IMMOBILIZATION OF EXCHANGEABLE CROMIUM IN A CONTAMINATED SOIL USING NATURAL ZEOLITE AS AN EFFECTIVE ADSORBENT

This work investigated the effects of soil pH and the content ratio of natural zeolite on Cr contaminated soil. The immobilization experiments of the exchangeable Cr in contaminated soils were conducted using the batch method. The incubation experiments were carried out over 30 days in plastic bottles to determine five fraction of Cr existence (exchangeable fraction (F1), Fe/Mn/Oxide (F2), carbonate bound (F3), organic matters (F4) and residual (F5)) in amended soils after incubation. Results showed that the content and proportion of the exchangeable Cr decreased with an increase in soil pH from 5 to 9. At soil pH 5, the exchangeable Cr in soil reduced from 44.80±0.772 mg/kg (initial soil) to 17.72±0.300 mg/kg after 30 days of incubation with natural Zeolite 3%. Meanwhile, the exchangeable Cr of soil also decreased with increasing the content ratio of natural zeolite from 1% to 5% in soil. The ratio of 3% was suitable for incubation of the exchangeable Cr in contaminated soil with natural zeolite. The exchangeable Cr in contaminated soil decreased from 80.34% at un-amended soil treatment to 25.06% after incubation of 30 days. The forms of carbonate bound (F3) and organic matters (F4) in amended soils increased to 36.54% and 28% compared with 4.26% and 6.90% in un-amended contaminated soil. Ion exchange, precipitation and adsorption on the surface of natural zeolite  might be the potential mechanisms of immobilization of the exchangeable Cr. The results indicated that natural zeolite can be used as the effective adsorbent for immobilizing the exchangeable Cr in contaminated soils and leading to a decrease in the environmental risk from Cr toxicity.