Using Kaolin in Reduction of Arsenic in Rice Grains: Effect of Different Types of Kaolin, pH and Arsenic Complex.

Kaolin was used as a soil amendment to study the effect of different types of kaolin, pH and arsenic complex on arsenic accumulation in rice grains from arsenic (As) contaminated soil. It was found that kaolin released soluble aluminium (Al) and silicon at a pH value of 3. As adsorption by crude kaolin was higher than by washed kaolin and treated kaolin due to the higher Al content found in crude kaolin. Furthermore, the addition of 5 % (w/w) crude kaolin in the solution of As-contaminated soil was able to reduce water-soluble As in the solution. In mesocosm experiments, As accumulation in rice grain was not found under the addition of kaolin conditions. Scanning electron microscopy with energy dispersive X-ray spectroscopy study found the crystallinity of Al-As complex in plant roots. This implies that while kaolin adsorbs As from As-contaminated soil, rice plants also simultaneously take up As and Al into their cells. This caused the decrease in As accumulation in rice grain.