric acid leaching of the third leached sludge, wherein an acid solution is used in a chloride environment in order to obtain a fourth leached sludge for final disposal and a fourth leach solution rich in silver, copper, lead and iron and optionally in arsenic, (v) precipitation of silver from the fourth leach solution rich in silver, copper and iron and optionally in arsenic with a neutralizing slurry in order to produce a fifth solution rich in chlorides and a first precipitated solid rich in iron, copper, lead and silver and optionally in arsenic, (vi) leaching of the first precipitated solid rich in iron, copper, lead and silver and optionally in arsenic with a sulfuric acid solution in order to produce a sixth leach solution rich in copper, iron and optionally in arsenic and a first silver and lead concentrate, and (vii) leaching of the first silver concentrate with a second carboxylate solution in order to produce a seventh leach solution and a second silver concentrate.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for the production of silver concentrates from metallurgical residues, in particular from residues containing copper, iron, lead, silicon and silver and optionally containing elements such as arsenic, antimony and bismuth.

[0002] In a more specific aspect, the metallurgical residue is a powder from a metal smelting process.

[0003] In an even more specific aspect, the metallurgical residue is a powder from a copper smelting process.

[0004] In an even more specific aspect, the metallurgical residue or in particular the smelting powder contemplates a material that has undergone a leaching process such as sulphuric acid leaching.

[0005] In the present disclosure, any metallurgical residue that has undergone a previous leaching process should be considered as a sludge.

[0006] BACKGROUND AND SUMMARY

[0007] Copper leaching

[0008] Copper in sludge is mainly comprised of substances such as ferrite and / or CuFe2O4, ZnFe2O4 as zinc and FeFe2O4 form of spinel with corresponding fractions of iron. The leaching of these substances is based on temperature, acid concentration and residence time, as described in the study by B.S. Boyanov et al. in World Academy of Science, Engineering and Technology, Vol. 9, 2015, 1592-1598, which carried out a study of leaching of synthetic ferrite of zinc, copper and cadmium, evaluating the variables mentioned earlier. The results of this study show that at elevated temperatures and high acid concentrations ferrite dissolves better in HC1 and H2SO4.

[0009] At high acid concentrations, it was observed that copper leaching has an asymptotic behaviour with respect to leaching temperature, reaching a copper leaching yield greater than 90% in the temperature range between 85 and 90°C once it has passed a reaction time of 60 minutes in sulphuric acid medium.

[0010] Lead leaching and precipitation

[0011] World lead consumption in 2011 was greater than one hundred million tons, of which approximately 80% of said lead was intended for the manufacture of lead-acid batteries. These batteries contain a certain amount of lead in the form of Pb, PbO2 and PbSO4. The most traditional way of recovering lead is the pyrometallurgical route, characterized by the addition of reducing agents such as carbon powder, iron chips and sodium oxalate. The operation is carried out in an oven at temperatures greater than 1000°C, which leads to a high energy demand process He et al., Minerals 7, Issue 6 (2017): 93.

[0012] In another aspect, the hydrometallurgical route to recover lead allows working at reduced temperatures, reducing energy consumption, and in turn not producing sulfur dioxide, a gas characterized as harmful to the environment. The hydrometallurgical route uses a desulfurizing agent such as sodium carbonate, ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, sodium hydroxide, sodium citrate, acetic acid, sodium acetate, among others. The purpose of these processes is to exchange other anions with sulfate ions in order to form insoluble salts. Once recovered, the lead salts such as lead citrate can be calcined in order to produce lead oxide (Zárate-Gutiérrez y Lapidus, Hydrometallurgy 144 (2014): 124-128).

[0013] Desulfurization with citrate

[0014] In the particular case of using citrate, the mixture of citric acid and sodium citrate favors the leaching of lead sulfate and the subsequent crystallization of lead citrate.

[0015] Leaching of lead in citrate solutions

[0016] The solubility product constant of lead vitriol at 20°C is 6.31-10 -7 , indicating that the solubility of PbS04is quite low. However, in the presence of a concentrated solution of citrate, lead forms a series of soluble complexes. In a solution with 0.12 M Pb 2+ , in the pH range of 4.6 to 11.5 there are various citrate complex species in solution. Below a pH of 4.6, there is mainly the presence of lead sulfate, while above a pH of 11.5 there is mainly the presence of lead hydroxide.

[0017] He et al., Minerals 7, Issue 6 (2017): 93 studied lead leaching from a paste with a lead to water weight ratio of 1 : 10 by adding 650 g / L sodium citrate at 35 °C. These conditions allowed more than 99% of lead sulfate to be converted into lead citrate once a 60 min reaction time had elapsed. The temperature was increased up to 95 °C, which allowed a near 99% efficiency to be obtained at a sodium citrate concentration of 300 g / L once a 60 min reaction time had elapsed. However, a decrease in lead citrate production was observed when citric acid was introduced into the mixture. The optimized pH for the production of lead citrate was in the range of 6 to 7. The use of citric acid and ammonium reagents at a pH of 5.5 also gave rise to an increased lead leaching efficiency from lead acid batteries. In the pH range of 5.2 to 5.5, the presence of lead citrate trihydrate ([Pb3(C6H5O7)2] - [3H2O]) was reported as the main species. At higher pH in the range of 8 to 10, lead recovery as citrate was lower due to the formation of lead hydroxide. When the lead residue was rich in oxides such as PbO and PbO2, leaching was performed with citric acid at 20 °C with a molar ratio of lead (II) oxide and lead (IV) oxide of 1 : 1 and 4: 1, with a reaction time between 15 and 60 min, reaching a leaching efficiency higher than 99% by weight, obtaining Pb(C6H6O7) - H2O as the main species (Sonmez and Kumar, Hydrometallurgy 95, Issues 1-2 (2009), 82-86).

