PRELIMINARY STUDY ON SEPARATION OF RARE EARTH METALS FROM LEACH SOLUTION OF DISCARDED FLUORESCENT POWDER BY SOLVENT EXTRACTION

Abstract

Discarded fluorescent lamps were considered as hazardous waste in Vietnam (code is 160106). However, its composition contained valuable rare earth metals, which can be recycled and recovered by leaching and solvent extraction processes. The present study sought to define the conditions of separation for rare earth elementals (REEs) from acid leach solution by solvent extraction using PC88A. The acid leach solution was obtained from leaching of fluorescent powder. Efficiencies on REEs extractions as functions of pH levels, extractant concentration, O/A ratio, metal concentration were investigated. For pH values greater than 0.0 and less than 1.0, the orders of the yields extraction were determined: yttrium > terbium > europium > aluminum and calcium. The best separation circuit included four-stage counter current extraction for yttrium separation with 20 %v/v PC88A in kerosene (O/A = 1/1, room temperature, 20 min of contact, pH of 0.38) and stripping step with 3 M HCl acid (O/A = 1/1, room temperature, 30 min of contact). After yttrium separation, the leach solution was extracted at pH of 0.98 in the same other conditions with two-stage counter current extraction to recover terbium and europium group. The final recovery from leach liquor was higher than 98 % and the grade of the final product was 94.2 % (for yttrium) and 93.8 % (for terbium and europium group).