[Preparation of Iron-Aluminum Modified Diatomite and Its Immobilization in Cadmium-Polluted Soil]

To improve the in-situ immobilization effect of diatomite on cadmium (Cd)-contaminated soil, diatomite was modified by hydroxyl iron-aluminum (Fe-Al). The soil incubation experiments were carried out to investigate the effect of Fe/Al molar ratio, OH/cation of molar ratio, pillaring agent aging time, (Fe+Al)/diatomite ratio, pillaring temperature, and pillaring product aging time on the immobilization of Cd in soils. The changes in properties of diatomite before and after modification were analyzed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that:the optimal preparation conditions for modification were:Fe/Al molar ratio=1:8, OH/cation molar ratio 2.0-2.2, pillaring agent aging time=2 d, (Fe+Al)/diatomite ratio=10 mmol·g^-1, pillaring temperature=60℃, pillaring product aging time=2 d. The hydroxyl-Fe-Al-modified diatomite significantly reduced the content of exchangeable Cd in soil, and the modification reduced soil exchangeable Cd from 11.83% to 39.52%. The SEM and FTIR analyses of hydroxyl-Fe-Al-modified diatomite revealed increase in the specific surface area of diatomite and the amount of the Si-O-H groups. After modification, the hydroxyl-Fe-Al successfully exchanged into the diatom shell forming available pillars, thus increasing channel spacing and enhancing the microporous surface activity. The modification with hydroxyl-Fe-Al increased the immobilization effect of diatomite on Cd in soil. The modification methods and data from this study will help increase the application of diatomite materials for the immobilization of soil containing heavy metals.