METHOD FOR ZINC RECOVERY

Description

[0001] The present invention relates to a method for recovering zinc from a zinc-containing material.

[0002] The Waelz method allows zinc to be extracted from an ore or by-product and recovered as a zinc oxide richer than the original ore or by-product. The enriched zinc oxide is sold to zinc smelters to produce the metal using conventional methods.

[0003] However, the Waelz method is a thermal method that consumes a lot of energy and is a high emitter of carbon dioxide.

[0004] There are also acid leaching methods for oxidized ores that involve purification and electrolysis to directly produce zinc in metallic form.

[0005] One of the disadvantages is the large amount of acid used during the method. Additionally, certain impurities harmful to electrolysis and very difficult to remove may be present in the ore and contaminate the leaching solution (Mg, Mn, F, etc.). Finally, the financial and human investment for an electrolysis plant is quite high and is only justified for very large deposits.

[0006] Document WO 2020 / 019834 suggests attacking a zinc-poor rock with ammonia and ammonium carbonate. After filtering the residue, a first direct addition of lime is made to obtain a first precipitate, which is filtered. Then, a second addition of lime causes the precipitation of a second precipitate. Calcination is performed on the second precipitate to provide a mixture containing zinc oxide, calcium oxides and / or carbonate. One of the drawbacks is the use of ammonia, which has environmental and safety implications. In addition, the zinc concentration in the final product remains low.

[0007] Methods using leaching with caustic soda (hydroxide of Petition 870250084017, dated 09 / 18 / 2025, page 6 / 54 2 / 36 sodium), purification and electrolysis have been suggested. Leaching with sodium hydroxide has the advantage of being more selective than acid leaching. Besides the investment represented by the electrolysis plant, another drawback is that, during the electrolysis of sodium zincate solutions, the zinc metal is recovered in powder form, while in an acidic medium it is recovered in the form of solid cathodes. The metal powder must be melted to cast the ingots. However, this melting method generates very high metal losses.

[0008] In 1965, Merrill and Lang investigated various methods for recovering zinc contained in leaching solutions of zinc ores oxidized by caustic soda. Apart from electrolysis, zinc can be precipitated by carbonation, sulfuration or dilution and recovered in the form of a marketable concentrate.

[0009] However, all of these methods have drawbacks. Carbonation aims to reduce the solubility of zinc by converting caustic soda into sodium carbonate by bubbling carbon dioxide through it. The zinc then precipitates as an oxide. The disadvantage is that the consumption of caustic soda is prohibitive. It can be regenerated by reacting sodium carbonate with lime. However, the lime consumption is very high, about three or four tons of quicklime per ton of zinc. Sulfuration consists of precipitating zinc sulfide by reacting a solution of sodium zincate with elemental sulfur. This method also involves a high consumption of sodium hydroxide, reducing profitability. Finally, zinc can be precipitated as an oxide by dilution. This method requires significant additions of water. To recover the caustic soda, all this water must be evaporated, resulting in high energy consumption.

[0010] Document WO 2013 / 036268 suggests a method for treating tailings containing, for example, 65% Zn, by attacking them with a NaOH solution. Most of the tailings are dissolved in the solution. Petition 870250084017, dated 09 / 18 / 2025, page 7 / 54 3 / 36 The resulting zinc-rich liquor is then separated from the tailings by filtration. This method involves adding powdered Zn metal to the liquor to separate Pb, Cu, Sn, and Cd. Zinc oxide then precipitates after the addition of methanol, which acts as an antisolvent. A disadvantage of this method is the use of an antisolvent, which needs to be distilled from the zinc-poor solution in order to recycle the NaOH.

[0011] In order to recover zinc from materials that cannot be sufficiently enriched by simple physical methods to be sold to foundries, there is a real need to provide a zinc recovery method that is energy-efficient, uses few reagents, has low carbon dioxide emissions, and does not require heavy investment by the user.

[0012] To solve this problem, the present invention provides a method for zinc recovery comprising the following steps:

[0013] - Supply of a material containing zinc in oxidized form,

[0014] - Leaching of the material in an alkaline basic medium with the formation of a solid residue and a zinc supersaturated solution (i) or a zinc-rich solution (ii),

[0015] - Separation (A') of the solid leaching residue from the zinc supersaturated solution (i) or from the zinc-rich solution (ii),

[0016] - Optionally:

[0017] · addition of a calcium compound, preferably selected from the group formed by lime, calcined dolomite and their combinations, to said zinc-rich solution (ii) or to the zinc-supersaturated solution (i) to form (with formation of) a pulp containing solid calcium zincate and a zinc-poor basic solution,

[0018] • separation (B') of at least part of the basic solution Petition 870250084017, dated 09 / 18 / 2025, page 8 / 54 4 / 36 low in zinc from calcium zincate pulp,

[0019] · heating of said calcium zincate pulp composed of solid calcium zincate and the remainder of the zinc-poor basic solution with the formation of a zinc supersaturated solution (iii) and a solid material,

[0020] · separation (C') of the solid material obtained after the heating step to preserve (with the preservation) the supersaturated zinc solution (iii) and possibly recycle this solid material for the calcium compound addition step,

[0021] - Heating said zinc supersaturated solution (i) obtained after said separation (A') or the zinc supersaturated solution (iii) possibly obtained after the separation step (C') of said solid material to precipitate (precipitant) zinc oxide, preferably as the predominant solid, in a zinc-poor solution,

[0022] - Separation (D') of zinc oxide formed during heating of the supersaturated zinc solution (i) or (iii),

[0023] - Optionally, recycling at least part of said (basic) zinc-poor solution formed during at least one of the steps of the method by adding it to the leaching step in basic medium or to said zincate pulp before heating and zinc supersaturation.

[0024] Starting from a material containing zinc, the method allows, in an uncomplicated and efficient way, the formation of a supersaturated solution in zinc (i; iii) which, after heating, produces a zinc oxide that can be sold to zinc smelters to produce metallic zinc or as technical zinc oxide, particularly for the vulcanization of elastomers, the production of enamels and animal feed.

[0025] The heating step allows zinc oxide to precipitate in the solution, which is then poor in zinc. This precipitation Petition 870250084017, dated 09 / 18 / 2025, page 9 / 54 5 / 36 spontaneous zinc oxide is a fundamental aspect of the present invention.

[0026] Preferably, the zinc oxide formed after the heating step is the predominant product present in the said zinc-poor solution.

[0027] In fact, the heating step that causes the precipitation of zinc oxide leads to the precipitation of a solid, the majority of which is formed of this zinc oxide, preferably at least 80% by weight of zinc oxide, preferably at least 90% by weight of zinc oxide, more preferably at least 95% by weight of zinc oxide, in relation to the total weight of the precipitate formed.

[0028] The method according to the present invention is therefore more economical, less energy-intensive, uses smaller quantities of reagents, and produces less CO2 (reduction of more than 70%) when compared to known methods, while still guaranteeing a high zinc production yield.

[0029] It is also possible, preferably, to produce a zinc-rich solution (ii) to which the calcium compound is added to form (with the formation of) a calcium zincate pulp. After removing part of the poor solution, a heating step of the calcium zincate pulp produces a zinc-supersaturated solution (iii) which will allow obtaining zinc oxide.

[0030] Advantageously, it is also possible to use the supersaturated zinc solution (i) and add the calcium compound to it to form (with the formation of) calcium zincate pulp. After removing part of the poor solution, when the thickened calcium zincate pulp is heated according to the steps described above, a supersaturated zinc solution (iii) is provided.

