Utilização de solo laterítico, fosfogesso e bentonita em barreiras hidráulicas: uma análise hidromecânica e ambiental
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2019-02-01
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Universidade Federal de Goiás
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The objective of this study is to evaluate the technical viability of using a sandy lateritic soil chemically stabilized as a liner material, regarding hydromechanical and environmental features. For the chemical stabilization, dehydrated phosphogypsum and sodic bentonite were added to the soil, such six samples were obtained: Soil (S), soil + 10% phosphogypsum (SP), soil + 10% phosphogypsum + 3% bentonite (SPB3), soil + 10% phosphogypsum + 6% bentonite (SPB6), soil + 3% bentonite (SB3) and soil + 6% bentonite (SB6). Since x-ray diffractions tests showed that phosphogypsum shouldn’t be subjected to temperatures above 70˚C, the moisture values of all samples containing this material were determined in this temperature. However, the moisture values obtained in this temperature were corrected, since the soil moisture was determined at 110 ˚C and bentonite’s one at 130 ˚C. It was done through mathematical correlations, obtained comparing samples of this materials in different temperatures. For the hydromechanical tests, specimens were compacted in miniature, in accordance to the Brazilian MCT methodology, in Proctor standard energy. The compaction curves presented similar apparent dry weight values, but the stabilized samples presented higher values of optimum water content than soil. The hydraulic conductivity tests were carried out using the same cylinders used in compaction, with variable hydraulic head and gradient of 10m∕m. Phosphogypsum did not modify the coefficient of hydraulic conductivity of samples, while for the 3% of bentonite addition, these values decreased approximately one order of magnitude. Samples containing 6% of bentonite presented coefficients lower than 1x10-9 m ∕s, therefore, acceptable values for liners. In unconfined compression tests, the samples containing phosphogypsum presented lower strength, while those containing bentonite had an increasing in these values, but all them presented results higher than 200 kPa. The compatibility with contaminants was analyzed through chemical percolation tests, similar to hydraulic conductivity tests, but substituting water with solutions of HNO3, NaOH, NaCl and ethanol. The results showed that the solution of NaOH decreased the coefficients of hydraulic conductivity of samples. On the other hand, the HNO3 increased the coefficients of samples containing bentonite, such all samples presented values higher than 1x10-9 m ∕s. No significant changes were observed for solutions of NaCl and ethanol. The risk of environmental contamination due to the use of phosphogypsum was investigated through chemical analysis of solubilized extracts obtained from samples containing this by-product, taking into account the parameters prescribed by the Brazilian resolution CONAMA 396, for groundwaters. The results obtained indicated excess of iron (attributed to soil) and manganese (attributed to phosphogypsum), but further analysis was recommended for that a precise risk diagnosis was delineated.
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BORGES, Y. I. S. Utilização de solo laterítico, fosfogesso e bentonita em barreiras hidráulicas: uma análise hidromecânica e ambiental. 2019. 45 f. Dissertação (Mestrado em Geotecnia, Estruturas e Construção Civil) - Universidade Federal de Goiás, Goiânia, 2019.