Synergistic removal of ammonia nitrogen and thallium using sodium sulphide precipitation and autotrophic nitrifying granular sludge biosorption

This study developed a novel hybrid process integrating sodium sulphide (Na₂S) precipitation with autotrophic nitrifying granular sludge (ANGS) biosorption for the efficient removal of thallium (Tl) and ammonium nitrogen (NH₄⁺-N) from ionic rare earth mining wastewater in South Jiangxi. Single-factor experiments and orthogonal optimization determined the optimal Na₂S precipitation conditions (pH 10, 0.3 mL Na₂S dosage, 9 min reaction time), achieving removal efficiencies of 94.47 ± 0.18% for Tl and 55.71 ± 1.42% for NH₄⁺-N. Subsequent ANGS biosorption further improved total removal efficiencies to 99.59 ± 0.36% for Tl and 74.15 ± 1.43% for NH₄⁺-N, with final effluent concentrations of 0.62 ± 0.54 μg/L Tl and 12.28 ± 0.68 mg/L NH₄⁺-N, complying with discharge standards (5 μg/L Tl, 15 mg/L NH₄⁺-N). X-ray photoelectron spectroscopy (XPS) analysis indicated that Tl removal was primarily mediated by thallium sulphide (Tl₂S) precipitation, while ANGS contributed to immobilization via functional group complexation and intracellular adsorption. This synergistic chemical–biological approach demonstrates high efficiency, cost-effectiveness, and operational simplicity, offering a promising solution for tailwater treatment in ionic rare earth mining.