DESORPTION KINETICS AND SPECIATION OF Zn, Pb AND Cd IN A SOIL CONTAMINATED BY MINING ACTIVITIES AMENDED WITH LIMESTONE, PHOSPHATE, BIOCHAR AND ORGANIC FERTILIZER

Abstract

Mining areas produce large amounts of waste that are important sources of potentially toxic elements, such as heavy metals, for the soils. These PTEs can contaminate the environment and cause serious threats to the ecosystem and human health. The in-situ remediation by conditioners is an efficient alternative for the immobilization of contaminants and for the reduction of the risks associated with these pollutants. Phosphate, lime and organic compounds are the most used conditioners for in-situ remediation. In this project, we aim to evaluate the effect of rates of conditioners in desorption kinetics and speciation of Zn, Cd, and Pb in a soil contaminated by mining activities. The soil was collected in a disabled Zn mining area in the city of Vazante, state of Minas Gerais, Brazil. The contaminated soil was incubated with either phosphate, or calcium carbonate, or biochar, or organic fertilizer. Desorption kinetics was evaluated after successive extractions with EDTA in 14 periods of time and adjusted to the double-first order model. The speciation will be performed by X-ray absorption spectroscopy (XAS). The analysis with synchrotron radiation X-ray absorption near the edge (XANES) and X-ray absorption fine structure (EXAFS) will be performed in the Brazilian Synchrotron Light Laboratory, and u-XANES, u-EXAFS, u-XRD, u-XRF will be performed in the NSLS-II or Stanford Synchrotron Radiation Light source, U.S. Data will be interpreted at the North Carolina State University, in Raleigh. An additional experiment with columns will be carried out in Raleigh aiming to evaluate leaching of Zn, Pb and Cd in amended soils. The leachate will be collected, centrifuged and quantified by ICP-OES. The least significant difference (LSD) method (p < 0.05) will allow us to obtain significant differences between treatment's means. It is expected to obtain information on which phases are controlling the bioavailability of metals in the soil after the addition of conditioners.