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SORPTION AND DESORPTION OF CADMIUM BY DIFFERENT FRACTIONS OF BIOSOLIDS - AMENDED SOILS
Citation:
Hettiarachchi**, G. M., J A. Ryan*, AND C. M. LaFleur*. SORPTION AND DESORPTION OF CADMIUM BY DIFFERENT FRACTIONS OF BIOSOLIDS - AMENDED SOILS. JOURNAL OF ENVIRONMENTAL QUALITY. ASA, CSSA, SSSA, Madison, WI, 32(5):1684-1693, (2003).
Description:
Series of Cd sorption and desorption experiments were conducted on different fractions of soils amended with biosolids, Cd-salt, and unamended soils (control) to test the hypothesize that not only organic but also inorganic fraction in biosolids controls the metal availability in biosolids amended soil systems. Biosolids amended soils were collected from a long-term field experiment established in Beltsville, MD in 1976. The sorption and desorption behavior were studied at pH 5.5 by batch experiments. Organic fraction of soils was removed by treating with 0.7 M NaOCl adjusted to pH 8.5. Easily reducible Fe and Mn fractions were removed with 0.04 M NH2OH.HCl in 25% HOAc. Cadmium sorption increased with increasing biosolid rate and the increase was different for the different biosolids. Removal of organic carbon reduced Cd adsorption but did not account for the observed differences between biosolid-amended soils and controls, indicating that the increased adsorption associated with biosolids application was not limited to the increased organic carbon due to addition of biosolids. After removal of both OC, and Fe/Mn the slopes of Cd sorption isotherms observed in the biosolids-amended soils and the control were the same. Desorption experiments showed that substantial proportion of Cd sorbed by soils cannot be readily desorbed back to the solution. This "apparent hysteresis" effect was higher for biosolids amended soils compared to the control. In the case of intact samples nearly 37.1% of the sorbed Cd was recovered from the control sample where as only 15.8 and 10.5% were recovered from two different biosolids amended soils. As for sorption removal of both organic and Fe/Mn fractions were more effective in removing the observed differences between the biosolids amended soils and the control than either of them alone. Results from this study show that Cd added to biosolids amended soils behaves differently than Cd added to soils without biosolids and support strongly the hypothesis that the addition of Fe and Mn in the biosolids increased the retention of Cd in biosolids-amended soils.