Effect of Diatomite on Distribution of Chemical Forms of Cd in two Contaminated Soils

In recent decades, soil pollution with heavy metals in world countries (such as Iran) has been one of the most challenging issues. Stabilization of heavy metals by using absorbent in remediation of heavy-metal-contaminated soils is one of the low-cost and fastest methods. In order to study the effect of diatomite on chemical forms of Cd in calcareous soils, a factorial experiment was conducted in a completely randomized design (CRD) with 3 levels of diatomite application in soil (0, 2 and 5 %), 4 levels of incubation time (1, 2, 4 and 8 weeks) and twocontaminated soils in three replications. Chemical distribution of Cd in soils were determined using Tessier sequential extraction method at the above-mentioned incubation time and reduced partition index (IR) and mobility factor (MF) of metal were calculated as a Cd mobility index in soils. Results showed that application of diatomite significantly (p ≤ 0.01) decreased the exchangeable and carbonate fractions and increased iron and manganese oxide bound organic and residual fractions in comparison to the control treatment. In 5% diatomite treatment after 8 weeks’ incubation the IR (42-71%) and pH (5-8%) values increased but the amounts of MF (30-33%) and DTPA-extractable Cd (33-28%) decreased, demonstrating a decrease in the mobility of metal in soils. It was concluded that addition of diatomite in soil lead decreasing the mobility of Cd and Pb in soils. According to the results, diatomite due to greater efficiency for immobilization of Cd in contaminated soils as a low-cost amendment can be used for immobilization of the high amount of Cd ions from contaminated soils.