Zinc Extraction from Chloride Solutions by Mixtures of Trialkyl Phosphine Oxide and
para-tert-Butylphenol
I. YU. FLEYTLIKH, G. L. PASHKOV, L. K. NIKIFOROVA, N. A. GRIGORIEVA
Institute of Chemistry and Chemical Technology, Siberian Branch of the Russian Academy of Sciences, Akademgorodok 50, build. 24, Krasnoyarsk 660036 (Russia)
Keywords: hydrochloric solutions, zinc, extraction, TAPO, alkylphenol, technological flowsheet
Abstract
Zinc extraction from hydrochloric solutions by trialkylphosphine oxide (TAPO) in toluene was studied. It is demonstrated that the dependence of zinc extraction into organic phase on the concentration of hydrochloric acid has an extreme: an increase in zinc extraction with an increase in acid concentration is due to an increase in the fraction of extractable zinc chloro complexes, while a decrease is due to the competitive effect of hydrochloric acid. The compositions of extracted compounds were determined: for the low concentration of hydrochloric acid (≤1.35 mol/L), zinc is extracted into the organic phase in the form of neutral molecules of zinc chloride having the composition [ZnCl2 × 2TAPO], while with an increase in acidity it is extracted in the form of complex metal halide acids like HZnCl3 and H2ZnCl4. Because of high zinc distribution coefficients, its re-extracted with water is strongly hindered. The introduction of para-tert- butylphenol (AP) into the organic phase containing TAPO simplifies zinc re-extraction and creates prerequisites for the development of extraction-based technological flowsheet allowing efficient recovery of zinc and its separation from admixtures (Fe, Cu, Mn и Pb), including reagent concentrations, flows of aqueous and organic phases, number of extraction steps. The coefficient of zinc separation from the major admixture (iron) is βZn/Fe = 15-25. The flowsheet includes zinc extraction with a mixture of TAPO and alkylphenol, removal of admixtures by washing the extract with diluted hydrochloric acid (~0.5 mol/L) and zinc re-extraction with water. Further zinc concentrating and its conversion into sulphate solution are carried out with the help of extraction with di(2-ethylhexyl)phosphoric acid (D2EHPA). The high degree of zinc recovery (~99 %) is achieved after only 11-13 extraction steps. The developed process may be used for efficient isolation of zinc from chloride and chloride-sulphate solutions from leaching zinc ores and concentrates.
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