[0018] Slurry density is another important parameter for the leaching of lead with citrate solutions. In the range of 10 to 50 g / L of lead vitriol slurry, leaching with a 1 M, pH 7 sodium citrate solution at 600 rpm and 25 °C, a higher level of lead extraction of 90 to 94% was reached at a slurry concentration of 10 g / L. The greater the slurry concentration, the less lead was extracted.

[0019] Therefore, the hydrometallurgical desulphurization process is affected by the diffusion of citrate ions in the lead paste in the reactor due to the increased density of the lead paste. In this context, it is crucial to design a reactor that maximizes the mass transfer in the system.

[0020] The technology is based on the recovery of lead from lead scrap using citric acid already developed by Cambridge Enterprise Limited (WO2008056125A1) and basically consists in treating a lead residue containing lead (II) oxide, lead (IV) oxide and lead sulfate with a citric acid solution and, alternatively, with sodium citrate at a pH that can vary in the range from 1.4 to 6. Finally, it is possible to add hydrogen peroxide as a reducing agent in an alkaline environment in order to promote the leaching reaction of lead (IV) oxide to produce lead citrate (Sonmez and Kumar, Hydrometallurgy 95, Issues 1-2 (2009), 82-86).

[0021] The present invention differs from patent WO2008056125A1, where the pH required for leaching varies from 5.33 to 8.8, using preferably a pH equal to 7 in this range. In addition, the present invention proposes to recycle the citric acid solution obtained after the precipitation step with sodium carbonate, in order to leach again the output metallurgical residue from the sulfuric acid leaching step.

[0022] Alkaline leaching

[0023] Mufakhir et al., IOP Conf. Series: Materials Science and Engineering, 285 (2017) 012003 study the leaching of silicon from slag coming from a process for obtaining nickel-iron alloys in the presence of sodium hydroxide. The alkaline leaching is evaluated if the slag has a NaOH concentration between 6 and 14 mol / L, a solid content between 5 and 25% w / w and a temperature between 25 and 110°C. The results show a maximum yield of silicon leaching of 31%. In the subject matter of the present application, a process is disclosed that maximizes the leaching of copper and lead, which includes the steps of sulfuric acid and citric acid leaching, with the aim of removing Cu and Pb present in the sludge, for subsequent alkaline leaching. The removal of Cu, Fe and Pb in the early steps allows the chemical modification of the sludge, leaving a silicon material that is more fragile to leaching, as shown by the results obtained in the present application.

[0024] Hydrochloric acid leaching

[0025] Patent US 7329396 describes a process for leaching valuable metals from oxidized materials, such as lateritic nickel ores, comprising the step of leaching the mineral with a lixiviant comprising a cation salt (such as magnesium chloride) and hydrochloric acid. Additional oxidizing agents or metal chlorides can be added (as a result of the leaching operation). In one embodiment, the process comprises the recovery of the valuable mineral metals from the mineral, comprising the steps of leaching the mineral with the lixiviant; separating the leachate enriched in valuable mineral metals in a first solid-liquid separation; oxidizing and neutralizing the leachate enriched in valuable metals thus obtained; and separating the magnesium chloride solution from the leachate thus obtained in a second solid-liquid separation. In another embodiment, the lixiviant solution is regenerated from the magnesium chloride solution. In an additional embodiment, the regeneration of the leaching solution comprises the step of producing magnesium oxide from the magnesium chloride solution.

[0026] The difference between the present invention and patent application US 7329396 is that it indicates that the pH is preferably greater than 0.4 so as to precipitate hematite. In the case of the present invention, it is convenient to work at low pH, preferably less than pH -0.25, with the aim of obtaining iron ions in solution, which facilitates the use of the leaching solution in other leaching processes, such as those of smelting powders. In addition, the precipitation of iron hydroxide is completely disadvantageous in the present invention, since each time the silver to iron concentration ratio corresponds to 0.01 g Ag / g Fe, and as a result, the precipitation of iron hydroxide can hinder the presence of silver in solution.

[0027] Patent application CA 2820631 A1 relates to a process that can efficiently treat several materials containing many different metals. These materials can be leached with HCl to obtain a leachate and a solid. Then, they can be separated from each other and the first leachate metals can be separated. Then, a second metal can be separated from the leachate. The first and second metals can be substantially separated from the leachate from each other. This can be done by controlling the leachate temperature, adjusting the pH, reacting even more leachate with HCl, etc. The metals that can be recovered in the form of metal chlorides can eventually be converted into the corresponding metal oxides, thus allowing the recovery of HCl. The several metals can be selected from aluminum, iron, zinc, copper, gold, silver, molybdenum, cobalt, magnesium, lithium, manganese, nickel, palladium, platinum, thorium, phosphorus, uranium, titanium, rare earths and rare metals.

