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Recuperação de metais de águas contaminadas por processos baseados na utilização de extratos das plantas Cistus ladanifer e Erica andevalensis
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Abstract(s)
Atualmente, devido à maior preocupação com os problemas ambientais que consequentemente levam a restrições à descarga de efluentes contaminados com metais, tornou-se essencial o desenvolvimento de processos sustentáveis e eficazes, visando a recuperação dos metais das águas residuais. Simultaneamente, inúmeras espécies vegetais foram descritas como tolerantes e acumuladores de metais, como é o caso de Erica andevalensis e Cistus ladanifer, ambas encontradas em Portugal na mina de São Domingos. Essa capacidade dessas plantas foi explorada no presente trabalho, visando a recuperação de metais de interesse a partir de soluções aquosas. Para essa finalidade, os principais objetivos desta pesquisa foram:
(1) obter extratos das plantas para serem utilizados em efluentes contaminados com metais, para remoção/recuperação dos metais de interesse e
(2) utilizar os compostos destas plantas em solventes orgânicos de forma a testar a sua eficácia para remoção/recuperação de metais pela técnica de extração por solvente (extração líquido-líquido).
Os testes com extratos hidroalcoólicos da planta E. andevalensis e C. ladanifer adicionados a soluções unimetálicas preparadas com HCl e H2SO4, mostraram que os metais do grupo platina (Pt e Pd) e ouro foram removidos (20 a 100%) em ambas as matrizes, bem como prata (90 a 100%) em H2SO4. O mesmo aconteceu com o ferro, mas em menor intervalo de remoção (15 a 25%). Por outro lado, a adição desses extratos a um efluente da eletrozincagem moderadamente contaminado com Zn e Fe resultou apenas em baixa remoção de Fe (≤ 21%). Já na AMD com o extrato de C. ladanifer houve remoção de todos os metais (Al: ~63%, Zn: ~51%, Fe: ~52%, Cu: ~43% e Mn: ~36%); assim como com o extrato de E. andevalensis, apesar de em percentagens mais baixas (Al: ~10%, Zn: ~16%, Fe: ~21%, Cu: ~6% e Mn: ~1%).
Nos testes de recuperação de metais por extração por solventes mostrou que nos extratos de folhas de C. ladanifer preparados com Shell GTL e Octanol ou apenas Shell GTL, houve baixa extração de ferro (<10%) e não houve extração de zinco do efluente da zincagem. Quando se utilizou acetato de etilo enriquecido com compostos fenólicos de C. ladanifer o melhor rendimento em compostos fenólicos foi obtido quando se usou 80% (v/v) de acetona em água acidificada (1,2 M HCl). Verificou-se também uma relação direta entre a concentração de fenóis no acetato de etilo e a eficiência das extrações de ferro e zinco (~34% e ~56%, respetivamente). Nos testes com os compostos fenólicos transferidos para outros solventes orgânicos (butirato de etilo, acetato de butilo, decanol e octanol) as eficiências das extrações de ferro e zinco foram relativamente baixas (<25%) para ambas as plantas.
