Successful plant growth in acid mine drainage-impacted soil using pot-based experiments with waste amendments

Abstract

This paper addresses the challenge of remediating soil impacted by acid mine drain- age (AMD) using an innovative and sustainable Technosol-based approach to stabi- lize soil and facilitate vegetation recovery. The study assessed the effectiveness of Technosols made from recycled organic (water clarification sludge) and inorganic (siderurgical slags and red gypsum) wastes in mitigating the detrimental effects of AMD on soil properties, pore water chemistry, and plant growth through a 4-month pot experiment. Technosols significantly improved soil health by neutralizing net acidity (296 mmol H+ kg 1), raising pH levels from extremely acidic (3.3) to mildly alkaline (7.7–8.0), and limiting the mobility of potentially toxic elements (PTEs). Dis- solved Cu and Zn concentrations dropped from 80.21 and 72.08 mg L 1, respec- tively, to below 1 mg L 1 by the end of the monitoring period. The experiment identified several concomitant mechanisms of PTE retention, such as decreased dis- solution of metal-bearing minerals, precipitation reactions and adsorption onto Fe and Al (oxy)hydroxides. Aqueous speciation modelling indicated a decline in toxic metal forms (e.g. Al3+, AlSO4+, Cu2+, Zn2+ and H2AsO4 ) in soil pore water after treatment, thus reducing phytotoxicity. Additionally, waste amendments enhanced nutrient availability, with nitrate concentrations reaching up to 417 mg L 1, support- ing seed germination and seedling establishment. The most effective Technosol, com- bining water treatment sludge and white steel slag (60:40 w/w), enabled robust growth of Brassica juncea. Principal component analysis showed a strong correlation between healthy plant responses (survival rate, plant height, leaf number, biomass production) and improved soil pore water parameters (pH, PTEs, aluminium, calcium, bicarbonate and nitrate ions), highlighting the benefits of waste amendments. These findings underscore the potential of waste-derived Technosols in stabilizing AMD- impacted soils and promoting thriving plant growth. However, further validation in field trials with diverse plant species is recommended for real-world applications.