[0028] The present invention differs from patent application CA 2820631 A1 because the former does not require a temperature greater than 90 °C in order to efficiently carry out the silver leaching, unlike this application, which requires a temperature greater than 125 °C.

[0029] In addition, the leaching of the aluminum-containing material is carried out with a hydrochloric acid concentration starting from 18%, while the present invention requires a hydrochloric acid concentration lower than 140 g / L (or lower than 11% w / w). BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A flowchart showing the process disclosed in the present invention. DETAILED DESCRIPTION

[0031] Broadly speaking, the present invention describes a process for the production of silver concentrates from metallurgical residues, in particular from residues containing copper, iron, lead, silicon, antimony and silver and optionally containing elements such as arsenic and bismuth, comprising:

[0032] a copper leaching step (I) of the metallurgical residue (1), in which a first acid leaching solution (2) is used in order to obtain a first leaching solution (3) rich in copper and iron and optionally in arsenic and bismuth and a first leached sludge (4) having reduced copper and iron content and optionally reduced arsenic content and being rich in lead and silicon,

[0033] a step (II) of leaching the first leached sludge (4), in which the first leached sludge (4) is treated with a first solution of carboxylate salt (5) in order to obtain a second leached sludge (6) lacking lead and a second leaching solution (7) rich in lead,

[0034] a basic leaching step (III) of the second leached sludge (6), in which a base is added in order to form a first basic leaching solution (8) in order to obtain a third leached sludge (9) having reduced silicon content and a third leaching solution (10) rich in silicon and optionally in arsenic,

[0035] a silver leaching step (iv) of the third leached sludge (9), in which an acid solution is used in a chloride environment (11) in order to obtain a fourth leached sludge (12) for final disposal and a fourth leaching solution (13) rich in silver, copper, iron, lead and optionally in arsenic,

[0036] a step (v) of precipitating silver from the fourth leaching solution (13) rich in silver, copper and iron and optionally in arsenic with a neutralization slurry (14) in order to produce a fifth solution (15) rich in chlorides and a first precipitated solid (16) rich in iron, copper, lead and silver and optionally in arsenic,

[0037] a step (vi) of leaching the first precipitated solid (16) rich in iron, copper, lead and iron and optionally in arsenic with a sulfuric acid solution (17) in order to produce a sixth leaching solution (18) rich in copper, iron and optionally in arsenic and a first silver and lead concentrate (19),

[0038] a step (vii) of leaching the first silver concentrate (19) with a second carboxylate solution (20) in order to produce a seventh leaching solution (21) and a second silver concentrate (22).

[0039] In a preferred embodiment, the metallurgical residue to be processed is a powder obtained by a metal smelting process.

[0040] In a more preferred embodiment, said powder obtained by a copper smelting process is a smelting powder.

[0041] In an even more preferred embodiment, the metallurgical residue has been subjected to a copper leaching process.

[0042] In an even more preferred embodiment, the metallurgical residue has been subjected to leaching with sulfuric acid.

[0043] In a preferred embodiment, the metallurgical residue to be processed comprises the mineral substances anglesite, azurite, copper-iron spinel in the form of CuOFe2O3, zinc spinel in the form of ZnOFe2O3, magnetite, iron(III) oxide, pirita, smoky quartz, mucovita, kaolinite and lead(II) sulfate.

[0044] In an even more preferred embodiment, the copper contained in the metallurgical residue is present as copper sulfate, calcosina, azurite and copper-iron spinel in the form of CuOFe2O3.

[0045] In an even more preferred embodiment, at least 50% of the copper contained in the metallurgical residue is present in the form of copper-iron spinel in the form of CuOFe2O3.

[0046] In a preferred embodiment, the silicon contained in the metallurgical residue is present as mucovita and kaolinite.

[0047] In another preferred embodiment, the lead contained in the metallurgical residue is present as lead(II) sulfate, galena or lead(II) oxide.

[0048] In an even more preferred embodiment, at least 95% of the lead is lead(II) sulfate.

[0049] In a preferred embodiment, the first H2SO4 solution can comprise sulfuric acid and / or refinery wastewater.

[0050] In a preferred embodiment, step (i) is carried out at a sulfuric acid concentration between 150 and 300 g / L, more preferably at a concentration of sulfuric acid of 250 g / L.

[0051] In a preferred embodiment, step (i) is carried out at a temperature between 50 and 130 °C, more preferably at a temperature of 85 °C.

[0052] In a preferred embodiment, step (i) is carried out for a time between 3 and 12 hours, more preferably for a residence time of 6 hours.

[0053] In a preferred embodiment, step (i) is carried out at a solid concentration between 5 and 20% w / w, more preferably at a solid concentration of 15% w / w.

[0054] In a preferred embodiment, in step (ii) of leaching, the carboxylate salt is sodium citrate.

