Zinc recovery method

Abstract

The present invention relates to a zinc leaching method comprising the following steps: supplying a material containing zinc in an oxidized form; leaching the material in an alkaline medium to produce a solid residue and a supersaturated zinc solution (i) or a zinc-rich solution (ii); separating the solid leaching residue from the supersaturated zinc solution (i) or zinc-rich solution (ii) (A'); heating the supersaturated zinc solution (i) to precipitate zinc oxide; and separating the zinc oxide (D').

Description

Technical Field

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

Background Art

[0002] The Waelz process extracts zinc from ores or secondary raw materials and recovers it in the form of zinc oxide at a higher concentration than the original ores or secondary raw materials. The concentrated zinc oxide is sold to zinc smelters for producing metals by conventional methods.

[0003] However, the Waelz process is a heat treatment process that consumes a large amount of energy and emits a large amount of carbon dioxide.

[0004] For oxide ores, an acid leaching process for directly producing metallic zinc through purification and electrolysis is also known.

[0005] One drawback is the use of a large amount of acid in this process. Furthermore, impurities (such as Mg, Mn, F, etc.) that are harmful to electrolysis and extremely difficult to remove are present in the ore, which may contaminate the leachate. Finally, electrolysis plants require a large investment in terms of funds and personnel, and it is difficult to justify unless the ore deposit is extremely large.

[0006] Patent document WO2020 / 019834 proposes leaching zinc-removed rock with ammonia and ammonium carbonate. After filtering the residue, lime is directly added to obtain a first precipitate and filtered, and then lime is added secondly to precipitate a second precipitate. The second precipitate is calcined to produce a mixture containing zinc oxide, oxides, and / or calcium carbonate. The drawback is the use of ammonia, which raises concerns in terms of environment and safety. Furthermore, the zinc concentration in the final product remains low.

[0007] A process combining leaching, purification, and electrolysis using caustic soda (NaOH) has also been proposed. Caustic soda leaching has the advantage of higher selectivity than acid leaching. However, in addition to investment in an electrolysis plant, electrolysis of sodium zincate solution recovers metallic zinc in powder form, not as a solid cathode as obtained in acidic media. The metal powder needs to be melted for ingot casting, and this melting process results in costly metal loss.

[0008] In 1965, Merrill and Lang investigated several methods for recovering zinc from leachate of zinc ore oxidized with caustic soda. Besides electrolysis, zinc can be precipitated by carbonation, sulfidation, or dilution and recovered as 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 blowing carbon dioxide into it. This causes zinc to precipitate in the form of an oxide. The drawback is the enormous amount of caustic soda consumed. Although sodium carbonate can be recycled by reacting it with lime, the lime consumption is very high, at about 3-4 tons of quicklime per ton of zinc. Sulfidation involves reacting a sodium zincate solution with elemental sulfur to precipitate zinc sulfide. This process also consumes a large amount of sodium hydroxide, reducing profitability. Finally, dilution can cause zinc to precipitate as an oxide. This method requires the addition of a very large amount of water. To recover the caustic soda, all of this water must be evaporated, which is extremely energy-intensive.

[0010] Patent document WO2013 / 036268 proposes a method for treating waste containing, for example, 65% zinc with an NaOH solution. After most of the waste has dissolved, the zinc-rich liquid is separated from the waste by filtration. In this process, powdered zinc metal is added to the liquid to separate lead, copper, tin, and cadmium. Subsequently, zinc oxide precipitates upon addition of methanol, which acts as an antisolvent. A drawback of this process is that the antisolvent must be removed from the zinc-poor solution by distillation in order to recycle the NaOH. [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] To recover zinc from materials that cannot be sufficiently concentrated through simple physical means to the point of being sold to smelters, there is a real need for a recovery process that is energy-efficient, uses fewer reagents, emits less carbon dioxide, and does not require excessive investment from the user. [Means for solving the problem]

[0012] To solve this problem, the present invention provides a zinc recovery method comprising the following steps. That is, the zinc recovery process includes the steps of: providing a material containing zinc in an oxidized form; forming a solid residue and a zinc supersaturated solution (i) or a zinc-rich solution (ii) and leaching the material in a basic alkaline medium; separating the solid leaching residue from the zinc supersaturated solution (i) or the zinc-rich solution (ii) (A'); optionally adding a calcium compound selected from the group consisting of lime, calcined dolomite and combinations thereof to the zinc-rich solution (ii) or the zinc supersaturated solution (i) to precipitate a calcium zincate slurry containing solid calcium zincate and a zinc-deficient basic solution; separating at least a portion of the zinc-deficient basic solution from the calcium zincate slurry (B'); and forming a zinc supersaturated solution (iii) and a solid material, along with solid calcium zincate and the remainder of the zinc-deficient basic solution. The process includes the steps of: heating a calcium zincate slurry containing; optionally reusing the solid material in the calcium compound addition step and separating the solid material obtained after the heating step in order to retain the zinc supersaturated solution (iii); heating the zinc supersaturated solution (i) obtained after the separation step (A') or the zinc supersaturated solution (iii) obtained in the step (C') for separating the solid material in order to precipitate zinc oxide, preferably as the main solid, in the zinc-deficient solution; separating the zinc oxide formed during heating of the zinc supersaturated solution (i) or zinc supersaturated solution (iii) (D'); and optionally reusing at least a portion of the zinc-deficient solution (basic) produced in at least one step by adding it to a leaching step in a basic medium or to the zincate slurry before heating and zinc supersaturation treatment.

[0013] Starting with zinc-containing materials, this process makes it possible to easily and efficiently form zinc supersaturated solutions ((i), (iii)). When heated, zinc oxide is produced, which can be sold to zinc smelters to produce metallic zinc, or used as industrial zinc oxide, particularly for applications such as elastomer vulcanization, enamel paint production, and animal feed.

[0014] The heating process causes zinc oxide to precipitate in the solution, resulting in zinc deficiency. This spontaneous precipitation of zinc oxide is an important feature of the present invention.

[0015] Preferably, the main product present in the zinc-deficient solution is zinc oxide, which is formed after the heating step.

[0016] In fact, the heating step that causes the precipitation of zinc oxide results in a solid precipitate, the majority of which is composed of this zinc oxide, preferably at least 80%, more preferably at least 90%, and even more preferably at least 95% by weight relative to the total amount of precipitate.

[0017] Therefore, the process according to the present invention is more economical and energy-efficient than known processes, uses fewer reagents, and reduces CO2 emissions (by more than 70%), while ensuring a high zinc production yield.

