Mitigação da lixiviação de arsênio, ferro e enxofre e revegetação de substratos minerados em área de ocorrência de drenagem ácida

• Autor(a) principal: Assis, Igor Rodrigues de
• Data de Publicação: 2006
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5462
• topic: Drenagem ácida; Arsênio; Ferro; Enxofre; Revegetação; Barreira geoquímica; Acid mine drainage; Arsenic; Iron; Sulfur; Revegetation; Chemical barriers; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

Sulfide mineral exploration shows large environmental risks when these materials are exposed to the surface. These minerals can be oxidized producing acid waters, known mining activities as acid mining drainage. These waters can reach the water table and channels, with high content of metals (Pb, Cd, Ni, etc.) and metalloids (As, B, etc), becoming solubilized by the process, and toxic to the food chain. The present work aimed to evaluate different acid drainage reducing practices and revegetation procedures, by laboratory and field experiments. In the laboratory experiment, lysimeters were tested with different combinations of cover, saddle and capillarity broken layers. For this last layer, additional treatments were used with sodium oxalic (saddle) and geochemical barrier induction (neoformation of jarosite and, or natrojarosite). Layers were constructed with different materials, all placed over a low oxidized sulfide containing-substrate (B2), forming 12 treatments, plus the reference (B2 substrate), in a incomplete factorial casualised blocks design. The water application was carried out at twice the monthly rain amount, observed at Paracatu-MG. The experiment was carried out during 24 months, and leached waters were collected from each lysimeter every month, to quantify the total volume and to determine As, Fe, S, Na and K contents, and pH value. After the end of the experimental time, lysimeters were opened to collect samples from B2 substrate, aiming to verify jarosite and, or natrojarosite neoformation and, from the cover layer, to determine chemical composition in terms of its revegetation potential. The best results the leachates showed lower amount of As, Fe and S, were found with the geochemical barrier induction-treaments. Jarosite formation could be observed by Mössbauer spectroscopy. Although some treatments have produced lower amounts of As, Fe and S in the leachates, none of those reduced its acidity. The pH of the leachates remained close to 3.0. The cover layer had low influence to the metals leaching, but the use of clay produced better results, probably because its As adsorption capacity. The presence of capillarity broken layers is very important due, probably, to promote a humidity gradient, reducing the amounts the As, Fe and S in the leached. The use of sodium oxalic in this layer did not produce any significant effect, showing no difference among treatments in terms of the amount of leached. The greatest Na and K leaching were obtained with the treatments which received the addition of these elements to geochemical barrier induction, being more intensive Na leaching, favoring jarosite formation instead natrojoraosite. The field experiment was set in March, 2000 with the aim to evaluate the effect of the B1 substrate (ore with low sulfide content) and clay as saddle and cover layers, to promote plant growth. Four treatments were set with different combinations of these materials forming the layers, and where shrubs and trees seedlings from nine species were planted. Height and steam diameter were determined along the experimental time. Superficial (0-20 cm) soil available As was also determinate for each treatment. The clay use in both layers showed better results, allowing more survival and growth for plants. The absence of clay in both layers resulted death for all species and more availability of As. Among species, outstanding performance was observed to Acacia holosericea with higher biomass production and good survival rate. Flemingia sp., Enterolobium timabuva and Acacia polyphylla showed lowers biomass production.