[0031] Note that when the supersaturated zinc (iii) solution is obtained in the manner previously described, this supersaturated solution Petition 870250084017, dated 09 / 18 / 2025, page 10 / 54 6 / 36 in zinc (iii) has a higher concentration of zinc than the supersaturated solution (i) or the zinc-rich solution (ii) initially provided. The effect of adding this step is both to obtain a more concentrated zinc solution and to obtain a purer solution.

[0032] The (basic) zinc-poor solution that was generated during the method, preferably by zinc oxide precipitation, can be recycled to the leaching step or to the thickened calcium zincate pulp by separating part of the zinc-poor solution before the heating and zinc supersaturation step.

[0033] Preferably, the precipitation of calcium zincate as a result of adding the calcium compound to said zinc-rich solution (ii) or to said zinc-supersaturated solution (i) is carried out by applying a temperature below 70°C or between 0 and 70°C, preferably below 50°C, more preferably below 30°C.

[0034] Advantageously, the precipitation of calcium zincate after the addition of the calcium compound to said zinc-rich solution (ii) or to said zinc-supersaturated solution (i) is carried out for a period between 1 and 4 hours.

[0035] Preferably, seeds containing hydrated calcium zincate can be added to said zinc-rich solution (ii) or to the zinc-supersaturated solution (i) after the addition of a calcium compound, preferably selected from the group formed by lime, calcined dolomite and their combinations, resulting in the formation of a pulp containing solid calcium zincate and a zinc-poor basic solution. This addition of seeds can therefore occur before this possible addition of the calcium compound.

[0036] More preferably, the heating step of said zinc supersaturated solution (i) obtained after said separation (A') or of the zinc supersaturated solution (iii) eventually Petition 870250084017, dated 09 / 18 / 2025, page 11 / 54 7 / 36 obtained after the separation step (C') of said solid material to precipitate a zinc oxide in a zinc-poor solution is carried out in the presence of zinc oxide, serving as precipitation seeds.

[0037] According to a particularly preferred embodiment, the heating step of said zinc supersaturated solution (i) obtained after said separation (A') or of the zinc supersaturated solution (iii) possibly obtained after separation step (C') of said solid material to precipitate (precipitant), preferably as the predominant portion, a zinc oxide in a zinc-poor solution, is carried out at a temperature above 70°C, preferably above 90°C, possibly for a minimum period of one hour, which may advantageously reach 8 hours.

[0038] According to an advantageous embodiment, during the leaching stage, the addition of the calcium and / or magnesium compound in stoichiometric quantity is carried out to precipitate (precipitant) selected impurities from the group formed by silica, alumina or carbonate. This allows the formation of calcium silicates, calcium aluminates and calcium carbonates.

[0039] A calcium and / or magnesium compound may also preferably be added to the zinc-supersaturated solution (i) or to the zinc-rich solution (ii) obtained after said separation of said solid residue. In this way, impurities such as silica, alumina or carbonate are separated from the zinc-containing solution and recovered in a separate solid. The calcium and / or magnesium compound is preferably selected from the group consisting of quicklime, hydrated lime, dolomite, calcined dolomite, magnesia, limestone and mixtures of the aforementioned substances.

[0040] The presence of silica in the supersaturated solution can inhibit the precipitation of zinc oxide upon heating. Eventually, if the Petition 870250084017, dated 09 / 18 / 2025, page 12 / 54 8 / 36 supersaturated zinc solution (i) or (iii) comprising silica, a specific purification step may be performed prior to zinc oxide precipitation, for example, by placing the supersaturated solution in contact with silica seeds to force the precipitation of dissolved silica. Once the silica concentration has been reduced, the supersaturated zinc solution may be forwarded to the zinc oxide precipitation step.

[0041] Advantageously, the leaching step is carried out at a temperature below 90°C, preferably below 70°C, possibly for a period equal to or less than 3 hours, preferably equal to or less than 2.5 hours, more preferably less than 2 hours to prevent premature precipitation of zinc oxide.

[0042] More advantageously, if a supersaturated solution (i) is generated during the leaching step, it is carried out at a temperature below 90°C, preferably below 70°C, possibly for a period equal to or less than 3 hours, preferably equal to or less than 2.5 hours, more preferably less than 2 hours to prevent premature precipitation of zinc oxide.

[0043] This approach is preferred and can be applied to all variants of the method.

[0044] According to a particularly advantageous alternative embodiment, the leaching step can be carried out at a temperature above 50°C, preferably above 90°C, more preferably above 150°C, possibly for less than 4 hours to prevent the precipitation of calcium zincate. This advantageous alternative embodiment is also preferred when a zinc-rich solution (ii) is generated.

[0045] This alternative embodiment is further advantageous when the material contains zinc and also calcium, or when a calcium-containing compound is added to the leaching step, a temperature above 50°C is applied, preferably for a period of less than 4 hours. Petition 870250084017, dated 09 / 18 / 2025, page 13 / 54 9 / 36 hours. This prevents premature precipitation of calcium zincate at this stage of the method.

[0046] Preferably, the heating step of said calcium zincate pulp composed of calcium zincate and the remainder of the zinc-poor basic solution is carried out at a temperature above 50°C, preferably between 80°C and 95°C. This heating step is preferably carried out for a period between 0.1 and 4 hours, preferably between 0.5 and 2 hours, more preferably between 0.5 and 1 hour.

[0047] According to an additional embodiment, leaching can be carried out in several stages, preferably in two countercurrent stages, as specified below:

[0048] - A first leaching of the material in a basic alkaline medium with the formation of a solid residue poor in zinc and a solution partially rich in zinc,

[0049] - A first separation of the solid leaching residue,

[0050] - A second leaching through the partially zinc-rich solution, with the formation of a zinc-rich solution or a zinc-supersaturated solution and a solid material,

[0051] - A second separation of the solid material generated during the second leaching and recovery of the zinc supersaturated solution (i) or the zinc-rich solution (ii),

[0052] - Eventually, recycling of the solid material recovered after the aforementioned second separation for the first leaching.

[0053] Preferably, a calcium or magnesium compound is added during the first leaching.

[0054] Preferably, the second leaching is carried out without the addition of a calcium compound.

[0055] Preferably, the aforementioned first leaching is carried out at a temperature of 60°C or higher, preferably 70°C or higher. This prevents the precipitation of calcium zincate. Petition 870250084017, dated 09 / 18 / 2025, page 14 / 54 10 / 36

[0056] According to an advantageous embodiment, the second leaching is carried out at a temperature below 70°C, preferably below 60°C, in order to prevent the precipitation of zinc oxide and minimize the solubilization of impurities.

[0057] Advantageously, the second leaching is carried out in a short period, i.e., less than 2 hours, preferably less than 1 hour, in order to prevent the precipitation of calcium zincate and minimize the solubilization of impurities.

[0058] Preferably, it is possible to add a solution purification step by cementing metals more noble than zinc into the zinc powder added to the solution.

[0059] According to an even more advantageous embodiment, the calcium and / or magnesium compound is selected from the group formed by lime, calcined dolomite, magnesia and mixtures thereof. This group is involved in the removal of the impurities mentioned above, preferably after the leaching step has been carried out.

[0060] However, when a calcium compound is added for the purpose of forming calcium zincate pulp, the calcium compound is selected from the group consisting of lime, calcined dolomite and their combinations.

[0061] The cementation step described in the present invention can be inserted at any stage of the method.