[0018] Furthermore, it is preferable to prepare a zinc-rich solution (ii) that generates a calcium zincate slurry while adding a calcium compound to form a calcium zincate slurry. After removing a portion of the consumed solution, a zinc supersaturated solution (iii) that generates zinc oxide is obtained by heating the calcium zincate slurry.

[0019] Advantageously, a calcium compound may be added to the zinc supersaturated solution (i) to form a calcium zincate slurry while simultaneously forming a calcium zincate slurry. After removing a portion of the deficient solution, the concentrated calcium zincate slurry is heated according to the above procedure to obtain a zinc supersaturated solution (iii).

[0020] It should be noted that when a zinc supersaturated solution (iii) is obtained by the method described above, this zinc supersaturated solution (iii) will have a higher zinc concentration than the initially supplied zinc supersaturated solution (i) or zinc-rich solution (ii). The effect of adding this step is either to obtain a higher concentration zinc solution or a higher purity solution.

[0021] The zinc-deficient (basic) solution generated during the process is preferably produced by precipitation of zinc oxide and can be reused in either the leaching step or the concentrated calcium zincate slurry by separating a portion of the deficiency solution before the heating and zinc supersaturation steps.

[0022] Precipitating calcium zincate salt by adding a calcium compound to a zinc-rich solution (ii) or a zinc supersaturated solution (i) is carried out at a temperature below 70°C or in the range of 0 to 70°C, preferably below 50°C, and more preferably below 30°C.

[0023] Advantageously, the precipitation of calcium zincate salt after the addition of the calcium compound to the zinc-rich solution (ii) or zinc supersaturated solution (i) is carried out over a period of 1 to 4 hours.

[0024] Preferably, a seed consisting of a hydrated calcium zincate salt may be added to the zinc-rich solution (ii) or zinc supersaturated solution (i) prior to or following the addition of the calcium compound. This forms a slurry containing a solid calcium zincate salt and a zinc-deficient basic solution. Therefore, the seed may be added prior to the addition of the calcium compound.

[0025] More preferably, the step of heating the zinc supersaturated solution (i) obtained after the separation step (A') or the zinc supersaturated solution (iii) optionally obtained in the step (C') for separating the solid material in order to precipitate zinc oxide in the zinc-deficient solution is carried out in the presence of zinc oxide as a precipitate seed.

[0026] In a particularly preferred embodiment, the step of heating the zinc supersaturated solution (i) obtained after the step (A') of separation for precipitating zinc oxide in a zinc-deficient solution, or the zinc supersaturated solution (iii) optionally obtained in the step (C') of separating the solid material, is carried out at a temperature above 70 °C, preferably above 90 °C, for a period of at least 1 hour, if necessary, and advantageously with a maximum of 8 hours.

[0027] According to an advantageous embodiment, a stoichiometric amount of a calcium compound and / or a magnesium compound is added during the leaching step to precipitate impurities selected from the group consisting of silicic acid, alumina or carbonates. Thereby, calcium silicate, calcium aluminate, and calcium carbonate are formed.

[0028] Also, a calcium compound and / or a magnesium compound may be added to the zinc supersaturated solution (i) or the zinc-rich solution (ii) obtained after separation of the solid residue. Thereby, impurities such as silicic acid, alumina, carbonates, etc. are separated from the zinc-containing solution and can be recovered as a separate solid. The calcium compound and / or the magnesium compound are preferably selected from quicklime, slaked lime, dolomite, calcined dolomite, magnesia, limestone, and mixtures thereof.

[0029] When silicic acid is present in the supersaturated solution, it may inhibit the precipitation of zinc oxide upon heating. Optionally, when the zinc supersaturated solution (i) or (iii) contains silicic acid, the dissolved silicic acid may be removed by precipitation by a special purification process such as contacting the solution with a silicic acid seed before the precipitation of zinc oxide. After the silicic acid concentration has decreased, the supersaturated solution can be fed to the zinc oxide precipitation step.

[0030] Advantageously, the leaching step is carried out at a temperature below 90 °C, preferably below 70 °C, for a time of 3 hours or less, preferably 2.5 hours or less, more preferably 2 hours or less, if necessary, to prevent premature precipitation of zinc oxide.

[0031] More advantageously, if a supersaturated solution (i) is generated in the leaching process, the leaching process is carried out at a temperature below 90°C, preferably below 70°C, and for a period of 3 hours or less, preferably 2.5 hours or less, and more preferably 2 hours or less, to prevent premature precipitation of zinc oxide.

[0032] This embodiment is preferred and can be applied to various modifications of the process.

[0033] In a particularly advantageous alternative embodiment, the leaching process may be carried out at a temperature above 50°C, preferably above 90°C, more preferably above 150°C, for a period of less than 4 hours to prevent precipitation of the calcium zincate salt. This alternative embodiment is also preferred when a zinc-rich solution (ii) is produced.

[0034] Furthermore, if the material contains calcium in addition to zinc, or if a calcium-containing compound is added to the leaching process, it is advantageous to apply a temperature above 50°C, preferably for a period of less than 4 hours, which can prevent premature precipitation of calcium zincate salt at this stage.

[0035] Preferably, the step of heating the calcium zincate slurry (consisting of the calcium zincate salt and the remainder of the basic solution from which zinc has been removed) is carried out at a temperature greater than 50°C, preferably 80 to 95°C. This heating step is preferably carried out for a period of 0.1 to 4 hours, more preferably 0.5 to 2 hours, and even more preferably 0.5 to 1 hour.

[0036] In further embodiments, leaching is carried out in a plurality of steps, preferably in reverse order, of the following: a first leaching step of leaching the material in an alkaline medium to produce a solid residue from which zinc has been removed and a partially zinc-rich solution; a first separation step of separating the solid leached residue; a second leaching step with a partially zinc-rich solution to produce a zinc-rich solution or a zinc supersaturated solution and a solid material; a second separation step of separating the solid material produced during the second leaching step; a step of recovering the zinc supersaturated solution (i) or the zinc-rich solution (ii); and optionally, a reuse step of reusing the solid recovered after the second separation step in the first leaching step.

[0037] In the first leaching step, it is preferable to add a calcium compound or a magnesium compound.

[0038] In the second leaching step, it is preferable to carry it out without adding calcium compounds.

[0039] Preferably, the first leaching step is carried out at a temperature of 60°C or higher, more preferably 70°C or higher. This prevents the precipitation of calcium zincate salt.

[0040] According to an advantageous embodiment, the second leaching step is carried out at a temperature below 70°C, preferably below 60°C, to prevent zinc oxide precipitation and minimize the dissolution of impurities.

