Study on Remediation of Cd-Contaminated Soil by Thermally Modified Attapulgite Combined with Ryegrass

Abstract

ABSTRACT In this work, the thermally modified attapulgite was prepared by high temperature modification and analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and specific surface area test (BET). The results showed that the crystal phase structure of the thermally modified attapulgite was not changed compared with the attapulgite, but the content of the adsorption water and zeolite water was reduced, the surface crystal bundle structure was more obvious and the specific surface increased. The adsorption capacity of attapulgite to Cd could be improved after thermal modification, and the adsorption mechanism was mainly through the coordination of hydroxyl and silica hydroxyl with Cd. Added different doses of thermally modified attapulgite combined with ryegrass to remediate low and high concentrations of Cd-contaminated soil showed that the thermally modified attapulgite could reduce the longitudinal migration of Cd in the soil layer and the risk of groundwater pollution, but increase the biomass of ryegrass and lower the concentration of Cd in the shoot of ryegrass. It could significantly improve the total Cd extracted from the ryegrass both in the low and high contamination pollution soils when the thermally modified attapulgite dosage were 20 g·kg−1. The mechanism of the thermally modified attapulgite combined with ryegrass was mainly increased the soil pH and surface adsorption of Cd by thermally modified attapulgite, thereby reduced the content of exchangeable Cd in soil, improved the activity of urease and catalase in the soil and the diversity of soil microflora, so as to reduced the malondialdehyde (MAD) content in ryegrass and the stress of Cd on ryegrass, increased ryegrass biomass. Added thermally modified attapulgite could effectively solve the problem that ryegrass could not grow normally in soil with high pollution of Cd. And the total amount of Cd extracted from ryegrass increased by increasing the biomass of ryegrass per unit area.