[0055] In a preferred embodiment, the sodium citrate solution in step (ii) has a molar concentration of sodium citrate between 0.5 and 1 M.

[0056] In a preferred embodiment, the first leached sludge is fed to the sodium citrate solution in step (ii) in a mass ratio of 1 :9.

[0057] In a preferred embodiment, step (ii) is performed at a temperature between 20 and 60 °C, more preferably at a temperature of 40 °C.

[0058] In a preferred embodiment, step (ii) is performed for a residence time between 1 and 23 h.

[0059] In a preferred embodiment, step (ii) is performed at a pH between 5.3 and 8.8, more preferably at a pH of 7.0.

[0060] In a preferred embodiment, in step (ii), an acid corresponding to the carboxylate salt is added for pH adjustment.

[0061] In an even more preferred embodiment, in step (ii), citric acid is added for pH adjustment.

[0062] In an even more preferred embodiment, the pH adjustment in step (ii) is performed with a citric acid solution between 600 and 900 g / L.

[0063] In a preferred embodiment, the base used in the leaching of step (iii) is selected from potassium hydroxide, magnesium hydroxide or sodium hydroxide.

[0064] In a preferred embodiment, the base added in step (iii) is added in a ratio between 5 and 10% w / w with respect to the total mass of the basic leaching solution, more preferably in a ratio of 6.0% w / w with respect to the total mass of the basic leaching solution.

[0065] In a preferred embodiment, the leaching reaction of step (iii) is performed at a temperature between 70 and 150 °C, more preferably at a temperature of 130 °C.

[0066] In a preferred embodiment, the leaching reaction of step (iii) is performed for a residence time between 1 and 12 hours, more preferably during a residence time of 3 hours.

[0067] In a preferred embodiment, the acid used in the leaching of step (iv) is hydrochloric acid.

[0068] In a preferred embodiment, the hydrochloric acid is provided in step (iv) in a concentration varying from 50 to 140 g / L.

[0069] In a preferred embodiment, the chloride environment is increased in step (v) by adding a chloride salt.

[0070] In an even more preferred embodiment, the chloride environment is increased in step (iv) by adding magnesium chloride.

[0071] In a preferred embodiment, the chloride is provided in step (iv) in a concentration between 140 and 240 g / L.

[0072] In a preferred embodiment, step (iv) is performed at a pH between -1.5 and 0, preferably in the range -0.73 to -0.65.

[0073] In a preferred embodiment, step (iv) is performed at a temperature between 40 and 95 °C.

[0074] In a preferred embodiment, the neutralization slurry of step (v) of silver precipitation is selected from calcium hydroxide, calcium oxide, calcium carbonate, lime, magnesium-containing lime, magnesium carbonate, magnesium hydroxide or magnesium oxide.

[0075] In an even more preferred embodiment, the neutralization slurry of step (vi) of silver precipitation is a magnesium oxide slurry.

[0076] In another preferred embodiment, step (v) is performed at a temperature between 50 and 95 °C.

[0077] In a preferred embodiment, the neutralization slurry added in step (v) is provided until a pH between 3 and 7 is reached.

[0078] In another preferred embodiment, step (v) has a residence time between 0.5 and 3 h.

[0079] In a preferred embodiment, the chloride-rich fifth solution of step (v) is sent to a crystallization process of magnesium chloride.

[0080] In another preferred embodiment, the chloride-rich fifth solution of step (v) is recycled to step (iv) of silver precipitation.

[0081] In another preferred embodiment, the sulfuric acid solution of step (vi) has a sulfuric acid concentration between 60 and 275 g / L.

[0082] In another preferred embodiment, the sulfuric acid solution of step (vi) is a sulfuric acid leaching solution of the smelted powder.

[0083] In another preferred embodiment, the sulphuric acid solution of step (vi) is the first leach solution enriched in copper and iron and optionally arsenic and bismuth of step (i), which has been adjusted in its acidity to be between 60 and 275 g / L.

[0084] In a preferred embodiment, the step (vi) of silver precipitation leaching is carried out at a temperature between 50 and 95 °C.

[0085] In a preferred embodiment, the carboxylate salt from step (vii) of leaching the first silver concentrate is preferably sodium citrate.

[0086] In an even more preferred embodiment, the sodium citrate concentration is between 0.5 and 1 M.

[0087] In a preferred embodiment, the step (vii) of leaching the first silver concentrate is carried out at a temperature between 25 °C and 90 °C.

[0088] In a preferred embodiment, the step (vii) of leaching the first silver concentrate is carried out at a solid content between 5 and 10%.

[0089] In a preferred embodiment, the step (vii) of leaching the first silver precipitation is carried out for 1 to 6 hours.

[0090] In a preferred embodiment, the seventh leach solution is recycled to the leaching step (ii).

[0091] In a preferred embodiment, the silver concentrate comprises silver antimonate.

[0092] In an even more preferred embodiment, the silver concentrate comprises silver antimonate and lead antimonate.

[0093] In a preferred embodiment, the first leach solution enriched in copper is sent to a copper leaching process of smelting powder.

[0094] In a preferred embodiment, the sixth leach solution enriched in copper, iron and optionally arsenic is sent to a copper leaching process of smelting powder.