[0041] Advantageously, the second leaching step is carried out for a short time, i.e., less than 2 hours, preferably less than 1 hour, to prevent the precipitation of calcium zincate salt and minimize the dissolution of impurities.

[0042] Preferably, a purification step may be included to remove metals nobler than zinc from the solution by cementation (for example, by precipitation onto zinc powder added to the solution).

[0043] In a more advantageous embodiment, the calcium compound and / or magnesium compound may be selected from lime, calcined dolomite, magnesia, and mixtures thereof. This relates to the removal of the above-mentioned impurities, preferably after leaching.

[0044] On the other hand, when adding a calcium compound for the purpose of forming a calcium zincate slurry, the calcium compound is selected from the group consisting of lime, calcined dolomite, and combinations thereof.

[0045] The cementation step described in the present invention can be included at any stage of the process.

[0046] Preferably, the zinc-deficient solution produced in the previous step is subjected to cementation to metal powder, preferably zinc metal powder, to remove metal impurities that are more precious than zinc, preferably before the reuse step.

[0047] In a preferred modification, the (i) zinc supersaturated solution (iii) or zinc-rich solution (ii) produced in the preceding step is cemented to a metal powder, preferably zinc metal powder, to remove metallic impurities that are more precious than zinc.

[0048] Advantageously, at least one solid separated from a solution containing zinc and alkali hydroxide is washed with water to recover the zinc and alkali hydroxide impregnated in the solid. The washing solution is preferably reused in one or more steps of the process of the present invention. The water balance of the process is maintained by compensating for the influent water through purging, evaporation, reverse osmosis, or a combination thereof. The amount of purging is preferably adjusted so that the concentration of impurities that are difficult to remove, such as alkali chlorides, is kept at an acceptable level. To complete the equilibrium, excess water is preferably removed while minimizing energy consumption by multiple-effect evaporation or mechanical vapor compression.

[0049] Advantageously, the zinc supersaturated solution (i) or zinc supersaturated solution (iii), or zinc-rich solution (ii) produced in the process is purified prior to the zinc oxide precipitation step to reduce the silicate concentration to less than 1 g / L, preferably less than 0.5 g / L, and more preferably less than 0.3 g / L.

[0050] This purification can be carried out by contacting the solution with a silicate precipitate seed, or by other equivalent methods.

[0051] The zinc recovery process of the present invention enables continuous operation by reusing as much of the product as possible within the process, supplying it to multiple processes, and allowing for continuous recycling.

[0052] Preferably, calcium zincate seeds are added to the precipitate of the calcium zincate slurry. [Brief explanation of the drawing]

[0053] [Figure 1] One embodiment of the present invention is schematically shown. [Figure 2] Another schematic modification of the invention is shown below. [Figure 3] A preferred embodiment of the invention is schematically shown. [Modes for carrying out the invention]

[0054] Other features and advantages of the present invention will become apparent from the following non-limiting description and reference to the drawings and embodiments.

[0055] Therefore, the present invention aims to extract zinc from materials known as primary (ore) or secondary materials and recover it as a higher value-added concentrate.

[0056] According to the present invention, the material containing zinc in an oxidized form is preferably a zinc-containing raw material or secondary raw material that can be leached in a caustic soda solution. The raw material may include at least one so-called oxide mineral, such as smithsonite, hemimorphite, hydrozincite, willemite, or zinc carbonate and / or zinc silicate and / or calcium zincate salt. The secondary raw material may be derived from lead metallurgy (slag), dust (EAFD) derived from scrap recycling, etc.

[0057] Within the scope of the present invention, the zinc-containing material is selected from the group consisting of ore (raw material), secondary raw material, or mixture thereof.

[0058] In the present invention, the leaching process is carried out in an alkaline medium selected from the group consisting of alkaline compounds, preferably sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, and mixtures thereof.

[0059] In a preferred embodiment, the concentration of an alkaline compound, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, and mixtures thereof, is 100 to 300 g / L, preferably 100 to 250 g / L, more preferably 100 to 200 g / L, and particularly 130 to 200 g / L.

[0060] Within the scope of the present invention, the addition of an antisolvent is not essential. In other words, an amount less than 80% of the volume of the zinc supersaturated solution (i) or (iii) may be added. Alternatively, an antisolvent may be added in an amount that does not sufficiently affect the zinc oxide precipitation described in the present invention.

[0061] According to a preferred embodiment of the process of the present invention, the formation of a zinc oxide precipitate in solution is carried out under conditions in which no additional antisolvents, such as ethanol or methanol, are present. “In the absence of additional antisolvents” as used herein means that any addition would have little to no effect on the zinc oxide precipitate described in the present invention.

[0062] The leaching process for the zinc-containing material is preferably carried out in a solution containing caustic soda, with a preferred concentration of 130-200 g / L.

[0063] The caustic soda-based solution may contain zinc dissolved in the medium in the form of sodium zincate (Na2ZnO2).

[0064] Caustic soda-based solutions may contain impurities such as traces of silicon, aluminum, or lead, or soluble salts such as carbonates and chlorides.

[0065] Advantageously, the leaching temperature is in the range of 0 to 300°C. If the leaching temperature exceeds the boiling point at atmospheric pressure, the process is carried out under saturated vapor pressure to prevent boiling and ensure leaching in the liquid phase. The leaching temperature is selected to maximize the leaching yield of zinc and other valuable metals, while minimizing side reactions such as the dissolution of impurities and excessive consumption of caustic soda by gangue.

[0066] Therefore, advantageously, if the material contains Ca, the leaching process is carried out at a temperature above 50°C for a period of less than 4 hours.

[0067] Advantageously, the leaching process is carried out at a temperature of less than 90°C, preferably less than 70°C, for an optional period of 3 hours or less, preferably 2.5 hours or less, and more preferably less than 2 hours, in order to prevent premature precipitation of zinc oxide.

[0068] More advantageously, if a supersaturated solution (i) is produced in the leaching step, it is carried out at a temperature below 90°C, preferably below 70°C, for an optional period of 3 hours or less, preferably 2.5 hours or less, and more preferably less than 2 hours, to prevent premature precipitation of zinc oxide.

[0069] This embodiment is preferred and applicable to all modifications of the process.

[0070] In a particularly advantageous alternative embodiment, the leaching step may be carried out at a temperature above 50°C, preferably above 90°C, and more preferably above 150°C, for an optional period of less than 4 hours to prevent precipitation of the calcium zincate salt. Another embodiment is also preferred when a zinc-rich solution (ii) is produced.

[0071] In other embodiments, when the material contains calcium in addition to zinc, or when a calcium-containing compound is added to the leaching process, it is advantageous to apply a temperature above 50°C (for a minimum of 4 hours), which prevents premature precipitation of the calcium zincate salt at this stage.

