Estudos de descontaminação de resíduos de lâmpadas fluorescentes utilizando soluções de lixiviação

Abstract

The objective of the present work was to search for optimal mercury (Hg) extraction conditions in residues of fluorescent lamps using acid and basic aqueous solutions. The use of a lower amount of reagent at lower temperatures and the establishment of relations between the extraction rates in relation to the concentration and the speciation of Hg were sought. The concentrations of Hg found for samples I (phosphorus powder obtainded from a recycling company), II (phosphorus powder obtained by manual scraping of the inner layer of used lamps) and III (glass powder of used lamps) were 116 ± 7, 2057 ± 120 and 22 ± 1 mg.kg-1 respectively. In samples I and III, the oxidized species, Hg2+2 and Hg+2, represented more than 95% of the total Hg. Sample II presented a higher percentage of Hg0, 35%. The concentration of other metals in samples I and II were in most similar comparisons, especially that of Ca. The efficiency of solutions of HNO3, HCl and 1: 1 V / V mixture of HNO3/HCl in the extraction of Hg from the three solids was evaluated. The HNO3/ HCl mixture showed to be the best Hg extraction solution: extraction percentages greater than 80% were obtained at the ambient temperature conditions, agitation time of 2 hours, and acid concentration of 2 mol.L-1, for the samples I and III. Sample II only presented such indices at the acid concentration of 6 mol.L-1. The percentages of Hg extraction increased with the elevation of temperature in 1:1 V/V HNO3/HCl solutions at concentrations 1 and 2 mol.L-1. For sample III, extraction rates higher than 100% were obtained at 90°C (concentration 1 mol.L-1) and 50 °C (concentration 2 mol.L-1). For the sample I, rates close to 100% were obtained for temperatures equal to or greater than 50oC (concentration 2 mol.L-1). An extraction rate of only 47% was found for the sample II in acid concentration of 2 mol.L-1 and temperature of 90oC. In NaClO/NaCl solutions the extraction of Hg in relation to the concentration of NaClO (0.41 to 1.62 mol.L-1) was evaluated, at the temperature and the time of contact with the extractor. Extraction rates increased with increasing concentration and temperature. For sample III, an extraction rate of 101 ± 2% at a temperature of 90 oC and a NaClO concentration of 0,81 mol.L-1 was obtained. For the sample I was found index greater than 100% in the concentrations 1,1 and 1,62 mol.L-1 at the temperature of 90 oC. In NaClO solution 0.41 mol.L-1, extraction increased up to 55% for contact time variation from 2 to 96 hours. In general the results of this work show that the composition of the residues of fluorescent lamps may be quite different and that these differences determine the efficiency of the leaching. A prior study of the speciation and concentration of these wastes is therefore important to optimize decontamination processes using less energy and chemical reagents. In this sense, the influence of other factors on the extraction, among which the use of microwave radiation and the exposure to the extractor and agitation in larger times, can still be studied.