Clean utilization of waste rocks as a novel adsorbent to treat the beneficiation wastewater containing arsenic and fluorine

Abstract

Waste rocks were obtained during the mining, and were identified as a solid waste. The waste rocks were mostly stockpiled due to lack of economic value, resulting in a large occupation of land and secondary pollution risks. Considering that the waste rocks mainly consisted of clay minerals, it was firstly speculated that the waste rocks might be used as a novel adsorbent to treat the beneficiation wastewater containing arsenic and fluorine. In the study, the compositions of waste rocks were studied by chemical analysis, XRD and SEM-EDS, and the stability of heavy metals in the waste rocks was examined by dissolution experiments. The optimum modification reagents and adsorption parameters were determined by a batch of experiments. Adsorption mechanisms were revealed by adsorption kinetics, adsorption isotherms, SEM, N2 adsorption-desorption isotherms, zeta potentials and XPS. The removal ratios of arsenic and fluorine in the beneficiation wastewater reached 98.13% and 86.13%, respectively. The interlayer spacing and average pore size of the waste rocks increased after the modification. In addition, zeta potentials moved from negative to positive, leading to the increase in adsorption capacity of the waste rocks. The data of adsorption experiments was well fitted by nonlinear pseudo-second-order kinetics and Langmuir isotherm, indicating that the adsorption was controlled by chemisorption and was a monolayer adsorption process. The adsorption of arsenic and fluorine on the waste rocks referred to the ligand exchange and electrostatic adsorption. It was a promising method to achieve the clean utilization of waste rocks and the sustainable development of mining.