Hydraulic and sorption performances of soil amended with calcium-magnesium composite powder against natural arsenic contamination

Abstract

Excavated soils and rocks, containing toxic metals and/or metalloids from geogenic sources, are usually generated in huge volumes at construction sites. And the post-excavation leaching of these toxic metals and/or metalloids with low concentrations, but higher than the environmental standards, is a major environmental concern. A sorption layer method was developed as a cost-effective countermeasure for treating and reusing such excavated soils and rocks. The method utilizes a permeable soil layer, with sorption capacity at the bottom of the embankment, to retain the chemicals of concern that have dissolved in the leachate. Clean host soil, amended with toxic metal-immobilizing agents, is often used as the sorption layer material to strengthen the sorption performance. This study examined the feasibility of applying decomposed granite soil, amended with calcium-magnesium (Ca-Mg) composite powder, as the sorption layer material against the natural contamination of arsenic (As). The hydraulic and sorption performances, along with the effect of the mix proportions and curing periods, were evaluated through batch sorption tests, hydraulic conductivity tests, and up-flow column percolation tests. The results showed that the sorption performance increased by 15 times when using an additive content of 5% Ca-Mg and that hydraulic conductivity was maintained at around 1 × 10−6 m/s. Neither the hydraulic nor the sorption performance was strongly affected by curing periods up to 28 days. The sorption performance increased with the addition of the Ca-Mg agent of up to 5% in the batch sorption tests. The permeable hydraulic property, with an improved sorption capacity due to the soil-agent mixture, indicated that it is a promising material for use with the sorption layer method for treating huge amounts of soils with low levels of contamination.