Contaminação do solo por alguns resíduos de curtume

• Autor(a) principal: Oliveira, Regina de Carvalho
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1584
• topic: Curtume; Cromo; Resíduo; Contaminação; Tannery; Chromium; Residues; Contamination; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

Due to the high organic contents and nutrients presence in tannery residues its use in agriculture, specially to small companies, it is a provisory alternative to recycle them. However, the presence of toxic elements such as sodium and chromium, commonly present in tannery residues, may have negative impact on the environment. In this context, this work was carried out aiming to: (i) characterize the chemical composition of tannery residues; (ii) characterize soil samples from disposal sites of tannery residues for more than 10 years, as well as evaluate the degradation of tannery residues when added to soils in controlled environmental conditions; (iii) evaluate the Cr adsorption and mobility in soils. Four types of residues were sampled from microregions of Minas Gerais: residue 1 (SR), residue 2 (LL/SGP), residue 3 (LS/SGP) and residue 4 (LS/TC). High total contents of Ca, Mg, S, N and C were found in all residues, indicating its potential use as nutrient source for plants. On the other hand, high Cr contents, as well as the presence of hexavalent chromium, do not recommend its use. Soil samples (n=5) of a anthropic Red-Yellow Argisol, collected at depths 0-2 and 0-30 cm, in the municipality of São Gonçalo do Pará MG, were used to evaluate contamination of disposal sites. For the residue degradation assay, under controlled environmental conditions, a dystrophic loamy Red yellow Latosol (LVA), were incubated with tannery residues and chromium high purety salts. Soil collected at the disposal area showed considerable amounts of residues, providing high concentrations of C, N and Cr, at both depths, 0-2 cm and 0- 30 cm. Cr contents obtained by the EPA-3051 method were above the intervention value for soils from polluted areas (400 mg kg-1). In spite of high C contents and low C/N ratios, CO2 evolution from soils incubated with residues, C and N contents in most of the humine fraction and FTIR spectra of contaminated soils, at 0-2 and 0-30 cm depth, confirmed that the organic matter (MO) of tannery residues consists mainly of recalcitrant compounds. In addition, C-CO2 evolution seemed to be more related with values of IH ratio (hydrophobicity index), C-humic acid and C-fulvic acid of tannery residues than with their Cr contents. The higher C content present in the fulvic acid fraction (C-fraction fulvic acid), the higher was the degradation rate of the residue added to soil. Adsorption of Cr(III) and Cr(VI) was performed with CrCl3 and CrCl3 6H2O and K2CrO4 solutions added to soils and synthetic minerals (gibbsite and hematite). The mobility of Cr(III) and Cr(VI) was evaluated in soil columns, filled with two soil types (loamy and sandy texture) treated with tannery residues (residue 1 - SR, residue 2 - LL/SGP, residue 3 - LS/SGP and residue 4 - LS/TC) and salts p.a. (CrCl3 6H2O and K2CrO4). Columns were leached 14 times, once a week, with deionized water. The total volume of water applied to the columns was approximately 1.300 mm. Adsorption data fitted to the Langmuir and Freundlich models suitably for both tri and hexavalent states. Application of trivalent Cr caused a decrease in the pH values of leachings in both soils, but pH increased with application of hexavalent Cr. The use of leather industry residues did not contribute to increase in Cr mobility of the soil columns. On the contrary, Cr leaching was lower in treatments with residues than in the control.