[0062] Preferably, the zinc-poor solution generated by the method is purified of metallic impurities more noble than zinc by cementation into a metallic powder, preferably a metallic zinc powder, preferably before the aforementioned eventual recycling step.

[0063] According to a preferred variant, the zinc supersaturated solution (i) (iii) or the zinc-rich solution (ii) generated in the method is purified of metallic impurities more noble than zinc by Petition 870250084017, dated 09 / 18 / 2025, p. 15 / 54 11 / 36 cementation into a metal powder, preferably a metallic zinc powder.

[0064] Advantageously, at least one of the solids separated from the solutions containing zinc and alkaline hydroxides is washed, preferably with water, in order to recover the zinc and alkaline hydroxides from the solution impregnated in said at least one solid. The washing solutions are preferably recycled to one or more steps of the method according to the invention. The water balance of the method is balanced by compensating for water inputs by bleed, water evaporation, reverse osmosis, or a combination of such techniques. The bleed volume is preferably adapted to maintain the concentration in the solution of the most difficult-to-remove impurities, such as alkaline chlorides, at an acceptable level. To finalize the balance, the excess water is preferably removed by multi-effect evaporation or mechanical vapor compression to minimize the amount of energy consumed.

[0065] Advantageously, the zinc supersaturated solution (i) or (iii) or the zinc-rich solution (ii) generated in the method is purified to reduce its silica concentration to less than 1 g / l, preferably less than 0.5 g / l, and even less than 0.3 g / l before the zinc oxide precipitation step.

[0066] This purification can be carried out by placing the solution in contact with precipitating silica seeds or any other equivalent method.

[0067] The method for zinc recovery according to the present invention can be operated continuously, in particular by reusing as much as possible the products generated in the method by feeding various stages and allowing continuous recycling.

[0068] Preferably, calcium zincate seeds are added to the precipitation of said calcium zincate pulp. Petition 870250084017, dated 09 / 18 / 2025, p. 16 / 54 12 / 36

[0069] Figure 1 is a schematic view of an embodiment of the method according to the present invention.

[0070] Figure 2 is a schematic view of a variant of the method according to the present invention.

[0071] Figure 3 is a schematic view of a preferred embodiment of the method according to the invention.

[0072] Other features and advantages of the present invention will be noted after the non-limiting description below, which refers to the drawings and examples.

[0073] The present invention therefore aims to extract zinc from a material called primary or secondary raw material and recover it in a higher value concentrate.

[0074] According to the invention, the material containing zinc in oxidized form is preferably any raw or secondary material containing zinc that can be leachable in a caustic soda solution. This raw material may include at least one so-called oxidized ore containing zinc in the form of an oxidized mineral such as smithsonite, hemimorphite, hydrozincite, willemite, or in the form of zinc carbonate and / or zinc silicate and / or calcium zincate. The secondary material may originate from lead metallurgy (slag), scrap metal recycling powder (SMP), etc.

[0075] Within the scope of the present invention, the zinc-containing material can be selected from the group consisting of ores (raw materials), secondary materials and their mixtures.

[0076] In the present invention, the leaching step takes place in an alkaline basic medium obtained by adding a solution containing an alkaline basic compound, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof.

[0077] According to a preferred embodiment, the compound Petition 870250084017, dated 09 / 18 / 2025, page 17 / 54 13 / 36 basic alkaline, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof, has a concentration between 100 and 300 g / l, preferably between 100 and 250 g / l, more preferably between 100 and 200 g / l, advantageously between 130 and 200 g / l.

[0078] The addition of an antisolvent is not necessary within the scope of the present invention. In other words, less than 80% by volume may be added to the supersaturated zinc solution (i) or (iii) relative to the volume of said supersaturated zinc solution (i) or (iii). Alternatively, an antisolvent may be added without having a sufficient effect on the precipitation of a zinc oxide as described within the scope of the present invention.

[0079] According to a preferred embodiment of the method according to the invention, the formation by precipitation of zinc oxide in solution is carried out in the absence of an added amount of an antisolvent, for example ethanol or methanol. In this context, the expression "in the absence of an added amount of an antisolvent" means that any amount added will have little or no effect on the precipitation of zinc oxide as described in the present invention.

[0080] Preferably, the leaching step of the zinc-containing material is carried out in a solution containing caustic soda, preferably at a concentration between 130 and 200 g / l.

[0081] The caustic soda-based solution may also contain zinc, which is soluble in this medium in the form of sodium zincate (Na2ZnO2).

[0082] The caustic soda-based solution may also contain impurities such as traces of silicon, aluminum, lead or soluble salts (carbonates, chlorides and others).

[0083] Advantageously, the leaching temperature is between 0 and 300°C. If the leaching temperature exceeds the boiling point. Petition 870250084017, dated 09 / 18 / 2025, page 18 / 54 14 / 36 of the solution at atmospheric pressure, leaching is carried out at saturated vapor pressure to prevent boiling and conduct leaching in the liquid phase. The leaching temperature is chosen, on the one hand, to maximize the leaching yield of zinc, including other valuable metals, and, on the other hand, to minimize parasitic reactions, such as the solubilization of impurities or the excessive consumption of caustic soda by the gangue.

[0084] Thus, and advantageously, when the material contains Ca, the leaching stage is carried out at a temperature above 50°C, possibly for a period of less than 4 hours.

[0085] Advantageously, the leaching step is carried out at a temperature below 90°C, preferably below 70°C, possibly for a period equal to or less than 3 hours, preferably equal to or less than 2.5 hours, more preferably less than 2 hours to prevent premature precipitation of zinc oxide.

[0086] More advantageously, if a supersaturated solution (i) is generated during the leaching step, this is carried out at a temperature below 90°C, preferably below 70°C, possibly for a period equal to or less than 3 hours, preferably equal to or less than 2.5 hours, more preferably less than 2 hours to prevent premature precipitation of zinc oxide.

[0087] This approach is preferred and applicable to all variants of the method.

[0088] According to a particularly advantageous alternative embodiment, the leaching step can be carried out at a temperature above 50°C, preferably above 90°C, more preferably above 150°C, possibly for a period of less than 4 hours to prevent the precipitation of calcium zincate. This advantageous alternative embodiment is also preferred when a zinc-rich solution (ii) is generated. Petition 870250084017, dated 09 / 18 / 2025, p. 19 / 54 15 / 36

[0089] This alternative method is also advantageous when the material contains zinc and also calcium, or when a calcium-containing compound is added to the leaching step, a temperature above 50°C is applied, preferably for a period of less than 4 hours. This prevents premature precipitation of calcium zincate in this step of the method.

[0090] Leaching can be carried out in a single step or in several steps (e.g., in two steps, see Figure 3). In the latter case, the leaching steps are preferably conducted countercurrently to the intermediate solid-liquid separation steps. At the end of the leaching, the zinc-rich solution is separated from the zinc-poor solids by vacuum filtration, pressure filtration, centrifugation, decantation, or any other appropriate technique. The solid residue is preferably washed with water to recover the zinc and the alkaline basic compound, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof, or caustic soda in the impregnated solution. The solid is then removed while the solution advances to the zinc precipitation step or, possibly, to an intermediate purification step.

