Evaluation of Different Amendment Combinations Associated with Trifolium repens to Stabilize Pb and As in a Mine-Contaminated Soil

Assisted phytoremediation using amendments is a cost-effective and environmentally friendly approach to control soil pollution. However, amendment type, combination and application rate can influence process effectiveness. In the present study, the effect of the association of red mud and carbon-based amendments on the physicochemical properties of a former mine soil as well as the growth and metal(loid) uptake of Trifolium repens was investigated. For this purpose, a mesocosm experiment was set up using a former mine technosol highly contaminated by As and Pb, amended with red mud combined with different carbon-based amendments, i.e., bamboo biochar, oak biochar, steam activated carbon and acidic activated carbon, and sown with Trifolium repens. The final goal was to determine which amendment combination allows soil metal(loid) immobilization and an efficient plant growth. Results showed that all the four different treatments improved soil characteristics by increasing pH and electrical conductivity and reducing redox potential. All the treatments were also effective in reducing soil pore water lead concentrations. Among the four treatments, the addition of red mud and acidic activated carbon in the soil showed better results regarding Trifolium repens growth. Finally, when grown on the soil amended with red mud and acidic activated carbon, Trifolium repens presented mainly a metal(loid) storage in roots, making it a right candidate for the establishment of a vegetation cover.