[0072] Leaching may be a single-stage or multi-stage process (e.g., two-stage, see Figure 3). In the latter case, leaching is preferably carried out in a backflow manner with an intermediate solid-liquid separation. At the end of leaching, the zinc-rich solution is separated from the deficient solid by any suitable means such as vacuum filtration, pressure filtration, centrifugation, or decantation. The solid residue is preferably washed with water to recover zinc and alkaline compounds in the impregnation solution, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, or mixtures thereof, or caustic soda. The solid is then removed, and the solution proceeds to a zinc precipitation step or any intermediate purification step.

[0073] Therefore, the resulting zinc supersaturated solution (i) or zinc-rich solution (ii) is subjected to the following steps. Optionally, • Adding a calcium compound to a zinc-rich solution (ii) or a zinc supersaturated solution (i) to precipitate solid calcium zincate salt in a zinc-deficient basic solution. (B) Separating at least a portion of the zinc-deficient basic solution from the calcium zincate slurry. • A calcium zincate slurry consisting of a solid calcium zincate salt and the remainder of a zinc-deficient basic solution is heated to form a zinc supersaturated solution (iii) and a solid material. • Separate the solid material obtained after heating (C), retain the zinc supersaturated solution (iii), and reuse the solid material in the calcium compound addition step as needed. The zinc supersaturated solution (i) obtained after separation (A), or the zinc supersaturated solution (iii) that can be obtained after separation of the solid material (C), is heated to precipitate zinc oxide, preferably as the main solid, in the zinc-deficient solution. The zinc oxide formed from the zinc supersaturated solution (i) or (iii) by heating may be separated (D). Furthermore, optionally, at least a portion of the zinc-deficient (basic) solution produced in at least one step of the process may be reused by returning it to the concentrated slurry of zincate before heating and supersaturation, or by adding it to the leaching step in a basic medium.

[0074] In the process of the present invention, the amount of ore or secondary raw material to be leached is selected to maximize the leaching yield while ensuring that the zinc concentration in the concentrated solution is as high as possible. When zinc in the material to be leached exists in the form of zinc oxide, zinc oxide is the least soluble compound in a solution containing alkaline compounds, preferably sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide, or mixtures thereof. Therefore, the maximum zinc concentration in the concentrated solution cannot exceed its solubility limit, preferably 130-200 g / L.

[0075] Particularly advantageous is that if the zinc in the material being leached exists not in the form of zinc oxide, but in the form of, for example, zinc carbonate and / or zinc silicate and / or calcium zincate, the zinc concentration in the leaching solution can reach a level exceeding the solubility limit of zinc oxide. To obtain the highest possible zinc supersaturation while ensuring a high leaching yield, it is often practical to perform multi-stage back leaching (see Figure 3). The operating conditions for each leaching stage may differ. For example, the leaching temperature of the newly introduced material can be set lower than the leaching temperature of the deficient material to prevent the re-precipitation of zinc oxide. Similarly, the leaching time of the new material can be set shorter to prevent the formation of sparingly soluble calcium zincate salts.

[0076] Caustic soda leaching has the advantage of high selectivity. Unlike acidic media, iron, calcium, and magnesium do not dissolve in basic media.

[0077] However, zinc-rich leaching solutions may contain impurities such as silica, alumina, carbonates, and lead. By adding lime, silica, alumina, and carbonates can be precipitated to concentrations of approximately 1 gram or less per liter for silica and alumina, and up to several tens of grams per liter for carbonates, depending on the concentration of the alkaline compound. The alkaline compound is preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, and mixtures thereof.

[0078] Purification by lime addition is preferably carried out at temperatures above 50°C, more preferably above 60°C, to prevent precipitation of calcium zincate salt. Vigorous stirring of the zincate slurry and the use of fine lime yield high purification yields. Purification can be carried out in the presence of the zinc-free product, i.e., before or after separation of the leachate residue. In the former case, the silica and / or alumina and / or carbonate precipitates are mixed with the leachate residue and simultaneously separated from the zinc-rich solution. In the latter case, they are recovered individually from the concentrated solution. In addition to removing impurities that may contaminate the final zinc-rich product, the silica, alumina, and carbonate precipitates contribute to the regeneration of free alkaline compounds (preferably sodium hydroxide, potassium hydroxide, lithium hydroxide, or mixtures thereof). These compounds are preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures of their free forms.

[0079] It should be noted that these advantageous methods can all be implemented in combination with each other in the first and / or second modifications of the present invention.

[0080] Furthermore, this "reverse flow" method can also be applied to the first and / or second modifications of the present invention.

[0081] Metals nobler than zinc (such as lead, copper, and silver) that migrate into the solution along with zinc during leaching can be completely or partially removed from the solution by cementation onto zinc powder.

[0082] Some impurities, such as sulfates, chlorides, and alkali fluorides, are more difficult to remove. These are generally tolerated in the leaching circuit at concentrations of several tens of g / L, and their accumulation can be controlled by purging.

[0083] Whether purified or not, zinc in a concentrated solution is recovered by precipitation by breaking its supersaturation. Zinc is recovered from the supersaturated solution, preferably in oxide form, by breaking the supersaturation. This involves raising the solution temperature to over 70°C, preferably over 100°C, for several hours. This alkaline compound is preferably selected from the group including sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, and mixtures thereof. Thus, the zinc in the solution precipitates as an oxide, continuing until the solubility of zinc oxide is reached. It is preferable to add a seed to promote precipitation.

[0084] In this invention, the precipitated seed refers to zinc oxide crystals, which can be obtained, for example, by reusing a portion of the precipitated slurry from above.

[0085] The precipitated zinc oxide is recovered by filtration or other solid-liquid separation. The solid is preferably washed to recover the alkaline compounds impregnated in the solid, preferably sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, or mixtures thereof. The solution from which the zinc has been removed can be reused in the leaching process with minimal consumption of alkaline compounds preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, and mixtures thereof.

[0086] The separation step included in the process of the present invention is liquid-solid separation, and various suitable separation methods are well known to those skilled in the art.

[0087] The wash water for various solids can also be reused at each stage. The water balance of the circuit is regulated by one or more evaporation processes and / or bleeding.

[0088] In this invention, a calcium zincate slurry consisting of a solid calcium zincate salt and a basic zinc-deficient solution is precipitated using a calcium compound, preferably lime.

[0089] This operation is particularly preferable when the zinc concentration in the concentrated solution (whether purified or not) is less than the solubility of zinc oxide. In this case, it is preferable to precipitate the calcium zincate salt and then form the zinc supersaturated solution of (iii) as described in the present invention.

