Adilson do Lago Leite

Reduction of acid rock drainage using steel slag in cover systems over sulfide rock waste piles

The extraction of gold, coal, nickel, uranium, copper and other earth-moving activities almost always leads to environmental damage. In metal and coal extraction, exposure of sulfide minerals to the atmosphere leads to generation of acid rock drainage (ARD) and in underground mining to acid mine drainage (AMD) due to contamination of infiltrating groundwater. This study proposes to develop a reactive cover system that inhibits infiltration of oxygen and also releases alkalinity to increase the pH of generated ARD and attenuate metal contaminants at the same time. The reactive cover system is constructed using steel slag, a waste product generated from steel industries. This study shows that this type of cover system has the potential to reduce some of the adverse effects of sulfide mine waste disposal on land. Geochemical and geotechnical characterization tests were carried out. Different proportions of sulfide mine waste and steel slag were studied in leachate extraction tests. The best proportion was 33% of steel slag in dry weight. Other tests were conducted as follows: soil consolidation, saturated permeability and soil water characteristic curve. The cover system was numerically modeled through unsaturated flux analysis using Vadose/w. The solution proposed is an oxygen transport barrier that allows rain water percolation to treat the ARD in the waste rock pile. The results showed that the waste pile slope is an important factor and the cover system must have 5 m thickness to achieve an acceptable effectiveness.

Estudos cinéticos de sistemas de coberturas alcalinas em pilha de estéril para a prevenção de drenagem ácida de mina.

Resumo A drenagem acida apresenta-se como um dos grandes problemas da mineracao em regioes que possuem minerais sulfetados. Tal fenomeno esta ligado especificamente ao processo de oxidacao destes minerais, na presenca de agua, oxigenio e bacterias. Particularmente, o problema da drenagem acida e critico na mina de urânio Osamu Utsumi, pertencente as Industrias Nucleares do Brasil (INB), Caldas MG. Nela ha geracao de drenagem acida em diversos locais, incluindo as grandes pilhas de esteril presentes, o reservatorio da cava da mina e outros. Sendo assim, o objetivo desta dissertacao foi avaliar medidas de remediacao passiva para a drenagem acida de uma das pilhas de esteril desta mina, utilizando-se para este fim colunas de lixiviacao em laboratorio. Os resultados obtidos mostram que a adicao de bentonita foi eficiente na diminuicao da infiltracao de agua na coluna, nao alterando, porem, a qualidade do lixiviado. Por sua vez, nas proporcoes utilizadas, a adicao de cal hidratada e dolomita aumentaram o pH do lixiviado um ponto em media, comprovando suas qualidades em combater a drenagem acida. Resultados de potencial de oxireducao, acidez, sulfato e alguns metais tambem sao apresentados. Palavras-chave: Drenagem acida de mina, remediacao passiva, colunas de lixiviacao.

Assessment of two kinetic tests to predict the acid mine drainage in waste rock samples of a uranium mine

Acid mine drainage is the result of the oxidation process of sulfide bearing rocks. This process occurs when the sulfide material is exposed to atmospheric conditions. Under these conditions, successive oxidation reactions yield sulfuric acid generating acidic waters. This problem becomes more serious when the surrounding rocks are not able to neutralize the acid. The low pH condition of the drained water accelerates the solubility process of solid materials (rocks, soils and sediments) and favors metal and metalloid leaching making them available to the environment, which impairs the hydric system quality. This is a quite common situation at abandoned mines where the material is exposed, as at theOsamu Utsumi Mine in Caldas, MG. The main goal of this work was to assess and compare two kinetic tests in an attempt to predict the acid generation from the waste rock of the Osamu Utsumi Mine. The tests were carried out using a Soxhlet extractor and a leaching column. The leachate from the two tests was analyzed for the physical-chemical parameters (pH, Eh and electric conductivity) and metals and metalloids.

Misturas de um solo laterítico com cimento e bentonita para uso em cortinas verticais

There is an increasing worldwide demand for slurry walls to contain contaminated groundwater. Lateritic soils, due to their wide distribution in the Brazilian territory, have great potential to be used in these cases. However, some issues remain uncertain and need investigation, including the interaction and compatibility of these soils with bentonite or cement, the most used additives to improve their geotechnical properties. This work evaluates some mechanical and hydraulic properties of a lateritic soil sample and its mixtures with bentonite and cement. The laboratorial procedures consisted of physical, physico-chemical and mineralogical characterization, hydraulic conductivity, uniaxial compression and direct shearing testing. The results demonstrate that the addition of 3% of bentonite in compacted samples did not decrease the hydraulic conductivity of the lateric soil as expected. On the other hand, the addition of cement has led to a 100-fold increase in this parameter, in spite of the substantial increase in the shear strength caused by the mixture.

Compatibility of Tropical Soil and Bentonite Mixtures Subjected To Chemical Solutions

Tropical soils cover vast regions of the globe and have great potential to be use as compacted clay liner in waste disposal facilities. When required, bentonite clay can be added to these soils so as to improve their hydraulic properties and contaminant retention capacity. One of the important issues to be addressed when evaluating bentonite as addictive material is the compatibility of the mixture when exposed to waste liquids, once the liner properties can be affected after waste disposition. This paper focus on the compatibility of mixtures of a tropical soil sample plus bentonite exposed to different chemicals solutions. This parameter is evaluated through modified Atterberg limits determination. The proportions used to compose the mixtures were 3, 6, 9 and 12% (dry weight basis). The chemical solutions applied were sodium hydroxide (pH11), nitric acid (pH3) and sodium chloride (5 g/L). The results indicate a small decrease in the plasticity of the mixtures when exposed to acidic and alkaline solutions, while greater variations were observed when the mixtures were exposed to the salty solution. The incompatibility index (ICp) shows that the addition of bentonite did not exert so much influence on the compatibility of the samples, especially at high proportions and for salty solutions.