Synergistic Extraction Of Zinc From Ammonium Sulfate Solution And Separation Of Zinc And Copper By Extraction

The sustainable development of zinc industry has been constrained by the lacking of zinc resources. To guarantee the effective supply of zinc resources and the sustainable development of zinc industry, it is an important direction that exploits the new process to efficiently recovery zinc from low-grade oxidized zinc ores and other intractable zinc resources for relieving the intense resource pressure. "Ammonia leaching-solvent extraction-electrowinning" process is a new technology for efficiently treating low-grade zinc oxide ores containing high basic gangues. And solvent extraction is a key link of this process.In this paper, Zn-(NH4)2SO4-NH3 and Zn-Cu-(NH4)2SO4-NH3 solutions is used as research object. The extraction and separation behaviors of zinc and copper from ammoniacal/ammonium sulfate solutions are systematical investigated using p-diketone and/or its mixture with neutral organophosphine extractant, respectively. The results obtained are shown as follows:(1) The complex extraction systems composed by 1-benzoyl-2-nonanone (Mextral54-100,HA) mixed with trioctylphosphine oxide(TOPO), trialkylphosphine oxide(TRPO,L) and tributyl phosphate(TBP) show evident synergistic effects on zinc extraction. The distribution ratio of zinc increases initially and decreases with the increasing pH, then decreases with increasing total ammonia concentration. An increase in the extractant and synergist concentration is benefit for zinc extraction. In single Mextral54-100 extraction system, the form of extracted complex is ZnA2. However, the type of extracted species is affected by aqueous pH in synergistic system. The extracted species are ZnA2L when pH is 8.42 and 9.42, while ZnA2L2 can be formed at pH of 7.25 in the high concentration region of TRPO. The IR analysis indicate the zinc ammine complexes are not extracted. Thermodynamic data indicates that the extraction and stripping processes are exothermic and endothermic reactions, respectively.(2) The extraction efficiency of zinc is affected by additional ligands in Zn-(NH4)2SO4-NH3 solution. It is affected most by critic ion concentration and zinc is hardly extracted when its concentration is over 0.2mol/L. The extraction efficiency decreases with increasing L-glutamic acid and chloride ion concentration, while nitrate and acetate ion concentration are not significant effect.(3) Based on the differences in extraction performance, the separation and recovery of zinc and copper is achieved using priority extraction of copper with Mextra154-100, and zinc extraction from raffinate using synergistic extraction method with Mextra154-100+TRPO from ammoniacal solution. For coexistence solution of copper and zinc, under the condition of initial pH of 9.06, phase ratio(O/A) of 1:1 and 25 ℃ for 10min, the copper extraction efficiency is over 99% using 7.5% Mextra154-100 from Zn-Cu-(NH4)2SO4-NH3 solutions through two counter-current extraction. Co-extraction of zinc is less than 2%. The copper stripping efficiency in organic phase is greater than 98% after three counter-current stripping at phase ratio(O/A) of 2:1 and 25 ℃ for 10 min. After complete copper extraction, zinc is extracted using the complex extraction system of 10% Mextra154-100 and 2%TRPO from the raffinate. The zinc extraction efficiency is greater than 99% through two counter-current extraction at initial pH of 7.25, phase ratio(O/A) of 1:1,25 ℃ for 10 min. After two counter-current stripping, zinc stripping efficiency is over 99% using 0.08 mol/L H2SO4 at phase ratio(O/A) of 1:1 and 25 ℃ for 5 min.The extraction and separation zinc can be obtained using complex extractant composed by Mextra154-100 and trialkylphosphine oxide(TRPO). This can provide guidance for extraction and separation of zinc from ammoniacal solution of non-traditional bearing zinc resources.