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Various mineral processing operations to produce pure metals from mineral ores generate sludges, residues, and other unwanted by-products/wastes. As a general practice, these wastes are either stored in a reservoir or disposed in the surrounding of mining/smelting areas, which might cause adverse environmental impacts. Therefore, it is important to understand the various characteristics like heavy metal leaching features and potential toxicity of these metallurgical wastes. In this study, zinc plant leach residues (ZLRs) were collected from a currently operating Zn metallurgical industry located in Minas Gerais (Brazil) and investigated for their potential toxicity, fractionation, and leachability. Three different ZLR samples (ZLR1, ZLR2, and ZLR3) were collected, based on their age of production and deposition. They mainly consisted of Fe (6-11.5 %), Zn (2.5 to 5.0 %), and Pb (1.5 to 2.5 %) and minor concentrations of Al, Cd, Cu, and Mn, depending on the sample age. Toxicity Characteristic Leaching Procedure (TCLP) results revealed that these wastes are hazardous for the environment. Accelerated Community Bureau of Reference (BCR) sequential extraction clearly showed that potentially toxic heavy metals such as Cd, Cu, Pb, and Zn can be released into the environment in high quantities under mild acidic conditions. The results of the liquid-solid partitioning as a function of pH showed that pH plays an important role in the leachability of metals from these residues. At low pH (pH 2.5), high concentrations of metals can be leached: 67, 25, and 7 % of Zn can be leached from leach residues ZLR1, ZLR2, and ZLR3, respectively. The release of metals decreased with increasing pH. Geochemical modeling of the pH-dependent leaching was also performed to determine which geochemical process controls the leachability/solubility of the heavy metals. This study showed that the studied ZLRs contain significant concentrations of non-residual extractable fractions of Zn and can be seen as a potential secondary resource for Zn.

RESUMO:Os murundus são micro-relevos muito comuns na região do Vale do Gorutuba. A sua presença desvaloriza a terra e indica solos de fertilidade inferior. Este trabalho tem como objetivo caracterizar física e quimicamente os murundus localizados na região do Vale do Gorutuba, nos municípios de Janaúba e Nova Porteirinha, Minas Gerais. O estudo foi conduzido em quatro áreas sob vegetação de mata nativa, para cada uma das áreas foram determinadas as coordenadas geográficas, altitude, altura, diâmetro e distância entre murundus vizinhos. Os solos foram amostrados nas camadas de 0-20, 20-40 e de 40-60 cm, nas porções de topo e entre os murundus. Nessas amostras foram efetuadas análises textural, matéria orgânica, pH, Ca, Mg, K, Na, P, Al e H+A. Os resultados mostraram que os solos das áreas estudadas apresentaram características físicas e químicas diferentes, estas diferenças podem ser atribuídas ao material de origem. A fertilidade de solo foi superior na P4, em relação às demais áreas estudadas, e isto provavelmente se explica pelos seus murundus, de cor vermelha, originarem-se de material calcário sendo, assim, mais férteis. Portanto, a destruição de murundus e incorporação de solo ao cultivo tende a propiciar resultados mais satisfatórios na P4, uma vez que a superioridade das propriedades químicas do solo é compatível com um menor gasto de adubação, o que pode aumentar a lucratividade da atividade agrícola. Os materiais de origem das outras áreas são siltitos, contendo baixos teores de nutrientes, formando murundus com baixa fertilidade. Palavras-chave: solos, fertilidade, manejo do solo ABSTRACT: PHYSICAL-CHEMICAL CHARACTERIZATION OF MICRO RELIEF OF LITTLE HILLS "MURUNDUS" IN THE REGION OF JANAÚBA, NORTH OF MINAS GERAIS. Murundus is very common micro relives in the Vale do Gorutuba region. Its presence devaluates the land andindicates soil of inferior fertility. The present research aimed to characterize physically and chemically murundus in the Vale do Gorutuba region, in Janaúba and Nova Porteirinha counties. The study was carried out in four areas under vegetation of native forest, determining for each one the geographic coordinates, altitude, height, diameter and distance between murundus. The soil samples were collected at 0-20, 20-40 and 40-60 cm, in the portions of top and between murundus. Texture, organic substance, pH, Ca, Mg, K, In, P, Al and H+Al were analyzed. For the results, the soil of the studied areas presented different physical and chemical characteristics, being attributed these differences to the origin material. The soil fertility was superior in P4, in relation to the other studied areas, and this probably justifies for its murundus, from red color, from limy material being, thus, more fertile. Therefore, the destruction of murundus and incorporation of soil to the culture tends to propitiate response more satisfactory in P4, because the superiority of the chemical properties of the soil is compatible with a lesser expense of fertilization, what can increase the profitability of the ag...

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BACKGROUND Gradual depletion of high‐grade ores for heavy metals has encouraged industries to search for alternative methods to recover metals. Wastes generated from metallurgical industries can be used as a secondary resource as it contains high concentrations of metals. RESULTS The bioleaching kinetics and biorecovery of zinc from Zn‐plant leach residues (ZLR), collected from a currently operating Zn‐plant in Três Marias (Minas Gerais, Brazil) were investigated using sulfuric acid producing Acidithiobacillus thiooxidans (A. thiooxidans). Response surface methodology (RSM) with full factorial central composite design (CCD) was applied to optimize Zn bioleaching by A. thiooxidans. The experiments were performed by varying the initial elemental sulfur concentration (5–30 g L−1), pulp density (5–50 g L−1) and initial pH (3.0–4.0 pH units). More than 75% of Zn was extracted from ZLR by A. thiooxidans under optimized conditions (sulfur concentration 25.1 g L−1, pulp density 21.5 g L−1 and initial pH 3.3). The leaching efficiencies of culture supernatant (biogenic sulfuric acid) and chemical sulfuric acid were compared to understand the leaching kinetics. The Zn leaching kinetics of ZLR followed the shrinking core diffusion model. Zn was selectively recovered from the Fe‐rich acidic bioleachate by biogenic sulfide precipitation. Fe was first removed (more than 85% of total Fe in the leachate) by adjusting the initial pH to 5.0, followed by selective Zn biorecovery. CONCLUSIONS Zn (>95%) was selectively recovered from Fe‐depleted ZLR by biogenic sulfides (with 1:1, Zn:biogenic sulfide mass ratio). Biohydrometallurgy can be a potential alternative resource recovery strategy for the selective recovery of Zn from ZLR. © 2016 Society of Chemical Industry