[0090] Calcium zincate has relatively low solubility and high temperature dependence in solutions containing less than 250 g / L of caustic soda. To precipitate zinc from a zinc-rich sodium zincate solution, a calcium compound (e.g., lime), preferably a finely ground product, is added at a temperature below 80°C, preferably below 50°C. The slurry is advantageously stirred vigorously with strong shear, and to achieve a complete reaction of lime, the peripheral speed of the stirrer is preferably at least 5 m / s.

[0091] The amount of calcium compound (e.g., lime) to be added is preferably a stoichiometric amount relative to the amount of zinc to be precipitated, i.e., 1 mole of calcium for every 2 moles of zinc.

[0092] Advantageously, the zinc-deficient solution can be reused in the leaching process, thereby minimizing the consumption of alkaline compounds, preferably sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, or mixtures thereof. This calcium zincate salt allows for the recovery of alkaline compounds selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonates, lithium hydroxide, and mixtures thereof, which have been impregnated into the solid by washing. The washing water can be reused at any stage of the process.

[0093] The zinc content of dried calcium zincate salt is approximately 40%. This means that it does not require roasting like sulfide concentrate or Würz oxide and can be used directly in smelters to produce metallic zinc.

[0094] The calcium zincate salt is obtained as a solution containing an alkaline compound, preferably sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide, or a mixture thereof, with a caustic soda concentration of 130-200 g / L being preferred. A zinc supersaturated solution can also be obtained by re-leaching in the solution, preferably at a temperature above 70°C. During leaching, the calcium oxide constituting the calcium zincate salt does not dissolve. After leaching, this can be separated from the concentrated solution and reused advantageously for precipitation of calcium zincate salt or precipitation (purification) of silicic acid.

[0095] The resulting zinc supersaturated solution can be further heated to a higher temperature in the presence of precipitated seed (zinc oxide crystals) to promote the precipitation of zinc oxide.

[0096] The zinc oxide obtained from the leaching of calcium zincate is of very high purity, typically containing 95% or more, preferably 97% or more, more preferably 98% or more, and most preferably 99% or more zinc oxide. This can be used in the production of metallic zinc and as technical zinc oxide (for applications such as elastomer vulcanization, glaze production, and animal feed).

[0097] According to the first modification, the following steps are included: • A process of supplying materials containing zinc in an oxidized form. • A process of forming a solid residue and a zinc supersaturated solution (i), and leaching in an alkaline medium. • Separation step (A') of leached solid residue from zinc supersaturated solution (i), Preferably, zinc oxide is precipitated as the main solid in the zinc-deficient solution by heating the zinc supersaturated solution (i) obtained after separation (A'). • Separation step (D') of zinc oxide formed during heating of the zinc supersaturated solution (i).

[0098] In a preferred embodiment of the first modification, after the formation of the solid residue and the zinc supersaturated solution (i), the following sequential steps may be further included after optional separation (A'): • A step to add a calcium compound to a zinc supersaturated solution (i) in order to form a zinc acid slurry consisting of a solid calcium zincate salt and a zinc-deficient basic solution. (B') A step of separating at least a portion of the zinc-deficient basic solution from the calcium zincate slurry. The process involves forming a solid material with a zinc supersaturated solution (iii), and heating a calcium zincate slurry consisting of a solid calcium zincate salt and the remainder of a zinc-deficient basic solution. • A step (C') to retain the zinc supersaturated solution (iii) and separate the solid material obtained after heating in order to reuse the solid material in the calcium compound addition step if necessary.

[0099] The zinc supersaturated solution (iii) obtained in this way is then heated to precipitate zinc oxide, preferably as the main solid. By separating the zinc oxide formed by heating the zinc supersaturated solution (i) from the zinc-deficient solution (D'), the zinc oxide according to the present invention can be provided.

[0100] In particular, the supersaturated solution (iii) formed in the preferred embodiment of the first modified example described above has a higher degree of zinc supersaturation and higher purity compared to the initial supersaturated solution (i).

[0101] Preferably, at least a portion of the zinc-deficient (basic) solution produced in at least one step of the process can be reused by returning it to the leaching step in a basic medium.

[0102] Advantageously, when carrying out the first modification of the present invention, it is necessary to produce a zinc supersaturated zincate solution. To do this, the zinc-containing material is leached with an optionally zinc-saturated alkaline solution. Under these conditions, it is observed that precipitation does not occur even if the zinc in the solution exceeds the upper limit of zinc oxide solubility. The solid residue from which the zinc has been removed is separated by filtration. The zinc-rich solution is preferably heated to above 70°C in the presence of crystallization seeds (zinc oxide particles). Under these conditions, zinc oxide precipitates over time. After the zinc oxide is recovered by filtration, the zinc-saturated alkaline solution can be advantageously reused for leaching.

[0103] According to the second modification, the following steps are included: namely, • Supply process of materials containing zinc in oxidized form, • Forming a solid residue and a zinc-rich solution (ii), and a leaching process in an alkaline medium, • A step (A') to separate the leached solid residue from the zinc-rich solution (ii), - A step of adding a calcium compound to a zinc-rich solution (ii) in order to precipitate a zinc acid slurry containing solid calcium zincate salt and a zinc-deficient basic solution. (B') A step of separating at least a portion of the zinc-deficient basic solution from the calcium zincate slurry. • A step of heating a calcium zincate slurry consisting of a zinc supersaturated solution (iii), a solid calcium zincate salt, and the remainder a zinc-deficient basic solution to form a solid material. • A step (C') to separate the solid material obtained after heating in order to retain the zinc supersaturated solution (iii) and reuse the solid material in the calcium compound addition step as needed. Preferably, zinc oxide is separated (C') to precipitate in a zinc-deficient solution, and the zinc supersaturated solution (iii) obtained after separation is heated. • A step (D') to separate the zinc oxide formed during heating of the zinc supersaturated solution (iii).

[0104] Preferably, in the second modified version of the process, at least a portion of the zinc-deficient (basic) solution produced at each stage of the process can be reused by returning it to the leaching step in a basic medium, or by separating at least a portion of the deficient solution from the zinc acid slurry and returning it to the slurry before heating and zinc supersaturation.

