Experimental study on phosphate rock modified soil-bentonite as a cut-off wall material

Abstract

Phosphate rock has great potential value in the application of cut-off walls for heavy metal contaminated sites. The effects of initial concentration of Pb2+, contact time, temperature and pH on the adsorption performance of phosphate rock modified soil-bentonite (PSB) were analyzed by Batch tests, and the microstructure and physicochemical properties of the adsorbent were characterized and analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results showed that the incorporation of phosphate rock improves the adsorption performance of the mixed material for Pb2+ in an acidic environment, and the maximum adsorption amount of PSB can be 154% greater than that of soil-bentonite (SB). Kinetic analysis showed that intraparticle diffusion and liquid film diffusion both participate in control of the adsorption process, and the Langmuir model fitted the isothermal adsorption data better. The adsorption process of PSB to Pb2+ is an exothermic reaction process, and a low temperature environment is beneficial to the adsorption of Pb2+. Studies on the microscopic mechanism show that PO43− reacts with Pb2+ in solution to form phosphate precipitation, and –OH and PO43− are on the surface or interlayer of the adsorbent participate in the adsorption process of Pb2+. HIGHLIGHTS Proposes a new modified material to be used for a cut-off wall.; The adsorption mechanism is investigated by kinetic, thermodynamic and microscopic analyses.;

Keywords

• adsorption
• cut-off wall
• heavy metals
• lead
• phosphate rock
• soil-bentonite