[0091] Thus, the zinc supersaturated solution (i) or the zinc-rich solution (ii) obtained is used for the following steps:

[0092] Eventually:

[0093] * addition of a calcium compound to said zinc-rich solution (ii) or to the zinc-supersaturated solution (i) to precipitate (precipitant) solid calcium zincate in a zinc-poor basic solution,

[0094] * separation (B) of at least part of the zinc-poor basic solution from the calcium zincate pulp,

[0095] * heating of said calcium zincate pulp Petition 870250084017, dated 09 / 18 / 2025, page 20 / 54 16 / 36 composed of solid calcium zincate and the remainder of the zinc-poor basic solution with the formation of a zinc supersaturated solution (iii) and a solid material,

[0096] * separation (C) of the solid material obtained after the heating step to preserve the zinc supersaturated solution (iii) and possibly recycle this solid material for the calcium compound addition step,

[0097] - Heating said zinc supersaturated solution (i) obtained after said separation (A) or the zinc supersaturated solution (iii) possibly obtained after separation step (C) of said solid material to precipitate (precipitant) zinc oxide, preferably as the predominant solid, in a zinc-poor solution,

[0098] - Separation (D) of zinc oxide formed during heating of the supersaturated zinc solution (i) or (iii),

[0099] - Optionally, recycling at least part of said (basic) zinc-poor solution formed during at least one of the steps of the method by adding it to the leaching step in basic medium or to said thickened zincate pulp, preferably after removing at least part of the zinc-poor solution and before heating and zinc supersaturation.

[0100] In the method according to the invention, the amount of ore or secondary material introduced into the leaching is selected in order to obtain the maximum possible concentration of zinc in the enriched solution, while maximizing the leaching yield. If the zinc contained in the material to be leached is in the form of zinc oxide, the maximum concentration of zinc in the enriched solution cannot exceed the solubility limit of zinc oxide, since it is the most insoluble zinc compound in a solution containing an alkaline basic compound, preferably selected from the group formed Petition 870250084017, dated 09 / 18 / 2025, p. 21 / 54 17 / 36 by sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof, preferably at a concentration between 130 and 200 g / l.

[0101] Particularly advantageously, when the zinc contained in the material to be leached is not in the form of zinc oxide but, for example, in the form of zinc carbonate and / or zinc silicate and / or calcium zincate, a zinc concentration above the solubility limit of zinc oxide can be achieved in the leaching solution. To achieve the maximum possible zinc supersaturation and still a high leaching yield, it is generally practical to carry out several countercurrent leaching stages (see the diagram in Figure 3). The operating conditions in the different leaching stages may differ. For example, the leaching temperature of fresh materials may be cooler than the leaching temperature of the poor material in order to prevent the reprecipitation of zinc oxide. Similarly, the leaching duration for a fresh material may be shorter to prevent the formation of insoluble calcium zincate.

[0102] Leaching with caustic soda has the advantage of being quite selective. Iron, calcium, and magnesium do not dissolve in a basic medium, unlike what occurs in an acidic medium.

[0103] The zinc-rich leaching solution, however, may contain impurities such as silica, alumina, carbonate, or lead. Silica, alumina, and carbonate can be precipitated by adding lime to concentrations of one gram per liter, or even less for silica and alumina, and to concentrations of several tens of grams per liter for carbonate, depending on the concentration of the alkaline basic compound, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide, and mixtures thereof.

[0104] Purification by adding lime is preferably carried out Petition 870250084017, dated 09 / 18 / 2025, page 22 / 54 18 / 36 at temperatures above 50°C, including above 60°C, to prevent the precipitation of calcium zincate. Vigorous agitation of the zincate pulp and the use of finely chopped lime favor high purification yields. Purification can be carried out in the presence of a zinc-poor material, that is, before or after separation from the leaching residue. In the first case, the silica and / or alumina and / or carbonate precipitate is mixed with the leaching residue and simultaneously separated from the zinc-rich solution. In the second case, it is separated from the rich solution and recovered without being mixed with the residue. In addition to removing impurities that would contaminate the final zinc-rich product, the precipitation of silica, alumina, and carbonate causes the regeneration of a basic alkaline compound, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof in free form.

[0105] Note that these advantageous methods can all be combined with each other, either for the first and / or for the second variant according to the invention.

[0106] Furthermore, the countercurrent mode can also be applied to the first and / or second variant of the method according to the invention.

[0107] Metals more noble than zinc that pass into solution with zinc during leaching, such as lead, copper or silver, can be wholly or partially removed from the solution by cementation, preferably into a zinc powder.

[0108] Certain impurities, especially sulfates, chlorides or alkaline fluorides, are more difficult to remove. They are generally tolerated in the leaching solution up to a certain level, of a few tens of grams per liter. The accumulation of impurities in the leaching circuit can be controlled by bleeding.

[0109] The zinc contained in the rich solution, purified or not, is then Petition 870250084017, dated 09 / 18 / 2025, page 23 / 54 19 / 36 recovered by precipitation. Zinc is recovered from the supersaturated solution, preferably in the form of oxide, breaking the supersaturation. For this purpose, the temperature of the solution is increased above 70°C, and preferably above 100°C, for several hours. The zinc then precipitates in the form of oxide until it reaches the solubility limit of zinc oxide in the solution comprising the alkaline basic compound, preferably selected from the group formed by a compound selected from the group formed by sodium hydroxide, potassium hydroxide, carbonate of an alkali metal, lithium hydroxide and mixtures thereof. Preferably, precipitation seeds are added to accelerate precipitation.

[0110] In the sense of the present invention, precipitation seeds are understood to be zinc oxide crystals resulting, for example, from the recycling of a portion of the precipitation pulp at the top.

[0111] The precipitated zinc oxide is recovered by filtration or by any other solid-liquid separation method. The solid is preferably washed to recover the alkaline basic compound, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof impregnated in the solid. The zinc-poor solution can advantageously be recycled to the leaching method, so as to minimize the consumption of the alkaline basic compound in the method, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof.

[0112] The separation steps included in the method according to the invention are liquid / solid separations, and persons skilled in the art are familiar with various suitable separation methods.

[0113] The wash water from the different solids can also Petition 870250084017, dated 09 / 18 / 2025, page 24 / 54 20 / 36 can be recycled at each stage of the method. In this way, the water balance of the circuit is balanced by one or more evaporation and / or bleeding stages.

[0114] The invention provides for the use of a calcium compound, preferably lime, which allows the precipitation of a calcium zincate pulp composed of solid calcium zincate and a zinc-poor basic solution.

[0115] This is particularly preferable when the zinc concentration of the rich solution, purified or not, is below the solubility limit of zinc oxide. In this case, it is preferable to precipitate this calcium zincate and then form a zinc supersaturated solution (iii) as described in the present invention.

[0116] Calcium zincate has a relatively low solubility and is highly temperature-dependent in solutions containing less than 250 grams per liter of caustic soda. To precipitate zinc from the rich sodium zincate solution, a calcium compound (e.g., lime), preferably finely chopped, is added to the solution at a temperature below 80°C, preferably below 50°C. Advantageously, the pulp is vigorously stirred, with high shear, to achieve a complete reaction of the lime, preferably using a peripheral speed of the stirring device of at least 5 m / s.

[0117] The amount of calcium compound (e.g., lime) added is preferably equal to the stoichiometric amount of zinc to be precipitated, i.e., one mole of calcium for every two moles of zinc to be precipitated.

[0118] The zinc-poor solution can be advantageously recycled by leaching, thus minimizing the consumption of the alkaline base compound, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof. The calcium zincate can be washed with water to recover the aforementioned base compound. Petition 870250084017, dated 09 / 18 / 2025, page 25 / 54 21 / 36 alkaline, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof, impregnated in the solid. The wash water can be recycled at any stage of the method.

