Combined procedure of metal removal and recovery of technology elements from fertilizer industry effluents

Abstract

This study focuses on the search for a sustainable treatment and metal recovery system for acid discharges from a fertilizer industry in SW Spain. The methodology proposed involves the addition of two types of alkaline materials (an industrial waste and a commercial reagent) to neutralize the acidity and remove dissolved elements. In the first case, the treatment consisted on batch reactions between biomass ashes and phosphogypsum leachates at different solid-liquid ratios (i.e. 1:2.5, 1:5, and 1:10). On the other hand, a 0.01 M solution of Ca(OH)2 was used. The experiment with biomass ashes at a solid:liquid ratio of 1:2.5 showed a high effectiveness, reaching removal percentages close to 100% for F, Fe, Zn, Al, Cr, U, Cu and Cd. The depletion of contaminants from solutions during the alkaline treatments occurred mainly by co-precipitation and/or adsorption onto phosphate phases, in addition to precipitation of fluorides. Moreover, the solids precipitated during the alkaline treatments contain elements of high economic interest such as rare earth elements plus Y (353–3992 mg/kg), Sc (21–164 mg/kg), Be (5.0–7.0 mg/kg), V (1036–2974 mg/kg), Ga (16–40 mg/kg) or U (721–2963 mg/kg). These values could make this by-product a promising source of technology metals. This study proposes an environmentally-friendly solution for these industrial leachates, removing selectively impurities and target elements and producing a promising exploitable metal concentrate. This research could lay the foundations for an effective and sustainable treatment system for acid leachates from phosphogypsum stacks. Furthermore, the costs related with the treatments could be covered by recovering the valuable elements contained in the newly-formed precipitates during the treatments.