Industry By-Products As Amendments for Phytoremediation of An As-Contaminated Soil From a Gold Mining Area, Brazil.

Arsenic release into soils and sediments is a well-known problem nearby gold mining areas and studies involving phytotechnologies for remediation of such areas may require the use of soil amendments to decrease As phytotoxicity, thus allowing a better soil coverage by plants. Also, the generation of large volumes of secondary materials (by-products) due to industrial activities is a worldwide concern. This study evaluated the efficiency of two industry by-products – red mud (RM), as well as its mixture (RMG) with phosphogypsum, as amendments in an As-contaminated soil from a gold mining area in Brazil. Due to the alkaline reaction of RM and RMG, these amendments were applied to reach a soil pH of approximately 6.0. Additional treatments included the untreated As-contaminated soil, as well as an uncontaminated soil from a Private Natural Reserve (PNR). After 60 days of growth we evaluated dry matter production of shoots (SDM) and roots (RDM) of three different plant species: Brachiaria decumbens, Crotalaria spectabilis, and Stylosanthes cv. Campo Grande. Using RM and RMG increased SDM and RDM of most plants, with RMG being more effective than RM. Adding RMG to the As-contaminated soil increased the SDM of Brachiaria and Crotalaria by 18 and 25% and the RDM by 25 and 12%, respectively. Stylosanthes was found to be more sensitive to As toxicity and grew badly in all As-contaminated soils, irrespective of the use of any soil amendment. Arsenic concentration in shoots of Brachiaria and Crotalaria decreased by 26% with the use of RMG while As in roots reduced by 11 and 30%, respectively. Brachiaria and Crotalaria could be considered as tolerant to As toxicity and thus liable to be exploited for phytoremediation purposes, especially with the use of RMG due to its potential advantage in terms of nutrient supply (Ca²⁺ and SO₄^2- from phosphogypsum). Sponsored by FAPEMIG/CNPq/CAPES.