Arsenic pollution of a loam soil: Retention form and decontamination

A study was conducted to assess the retention form of arsenic in soil and t o evaluate the use of phosphate for releasing it from the soil. In this stu dy, a loam soil was artificially polluted with arsenate at pH 5.5 which is one of the pH values at which maximum arsenic adsorption occurred. The soil was kept for 2.5 months under wet conditions to allow for stabilization. T he soil was maintained under aerobic condition and losses of arsenic by vol atilization were determined to be minimal. The soil was then sequentially e xtracted with a seri;es of chemicals to identify the soil fractions in whic h the arsenic was bound. The percentage of arsenic found in the Fe bound-ex changeable, reducible-residual, Al bound exchangeable, residual, calcium bo und exchangeable, and easily exchangeable forms was 31.6 27.3 25.2, 55 4.9, and 4.7%, respectively A batch experiment showed that at 20 degrees C, 80% of the bound arsenic was removed by phosphate it? the pH range of 5 to 7. A power function model was found to fit the data with a desorption rate con stant of 402 mg/kg As h(-1).