Novel strategy for recovering phosphorus from sulfate-rich wastewater combined with phosphogypsum recycling

Abstract

With global phosphorus depletion, recovering PO₄³⁻ from papermaking wastewater is crucial. However, high SO₄²⁻ hinders removal efficiency. This study proposes a novel strategy for recovering of PO₄³⁻ from papermaking wastewater combined with phosphogypsum recycling to form hydroxyapatite (Ca₅(PO₄)₃OH), using sulfur-metabolizing bacteria to address SO₄²⁻. Optimally, 0.1 g phosphogypsum achieved 95 % PO₄³⁻ recovery. During the chemical stage, PO₄³⁻ decreased at a rate of 0.0556 d⁻¹ through phosphogypsum hydrolysis and subsequent adsorption. During the biological reaction stage, sulfate-reducing bacteria, represented by Desulfobacteraceae, biologically transform SO₄²⁻ in phosphogypsum into S²⁻ while increasing alkalinity. Subsequently, sulfate-oxidizing bacteria, represented by Alcaligenaceae, biologically oxidize S²⁻, releasing accumulated polyphosphate to PO₄³⁻. Finally, the Ca²⁺ released from phosphogypsum declined PO₄³⁻ from wastewater at rates of 0.0479 d⁻¹ to form hydroxyapatite. Given that hydroxyapatite and phosphogypsum are critical raw material and product for wet-process H₃PO₄ production, this strategy establishes a closed-loop cycle for sustainable phosphorus recovery.