Process for electrolytic production of ultra-pure zinc or zinc compounds from zinc primary and secondary raw materials

Abstract

The process comprises the following stages: a) leaching; b) solid-liquid separation; c) neutralization of the aqueous solution; d) solid-liquid separation of the zinc-rich solution; e) zinc extraction; f) purification of the organic solvent from the extraction stage; g) stripping the ionic zinc loaded in the organic solvent; h) recovering the zinc contained in the aqueous acid solution from the stripping. The following barriers to impurities have been established: gentle leaching; alkaline pulp treatment; treatment of a small stream of aqueous solution, collected before and/or after the zinc extraction at step e); high selectivity of the dissolved zinc extraction; treatment of the zinc loaded in the organic solvent; cleaning treatment of the zinc-laden organic solvent, with an ultra-pure acid solution; partial bleeding and treatment of the stripped organic solvent; bleed of small stream of the final product producing loop, which will be recycled to the organic loop.

1 . A process for the continuous production of ultra-high purity electrolytic zinc or ultra-high purity zinc compounds from raw materials containing zinc which can be extracted by a hydrometallurgic treatment characterized in that it comprises the following stages: 
 a) if the raw material is solid, this raw material will be leached with an aqueous acid solution to dissolve the zinc;    b) optionally, depending on the nature of the raw material, if the leaching residue has any valuable elements, a solid-liquid separation can be included after leaching;    c) neutralization of the aqueous solution or leaching pulp, or of a zinc-laden solution when the zinc containing raw material is liquid;    d) solid-liquid separation of the zinc-rich solution (pregnant solution) from the solids (inert residues and/or precipitates in the neutralizing stage);    e) extraction of the zinc contained in the pregnant solution by an organic acid solvent;    f) purification of the zinc-laden organic solvent from the extraction stage;    g) stripping of the ionic zinc loaded in the organic solvent by an aqueous acid solution;    h) recovery of the zinc contained in the aqueous acid solution produced from stripping by electrowinning and/or crystallization and/or precipitation, and    characterized in that: 
 the different stages of the process are organized in three interrelated loops, each containing successive combined barriers to impurities, 
 within the first loop-leaching-neutralization-solvent extraction and further leaching, the first barrier to impurities, consisting of leaching in gentle conditions; a second barrier consists of the alkaline treatment of the raw material pulp and aqueous solution or of the zinc-rich aqueous solution originating in the leaching; a third barrier consists of the bleeding and treatment of a small aqueous solution stream, collection before and/or after the zinc extraction in step e) by an organic solvent;  
 within the second loop, the organic loop, the fourth barrier consists of the highly-selective zinc extraction of the aqueous solution with said organic solvent; the fifth barrier consists of the treatment of the zinc-laden organic solvent, through a physical and chemical purification system; a sixth barrier consists of the treatment to clean the zinc-laden organic solvent with an ultra-pure acid solution to strip the zinc from the ultra-pure organic solution; a seventh barrier consists of the partial bleeding and treatment of the stripped organic solvent; and  
 within the third loop, the eight barrier consists of the bleed of a small stream of the final product producing loop, which will be recycled into the organic loop.  
 
   
     
     
         2 . The process according to  claim 1 , characterized in that the raw material from which the zinc will be extracted is solid, either from primary or secondary materials, and contains between 3 and 80% by weight of zinc, which can be in the chemical form of oxides and/or salts and/or metal.  
     
     
         3 . The process according to  claim 1 , characterized in that the raw materials are impure zinc aqueous solutions, with other cations and anions in variable quantities.  
     
     
         4 . The process according to  claim 1 , characterized in that, within the first loop, the first barrier to impurities consists of leaching in gentle conditions of the raw material, conditions relating to temperature, acidity and residence time, to limit the solubilization of impurities, maintaining them in the solid raw materials.  
     
     
         5 . The process according to claims  1 ,  2  or  4 , characterized in that the leaching conditions, are maintained at a pH between 0 and 3.0 and, preferably, between 1.5 and 2.5.  
     
     
         6 . The process according to claims  1 ,  2  or  4 , characterized in that the leaching is carried out at a maximum temperature equal to 95° C., preferably, between 45° C. and 65° C.  
     
     
         7 . The process according to claims  1 ,  2  or  4 , characterized in that the leaching is carried out with a residence time of 0.5 to 7 hours and, preferably, with a residence time between 0.5 and 2 hours.  
     
     
         8 . The process according to  claim 1 , characterized in that, within the first loop, the second barrier to impurities consists of the precipitation of several impurities, co-leached with the zinc and/or present in aqueous solution, by neutralizing an aqueous solution at a controlled pH between 3 and 5, and, preferably, between 3.5 and 4.3 to selectively precipitate each impurity, in particular, silicon, iron, aluminium and antimony, removing them from the solution.  
     
