Extraction and separation of Zn and Ca from solution using thiophosphinic extractant

Abstract

In view of the increasing importance of waste processing and recycling to meet the stringent environmental regulations and to conserve natural resources, solvent extraction studies have been carried out for the separation of zinc and calcium from the sulphate leach solution of the sludge of a rayon plant. The leach solution contains calcium which is required to be removed before recycling in the spinning bath because it will precipitate as gypsum and forms a scale in the bath with the increase in concentration. Different process parameters such as effect of equilibration time on extraction, separation of metals, stripping of the loaded zinc etc. with synthetic solution have been studied using thiophosphinic extractants viz. Cyanex 272, Cyanex 302 and Cyanex 301 modified with isodecanol and diluted in kerosene. Cyanex 302 has been found to be a suitable reagent for the selective extraction of zinc at pH 3.0–4.5 in 120 seconds leaving all calcium in the raffinate. Both Cyanex 272 and Cyanex 302 form complex [R2Zn.3RH]org during the extraction of zinc from aqueous solutions. The stage analysis of zinc extraction with 5% Cyanex 302 revealed that zinc is effectively extracted in one stage at an organic to aqueous ratio of 1 at a controlled pH of 3.75–4.0 from the aqueous solution containing 4 g/L zinc. Under the optimised condition, total zinc was extracted from the purified leach liquor solution at pH 4.0 and O/A ratio 1 with Cyanex 302. The loaded zinc can be stripped in one stage with sulphuric acid.