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

Abstract

\n The 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, also 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 acidic environment, and the maximum adsorption amount of PSB can be 154% greater than that of soil-bentonite (SB). The kinetic analysis showed that intraparticle diffusion and liquid film diffusion participate in control of the adsorption process at the same time, and the Langmuir model could fit the isothermal adsorption data better. The adsorption process of PSB to Pb2+ is an exothermic reaction process, and the low temperature environment is beneficial to the adsorption of Pb2+. Studies on the microscopic mechanism show that the PO43− react with Pb2+ in the solution to form phosphate precipitation, and –OH and PO43− on the surface or interlayer of the adsorbent participate in the adsorption process of Pb2+.