Lixiviação de cromo hexavalente em solos tratados com vinhaça

Abstract

Chromium (Cr) is an element that presents high polluting potential in the environment, especially when it is in hexavalent form. In this oxidation state Cr has greater mobility in soils when compared to its reduced form. Thus the reduction of Cr 6+ to Cr 3+ is a way of reducing the negative impacts of chromium in the soil. Cr 3+ is more stable in soil, has less mobility than Cr 6+ and is more retained. In the process of reduction, soil organic matter stands out as a str ong donor of electrons. Thus, vinasse, residual liquid from the sugar and alcohol industry, presenting soluble organic compounds may have a significant potentiating effect on Cr 6+ reduction. The objective of this work was to evaluate the potential of vinasse of cachaça in the reduction of the hexavalent Cr Two tests were carried out. The first one consisted of the use of a residual sulphochromic solution from the soil organic matter analysis. To this solution vinasse was added in the following ratios (vinasse: solution): 1 mL: 29 mL; 2 mL: 28 mL; 4 mL: 26 mL; 8 mL: 22 mL and 16 mL: 14 mL. After 12 hours of horizontal stirring, the total Cr concentration was determined by atomic absorption spectrophotometry (graphite furnace module) and Cr 6+ by colorimetry in diphenylcarbazide solution. In the second test, superficial samples of a Dystroferric Red Latosol and a Haplic Gleisol were used. A solution of potassium dichromate (7.5 mL) with a high concentration of Cr 6+ (~ 13,000 mg L-1) was applied to 40 g of soil in perforated plastic cups. After five successive leaching, the concentration of hexavalent chromium was quantified and it was possible to recover in the soil with and without vinasse. After two months of incubation, the Cr 6+ content in the leachate was quantified again. In both trials, the addition of vinasse to reduce Cr was effective. In the sulphochromic solution, it was observed that the reduction was potentiated as the vinasse: residue ratio increased and that there was an expressive reduction of Cr 6+ up to 8mL: 22mL (0.4). In the Latosol and Gleisol, the vinasse significantly decreased the presence of Cr in the leachate.