[0095] In a preferred embodiment, the first leach solution enriched in copper is sent to an arsenic abatimiento process.

[0096] In another preferred embodiment, the sixth leach solution enriched in copper, iron and optionally arsenic is sent to an arsenic abatimiento process.

[0097] In a preferred embodiment, the arsenic abatimiento process is selected from those that contemplate the production of ferric arsenate.

[0098] In an even more preferred embodiment, the arsenic abatimiento process is a process of production of realgar.

[0099] Application Examples

[0100] The following embodiments should be considered as implementations of the present invention and should not in any way be considered as limitations on the present invention, as various modifications that may be made therein should be covered within the scope of the subject matter claimed in the present invention.

[0101] Sulfuric acid leaching

[0102] Examples 1 to 7

[0103] A sulfuric acid solution with H₂SO₄ concentrations between 150 and 250 g / L was prepared at a concentration between 2550 and 2850 g, and arranged in a 5 L glass reactor. Sludge previously subjected to a copper leaching process was added to the reactor until the solids content was between 5% and 10% w / w. The mineralogical composition of the sludge is shown in Table 1. The reactor was stirred at 300 rpm for 3 to 6 hours at 85 °C. Once the reaction time was complete, the slurry was filtered through a Büchner system. The results are shown in Table 2.

[0104] Table 1 Mineralogical composition of sludge

[0105] Substance Units Value PbSO4 ％ 12.84 PbS ％ 0.1 PbO ％ 0.1 [CuSO4] ％ 2.54 [Cu2S] ％ 0.63 CuS ％ 4.02 CuO ％ 0.71 [CuOFe2O3] ％ 15.09 ZnO Fe2O3 ％ 4.46 ZnS ％ 2.94 Fe3O4 ％ 4.74 Fe2O3 ％ 4.91 FeS2 ％ 6.32 Ag2S ％ 0.1 FeAs04*2H20 ％ 5.18 Bi2O3 ％ 0.59 Sb2O3 ％ 0.5 KAl3Si3O 10 (OH)2]]> ％ 7.01 Al2Si2O3(OH)4 ％ 2.92 Ge g / tonne 548

[0106] Table 2 Results of sulfuric acid leaching in Examples 1 to 7

[0107]

[0108]

[0109] Examples 8 to 10

[0110] 2.550 g of a 250 g / L H₂SO₄ solution was prepared and placed in a 4 L pressure vessel, to which sludge from a previous copper leaching process was added until the solids content was 15% w / w. The reactor was stirred at 130 °C and 300 rpm for 1 to 6 hours. Once the reaction time was complete, the slurry was filtered through a Büchner system. The results are shown in Table 3.

[0111] Table 3 Results of sulfuric acid leaching in Examples 8 to 10

[0112] Variable / Example Units 8 9 10 Leach time h 1 3 6 Cu leach yield ％ 75.9 76.1 82.0 Mass loss ％ 35.0 41.0 42.0

[0113] Example 11

[0114] A refining wastewater solution was prepared, adjusting its sulfuric acid concentration to 250 g / L, and it was arranged in a 5 L glass reactor, where 450 g of sludge previously subjected to the copper leaching process were added. The reactor was stirred at 300 rpm at 85 °C for 6 h. Once the reaction time was finished, the slurry was filtered in a Buchner system. The results showed a leaching yield of Cu of 72.0%, a leaching yield of Fe of 62.0%, a leaching yield of As of 71.5%, a leaching yield of Zn of 57.0% and a mass loss of 38.5%.

[0115] Table 4 Refining wastewater composition

[0116]

[0117]

[0118] Citric acid leaching

[0119] Example 12

[0120] A solution was prepared with 40 L of water, to which 14 kg of sodium citrate were added, and the pH was adjusted to 7.0 with a 800 g / L citric acid solution. Once the reagents were dissolved, 6 kg of leached sludge were added as in example 3. The head sludge (La borra de cabeza) had a Pb content of 15.4%. The leaching was carried out at 20 °C and stirred at 1,000 rpm for 9 h. A Pb leaching efficiency of 94% was obtained, obtaining a leached sludge with a mass reduction of 24% and a Pb content of 1.19%.

[0121] Examples 13 to 19

[0122] A solution was prepared with 2 L of water, with a sodium citrate concentration between 323 and 368 g / L and a pH between 5.3 and 8.8. The pH was adjusted with a 800 g / L citric acid solution. Once the reagents were dissolved, the sludge treated as in example 3 was added at a ratio between 1.2 and 2.3 g of sodium citrate / g of sludge. The head sludge had a Pb content between 15.0 and 15.1%. The leaching was carried out between 30 and 60 °C and stirred between 500 and 700 rpm for a time between 2 and 4 h. The results are shown in Table 5.

[0123] Table 5 Citric acid leaching results of examples 13 to 19

[0124]

[0125]

[0126] Alkaline leaching

[0127] Examples 20 to 28

[0128] A slurry was prepared with a sodium hydroxide solution with a concentration between 5.4 and 8.7% w / w and a leached residue that had undergone a sequential copper and lead leaching process, with a solid content between 5.0 and 7.0% w / w. The slurry was disposed in a 4L pressurized autoclave and heated at 600 rpm at a temperature between 100 and 140°C for between 1 and 6 hours. Once the leaching time was completed, the slurry was cooled and filtered in a Büchner system. The results are shown in Table 6.