     
         9 . The process according to  claim 8 , characterized in that the operating temperature of the neutralization stage in 95° C. maximum and, preferably between 40° C. and 60° C.  
     
     
         10 . The process according to  claim 8 , characterized in that the neutralization is carried out with a residence time of between 0.5 and 7 hours, preferably between 1 and 4 hours.  
     
     
         11 . The process according to claims  1 , characterized in that, within the first loop, the third barrier to impurities consists of the bleed of a small stream of neutralized zinc-laden aqueous solution and/or the zinc-discharged, aqueous solution originating in the zinc extraction to remove water and other soluble impurities, in particular magnesium, sodium, potassium, manganese, copper, nickel, cabalt, chlorides and fluorides, thus avoiding their accumulation in the circuit.  
     
     
         12 . The process according to  claim 11 , characterized in that a small stream of the zinc-laden aqueous solution originating at the zinc extraction stage c) and/or zinc-discharged aqueous acid solution originating at the zinc extraction stage e) undergoes controlled neutralization followed by zinc precipitation and a subsequent solid-liquid separation, from where the solid zinc precipitate moiety is recycled to the neutralization stage c) of the pulp and/or solution originating in the raw material leaching, and the liquid moiety undergoes an impurity removal stage by controlled neutralization.  
     
     
         13 . The process, according to  claim 11 , characterized in that the small stream of the neutralized zinc-laden aqueous solution originating at stage c), undergoes a cementation stage by introducing metallic zinc and removing the solid with the metallic impurities, followed by zinc precipitation of the resulting aqueous solution and a subsequent solid-liquid separation, from where the solid zinc precipitate moiety is recycled to the neutralization stage at c) of the pulp and/or solution originating from the raw material leaching, and the liquid moiety undergoes a impurity removal stage by controlled neutralization.  
     
     
         14 . The process according to  claim 11 , characterized in that the small stream of zinc-laden aqueous acid solution originating in the extraction stage e) undergoes neutralization and/or cementation stages by controlled neutralization of the acidity and subsequent zinc precipitation from the resulting aqueous solution and followed by a solid-liquid separation, from where the solid moiety of zinc precipitate is recycled to the neutralization stage at c) of the pulp and/or of the solution originating in the raw material leaching, and the liquid moiety undergoes an impurity removal stage by controlled neutralization.  
     
     
         15 . The process according to claims  13 , characterized in that the liquid moiety is sent to a depletion stage within the organic loop, where the zinc present in the aqueous stream is extracted in a depletion stage by the organic phase, whilst the zinc depleted aqueous solution originating in the depletion stage is recycled to neutralization and/or cementation.  
     
     
         16 . The process according to  claim 12 , characterized in that: 
 a moiety of the small stream of the neutralized zinc-laden aqueous solution and/or the zinc discharged aqueous acid solution originating in the extraction, is/are sent to the zinc precipitation stage, followed by a solid-liquid separation after which, the zinc precipitate is recycled to the neutralization stage c) of the pulp and/or of the leached solution originating in the raw material leaching stage;    the other moiety of the small stream is sent to the neutralization and/or cementation stage and, in the case that the small stream comes from the zinc-discharged, aqueous acid solution, after neutralization, it is optionally sent to the depletion stage;    and the liquid fractions, resulting from the zinc precipitation and/or neutralization and/or cementation and/or depletion are sent to the impurity removal stage by controlled neutralization.    
     
     
         17 . The process according to claims  13 ,  14  or  15 , characterized in that the pH of the controlled neutralization treatment of the acidity with an alkaline/cementation agent with metallic zinc, is between 2.0 and 4.0.  
     
     
         18 . The process according to  claim 12 , characterized in that the zinc in solution in the small stream in the neutralized zinc-laden aqueous solution and/or the zinc-discharged, aqueous acid solution originating in the zinc extraction, is precipitated with an alkaline agent at a pH between 6.0 and 8.0.  
     
     
         19 . The process according to  claim 17 , characterized in that the temperature of the neutralization, cementation and zinc precipitation treatments is between 70° C. and 90° C.  
     
     
         20 . The process according to  claim 1 , characterized in that the aqueous solution containing impurities, originating, by the bleed treatment, in neutralization, cementation, depletion and/or zinc precipitation, is treated with an alkaline agent, at a pH between 8.0 and 12.0 to precipitate the impurities which are removed, whilst the liquid obtained after the separation of impurities is recycled to the process.  
     
