Evaluation of membrane separation process for the treatment of gold mining effluent

• Ano de defesa: 2016
• Autor(a) principal: Laura Hamdan de Andrade
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Ultrafiltração; Precipitação intermediária; Condições operacionais; Nanofiltração; Vida útil; Efluente de mineração de ouro; Engenharia sanitária; Saneamento
• Link de acesso: http://hdl.handle.net/1843/BUBD-ABYNBC

This study aimed to carry out a systematic and detailed evaluation of integrated ultrafiltration (UF) and nanofiltration (NF) applied to the treatment of gold mining effluent, which is characterized by high concentrations of sulfate, calcium and arsenic and acid pH. The operating conditions type of process (NF or reverse osmosis), membrane type, application of pre-treatment, feed pH, temperature and permeate recovery rate (RR) were evaluated in bench scale trials. The best conditions found were: NF90 nanofiltration membrane, pre-treatment with UF, feed pH adjustment up to 5.0, and filtration carried out at room temperature. The high supersaturation index of calcium sulfate limited the first-stage NF RR at 40%. The chemical cleaning procedure was also studied and the better cleaning efficiency was found for recirculation of 0.2% HCl solution for 90 minutes. Moreover, operating pressure, cross-flow velocity, antiscalant dosage, application of physical cleaning and chemical cleaning frequency were evaluated on a pilot scale plant. It was observed that the increase in pressure and physical cleaning did not bring benefits to the process, while increasing the cross-flow velocity was able to reduce fouling and increase solute retention efficiency. The addition of antiscalant also reduced the permeate flux decay for RR greater than 40%. The stability of the membrane was evaluated by its exposure to the effluent and to both the effluent and the cleaning solution. The membranes rejection and permeability variations over time were not very significant, and they have demonstrated good performance even after 285 days of exposure. The conditions for intermediate precipitation of the first-stage NF concentrate were studied. The optimized conditions for the precipitation of arsenic and calcium were, respectively, molar ratio Fe/As 4.0 and pH 7.0, and molar ratio CO3/Ca 3.5 and pH 11.5. It was possible to achieve a 60% RR in the second-stage UF-NF without occurrence of scaling or irreversible fouling, which indicated the possibility of operation at higher RR. Despite the fact that the inclusion of intermediate precipitation and second stage UF-NF increases the cost of the treatment from US$ 1.34 / m³ to US$ 6.28 / m³, it also allows the generation of 187 m³/h of reusable water. Thus, this study demonstrated the high potential of UF and NF technologies for the treatment of gold mining effluents aiming at water reuse.