[0129] Table 6 Results of examples 20 to 28

[0130]

[0131]

[0132] Examples 29 and 30

[0133] A slurry was prepared with 6230 mL of water, to which 420 g of sodium hydroxide and 350 g of leached residue that had undergone a sequential copper and lead leaching process were added, in order to obtain a NaOH concentration of 6.0% w / w and a solid of 5.0% w / w. The slurry was disposed in a 10L glass reactor and heated at 90°C for between 1 and 6 hours and stirred at 900 rpm. Once the leaching time was completed, the slurry was cooled and filtered in a Büchner system.

[0134] Table 7 Results of examples 29 and 30

[0135] Variable / Example Units 29 30 Residence time Hours 1 6 Leach yield Ge ％ 78.1 82.0 Si ％ 63.2 63.0

[0136] Hydrochloric acid leaching

[0137] Examples 31 to 38

[0138] A solution was prepared with a HCl concentration between 54 and 160 g / L and with a chloride concentration of 140 to 237 g / L. The chloride concentration was increased by adding magnesium chloride hexahydrate. Such a solution was added to 180 g of residue that had undergone a sulfuric acid and citric acid leaching process and, on the other hand, a residue that had undergone a sulfuric acid, citric acid and alkaline leaching process as described in experiments 1 to 37. The slurry was fed to a 5L glass reactor, heated at 90°C and kept under constant stirring for 6 hours. Once the slurry test was finished, the slurry was filtered in a Büchner system. The results of these tests are shown in Table 8.

[0139] Table 8 Results of examples 31 and 38

[0140]

[0141]

[0142] The results show a significant contribution to copper leaching, including the alkaline leaching step, which improves the overall copper leaching yield. This observation is explained by the presence of chrysocolla in the sludge matrix from step ii, which is effectively modified in step ii by the addition of silicon to remove the alkali, making the copper more vulnerable to the alkaline erosion in step 4, as understood in the results presented herein.

[0143] The final residue from the hydrochloric acid leaching test undergoes stability testing according to the TCLP and SPLP protocols to obtain cadmium, arsenic, and lead release values ​​below the standard allowable values.

[0144] Example 39

[0145] A silver precipitate solution with a magnesium chloride concentration of 300 g / L was subjected to an evaporation process until the liquid culture medium was concentrated to a magnesium chloride concentration of 500 g / L. 358 mL of the evaporated solution, 385 mL of concentrated hydrochloric acid, and 94 mL of water were added to 274 g of sludge subjected to the sequential leaching process described in Examples 1 to 28 in a 5 L reactor. The reactor was heated at 90 °C and kept under constant stirring for 6 hours. Once the slurry test was completed, the slurry was filtered through a Büchner system. The results showed an 86% silver leaching yield, a 95% iron leaching yield, and a 94% copper leaching yield. At least 98% of the leached iron was iron ions.

[0146] silver precipitate

[0147] Examples 40 to 46

[0148] 450 g of PLS ​​obtained from the hydrochloric acid leaching test with 508 mg / L Ag was added to a 600 mL precipitation flask and heated between 25 and 80 °C. The silver leaching solution was neutralized using 15% by volume magnesium oxide slurry until the pH was in the range of 3 to 6. The slurry was then filtered through 45 μm filter paper.

[0149] Table 9 Results of Examples 40 to 46

[0150] Variable / Example Units 40 41 42 43 44 45 46 Neutralisation pH - 6 3 3 5 5 6 6 Temperature ℃ 25 50 80 50 80 50 80 Precipitation yield Ag ％ >99.5 >99.5 >99.5 >99.5 >99.5 >99.5 >99.5 Fe ％ 97 85 80 98 97 100 99 Cu ％ 18 5 2 16 15 20 23

[0151] Silver Concentrate

[0152] Examples 47 to 49

[0153] 50 g of silver precipitate with 3950 g / ton Ag was placed in a 600 mL precipitation flask, and sulfuric acid was added to obtain an H2SO4 concentration between 60 and 257 g / L. The slurry was stirred with a magnetic rod and heated to 60°C for 5 h, and once the leaching time was complete, the slurry was filtered through 45 μm paper.

[0154] Table 10 Results of Examples 47 to 49

[0155] Variable / Example Units 47 48 49 Sulphuric acid concentration - 60 80 120 Temperature ℃ 60 60 60 Residence time h 3 3 3 Concentrate regime Ag ％ 0.2 0.58 13 Fe ％ Cu ％

[0156] Examples 50 to 51

[0157] 1700 g of silver precipitate were put in a 20 L glass reactor at 4598 g / ton, to which 15300 g of a 275 g / L H2SO4 solution were added. The slurry was kept between 25 and 80 °C and mechanically stirred at 450 rpm for 5 h, and once the leaching time was completed, the slurry was filtered with filter paper N° 42.

