Acid mine drainage sludge-modified biochar for the efficient removal of As (III) in wastewater: Adsorption performance and mechanism

The prolonged consumption of arsenic-contaminated water is linked to an elevated risk of cancer. As(III) in wastewater exhibits greater mobility, biotoxicity, and removal challenges than As(V). Acidic mine drainage (AMD) sludges are solid wastes produced by mining industry. In this study, a novel biochar modified with AMD sludge (AMDs@PB2) was prepared via co-pyrolysis of AMD sludge and pine needles to remove As(III) from the solution. The effects of preparation conditions (pyrolysis temperature, raw material ratio) and environmental factors (solution pH, solution temperature, coexisting ions) of biochar on arsenic adsorption were investigated, and the arsenic adsorption performance of AMDs@PB2 was analyzed by kinetic, isothermal and thermodynamic models. The results show that the optimal pyrolysis temperature for AMDs@PB2 is 800 degrees C, and the mass ratio of AMD sludge to pine needles is 2:1. AMDs@PB2 can effectively remove As(III) from water, thereby achieving the 'treating waste with treated waste' concept. The maximum theoretical adsorption capacity (Qe, the) of AMDs@PB2 for As(III) in wastewater is 83.35 mg g- 1, which is approximately 1.07-31.18 folds greater than Qe, the reported in previous studies. AMDs@PB2 adsorption was slightly affected by anions (15-75 mg L- 1 CI-, NO3-, SO42-, PO43-) and humic acid and its removal rate ranged from 83.48 to 97.57 %. In addition, the AMDs@PB2 adsorption process involves multilayer heterogeneous adsorption. As(III) adsorption by AMDs@PB2 at 25 degrees C is thermo respiratory and spontaneous. The oxidation-reduction reaction, surface complexation, and coprecipitation dominated the immobilization of As(III) in the water environment by AMDs@PB2.