[0105] According to a second modification of the present invention, zinc can be leached in an alkaline solution with a zinc content below its solubility. In this case, zinc can be precipitated from the concentrated solution by adding finely ground lime, preferably at a temperature below 50°C. The lime reacts with the zincate solution to form an insoluble calcium zincate salt, which can be recovered by filtration. This calcium zincate salt can be put on the market as is after washing and drying, or it can be optionally releached in a zinc-saturated alkaline solution, preferably above 50°C, to produce a zinc supersaturated solution (iii). The lime itself is insoluble and can be recovered by filtration and can be advantageously reused in the calcium zincate precipitation step. The supersaturated solution is heated above 70°C and, optionally in the presence of a precipitated seed (zinc oxide crystals), zinc oxide is precipitated, preferably as the main solid. The alkaline solution from which the zinc has been removed can be advantageously reused in the calcium zincate leaching step.

[0106] The recovered zinc oxide is of high purity (95-100%) and, according to evaluation methods known to those skilled in the art, is a suitable material for the production of metallic zinc.

[0107] As described above, what is common to all embodiments is the step of forming a supersaturated solution and heating it to obtain the zinc oxide according to the present invention.

[0108] The above embodiments can also be combined with each other.

[0109] Figure 1 shows one embodiment relating to a first modification of the present invention.

[0110] A material (B) containing zinc in an oxidized form is supplied and leached in an alkaline medium (1) to form a zinc supersaturated solution (i). In the leaching step (1), lime (A) may be added to remove impurities. Then, the solid residue (C) is separated by solid-liquid separation (2), and the recovered supersaturated solution (3) is heated (7) optionally in the presence of precipitated seed (F) (zinc oxide crystals) to form zinc oxide in a zinc-deficient basic solution.

[0111] Prior to heating the zinc supersaturated solution (i), a purification step may be performed to remove metals nobler than zinc (e.g., Ag, Pb, Cu, etc.). That is, cementation (4) is performed on metal powder (D), for example, zinc powder (D). After solid-liquid separation (5), the purified zinc supersaturated solution (6) is recovered and a heating step (7) is performed.

[0112] After heating (7) and the addition of precipitated seed (F), solid-liquid separation (8) is performed to recover zinc oxide (G). The zinc-deficient basic solution (9) is purified (10) by extracting impurities by adding a calcium compound (H) (lime (H)) as needed, if lime was not added in the leaching process (1). After separation of solid impurities (I) (11), the purified zinc-deficient solution (12) is recovered and optionally reused in the first leaching (1).

[0113] Figure 2 shows an embodiment relating to a second modified example of the present invention (in the presence of calcium zincate salt).

[0114] A zinc-containing material (A) is added and leached (1) in an alkaline medium (NaOH aqueous solution) to form a zinc-rich solution (ii) in the presence of a solid residue. The solid residue (B) is removed by solid-liquid separation (2) to retain the zinc-rich solution (3). Next, a calcium compound (C) (lime) is added to the zinc-rich solution to form a slurry consisting of calcium zincate salt (4) as a precipitate and a zinc-deficient basic solution. The addition of the calcium compound (C) is preferably carried out at room temperature or below 70°C. At least a portion of the zinc-deficient basic solution (D) is separated (5) and reused in the leaching step (1). The calcium zincate slurry (6) is heated above 70°C (7) to form a zinc supersaturated solution (iii) and a solid material. The solid material (E) is removed by solid-liquid separation (8), and the insoluble lime is extracted and can be advantageously reused in the addition step as shown in Figure 2. The zinc supersaturated solution (9) after separation (8) is heated (10) to precipitate zinc oxide in the zinc-deficient solution. Adding precipitated seed (F) (zinc oxide crystals) at this stage is also advantageous. Next, the formed zinc oxide (G) is separated (11), and the zinc-deficient basic solution (H) is optionally reused in the heating step (7). A portion of this zinc-deficient basic solution can also be advantageously returned to the first step (1).

[0115] Figure 3 shows a so-called "backflow" leaching process, in which the leaching process is carried out in two stages. Specifically, a zinc-containing material (A) is supplied to the first leaching (1) (NaOH aqueous solution), which forms a zinc-deficient solid residue and a partially zinc-rich solution. Subsequently, the solid leaching residue (C) is separated in the first separation (2), and the partially zinc-rich solution (3) is retained. Then, a second leaching is performed using this partially concentrated solution to form a zinc-rich solution in the presence of solids. The zinc-rich solution (E) is separated (5), and the solid material is replenished to the first leaching (1). Preferably, material (optionally zinc-rich material) may be added to the second leaching (4). Finally, the zinc-deficient basic solution (B) produced in the zinc oxide precipitation step can also be reused in the first leaching (1).

[0116] The above diagram illustrates the general steps common to each of the modifications of the present invention.

[0117] The aforementioned time and temperature conditions also apply to each of the processes described in these three diagrams.

[0118] According to the present invention, the material containing zinc in an oxidized form is preferably any raw or secondary raw material containing zinc that can be leached in solution using an alkaline compound, preferably selected from the group consisting of sodium hydroxide, potassium hydroxide, alkali metal carbonate, lithium hydroxide, and mixtures thereof. The raw material may contain at least one so-called oxide ore such as sphagnum ore, hemipolar ore, hydrizite, or siliconite. The secondary raw material may be derived from lead metallurgy (slag), dust (EAFD) derived from scrap recycling, etc.

[0119] The raw materials used in the process of the present invention may, in part, advantageously contain minerals selected from (but not limited to) zinc hydroxide (Zn(OH)2), zinc oxide (ZnO), rhomboid (ZnCO3), hemipolarite (Zn4Si2O7(OH)2(H2O)), hydrizite (Zn5(CO3)2(OH)6), zinc silicate (Zn2SiO4), and garnite (ZnAl2O4).

[0120] In this invention, the word "for" can be used to indicate a limited stage. Therefore, as needed, it can be replaced with an expression that limits the scope, such as "with formation of," depending on the content of the term that follows "for."

[0121] Within the scope of this invention, multiple chemical reactions can occur. Examples are given below, but it will be apparent to those skilled in the art that the reactions can be appropriately adjusted depending on the raw materials used.

[0122] (Leaching of sphagnum tincture) ZnCO3+4NaOH=Na2ZnO2+Na2CO3+2H2O

[0123] (Leaching of hemipolarite) Zn4Si2O7(OH)2(H2O)+12NaOH=4Na2ZnO2+2Na2SiO3+8H2O

[0124] (Calcium zincate precipitation) 2Na2ZnO2+CaO+7H2O=CaZn2(OH)6·2H2O+4NaOH

[0125] (Redissolution of calcium zincate) CaZn2(OH)6·2H2O+4NaOH=2Na2ZnO2+Ca(OH)2+6H2O

[0126] (Precipitation of carbonates by lime) Na2CO3 + Ca(OH)2 = 2NaOH + CaCO3

[0127] (Precipitation of silicic acid by lime) Na2SiO3 + Ca(OH)2 = 2NaOH + CaSiO3

[0128] (Zinc oxide precipitate) Na2ZnO2 + H2O = ZnO + 2NaOH [Examples]

[0129] Examples 1 and 2 describe experiments to obtain a zinc supersaturated basic solution by leaching of an oxide mineral.

