Reduction of chromium toxicity by applying various soil amendments in artificially contaminated soil

Six soil amendments including municipal solid waste compost (MSWC), coal fly ash (CFA), rice husk biochar prepared at 300°C (B300) and 600°C (B600), zerovalent iron (Fe0), and zerovalent manganese (Mn0) were evaluated to determine their ability to reduce mobility of chromium (Cr) in a Cr-spiked soil. The Cr-spiked soil samples were separately incubated with selected amendments at 2 and 5% [weight by weight (W/W)] for 90 days at 25°C. The efficacy of amendment treatments was evaluated using desorption kinetic experiment and sequential extraction producer. Results showed that applications of various amendments had significant effects on desorption and chemical forms of Cr. Addition of amendments considerably decreased mobility factor (except for CFA5%) of Cr compared to the control treatment. The addition of Fe0, MSWC, and B300 to soil significantly decreased Cr release, compared to other amendments. The lowest Cr desorption was achieved by Fe0 at 5%. Application of B600 and CFA increased soil pH and caused the oxidation of Cr(III) to Cr(VI). Based on the obtained highest values of coefficient of determination (R2) and lowest values of standard error (SE) of the estimate, the two first-order reaction model could be best fitted for describing Cr release in soil samples. In general, from the practical view, Fe0, MSWC, and B300 treatments are effective in Cr immobilization, while application of Fe0 at 5% was the best treatment for stabilization of Cr. Therefore, these treatments can be recommended for the immobilization of Cr from polluted soil