The use of modified coal gangue for the remediation and removal of phosphorus in an enclosed water area

Abstract

Thermally activated coal gangue and lanthanum-modified coal gangue were prepared by thermal activation and hydrothermal methods, respectively. Their structures and properties were characterized by X-ray diffraction (XRD), attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR) and transmission electron microscopy (TEM). Thermally activated coal gangue and coal gangue modified by lanthanum were used in a closed water body and compared to polymeric ferric sulfate. The results show that gangue modified by lanthanum exhibits stronger chemical oxygen demand by chromium method (CODcr), total phosphorus (TP) and ammonia nitrogen (NH4-N) removal capacities in overlying water than thermally activated coal gangue. The concentrations of CODcr, TP and NH4-N in overlying water during the stable period reached 11–14 mg/L, 0.023–0.028 mg/L and 0.16–0.20 mg/L, respectively. Thermally activated coal gangue had a good removal effect on CODcr but a poor inhibition effect on the TP. Compared to the thermally activated coal gangue and polymerized ferric sulfate, the lanthanum-modified coal gangue exhibited a better capacity to fix phosphorus in sediment, and the phosphorus extracted by hydrochloric acid (HCL-P) and residual phosphorus (Res-P) levels in the sediment increased, where HCL-P accounted for 57.40% of the TP, exceeding the control group’s value by 34.15%. Thermally activated coal gangue showed a limited capacity to fix phosphorus in sediment, while polymeric ferric sulfate improved phosphorus extracted by bicarbonate dithionite (BD-P) content in the sediment.