Effects of Citrus Peel Amendment on the Mobility of Heavy Metals in Contaminated Soil

Abstract

To estimate the effect of aging on the mobility of heavy metals in soil, relationships between mobility of metals in soil and time after contamination were investigated. Copper, nickel and zinc were added as chloride solution to soil sample. Citrus peel as soil amendments was used at the rate of 5% to immobilize copper, nickel and zinc in contaminated soil. The soils were incubated at field capacity for 3 h, 1, 3, 7, 14, 21 and 28 days at 25°C. Mobility of copper, nickel and zinc from control soils and soils amended with citrus peel were studied with the aid of reduction of metals concentration in the exchangeable fraction. Results indicated that the citrus peel reduced the exchangeable fraction of metals in contaminated soil after 28 days. Application of citrus peel amendment with acidic pH value showed the low immobilizing efficiency of copper, nickel and zinc in the beginning of incubation time in this study due to decrease in soil pH. Batch adsorption of copper, nickel and zinc was conducted to evaluate the effect of contact time, from aqueous solution to understand the mechanism of sorption involved. Fit of the sorption experimental data was tested on the pseudo-first and pseudo-second-order kinetics mathematical equations, which was noted to follow the pseudo-second-order kinetics better, with coefficient of correlation ≥0.99.