     
         21 . The process according  claim 11 , characterized in that the moieties of neutralized zinc-rich liquid and or zinc-discharged aqueous acid solution, originating at the extraction stage e), represents, at most, 25% of the volume of the total stream and, preferably, between 8% and 15% in volume.  
     
     
         22 . The process according to  claim 1 , characterized in that, within the first loop and second loop, the fourth barrier to impurities consists of the highly-selective extraction of dissolved zinc, by an organic acid solvent, stage e) feeding the aqueous zinc solution neutralized to a pH between 2.0 and 5.0 and, preferably, between 3.5 and 4.3.  
     
     
         23 . The process according to  claim 1 , characterized in that the extraction of the zinc contained in the neutralized zinc-rich aqueous solution, takes place in an acidity range between 0.01 and 3.0 g/l of equivalent H +  and at a temperature between room temperature and 80° C., preferably 40° C.  
     
     
         24 . The process according to  claim 1 , characterized in that the extraction of the zinc contained in the neutralized zinc-rich aqueous solution, is performed using an organic acid solvent, dissolved in kerosene, chosen from the group constituted by alkyl phosphoric acids, alkyl phosphonic acids, alkyl phosphinic acids and, preferably within the group constituted by di-(2-ethylhexyl) phosphoric acid (D 2 EPHA), di- (2-ethylhexyl) phosphonic acid and di-(2,4,4-trimethylpentyl) phosphinic acid.  
     
     
         25 . The process according to  claim 22 , characterized in that the ratio of phases between the organic solvent and the aqueous solution (ratio written as O/A) is between 0.1 and 10 and, preferably, between 1.0 and 3.0.  
     
     
         26 . The process according to  claim 1 , characterized in that the fifth barrier to impurities consists of the treatment of the zinc-laden organic solvent from the extraction, with a double purification system, physical and chemical treatment (scrubbing/washing), used in the aqueous acid solution to remove impurities from the aqueous phase entrained in the organic phases, and other impurities co-extracted with the zinc.  
     
     
         27 . The process according to  claim 26 , characterized in that the physical treatment consists of washing the organic solvent with zinc from the extraction, with acidulated water containing between 0.01 and 4.0 g/L of equivalent H + , with an organic/aqueous ration between 5 and 100 and, preferably, between 15 and 25.  
     
     
         28 . The process according to  claim 26 , characterized in that the chemical treatment is carried out with a recycled acidulated solution containing between 0.1 and 5 g/L of equivalent H + .  
     
     
         29 . The process according to  claim 26 , characterized in that the physical and chemical purification is carried out counter-current, in successive area(s) which are “q” physical and/or “r” chemical, so that “r”+“q” should be at least equal to one, number “q” for areas of physical purification treatment (scrubbing) should be preferably between 1 and 4 and number “r” for chemical purification treatment areas (washing) should, preferably between 1 and 4.  
     
     
         30 . The process according to  claim 1 , characterized in that the sixth barrier to impurities, still within the second loop, consists of the treatment of the loaded organic solvent, in the stripping stage, with an aqueous acid solution wherein the acidity is between 0.5 and 5 g/L or equivalent H + .  
     
     
         31 . The process according to  claim 30 , characterized in that the aqueous acid solution used in stripping contains a maximum of 250 g/l of dissolved zinc.  
     
     
         32 . The process according  claim 29 , characterized in that the treatment temperature is between 20° C. and 60° C. and, preferably, between 35° C. and 40° C.  
     
     
         33 . The process according to  claim 1 , characterized in that, within this second loop, the seventh barrier to impurities is that sent from a small bleed stream of the stripped organic phase to the regeneration phase, treating this organic solution with a hydrochloric acid solution, and subsequently recycling this treated organic bleed to the circuit.  
     
     
         34 . The process according to  claim 33 , characterized in that the hydrochloric acid solution has an acidity between 2 and 10 mol/L and, preferably, between 4 and 8 mol/L.  
     
     
         35 . The process according to  claim 31 , characterized in that the organic bleed sent to regeneration represents, at most, 20% of the volume of the total stream and, preferably, between 1% and 5% in volume.  
     
     
         36 . The process according to  claim 1 , characterized in that, within the third loop to produce the final product, the eighth barrier to impurities is the bleed from a small stream of ultra-pure aqueous acid solution, which is sent to the scrubbing/washing stage, to purify the zinc-laden organic solution.  
     
     
         37 . The process according to  claim 36 , characterized in that the small stream of ultra-pure aqueous acid solution contains between 0.5 and 5 g/L of equivalent H +  and between 0 and 250 g/L of zinc  
     
     
         38 . Ultra-pure zinc or ultra-pure zinc compounds, characterized in that they are produced according to the process of  claim 1.