Spent Electrolyte Regeneration and Recovery of Associated Valuable Metals from Lean Leaching Solution

Abstract

The impurities in the electrowinning solution can be accumulated during the cycle of alkaline solutions. The integrated process of regeneration and purification of spent electrolyte by causticization is developed. The addition of solid NaOH can be used to separate Na2CO3 in the spent electrolyte. The Na2CO3 is causticized using CaO to regenerate NaOH. During this separation and causticization process, the impurity ions in the spent electrolyte are removed simultaneously. The causticized alkaline solution is recycled to the next leaching step. Moreover, Mo, W, Nb, Ta, etc., will be also dissolved in alkaline solution under the leaching conditions of zinc and lead hazardous wastes. The Mo and W can be recovered with ion flotation and adsorbing colloid flotation process using primary amine dodecylamine (RNH2) as collector and ferric ions or magnesium chloride as co-precipitants or depressant (modifier). Adsorbing colloid flotation (ACF) and ion flotation (IF) using ferric ions as the co-precipitant or sorbent and sodium dodecyl sulfate as the collector can be used for the effective removal of arsenic and molybdenum from aqueous solution. The synergistic extraction of phosphorus, arsenic, and silica from tungstate and molybdate solutions with primary amines and TBP can be realized. Mixed solutions of 12-molybdophosphoric acid and its reduced molybdenum blue solutions are found to be an effective scrubbing process for the combined removal of H2S, SO2, and NOx from gas streams. When the molar ratio of NO2/(SO2 + H2S) in the waste gases is just equal to 1/2, H2S, SO2, and NOx will be removed quantitatively, while the regeneration of scrubbing solution is not needed. H2S and SO2 react with molybdophosphoric acid solution to form elemental sulfur and H2SO4, respectively, while molybdophosphoric acid is reduced into blue species, molybdenum blue solution. The reactions of H2S are rather quickly, while those of SO2 are much more slowly. The resulting molybdenum blue solution is used further for the removal of NOx, in which molybdenum blue is rapidly oxidized back into molybdophosphoric acid and NOx is reduced into N2. Porous white tungstic acid (white tungstic acid), whose composition is firstly revealed in this work, is used to produce new tungstoniobates and tungstotantalates and a series of heteropoly compounds. Moreover, a quick determination method of tungsten concentration is proposed according to the quantitative relationship between the precipitate of white tungstic acid and pH value of a certain range.