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.