Remediation of cadmium- and lead-contaminated soils with an aluminum industry by-product / Subproduto da indÃstria de alumÃnio na remediaÃÃo de Ãreas contaminadas com cÃdmio e chumbo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Mining activities have been increasing each day and generate large amounts of residues or by-products, which have caused a lot of interest by researchers in evaluating their potential use as soil amendments. One of the applications of such amendments is on the remediation of soils contaminated with trace elements, which might pose a threat to animals and plants if present in high concentrations in the environment. The present work had as objectives: i) characterize an aluminum industry by-product and evaluate its adsorption/desorption capacity of Cd and Pb in its in natura form and after phosphate and thermal pretreatments, comparing it with an in natura iron mining by-product, and, ii) compare the performance of an aluminum industry by-product with that of other organic and inorganic soil amendments in cadmium- and lead-contaminated soils. All experiments were conducted in the Soil Science Departament at UFLA (Federal University of Lavras). In the first experiment, the in natura Al industry by-product was pretreated either with increasing doses of phosphoric acid (0, 21.5, 43.0, and 86.0 mmol L-1; solid:solution ratio of 1:1,5) or thermally at 105, 300, and 600ÂC and then analyzed for: soil fertility, sulfuric-attack and microwave furnace digestion, zero point of charge, X-ray diffraction. Adsorption and desorption of Cd and Pb were measured in monoelementary systems using 0.01 mol L-1 Ca(NO3)2 as the background solution. Cadmium and Pb were analyzed by either flame or graphite furnace atomic absorption espectrofotometry. In the second experiment, samples from a sandy and a clayey soil were previously mixed with a polluted soil containing high concentrations of Cd and Pb and then treated with increasing doses - 0, 0.25, 0.50, 1.00, and 2.00% (dry weight basis) - of an Al industry by-product in its in natura form. For comparison purposes, additional treatments consisted of: lime, a silicate by-product and turf at a rate of 0.25, 0.50, and 2.00% respectively, as well as the non-contaminated soils. Comparison among treatments were done by evaluation of the root and shoot dry matter production of Brachiaria decumbens as well as their Cd and Pb concentrations and the Cd and Pb concentrations, in addition to the pH and the electrolytic conductivity (EC) of 0.45-μm filtered and non-filtered soil leachates. The Al industry by-product presented a high pH as well as a high Na concentration and also an oxide rich mineralogy. Pretreatment of the by-product with either phosphate or thermally had no significant effect upon Cd and Pd adsorption/desorption. The in natura Al industry by-product performed better than the iron-mining by-product as an Cd and Pb amendment. Increasing the application rates of the in natura Al industry by-product caused an increase in pH of the leachates. A 2.00% rate of application of the by-product decreased the EC in the sandy soil whereas a 1.00% and 2.00% application rate increased the EC in the clayey soil. The Pb concentration differed between filtered and non-filtered soil leachates whereas that of Cd did not. The Al industry by-product has favored the root and shoot dry matter production of B. decumbens and reduced the latterâs Cd concentrations (mg kg-1) while Pb concentration was not significantly altered.

ASSUNTO(S)

soil amendments desorption adsorption quimica do solo adsorÃÃo dessorÃÃo amenizantes de solo contaminated soils Ãreas contaminadas

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