Upgrading low-grade flotation apatite tailings via selective leaching with citric acid

Abstract

Depletion of high-grade phosphate resources necessitates the recovery of phosphorus (P₂O₅) from flotation tailings. This study investigated a citric acid leaching process for selectively dissolving carbonate gangue minerals and enriching P₂O₅ in low-grade apatite flotation tailings. Mineralogical and chemical characterizations revealed an initial P₂O₅ grade of 3.20%, with calcite, dolomite, and silicate minerals identified as the predominant impurities. The effects of citric acid concentration (1–11% w/v), temperature (30–60 °C), leaching duration (20–80 min), and agitation speed (300–600 rpm) were systematically evaluated. The selected operating conditions were 3% (w/v) citric acid, 50 °C, 40 min, and 400 rpm, with a liquid-to-solid ratio of 10 mL/g. Under these conditions, the P₂O₅ grade of the solid residue increased to 9.16%, corresponding to an enrichment factor of 2.86, with a reported P₂O₅ recovery of 88.50%. The MgO grade decreased from 5.40% to 0.85%, representing an 84.26% relative decrease in grade. Higher acid concentrations and prolonged leaching were associated with lower P₂O₅ grades, suggesting reduced selectivity and possible dissolution of phosphate-bearing phases. Although citric acid leaching enhanced the P₂O₅ grade of the tailings, the resulting product should be considered a pre-enriched intermediate rather than a directly qualified feedstock for wet-process phosphoric acid production. Further beneficiation, process qualification, and techno-economic evaluation are required to assess its potential for industrial application.