Remoção de sulfato de efluentes industriais por precipitação

Abstract

ResumoO objetivo deste trabalho foi estudar a remoção de íons sulfato, encontrados em efluentes de diversas atividades do setor mínero/metalúrgico. Os processos de remoção de sulfato desses efluentes são, em geral, caros e com baixa eficiência de remoção para essa espécie. Foram estudadas duas alternativas de tratamento para soluções ricas em sulfato. A primeira consistiu na investigação da remoção do íon em pH ácido, na forma de jarosita. Na segunda, foi estudada a remoção do sulfato como etringita, em pH alcalino. A etringita mostrou-se uma boa opção para o tratamento de efluentes líquidos contendo sulfato, pois apresentou baixa solubilidade em água em pH acima de 11,5. Em seguida, foi investigada a precipitação química de sulfato em soluções sintéticas contendo 1.500 mg/L do íon, em temperatura ambiente (22±1º C), observando-se remoções próximas de 85% em sistemas contínuos de precipitação. Esses estudos mostram a redução dos teores finais de sulfato a valores inferiores a 250 mg/L, ou seja, abaixo do que é recomendado pela legislação brasileira.Palavras-chave: remoção de sulfato; drenagem ácida; etriginta; jarosita. AbstractThe aim of this study was to develop alternative techniques for removing sulfate ions from mining/metallurgy effluents. Sulfate removal processes are generally expensive and show low removal efficiency. Two alternatives to treat sulfate-rich solutions were studied in this work. The first alternative was sulfate removal in acidic pH, as jarosite. Moreover, the second precipitating alternative was tested in alkaline conditions, as ettringite. Sulfate removal as ettringite was considered the preferable form for treating sulfate-containing wastewaters due to its low solubility in water, close to 10 mg/L at the pH of 11.5. Chemical precipitation of sulfate in synthetic solutions containing 1,500 mg/L sulfate, at the temperature of 22±1º C, was thus investigated, and removals close to 85% in continuous precipitation systems were observed. This study showed sulfate reduction to final concentration values below 250 mg/L -lower than that recommended by environmental regulations.

Mine water treatment with limestone for sulfate removal

“…However, barium compounds are usually expensive whereas any residual Ba 2+ ions in solution is of greater concern than the sulfate ion itself. Ettringite precipitation can also reduce sulfate concentrations to within regulatory limits and it does not utilize any toxic element (barium), but requires alkaline pH for effective sulfate removal [10]. Examples of industrial sulfate precipitation technologies comprise the SAVMIN and CESR (cost effective sulfate removal) processes, the integrated lime/limestone process and the BaS process [4].…”

Kinetic and thermal decomposition of ettringite synthesized from aqueous solutions

“…The compound can be easily synthesized in an aqueous solution through a pH-controlled reaction (with a pH above 10) from compounds containing calcium, aluminum, and sulfate. Depending on the required purity and intended application for the ettringite, analytical grade reactants, fly ash, blast furnace slags, lime, gypsum, alumina, or others can be used in the synthesis process [4][5][6][7][8][9][10][11][12][13][14][15][16].…”

“…Recently, ettringite has also received special attention in the mining-metallurgical sector because its precipitation can be used to remove sulfate from effluents and mine waters [12][13][14][15][16][23][24][25], due to its low solubility in aqueous media (log Ksp (298 K) = 44.91 ± 1.06) [26][27][28][29]. Moreover, ettringite forms quickly, and the residual sulfate content in the effluent can be as low as 200 mg L -1 [12], which enables the final sulfate concentration in the effluent to comply with environmental regulations and recommendations of the World Health Organization, for example [30].…”

Fundamental aspects related to batch and fixed-bed sulfate sorption by the macroporous type 1 strong base ion exchange resin Purolite A500

“…Barium sulfate precipitation ensures very low residual sulfate concentrations, however, barium compounds are usually expensive, and any Ba 2þ ions remaining in solution are a much greater environmental concern. Ettringite precipitation can also effectively remove sulfate, although it requires an alkaline pH to function properly (Ferreira et al, 2012). The eMalahleni Project in South Africa, for instance, applies a sequence of oxidation and precipitation steps before pumping mining water to a membrane system that uses ultrafiltration and reverse osmosis to produce a <200 mg L À1 TDS water.…”