[0158] Table 11 Results of examples 50 to 51

[0159] Variable / Example Units 50 51 Sulphuric acid concentration - 275 275 Temperature ℃ 25 80 Residence time h 5 5 Concentrate regime Ag ％ 11.3 11.5 Fe ％ 4.0 3.5 Cu ％ 0.35 0.15 Pb ％ 29.0 28.6

[0160] Silver concentrate cleaning

[0161] Examples 52 to 55

[0162] A silver concentrate leaching test was performed with sodium citrate due to the presence of lead in the silver concentrate. In a 5 L glass reactor, 120 g of silver concentrate obtained from silver precipitate leaching test and a sodium citrate solution between 0.5 and 1 M adjusted at pH 7 with citric acid were added. The slurry was kept between 20 and 70 °C and stirred at 700 rpm for 3 h. The lead leaching yield varied between 80 and 82. The results show that there is no silver leaching in this step, while the Sb leaching yield varied between 7 and 10%.

[0163] Table 12 Results of examples 52 to 55

[0164]

[0165]

[0166] Quemscan analysis performed on silver concentrate produced in examples of the present application revealed the presence of compounds such as silver antimonate and lead antimonate.

Claims

1. Process for the production of silver concentrates from metallurgical residues containing copper, iron, lead, silicon, silver, antimony, arsenic and bismuth, characterized in that it comprises: i. leaching of copper from the metallurgical residues with a first acid solution in order to obtain a first leach solution rich in copper, iron and arsenic and a first leached sludge rich in lead, germanium, silver and silicon with reduced copper, iron content and reduced arsenic content, ii. leaching of the first leached sludge, wherein the first leached sludge is treated with a first solution of carboxylate in order to obtain a second leached sludge lacking lead and a second leach solution rich in lead, iii. alkaline leaching of the second leached sludge, wherein a base is added in order to form an alkaline leach solution in order to obtain a third leached sludge with reduced silicon content and an alkaline leach mixture rich in silicon and arsenic, iv. hydrochloric acid leaching of the third leached sludge, wherein an acid solution is used in a chloride environment in order to obtain a fourth leached sludge for final disposal and a fourth leach solution rich in silver, copper, lead, iron and arsenic, v. precipitation of silver from the fourth leach solution rich in silver, copper, iron and arsenic with a neutralizing slurry in order to produce a fifth solution rich in chlorides and a first precipitated solid rich in iron, copper, lead, silver and arsenic, vi. leaching of the first precipitated solid rich in iron, copper, lead, silver and arsenic with a sulfuric acid solution in order to produce a sixth leach solution rich in copper, iron and arsenic and a first silver and lead concentrate, and vii. leaching of the first silver concentrate with a second carboxylate solution in order to produce a seventh leach solution and a second silver concentrate.

2. Process according to claim 1, characterized in that the metallurgical residues to be treated are powders obtained by a metal smelting process.

3. Process according to claim 2, characterized in that the powders obtained by a copper smelting process are smelting powders.

4. Process according to any one of claims 1 to 3, characterized in that the metallurgical residues have undergone a copper leaching process.

5. Process according to claim 4, characterized in that the metallurgical residues have undergone a leaching with sulfuric acid.

6. Process according to any one of claims 1 to 3, characterized in that the metallurgical residues to be processed comprise the mineral substances anglesite, covellite, copper-iron spinel in the form of CuOFe2O3, zinc spinel in the form of ZnOFe2O3, magnetite, iron (III) oxide, pyrite, orpiment, muscovite, kaolinite, lead (II) sulfate, galena and lead (II) oxide.

7. Process according to claim 6, characterized in that the copper contained in the metallurgical residues is present as copper sulfate, chalcocite, covellite and copper-iron spinel in the form of CuOFe2O3.

8. Process according to any one of claims 1 to 7, characterized in that the silicon contained in the metallurgical residues is present as muscovite and kaolinite.

9. Process according to any one of claims 1 to 8, characterized in that the lead contained in the metallurgical residues is present as lead (II) sulfate, galena or lead (II) oxide.

10. Process according to claim 9, characterized in that at least 95% of the lead is lead (II) sulfate.

11. The process according to any one of claims 1 to 10, characterized in that the first acid solution can comprise sulphuric acid and / or refinery wastewater.

12. The process according to claim 11, characterized in that step (i) is performed at a sulphuric acid concentration between 150 and 300 g / L.

13. The process according to any one of claims 1 to 12, characterized in that step (i) is performed at a temperature between 50 and 130 °C.

14. The process according to any one of claims 1 to 13, characterized in that step (i) is performed for a time between 3 and 12 hours.

15. The process according to any one of claims 1 to 14, characterized in that step (i) is performed at a solids concentration between 5 and 20% w / w.

16. The process according to any one of claims 1 to 15, characterized in that in the leaching step (ii) the carboxylate salt is sodium citrate.

17. The process according to any one of claims 1 to 16, characterized in that in step (ii) the sodium citrate solution has a molar concentration of sodium citrate between 0.5 M and 1 M.

18. The process according to any one of claims 1 to 17, characterized in that in step (ii) the first leached sludge is dosed to the sodium citrate solution in a mass ratio of 1 :9 to the sodium citrate solution.

