[Ex-situ remediation on co-contaminated arid loess in column with spectral methods]

The arid loess in northwestern China is one of the dominant soil types nationwide, the removal efficiency of Pb and chlorpyrifos in simulated co-contaminated loess was investigated by ethylene diamine tetra-acetic acid (EDTA) in ex-situ column experiment, and methods of ultraviolet spectroscopy (UV), atomic absorption spectroscopy (AAS), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR) were used to reveal the remediation characteristics and mechanism. The results showed that the flow rate and pH value of EDTA are responsible for the reaction curves. In the experimental conditions, the removal rates of Pb and chlorpyrifos are more than 70% and 90%, respectively, and the bioavailability of heavy metals decreases greatly. The SEM micrographs indicate the dense and rough surface of loess, and unclear surface and enhanced dispersion of particles appear after the reaction. The EDS results explain the phenomenon of Pb removal and elemental loss. The move, disappearance and decrease of wave peaks, shown from FTIR spectra, are the effect of various chemical environment in loess, and the reaction is more appropriate for physisorbed pollutants removal. The achievements are acceptable for co-contaminated loess remediation by EDTA in ex-situ column, showing potential for future application.