[0119] After drying, calcium zincate has an approximate zinc content of 40%. It can be used by foundries to produce metallic zinc without the need for pre-cooking like sulfur concentrates or Waelz oxides.

[0120] Calcium zincate can also be advantageously released into a solution containing the alkaline basic compound, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, carbonate of an alkali metal, lithium hydroxide and mixtures thereof, preferably containing between 130 and 200 grams per liter of hot caustic soda, preferably at a temperature above 70°C, so as to produce a zinc supersaturated solution. During leaching, calcium oxide, one of the components of calcium zincate, is not dissolved. After leaching, it is separated from the enriched solution and can be advantageously recycled for the precipitation of calcium zincate or for leaching in order to precipitate impurities such as silica.

[0121] The supersaturated zinc solution can then be heated to a higher temperature in the presence of precipitation seeds (zinc oxide crystals) to force the precipitation of zinc oxide.

[0122] The zinc oxide produced from the leaching of calcium zincate is quite pure; typically, it contains more than 95%, preferably more than 97%, more preferably more than 98%, and advantageously more than 99% zinc oxide. It can be used to produce metallic zinc or as technical zinc oxide, particularly for the vulcanization of elastomers, the production of enamels, and animal feed.

[0123] According to an earlier variant of the method, the Petition 870250084017, dated 09 / 18 / 2025, page 26 / 54 The following steps are planned: 22 / 36

[0124] - Supply of a material containing zinc in oxidized form,

[0125] - Leaching of the material in an alkaline basic medium with the formation of a solid residue and a supersaturated zinc solution (i)

[0126] - Separation (A') of solid leaching residue from zinc supersaturated solution (i),

[0127] - Heating the said zinc supersaturated solution (i) obtained after the said separation (A') to precipitate (precipitant) zinc oxide, preferably as the predominant solid, in a zinc-poor solution,

[0128] - Separation (D') of zinc oxide formed during heating of the supersaturated zinc solution (i).

[0129] According to a preferred embodiment of the first variant, the method may further comprise the following successive steps, after the formation of the solid residue and the zinc supersaturated solution (i) and possibly after the separation step (A'):

[0130] - addition of a calcium compound to a zinc supersaturated solution (i) to form a zincate pulp composed of solid calcium zincate and a zinc-poor basic solution,

[0131] - separation (B') of at least part of the zinc-poor basic solution from the calcium zincate pulp,

[0132] - heating of said calcium zincate pulp composed of solid calcium zincate and the remainder of the zinc-poor basic solution with the formation of a zinc supersaturated solution (iii) and a solid material,

[0133] - separation (C') of the solid material obtained after the heating step to preserve the zinc supersaturated solution (iii) and possibly recycle this solid material for the addition step of Petition 870250084017, dated 09 / 18 / 2025, page 27 / 54 23 / 36 calcium compound.

[0134] Thus, the zinc supersaturated solution (iii) obtained is heated to precipitate (precipitant) zinc oxide, preferably as the predominant solid. The separation (D') of the zinc oxide formed during heating of the zinc supersaturated solution (i) and the zinc-poor solution allows the supply of zinc oxide according to the invention.

[0135] In particular, the supersaturated solution (iii) formed in the preferred embodiment of the first variant has a higher zinc saturation compared to the initial supersaturated solution (i) and is purer.

[0136] Preferably, it is possible to recycle at least part of the (basic) zinc-poor solution formed during at least one of the steps of the method by adding it to the leaching step in basic medium.

[0137] Advantageously, during the execution of the first variant of the method according to the invention, it is necessary to produce a supersaturated zinc zincate solution. For this, the zinc-containing material is leached with an alkaline solution, possibly saturated with zinc. Under these conditions, it is observed that the zinc content can exceed the solubility limit of zinc oxide in the alkaline solution without precipitating. The solid residue, poor in zinc, is separated by filtration. Preferably, the zinc-rich solution can be heated to temperatures above 70°C in the presence of crystallization seeds (zinc oxide particles). Under these conditions, the precipitation of zinc oxide is observed over time. After recovery of the zinc oxide by filtration, the zinc-saturated alkaline solution can be advantageously recycled for leaching.

[0138] According to a second variant of the invention, the following steps are provided:

[0139] - Supply of a material containing zinc in the form Petition 870250084017, dated 09 / 18 / 2025, page 28 / 54 24 / 36 oxidized,

[0140] - Leaching of the material in an alkaline basic medium with the formation of a solid residue and a zinc-rich solution (ii)

[0141] - Separation (A') of solid leaching residue from zinc-rich solution (ii),

[0142] - addition of a calcium compound to said zinc-rich solution (ii) to precipitate (precipitant) a zincate pulp containing solid calcium zincate and a zinc-poor basic solution,

[0143] - separation (B') of at least part of the zinc-poor basic solution from the calcium zincate pulp,

[0144] - heating of the said calcium zincate pulp composed of calcium zincate and the remainder of the zinc-poor basic solution with the formation of a zinc supersaturated solution (iii) and a solid material,

[0145] - separation (C') of the solid material obtained after the heating step to preserve the zinc supersaturated solution (iii) and possibly recycle this solid material for the calcium compound addition step,

[0146] - Heating the said zinc supersaturated solution (iii) obtained after the separation step (C') of said solid material to precipitate (precipitant) zinc oxide, preferably as the predominant solid, in a zinc-poor solution,

[0147] - Separation (D') of zinc oxide formed during heating of the zinc supersaturated solution (iii).

[0148] Preferably, recycling at least part of said (basic) zinc-poor solution formed during at least one of the steps of the method according to the second variant by adding it to the leaching step in basic medium or to said zincate pulp after removing at least part of the zinc-poor solution and before heating and supersaturation in zinc. Petition 870250084017, dated 09 / 18 / 2025, page 29 / 54 25 / 36

[0149] This second variant according to the invention allows leaching zinc in an alkaline solution whose zinc content is below its solubility limit. In this case, the zinc can be precipitated from the rich solution by adding finely broken lime, preferably at a temperature below 50°C. The lime reacts with the zincate solution to form an insoluble calcium zincate that can be recovered by filtration. This calcium zincate can be marketed in this state, optionally after washing and drying, or released in an alkaline solution, optionally saturated with zinc, preferably at a temperature above 50°C, to produce a zinc supersaturated solution (iii). The lime remains insoluble and can be recovered by filtration. Advantageously, it can be recycled to the calcium zincate precipitation step.The supersaturated solution can then be heated to a temperature above 70°C, possibly in the presence of precipitation seeds (zinc oxide crystals) to precipitate (precipitant) zinc oxide, preferably as the predominant solid. The zinc-poor alkaline solution is advantageously recycled for the leaching of calcium zincate.

[0150] The recovered zinc oxide is highly pure (95 to 100% purity) and is a suitable material for the production of metallic zinc, determined by a method known to those skilled in the art.

[0151] As can be seen, in any of the chosen embodiments, the common step is to form a supersaturated solution that will be heated to provide the zinc oxide according to the invention.

[0152] The modalities described above can also be combined.

[0153] Figure 1 illustrates an exemplary embodiment relating to the first variant of the method according to the invention.

[0154] A material containing zinc (B) in oxidized form is provided Petition 870250084017, dated 09 / 18 / 2025, page 30 / 54 26 / 36 and leached (1) in alkaline basic medium to form a zinc supersaturated solution (i). Lime (A) may be added at this leaching stage (1) to remove impurities. A solid / liquid separation (2) of the solid residue (C) is then carried out, and the collected supersaturated solution (i) (3) is heated (7), possibly in the presence of precipitation seeds (F) (zinc oxide crystals), to form zinc oxide in a zinc-poor basic solution.

