Home – Home – Jornals – Chemistry for Sustainable Development 2016 number 5

The chloride ion is harmful impurity in zinc sulphate electrolyte. The possibility of extraction purification of zinc solutions from the chloride ion using trialkylphosphine oxide (TRPO, Cyanex 923) as an extractant in petroleum paraffins. It was shown that the extraction degree of the chloride in the form of HCl is low - no more than 14.3 %. The chloride ion is extracted as zinc chloride in the composition of the extractable compound of the composition [ZnCl₂ x 2TRPO] with a high purification degree of zinc solutions (≥90 %). Analysis of extraction equations of zinc chloride showed that extraction of the chloride ion in a great extent depends on its starting concentration in the water phase; moreover, distribution indexes of the chloride are reduced with decreasing the concentration. It was also shown that with increasing the concentration of zinc in the starting water solution and extractant, distribution coefficients of the chloride ion are increased. Judging by the extraction isotherm of the chloride with 50 % of TRPO, three extraction stages at O/W = 1 : 1 are necessary to achieve the residual content of the chloride in the raffinate from 5 to 0.1 g/L. Reextraction of zinc chloride from the organic phase is hampered. The attempts to reextract the chloride with water, solutions of phosphoric acid and Trilon B proved to be ineffective. Virtually complete reextraction zinc chloride (ε_Cl = 99.2 %) is achieved when processing the organic phase that represent a mixture of TRPO with tributyl phosphate, 5 % aqueous ammonia solutions. Taking into account good results on purifying zinc electrolytes from the chloride ion obtained with TRPO further studies should be directed at a broader search for reextractants and new extraction systems based on TRPO that ensure not only efficient extraction of the chloride ion from solutions but also its reextraction.