Processing of rayon waste effluent for the recovery of zinc and separation of calcium using thiophosphinic extractant

Abstract

Zinc is used in various metallurgical, chemical and textile industries. In textile industries, waste effluent containing zinc is generated during the manufacture of rayon yarn. Due to the strict environmental regulations and the presence of toxic metallic and other constituents, the discharge of effluents in sewage is restricted. In view of above a process has been developed for the recovery of zinc from rayon waste effluent following solvent extraction technique using thiophosphinic extractants Cyanex 272 and 302. Before recycling of zinc sulphate solution in spinning bath, solution must be free from calcium, which is deleterious to the process as gypsum precipitates and forms scale. The extractant Cyanex 302 has been found selective for the recovery of 99.99% of zinc in the form of [R2Zn]org from the effluent above equilibrium pH 3.4 maintaining the O/A ratio of 1/30 leaving all the calcium in the raffinate. The zinc from the loaded Cyanex 302 can be stripped with 10% sulphuric acid at even O/A ratio of 10. The stripped solution thus obtained could be recycled in the spinning bath of the rayon plant and raffinate could be disposed safely without affecting environment.