[0155] Before heating the supersaturated zinc solution (i), it is possible to perform a purification step of metals more noble than zinc (e.g., Ag, Pb, Cu, etc.). Therefore, a cementation (4) is performed on a metal powder (D), such as a metallic zinc powder (D). After a solid / liquid separation step (5), the purified supersaturated zinc solution (6) is recovered to perform the aforementioned heating step (7).

[0156] After heating (7) and the addition of precipitation seeds (F), a solid / liquid separation (8) occurs, allowing the recovery of zinc oxide (G). The zinc-poor basic solution (9) is eventually purified (10) by the addition of a calcium compound (H), such as lime (H), to extract impurities, provided that lime is not added during the leaching stage (1). Following the separation (11) of solid impurities (I), the purified zinc-poor solution (12) is recovered and eventually recycled to the first leaching stage (1).

[0157] Figure 2 is an illustrative embodiment relating to the second variant of the method according to the present invention - presence of calcium zincate.

[0158] A material (A) containing zinc is introduced to perform a leaching (1) in a basic alkaline medium (aqueous NaOH solution), which allows the formation of a zinc-rich solution (ii) in the presence of a solid residue. A solid / liquid separation (2) is performed to Petition 870250084017, dated 09 / 18 / 2025, page 31 / 54 27 / 36 remove the solid residue (B) and thus preserve the zinc-rich solution (3). After that, a calcium compound (C) (lime) is added to the zinc-rich solution, leading to the formation of a pulp containing calcium zincate (4) in the form of a precipitate and a zinc-poor basic solution. The addition of the calcium compound (C) is preferably carried out cold or at a temperature below 70°C. Separation (5) of at least part of the zinc-poor basic solution (D) occurs, allowing its recycling to the leaching step (1). The calcium zincate pulp (6) is heated to a temperature above 70°C (7) to form a zinc-supersaturated solution (iii) and a solid material. A solid / liquid separation (8) of the solid material (E) is carried out, which allows the extraction of the calcium compound (insoluble lime), which can be advantageously recycled to the step of adding said compound, as illustrated in Figure 2.Heating (10) the zinc supersaturated solution (9) after the separation step (8) allows a zinc oxide to precipitate in a zinc-poor solution. Furthermore, it is advantageous to add precipitation seeds (F) (zinc oxide crystals) at this stage. Then, the separation (11) of the zinc oxide (G) formed is collected, and the zinc-poor basic solution (H) is eventually recycled to the heating step (7). Part of this zinc-poor basic solution can be advantageously reintroduced into the first step of the method (1).

[0159] Figure 3 illustrates a leaching method known as countercurrent leaching, in which the leaching step is carried out in two stages. Thus, the zinc-containing material (A) is fed to the first leaching step (1) in an alkaline basic medium (aqueous NaOH solution). This allows the formation of a zinc-poor solid residue and a partially zinc-rich solution.After that, a first separation (2) of the solid leaching residue (C) is carried out to preserve the partially zinc-rich solution (3). A second leaching operation is then carried out on the partially zinc-rich solution. Petition 870250084017, dated 09 / 18 / 2025, page 32 / 54 28 / 36 zinc, with the formation of a zinc-rich solution in the presence of a solid material. The zinc-rich solution (E) is separated (5), and the solid material is replenished in the first leaching stage (1). Advantageously, the zinc-containing material (possibly the zinc-rich material) can be added to the second leaching stage (4). Finally, the zinc-poor basic solution (B) generated during a zinc oxide precipitation stage can be further recycled to the first leaching stage (1).

[0160] The figures above describe the general steps of the variants of the method according to the invention.

[0161] All the aforementioned time and temperature characteristics apply specifically to the steps described for these three Figures.

[0162] According to the invention, the zinc-containing material in oxidized form is preferably any zinc-containing raw or secondary material that can be leached in a solution containing an alkaline basic compound, preferably selected from the group formed by sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide and mixtures thereof. This raw material may include at least the so-called oxidized ore containing zinc in the form of smithsonite, hemimorphite, hydrozincite or willemite. The secondary material may be derived from lead metallurgy (slag), recycled metal scrap powder (EAFD), etc.

[0163] The raw material used in the method according to the invention may advantageously contain a mineral selected (but not limited to) from the group consisting of zinc hydroxide ((Zn(OH)2), zinc oxide (ZnO), Smithsonite (ZnCO3), hemimorphite (Zn4Si2O7(OH)2(H2O)), hydrozincite (Zn5(CO3)2(OH)6), willemite (Zn2SiO4) and ganite (ZnAl2O4).

[0164] In the sense of the present invention, the term for can be Petition 870250084017, dated 09 / 18 / 2025, page 33 / 54 29 / 36 is used to indicate a limiting step. Thus, it is possible to replace the expression "para" (for), if necessary, with an expression that restricts the scope according to the term used after "para", for example, indicating "com a formação de" (with the formation of).

[0165] Within the scope of the present invention, several chemical reactions can occur and these are listed below. It is clear that a person skilled in the art may adjust the reactions according to the raw material used.

[0166] Smithsonite leaching

[0167] ZnCO3 + 4 NaOH = Na2ZnO2 + Na2CO3 + 2 H2O

[0168] Leaching of the hemimorphite

[0169] Zn4Si2O7(OH)2(H2O) + 12 NaOH = 4 Na2ZnO2 + 2 Na2SiO3 + H2O

[0170] Calcium zincate precipitation

[0171] 2 Na2ZnO2 + CaO + 7 H2O = CaZn2(OH)6.2H2O + 4 NaOH

[0172] Resolubilization of calcium zincate

[0173] CaZn2(OH)6.2H2O + 4 NaOH = 2 Na2ZnO2 + Ca(OH)2 + 6 H2O

[0174] Carbonate precipitation with lime

[0175] Na2CO3 + Ca(OH)2 = 2 NaOH + CaCO3

[0176] Silica precipitation with lime

[0177] Na2SiO3 + Ca(OH)2 = 2 NaOH + CaSiO3

[0178] Zinc oxide precipitation

[0179] Na2ZnO2 + H2O = ZnO + 2 NaOH

[0180] Examples 1 and 2 present the leaching tests of an oxidized ore to produce a zinc supersaturated basic solution.

[0181] Example 3 refers to the precipitation of zinc oxide from a supersaturated basic solution.

[0182] Examples 4 and 5 illustrate the results of leaching tests of a lead slag by a basic solution for Petition 870250084017, dated 09 / 18 / 2025, page 34 / 54 30 / 36 produce a zinc-rich solution not saturated with zinc (ii).

[0183] Example 6 shows the precipitation of calcium zincate by adding lime to the leaching solution of Example 5.