[0130] Example 3 relates to the precipitation of zinc oxide from a supersaturated basic solution.

[0131] Examples 4 and 5 illustrate the results of leaching lead slag with a basic solution, which produces a zinc-rich solution (ii) that is not saturated with zinc.

[0132] Example 6 describes the addition of lime to the leachate solution of Example 5 to precipitate calcium zincate.

[0133] Example 7 relates to obtaining a zinc supersaturated solution by leaching of calcium zincate salt.

[0134] <Example 1> A zinc oxide ore sample containing 14.7% zinc (primarily as sphagnum tincture), 25.0% iron, 5.6% calcium, and 4.8% silicon was ground to less than 80 μm. 300 g of the ground ore was leached into 2 L of a solution containing 175 g / L of NaOH, 65 g / L of Na2CO3, and 10 g / L of Zn (as ZnO). The slurry was heated to 70°C, and 30 g of finely ground lime (CaO) was added at the start of leaching. After continuously stirring the slurry for 2 hours, it was filtered using a Buchner funnel. The filtrate was separated, and the zinc and silicon concentrations were measured by spectroscopy. The filtration cake was washed with 250 mL of water, dried, and then subjected to acid decomposition, after which the zinc content was measured by spectroscopy. The test results are shown in Table 1.

[0135] [Table 1]

[0136] The zinc concentration in the leachate was 28.5 g / L, the silicon concentration was 0.85 g / L, and only 3.6% of the residue was zinc-deficient. The zinc leaching yield reached 77%. The filtrate was slightly supersaturated with respect to zinc.

[0137] <Example 2> 150 g of the same fresh oxide ore as in Example 1 was ground to less than 80 μm and leached into 1 L of the filtrate from the leaching test in Example 1. The slurry was heated to 50°C, stirred for 30 minutes, and then filtered using a Buchner funnel. The filtrate was separated, and the zinc and silicon concentrations were measured by spectroscopy. The filtration cake was washed with 125 mL of water, dried, and then subjected to acid decomposition before the zinc content was measured by spectroscopy. The test results are shown in Table 2 below.

[0138] The zinc content in the leached filtrate was 41.3 g / L, the silicon content was 1.51 g / L, and the zinc content in the deficient residue was 7.8%. The zinc leaching yield was 55%. This yield is lower than that of Example 1, but in this case the filtrate is highly supersaturated with zinc (i.e., a zinc supersaturated solution).

[0139] As the next step, to illustrate a backflow leaching scheme, 121 g of filtrate residue was re-leached into 840 mL of filtrate from zinc oxide precipitated from a supersaturated solution. 15 g of lime was added to the slurry, and after heating to 80°C and stirring for 2 hours, it was filtered using a Buchner funnel. The filtrate was separated and the zinc and silicon concentrations were measured by spectroscopy. The filtration cake was washed with 120 mL of water, dried, and then subjected to acid decomposition before measuring the zinc content by spectroscopy. The results are shown in Table 2.

[0140] [Table 2]

[0141] The zinc concentration in the filtrate from the second stage of leaching was 26.7 g / L, the silicon concentration was 0.75 g / L, and the zinc content in the residue was only 3.7%. The zinc leaching yield was 46%. Carbon analysis of the filtrate showed that the carbon dioxide content of the solution decreased from 37 g / L to 29 g / L as CO2 due to the addition of CaO during leaching. The overall zinc recovery rate from the ore after both stages of leaching was 76%. A zinc-rich solution (41.3 g / L) was obtained by the two-stage backflow leaching.

[0142] <Example 3> 900 mL of supersaturated zinc leaching filtrate obtained by leaching zinc oxide ore with a zinc oxide content of 22.2% was mixed with 90 g of pure zinc oxide as a precipitate seed. The slurry was brought to a boil (over 90°C) in a flask and stirred. The generated vapor was condensed using a water-cooled column and returned to the flask to minimize liquid loss. After boiling for 8 hours, the slurry was filtered using a Buchner funnel. The filtrate was separated and the zinc concentration was measured by spectroscopy. The filter cake was washed with 100 mL of water and dried. The test results are shown in Table 3.

[0143] [Table 3]

[0144] The zinc concentration in the filtrate was only 20.8 g / L. 111.6 g of dried solid was recovered. X-ray analysis revealed that the solid consisted solely of zinc oxide.

[0145] <Examples 4 and 5> A lead furnace slag sample containing 9.4% zinc, 17.4% iron, and 13.6% silicon was pulverized to less than 80 μm. 200 g of the pulverized slag was leached into 1 L of a solution containing 175 g / L of NaOH, 65 g / L of Na2CO3, and 10 g / L of Zn (as ZnO) (Example 4). The slurry was heated to 90°C and stirred continuously for 4 hours, then filtered through a Buchner funnel. The filtrate was separated and the zinc and silicon concentrations were measured by spectroscopy. The filtered cake was washed with 250 mL of water, dried, and then subjected to alkaline fusion and acid decomposition before the zinc content was measured by spectroscopy.

[0146] The same test was repeated, but this time the slurry was heated to 200°C in a pressurized reactor (Example 5). Before filtration, it was cooled to approximately 90°C in a water-cooled coil. The results of both tests are shown in Table 5.

[0147] [Table 4]

[0148] At 200°C, the zinc yield reached 68%, which was higher than the 53% at 90°C. The zinc concentrations in the filtrates were 20.7 g / L and 23.5 g / L, respectively, and neither was saturated with zinc.

[0149] <Example 6> 4.6 g of finely ground lime (CaO) was added to 800 mL of the filtrate from the leaching test in Example 5. The slurry was stirred in a high-shear agitator at room temperature for 6 hours, and then filtered using a Buchner funnel. The filtrate was separated and the zinc concentration was measured by spectroscopy. The filtration cake was washed with 50 mL of water, dried, and then subjected to acid decomposition before the zinc content was measured by spectroscopy. The test results are shown in Table 5.

[0150] [Table 5]

[0151] 30.3 g of dried solid with a zinc content of 39.9% was recovered. X-ray analysis revealed that the solid consisted of hydrated calcium zincate. The zinc concentration in the filtrate was only 12.4 g / L, which was significantly lower than the solubility of zinc oxide without lime addition.