Nowadays, due to the greater concern about environmental problems and considering the restrictions on the discharge of effluents contaminated with metals, it is essential to develop sustainable and effective processes aiming the recovery of metals from waste streams. At the same time numerous plant species have been described as metal tolerant and accumulators, as is the case of Erica andevalensis and Cistus ladanifer, both found in Portugal in the São Domingos mining area. That capacity of those plants has been explored in the present work aiming the recovery of strategic metals from aqueous solutions. To achieve that purpose the main objectives of this research included: (1) to assess the use of hydroalcoholic plant extracts directly in metal contaminated effluents and artificial solutions for the removal / recovery of the metals of interest and (2) to assess the use of phenolic compounds extracted from those plants diluted in organic solvents for the removal / recovery of metals by solvent (also known as liquid-liquid) extraction technique. The tests in which hydroalcoholic extracts of E. andevalensis and C. ladanifer were added to unimetallic solutions prepared with HCl and H2SO4, showed that the platinum group metals (Pt and Pd) and gold were removed (20 to 100%) from both matrices, as well as silver (90 to 100%) in H2SO4. The same happened with iron(III) but in a lower range of removal (15 to 25%). On the other hand, the addition of these extracts to a zinc plating effluent moderately contaminated with Zn an Fe resulted in no removal of Zn and low removal of Fe (≤ 21%). On the contrary, when the hydroalcoholic extract of C. ladanifer was added to an extremely concentrated acid mine drainage (AMD) collected in the São Domingos mining area, all metals were removed in medium percentages (Al: ~ 63%, Zn: ~ 51%, Fe: ~ 52%, Cu: ~ 43% and Mn: ~ 36%); as with the extract of E. andevalensis, albeit in lower percentages (Al: ~ 10%, Zn: ~ 16%, Fe: ~ 21%, Cu: ~ 6% and Mn: ~ 1%). The solvent extraction tests aiming metals recovery from the zinc plating effluent showed that for the extracts of C. ladanifer prepared with Shell GTL and Octanol, or only Shell GTL, there was low extraction of Fe (<10%) and no extraction of Zn from the zinc plating effluent. On the other hand, when using ethyl acetate enriched with C. ladanifer phenolic compounds, the best yield on phenolic compounds was obtained with 80% (v/v) acetone in acidified water (1.2 M HCl) and there was a direct relationship between the concentration of phenols in ethyl acetate and the efficiency of iron and zinc extractions (which reached ~ 34% and ~ 56%, respectively). Moreover, in tests with phenolic compounds transferred to ethyl butyrate, butyl acetate, decanol and octanol, extraction efficiencies of Zn and Fe (<25%) were relatively lower for both plants than when ethyl acetate was used.
Nowadays, due to the greater concern about environmental problems and considering the restrictions on the discharge of effluents contaminated with metals, it is essential to develop sustainable and effective processes aiming the recovery of metals from waste streams. At the same time numerous plant species have been described as metal tolerant and accumulators, as is the case of Erica andevalensis and Cistus ladanifer, both found in Portugal in the São Domingos mining area. That capacity of those plants has been explored in the present work aiming the recovery of strategic metals from aqueous solutions. To achieve that purpose the main objectives of this research included: (1) to assess the use of hydroalcoholic plant extracts directly in metal contaminated effluents and artificial solutions for the removal / recovery of the metals of interest and (2) to assess the use of phenolic compounds extracted from those plants diluted in organic solvents for the removal / recovery of metals by solvent (also known as liquid-liquid) extraction technique. The tests in which hydroalcoholic extracts of E. andevalensis and C. ladanifer were added to unimetallic solutions prepared with HCl and H2SO4, showed that the platinum group metals (Pt and Pd) and gold were removed (20 to 100%) from both matrices, as well as silver (90 to 100%) in H2SO4. The same happened with iron(III) but in a lower range of removal (15 to 25%). On the other hand, the addition of these extracts to a zinc plating effluent moderately contaminated with Zn an Fe resulted in no removal of Zn and low removal of Fe (≤ 21%). On the contrary, when the hydroalcoholic extract of C. ladanifer was added to an extremely concentrated acid mine drainage (AMD) collected in the São Domingos mining area, all metals were removed in medium percentages (Al: ~ 63%, Zn: ~ 51%, Fe: ~ 52%, Cu: ~ 43% and Mn: ~ 36%); as with the extract of E. andevalensis, albeit in lower percentages (Al: ~ 10%, Zn: ~ 16%, Fe: ~ 21%, Cu: ~ 6% and Mn: ~ 1%). The solvent extraction tests aiming metals recovery from the zinc plating effluent showed that for the extracts of C. ladanifer prepared with Shell GTL and Octanol, or only Shell GTL, there was low extraction of Fe (<10%) and no extraction of Zn from the zinc plating effluent. On the other hand, when using ethyl acetate enriched with C. ladanifer phenolic compounds, the best yield on phenolic compounds was obtained with 80% (v/v) acetone in acidified water (1.2 M HCl) and there was a direct relationship between the concentration of phenols in ethyl acetate and the efficiency of iron and zinc extractions (which reached ~ 34% and ~ 56%, respectively). Moreover, in tests with phenolic compounds transferred to ethyl butyrate, butyl acetate, decanol and octanol, extraction efficiencies of Zn and Fe (<25%) were relatively lower for both plants than when ethyl acetate was used.
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Keywords
Extratos de plantas Recuperação de metais Água ácida de mina Efluente da zincagem Extração por solvente