[0184] Example 7 refers to the production of a supersaturated zinc solution by leaching calcium zincate. EXAMPLE 1

[0185] A sample of oxidized zinc ore containing 14.7% zinc, essentially in the form of smithsonite, 25.0% iron, 5.6% calcium, and 4.8% silicon was ground to a particle size of less than 80 µm. 300 g of this ground ore were then leached in 2 liters of a solution containing 175 g / L NaOH, 65 g / L Na2CO3, and 10 g / L Zn added as ZnO. The pulp was heated to 70°C, and 30 g of finely chopped lime (CaO) were added to the pulp at the beginning of the leaching method. The pulp was stirred continuously for 2 hours before being filtered through a Buchner funnel. The filtrate was separated, and the zinc and silicon concentrations were determined by spectrometry. The filtered cake was washed with 250 ml of water, dried, and the zinc content was determined by spectrometry after acid digestion. The assay results are shown in Table 1 below. Table No. 1: Conditions and results of leaching test No. 1 Mass of crushed ore (g) 300 Addition of CaO (g) 30 Volume of leaching solution (ml) 2000 Composition of leaching solution NaOH (g / l) 175 Na2CO3 (g / l) 65 Zn (g / l) 10 Temperature 70 Leaching time (min) 120 Mass of dry residue (g) 285 Petition 870250084017, dated 09 / 18 / 2025, page 35 / 54 31 / 36 Zn content of the residue (%) 3.6 Filtrate volume (ml) 1780 Zn content of the filtrate (g / l) 28.5 Si content of the filtrate (g / l) 0.85 Zinc yield from leaching (%) 77

[0186] The leaching filtrate contained 28.5 g / l of zinc and 0.85 g / l of silicon, while the poor residue contained only 3.6% zinc. The zinc leaching yield reached 77%. The filtrate is slightly supersaturated in zinc. EXAMPLE 2

[0187] 150 g of the same fresh oxidized ore from Example 1, ground to a particle size smaller than 80 µm, were leached into 1 liter of the filtrate from the leaching test of Example 1. The pulp was heated to 50°C and stirred for 30 minutes before being filtered through a Buchner funnel. The filtrate was separated and the zinc and silicon concentrations were determined by spectrometry. The filtered cake was washed with 125 ml of water, dried, and the zinc content was determined by spectrometry after acid digestion. The test results are presented in Table 2 below.

[0188] The leaching filtrate contained 41.3 g / l of zinc and 1.51 g / l of silicon, while the lean residue contained 7.8% zinc. The zinc leaching yield was 55%. This yield is lower than the yield in Example 1, but here the filtrate is highly supersaturated in zinc (i.e., a zinc supersaturated solution).

[0189] In a second step, and to illustrate a countercurrent leaching scheme, 121 g of the leaching residue were re-leached into 840 milliliters of a filtrate of zinc oxide precipitation from a supersaturated solution. 15 g of lime were added to the pulp, which was then heated to 80°C and stirred for 2 hours before being filtered in a Buchner funnel. The filtrate was separated and the zinc concentrations were determined. Petition 870250084017, dated 09 / 18 / 2025, page 36 / 54 32 / 36 and silicon were determined by spectrometry. The filtered cake was washed with 120 ml of water, dried, and the zinc content was determined by spectrometry after acid digestion. The results are also shown in Table 2 below. Table 2: Conditions and results of leaching tests in example 2 Leaching Stage 1 2 Mass of crushed ore (g) 150 Mass of residue (g) 121 Addition of CaO (g) 0 15 Volume of leaching solution (ml) 1000 840 Composition of leaching solution NaOH (g / l) 171 154 Na2CO3 (g / l) 69 90 Zn (g / l) 28.5 20.8 Si (g / l) 0.85 at Temperature 50 80 Leaching time (min) 30 120 Mass of dry residue (g) 126 140 Zn content of residue (%) 7.8 3.7 Volume of filtrate (ml) 920 760 Zn content of filtrate (g / l) 41.3 26.7 Si content of filtrate (g / l) 1.51 0.75 Leaching yield (%) 55 46

[0190] The filtrate from the second leaching stage contained 26.7 g / l of zinc and 0.75 g / l of silicon, while the residue contained only 3.7% zinc. The zinc leaching yield reached 46%. Carbon analysis of the filtrate showed that, during leaching, the carbonate content of the solution decreased from 37 g / l of CO2 to 29 g / l with the addition of lime. The overall zinc yield from ore leaching after both stages was 46%. Petition 870250084017, dated 09 / 18 / 2025, page 37 / 54 33 / 36 of the steps was 76%. Two-stage countercurrent leaching produced a zinc-rich solution (41.3 g / l). EXAMPLE 3

[0191] 90 g of pure zinc oxide were introduced as precipitation seeds into 900 ml of a highly zinc-supersaturated leaching filtrate from the leaching of an oxidized ore containing 22.2% zinc. The pulp was brought to a boil (>90°C) in a flask and stirred. The released vapors were condensed in a water-cooled column and returned to the flask to minimize liquid loss. After 8 hours of boiling, the pulp was filtered using a Buchner funnel. The filtrate was separated and the zinc concentration was determined by spectrometry. The filtered cake was washed with 100 ml of water and dried. The results of the assay are presented in Table 3 below. Table #3:

[0192] Conditions and results of the zinc oxide precipitation test Initial solution volume (ml) 900 Initial Zn content (g / l) 40.4 Initial Si content (g / l) 0.08 Addition of seeds (g of ZnO) 90.0 Temperature 105 Duration (h) 8 Mass of dry solid recovered (g) 111.6 Filtrate volume (ml) 860 Zn content of filtrate (g / l) 20.8

[0193] The filtrate contained only 20.8 g / l of zinc. 111.6 g of dry solid were recovered. X-ray analysis showed that the solid consisted exclusively of zinc oxide. EXAMPLES 4 and 5 Petition 870250084017, dated 09 / 18 / 2025, pp. 38 / 54 34 / 36

[0194] A sample of slag from a lead smelting furnace containing 9.4% zinc, 17.4% iron, and 13.6% silicon was ground to a particle size of less than 80 µm. 200 g of the ground slag were then leached into 1 liter of solution containing 175 g / L NaOH, 65 g / L Na2CO3, and 10 g / L Zn added as ZnO (Example 4). The pulp was heated to 90°C and stirred continuously for 4 hours before being filtered through a Buchner funnel. The filtrate was separated, and the concentrations of zinc and silicon were determined by spectrometry. The filtered cake was washed with 250 mL of water, dried, and the zinc content was determined by spectrometry after alkaline fusion and acid digestion.

[0195] The test was repeated, but this time the pulp was heated to 200°C (Example 5) in a pressurized reactor. Before filtration, the pulp was cooled to approximately 90°C by a water-cooled coil. The results of both tests are shown in Table 5 below. Table #4:

[0196] Leaching test conditions and results for examples 4 and 5 Example 4 Example 5 Mass of crushed slag (g) 200 200 Volume of leaching solution (ml) 1000 1000 Composition of leaching solution NaOH (g / l) 175 175 Na2CO3 (g / l) 65 65 Zn (g / l) 10 10 Temperature 90 200 Leaching time (min) 240 240 Mass of dry residue (g) 216 204 Zn content of residue (%) 4.1 3.0 Petition 870250084017, dated 09 / 18 / 2025, page 39 / 54 35 / 36 Filtrate volume (ml) 850 870 Zn content of filtrate (g / l) 20.7 23.5 Si content of filtrate (g / l) 0.69 0.76 Leaching yield (%) 53 68

[0197] Zinc yield reached 68% at 200°C, compared to 53% at 90°C. The filtrates contained 20.7 g / l and 23.5 g / l of zinc, respectively. They are not saturated in zinc. EXAMPLE 6

[0198] 4.6 g of finely chopped lime (CaO) were added to 800 ml of the filtrate from the leaching test of Example 5. The pulp was then stirred at room temperature for 6 hours with a high shear stirrer before being filtered through a Buchner funnel. The filtrate was separated and the zinc concentration was determined by spectrometry. The filtered cake was washed with 50 ml of water, dried, and the zinc content was determined by spectrometry after acid digestion. The test results are presented in Table 5 below. Table #5:

[0199] Conditions and results of the calcium zincate precipitation test Initial solution volume (ml) 800 Initial Zn content (g / l) 23.5 Addition of CaO (g) 4.6 Temperature (°C) ambient Duration (h) 8 Mass of recovered dry solid (g) 30.3 Filtrate volume (ml) 780 Zn content of filtrate (g / l) 12.4 Zn content of solid (%) 39.9

[0200] 30.3 g of dry solid containing 39.9% zinc were recovered. X-ray analysis showed that the solid consisted of zincate. Petition 870250084017, dated 09 / 18 / 2025, pages 40 / 54 36 / 36 of hydrated calcium. The filtrate contained only 12.4 g / l of zinc, well below the solubility of zinc oxide in the absence of lime. EXAMPLE 7

[0201] 25 g of hydrated calcium zincate from assay no. Example 6: Samples were suspended in 500 ml of a solution containing 175 g / l of NaOH and 65 g / l of Na2CO3. The pulp was heated to 90°C and stirred for 2 hours before being filtered through a Buchner funnel. The filtrate was separated, and the zinc concentration was determined by spectrometry. The filtered cake was washed with 20 ml of water, dried, and the zinc content was determined by spectrometry after acid digestion.

[0202] 5.7 g of dry solid were recovered. The solid consisted almost exclusively of lime and contained only 2% zinc, indicating a zinc leaching yield greater than 98%. The zinc content of the filtrate was 36.8 g / l, well above the saturation concentration of zinc in this solution.

[0203] Within the scope of the present invention, any singular article such as, for example, “a” or “an” can be replaced by an article that designates a plural such as, for example, at least 2, at least 3, several, etc.

[0204] The term include, contain or any equivalent term or derivative may be replaced by consisting of to define a list or exclusive selection possibilities, so as not to include other elements not mentioned in the expression used.

[0205] It should be clear that the present invention is not limited to the embodiments described and that modifications may be made without detracting from the scope of the appended claims.

Claims

1. Method for recovering zinc, characterized in that it comprises the following steps: - Providing a material containing zinc in oxidized form, - Leaching the material in an alkaline basic medium with the formation of a solid residue and a zinc-supersaturated solution (i) or a zinc-rich solution (ii), - Separating (A') the solid leaching residue from the zinc-supersaturated solution (i) or the zinc-rich solution (ii), - Optionally: * Adding a calcium compound to said zinc-rich solution (ii) or to the zinc-supersaturated solution (i) to precipitate (precipitant) a zincate pulp containing solid calcium zincate and a zinc-poor basic solution, * separating (B') at least part of the zinc-poor basic solution from the calcium zincate pulp, * heating said calcium zincate pulp composed of solid calcium zincate and the remainder of the zinc-poor basic solution with the formation of a zinc-supersaturated solution (iii) and a solid material,* Separate (C') the solid material obtained after the heating step to preserve the zinc supersaturated solution (iii) and possibly recycle this solid material for the calcium compound addition step, - Heat the aforementioned zinc supersaturated solution (i) obtained after the aforementioned separation (A') or the zinc supersaturated solution (iii) possibly obtained after the separation step (C') of the aforementioned solid material to precipitate (precipitant) zinc oxide, preferably as the predominant solid, in a zinc-poor solution, - Separate (D') the zinc oxide formed during Petition 870250084017, dated 09 / 18 / 2025, page. 42 / 54 2 / 5 heating of the zinc supersaturated solution (i) or (iii), - Optionally, recycle at least part of said (basic) zinc-poor solution formed during at least one of the steps of the method, adding it to the leaching step in basic medium or to said zincate pulp before heating and zinc supersaturation.

2. Method according to claim 1, characterized in that the addition of the calcium compound to said zinc-rich solution (ii) or to said zinc-supersaturated solution (i) to precipitate calcium zincate is carried out by applying a temperature below 70°C or between 0 and 70°C, preferably below 50°C, more preferably below 30°C.

3. Method, according to any of the preceding claims, characterized in that the heating step of said zinc supersaturated solution (i) obtained after said separation (A') or of the zinc supersaturated solution (iii) possibly obtained after separation step (C') of said solid material to precipitate a zinc oxide in a zinc-poor solution is carried out in the presence of zinc oxide, serving as precipitation seeds.

4. Method according to claim 3, characterized in that the heating step of said zinc supersaturated solution (i) obtained after said separation (A') or of the zinc supersaturated solution (iii) possibly obtained after separation step (C') of said solid material to precipitate a zinc oxide in a zinc-poor solution is carried out at a temperature above 70°C, preferably above 90°C, possibly for a period of time of at least one hour.

5. Method, according to any of the preceding claims, characterized in that, during the leaching step, a calcium and / or magnesium compound is added in a stoichiometric amount to precipitate impurities selected from the group formed by silica, alumina or carbonate.

6. A method, according to any of the preceding claims, characterized in that the leaching step is carried out at a temperature below 90°C, preferably below 70°C, optionally for a period of less than 2 hours.

7. A method according to any one of claims 1 to 5 or 6, characterized in that the leaching step is carried out at a temperature above 50°C, possibly for a period of less than 4 hours.

8. Method, according to any of the preceding claims, characterized in that a calcium and / or magnesium compound is added to the supersaturated zinc solution (i) obtained after said separation of said solid residue, preferably before the formation of zinc oxide.

9. Method, according to any of the preceding claims, characterized in that the leaching step is carried out in several stages, preferably in two stages, comprising the following steps: - A first leaching of the material in an alkaline basic medium with the obtaining of a zinc-poor solid residue and a partially zinc-rich solution, - A first separation of the solid leaching residue, - A second leaching by the partially zinc-rich solution, with the formation of a zinc-rich solution or a zinc-supersaturated solution and a solid material, - A second separation of the solid material generated during the second leaching and recovery of the zinc-supersaturated solution (i) or the zinc-rich solution (ii), Petition 870250084017, dated 09 / 18 / 2025, p. 44 / 54 4 / 5 - Optionally, recycling the solid material recovered after the said second separation for the first leaching.

10. Method according to claim 9, characterized in that a calcium compound is added during the first leaching.

11. Method, according to claim 9 or 10, characterized in that said first leaching is carried out at a temperature greater than or equal to 60°C, preferably greater than or equal to 70°C.

12. Method, according to any one of claims 9 to 11, characterized in that the second leaching is carried out at a temperature below 70°C, preferably below 60°C, or for a period of less than two hours, preferably less than one hour.

13. A method, according to any of the preceding claims, characterized in that the calcium and / or magnesium compound is selected from the group consisting of lime, calcined dolomite, and magnesia.

14. A method, according to any of the preceding claims, characterized in that the zinc-poor solution generated in the method is purified of metallic impurities more noble than zinc by cementation into a metallic powder, preferably a zinc metallic powder, preferably before the aforementioned optional recycling step.

15. Method, according to any of the preceding claims, characterized in that the zinc supersaturated solution (i) (iii) or the zinc-rich solution (ii) generated in the method is purified of metallic impurities more noble than zinc by cementation into a metallic powder, preferably a zinc metallic powder.

16. Method, according to any of the preceding claims Petition 870250084017, dated 09 / 18 / 2025, p. 45 / 54 5 / 5, characterized in that calcium zincate seeds are added to the precipitation of said calcium zincate pulp.

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