[0152] <Example 7> 25 g of hydrated calcium zincate salt obtained in the test of Example 6 was suspended in 500 mL of a solution containing 175 g / L NaOH and 65 g / L Na2CO3. The slurry was heated to 90°C and stirred for 2 hours, then filtered through a Buchner funnel. The filtrate was separated and the zinc concentration was measured by spectroscopy. The filtration cake was washed with 20 mL of water, dried, and then subjected to acid decomposition before the zinc content was measured by spectroscopy.

[0153] 5.7 g of dried solid was recovered. The solid was almost entirely composed of lime, with zinc making up only 2%. This indicates a zinc leaching yield of over 98%. The zinc concentration in the filtrate was 36.8 g / L, significantly exceeding the zinc saturation concentration of the solution.

[0154] Within the scope of the present invention, articles indicating a singular number, such as "a" or "an," can be replaced with words indicating a plural number, such as "at least two," "at least three," or "plural."

[0155] The terms "include," "contains," or synonyms can be replaced with "consisting of" to define an enumeration of exclusive choices, which may mean that the expression does not include other elements not listed.

[0156] It will be obvious to those skilled in the art that the present invention is not limited to the embodiments described above, and that many modifications are possible without departing from the scope of the appended claims.

Claims

1. A process of supplying a material containing zinc in an oxidized form, A step of forming a solid residue and a zinc supersaturated solution (i) or a zinc-rich solution (ii), and leaching the material in a basic alkaline medium, A step (A') of separating a solid leachate from the zinc supersaturated solution (i) or the zinc-rich solution (ii), at will A step of adding a calcium compound to a zinc-rich solution (ii) or the zinc supersaturated solution (i) to precipitate a calcium zincate slurry containing solid calcium zincate and a zinc-deficient basic solution, (B') A step of separating at least a portion of the zinc-deficient basic solution from the calcium zincate slurry, A step of heating the calcium zincate slurry, which contains a zinc supersaturated solution (iii) and a solid material, as well as solid calcium zincate and the remainder of the zinc-deficient basic solution, The process involves optionally reusing the solid material in the calcium compound addition step, and separating the solid material obtained after the heating step in order to retain the zinc supersaturated solution (iii) (C'), In order to precipitate zinc oxide, preferably as the main solid, in the zinc-deficient solution, the zinc supersaturated solution (i) obtained after the separation step (A') or the zinc supersaturated solution (iii) obtained in the step (C') for separating the solid material is heated, A step (D') of separating the zinc oxide formed during heating of the zinc supersaturated solution (i) or zinc supersaturated solution (iii), A method for recovering zinc, characterized by optionally including a step of reusing at least a portion of the (basic) zinc-deficient solution generated in at least one step by adding it to a leaching step in a basic medium or to a zinc acid slurry before heating and zinc supersaturation treatment.

2. The zinc recovery method according to claim 1, characterized in that the step of adding a calcium compound to a zinc-rich solution (ii) or a zinc supersaturated solution (i) to precipitate calcium zincate salt is carried out at a temperature of less than 70°C or in the range of 0 to 70°C, preferably less than 50°C, and more preferably less than 30°C.

3. The zinc recovery method according to claim 1 or 2, characterized in that the step of heating the zinc supersaturated solution (i) obtained after the separation step (A') to precipitate zinc oxide in the zinc-deficient solution, or the zinc supersaturated solution (iii) optionally obtained in the step of separating the solid material (C'), is carried out in the presence of zinc oxide as a precipitate seed.

4. The zinc recovery method according to claim 3, characterized in that the step of heating the zinc supersaturated solution (i) obtained after the separation step (A') to precipitate zinc oxide in the zinc-deficient solution, or the zinc supersaturated solution (iii) optionally obtained in the step (C') for separating the solid material, is carried out at a temperature of over 70°C, preferably over 90°C, for a period of at least one hour if necessary.

5. A method for recovering zinc according to any one of claims 1 to 4, characterized in that a calcium compound and / or a magnesium compound are added in a stoichiometric amount during the leaching step to precipitate impurities selected from the group constituting silica, alumina, or carbonate.

6. The zinc recovery method according to any one of claims 1 to 5, characterized in that the leaching step is performed at a temperature of less than 90°C, preferably less than 70°C, for a period of less than 2 hours if necessary.

7. The zinc recovery method according to any one of claims 1 to 6, characterized in that the leaching step is carried out at a temperature exceeding 50°C and for a period of less than 4 hours if necessary.

8. The zinc recovery method according to any one of claims 1 to 7, characterized in that a calcium compound and / or a magnesium compound are added to the zinc supersaturated solution (i) obtained after the separation of the solid residue, preferably before the formation of zinc oxide.

9. The aforementioned leaching process is, A first leaching step involves generating a solid residue from which zinc has been removed and a partially zinc-rich solution, and then leaching the material in an alkaline medium. A first separation step for separating the solid leaching residue, A second leaching step with a partially zinc-rich solution to produce a zinc-rich solution or a zinc supersaturated solution and a solid material, A second separation step for separating the solid material generated during the second leaching step, and a step for recovering the zinc supersaturated solution (i) or the zinc-rich solution (ii), Optionally, a reuse step in which the solid material recovered after the second separation step is reused in the first leaching step. A method for recovering zinc according to any one of claims 1 to 8, characterized in that it is carried out in multiple steps, preferably two steps.

10. The zinc recovery method according to claim 9, characterized in that a calcium compound is added during the first leaching step.

11. The zinc recovery method according to claim 9 or 10, characterized in that the first leaching step is performed at a temperature of 60°C or higher, preferably 70°C or higher.

12. The zinc recovery method according to any one of claims 9 to 11, characterized in that the second leaching step is performed at a temperature of less than 70°C, preferably less than 60°C, or for less than 2 hours, preferably less than 1 hour.

13. The zinc recovery method according to any one of claims 1 to 12, characterized in that the calcium compound and / or magnesium compound are selected from the group comprising lime, calcined dolomite, and magnesia.

14. The zinc recovery method according to any one of claims 1 to 13, wherein the zinc-deficient solution produced in the above step is subjected to cementation to metal powder, preferably zinc metal powder, to remove metal impurities that are more precious than zinc, preferably before the reuse step.

15. The zinc recovery method according to any one of claims 1 to 14, characterized in that the (i) zinc supersaturated solution (iii) or zinc-rich solution (ii) produced in the above step is subjected to cementation to metal powder, preferably zinc metal powder, to remove metal impurities that are more precious than zinc.

16. The zinc recovery method according to any one of claims 1 to 15, characterized in that calcium zincate seeds are added to the precipitate of the calcium zincate slurry.

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