Resíduos de lâmpadas de LED : desmonte, caracterização e desempenho da integração de lixiviação, precipitação e ultrafiltração na recuperação de metais

Abstract

Considering the metals of interest in LED lamps and also the lack of detailed studies that allow the recycling of these lamps, the present work aims to evaluate the disassembly, the characterization of this residue and to evaluate ways of recovering Ga, Au and In using leaching techniques and membrane separation processes (MSPs). The proposed methodological steps were as follows: dismantling the lamps, preparing and characterizing the samples, leaching tests, firstly performed in a shaker and then conducted in a reactor, and finally ultrafiltration (UF) assays assisted by precipitation. To assess the disassembly, white LED lamps dumped after they use for lighting were manually disassembled, their components were grouped according to the type of material and then weighed. The average time taken to disassemble lamps varied between 1 and 7 minutes per lamp per person, depending on the lamp model. At the stage of preparation of the LED support strips and plates, two mechanical processing routes were evaluated, in which the LED support plates were processed by means of guillotine, bar mill and sieving (route A) or by thermal blower and mill pans (route B). The samples of LED support plates were characterized according to their chemical composition qualitatively via FRX and DRX and quantitatively via ICP-AES and ICP-MS. The mineral phases were evaluated by SEM/EDS technique. The concentrations of Ga found in the residue were 0.004% and 0.002%, processed by routes A and B, respectively. At the leaching tests, at the first stage, HCl was the acid that showed the best performance leaching Ga, compared to H2SO4 and HNO3. At best evaluated conditions, 79.1% of Ga, 26.9% Cu, 71.4% Al, 38.8% Fe, 47.2% In and 7.4% Au were solubilized in a 4 mol/L HCl solution, 200 rpm, 25oC, from the sample obtained by route A. In order to evaluate the behavior of Ga and, subsequently, the interaction with other metals in acid medium, preliminary UF tests were carried out with an acid synthetic solution containing only Ga, which pointed out, firstly, retention of 87.7% at pH 4 and at a next stage, a retention of 93.8% Ga, 15.0% Al, 40.0% Cu and 99.6% Fe, at pH 3.0, from a synthetic solution containing Al, Ga, Fe and Cu. At a third stage of UF applied to the real leachate, the best condition found was under pressure of 20 psi, using Milipore 10 kDa membrane, 25oC, pH 2.5, and the retentions were 47.3% Ga, 26.3% Al, 16.4% Cu and 50.5% In. The results point to a combination of techniques of manual disassembly, acid leaching at room temperature and UF associated with precipitation that allow solubilization and concentration of metals from LED lamps. The used techniques have advantages of low energy expenditure, as they are carried out at ambient pressure and temperature, and can integrate a metal recovery route from these residues.