Efficient extraction of phosphate from dephosphorization slag by hydrochloric acid leaching

Abstract

Phosphorus is an indispensable nutrient element in agriculture and its reserves are limited. To secure a sustainable supply of phosphorus, phosphate recovery from dephosphorization slag generated in steelmaking was considered a promising solution. In this study, acid leaching was adopted to separate the P-concentrating solid solution from dephosphorization slag. Selective leaching of P from slags with various basicity in the hydrochloric acid solution and chemical precipitation of phosphate ions in the leachate were investigated. Increasing slag basicity facilitated the enrichment of P2O5. Large amounts of Ca, Si, and P were leached from slag, whereas the leaching of Fe was negligible. The leaching efficiency of P increased with slag basicity. At pH 3, the leaching efficiency of P from slag with high basicity reached 96.8% while that of Fe was nearly zero. Almost all the P-concentrating solid solution was dissolved without significant dissolution of the Fe-bearing matrix phase and magnesioferrite. After leaching, the residue containing 57.8% Fe2O3 can be reutilized as a metallurgical feedstock. Through chemical precipitation, a precipitate containing 35.1% P2O5 was recovered from the leachate, which can be used as a phosphate fertilizer. The total recovery efficiency of P from dephosphorization slag in this process reached 95.8%.