19. The process according to any one of claims 1 to 18, characterized in that step (ii) is performed at a temperature between 20 and 60 °C.

20. The process according to any one of claims 1 to 19, characterized in that step (ii) is performed for a residence time between 1 and 23 h.

21. The process according to any one of claims 1 to 20, characterized in that step (ii) is performed at a pH between 5.3 and 8.

8.

22. The process according to any one of claims 1 to 21, characterized in that in step (ii) citric acid is added in order to adjust the pH.

23. The process according to claim 22, characterized in that the pH adjustment in step (ii) is performed with a citric acid solution of 600 and 900 g / L.

24. The process according to any one of claims 1 to 23, characterized in that the base used in the leaching of step (iii) is selected between Mg(OH)2, KOH or NaOH.

25. The process according to any one of claims 1 to 24, characterized in that the base added in step (iii) is added in a ratio between 5 and 10% w / w with respect to the total mass of the alkaline leaching mixture.

26. The process according to any one of claims 1 to 25, characterized in that the leaching reaction of step (iii) is performed at a temperature between 90 and 140 °C.

27. The process according to any one of claims 1 to 26, characterized in that the leaching reaction of step (iii) is performed for a residence time between 1 and 6 hours.

28. The process according to any one of claims 1 to 27, characterized in that in step (iv) the hydrochloric acid is provided at a concentration varying from 50 to 140 g / L.

29. The process according to any one of claims 1 to 28, characterized in that the chloride environment is increased in step (iv) by adding a chloride salt.

30. The process according to any one of claims 1 to 29, characterized in that the chloride environment is increased in step (iv) by adding magnesium chloride.

31. The process according to any one of claims 1 to 30, characterized in that the chloride is provided in step (iv) at a concentration between 140 and 240 g / L.

32. The process according to any one of claims 1 to 31, characterized in that step (iv) is carried out at a pH between -1.5 and -0.

25.

33. The process according to any one of claims 1 to 32, characterized in that step (iv) is carried out at a temperature between 40 and 95 °C.

34. The process according to any one of claims 1 to 33, characterized in that the neutralization slurry of step (v) of silver precipitation is selected from calcium hydroxide, calcium oxide, calcium carbonate, lime, magnesium carbonate, magnesium hydroxide or magnesium oxide.

35. The process according to claim 34, characterized in that the neutralization slurry of step (vi) of silver precipitation is a magnesium oxide slurry.

36. The process according to any one of claims 1 to 35, characterized in that step (v) is carried out at a temperature between 50 and 95 °C.

37. The process according to any one of claims 1 to 36, characterized in that the neutralization slurry added in step (v) is provided until a pH between 3 and 7 is reached.

38. The process according to any one of claims 1 to 37, characterized in that step (v) has a residence time between 0.5 and 3 hours.

39. The process according to any one of claims 1 to 38, characterized in that the fifth solution rich in chlorides of step (v) is sent to a crystallization process of magnesium chloride.

40. The process according to any one of claims 1 to 39, characterized in that the fifth solution rich in chlorides of step (v) is recycled to step (iv) of silver precipitation.

41. The process according to any one of claims 1 to 40, characterized in that the sulfuric acid solution of step (vi) has a sulfuric acid concentration between 60 and 275 g / L.

42. The process according to any one of claims 1 to 41, characterized in that the sulfuric acid solution of step (vi) is the first leaching solution rich in copper, iron and arsenic of step (i), which has been adjusted in its acidity to be between 60 and 275 g / L.

43. The process according to any one of claims 1 to 42, characterized in that step (vi) of leaching the silver precipitate is carried out at a temperature between 50 and 95 °C.

44. The process according to any one of claims 1 to 43, characterized in that the carboxylate salt of step (vii) of leaching the first silver concentrate is sodium citrate.

45. The process according to claim 44, characterized in that the sodium citrate concentration in step (vii) is between 0.5 M and 1 M.

46. The process according to any one of claims 1 to 45, characterized in that the step (vii) of leaching the first silver concentrate is carried out at a temperature between 25 and 70 °C.

47. The process according to any one of claims 1 to 46, characterized in that the step (vii) of leaching the first silver concentrate is carried out at a solids content between 5 and 10 wt.%.

48. The process according to any one of claims 1 to 47, characterized in that the step (vii) of leaching the first silver concentrate is carried out for 1 to 6 hours.

49. The process according to any one of claims 1 to 48, characterized in that the seventh leach solution of step (vii) is recycled to the leaching step (ii).

50. The process according to any one of claims 1 to 49, characterized in that the second silver concentrate comprises silver antimonate.

51. The process according to any one of claims 1 to 50, characterized in that the second silver concentrate comprises silver antimonate and lead antimonate.

52. The process according to any one of claims 1 to 51, characterized in that the first leach solution enriched in copper, iron and arsenic is sent to a copper leaching process of the smelted powder.

53. The process according to any one of claims 1 to 52, characterized in that the first leach solution enriched in copper, iron and arsenic is sent to an arsenic elimination process.

54. The process according to claim 53, characterized in that the arsenic elimination process is a realgar production process.

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