Caracterização, impactos e recuperação de resíduos de mineração de cobre na Amazônia oriental.

Abstract

Copper mining (Cu) residues in the Mineral Province of Carajás can be hazardous due to the presence of potentially toxic elements (EPTs) and unfavorable properties that regulate the release of EPTs into the environment. Microorganisms and organic compounds have been used to favor the establishment of plants used for phytoremediation of sites contaminated by EPTs. The aim of this study was to characterize and evaluate the risks of Cu mining residues, and to identify alternatives for the recovery of these materials. The study was carried out in two mining areas of Cu in the city of Canaã dos Carajás-Pará. Plants, soil, overburden and rock waste were collected in the artisanal mine, and in the industrial mine, tailings. Firstly, chemical and granulometric attributes and environmental indicators in soil and mining waste were determined. Posteriorly, the tailings of industrial mining were treated with soil and organic compound of açai kernel in different proportions, and sown with seeds of Cenostigma tocantinum without and with inoculation of bacterial growth-promoting strain, isolated from the roots of Solanum torvum. After 100 days of cultivation in greenhouse, the plants were evaluated for germination, growth and Cu absorption, and the substrates were analyzed for pH, organic matter (MO) and Cu concentration. Descriptive statistics were performed to characterize the residues, and the Scott-Knott test was used to compare the means after the experiment. The pH ranged from 6.2 to 8.0 and the pseudo-total Cu concentrations were high in all residues, reaching 19034 mg kg-1 in artisanal rock residue. The pollution indexes indicated that the residues are highly contaminated by Cu and moderately contaminated by chrome (Cr) and nickel (Ni). Carcinogenic risk to human health was detected by exposure to Cr in artisanal mining residues. With the addition of treatments, Cu availability was increased by up to 240%. Bacterial inoculation favored the germination of C. tocantinum seeds in untreated tailings. Plants cultivated in the tailings with the organic compound showed higher growth and higher tolerance index. Cu absorption by plants was influenced by bacteria, with root concentrations of 905 and 800 mg kg-1 in tailings treated with soil and untreated.