Biochar combined with hyperaccumulators: a strategy for remediation of heavy metal composite pollution in mining areas

In pursuit of a low-cost, pollution-free, and scalable technology for remediating heavy metal pollution in mining areas, this study examines a gold mining area with heavy metal pollution (Cd, Pb, and Hg) and employs soil replacement, biochar passivation, and a combination of hyperaccumulators for the remediation. Results show that both soil replacement and the application of biochar significantly reduce the effective content of these three heavy metals, with pig manure biochar demonstrating superior passivation effects on Pb and Hg compared to fruitwood biochar. Combining biochar with hyperaccumulators leads to better results than using either method alone. The combined approach achieved maximum reductions of 69.8, 70.1, and 56.0% for Cd, Pb, and Hg, respectively. The application of biochar improves the originally coarse soil structure, with maximum increases in organic carbon, available potassium, available phosphorus, and total nitrogen under different treatments being 6.26 times, 4.66 times, 4.04 times, and 3.21 times, respectively. Biochar anchors heavy metals around roots, while hyperaccumulators utilise their excellent stress-resistant physiological characteristics to thrive in nutrient-deficient soil enriched with biochar, thereby absorbing the heavy metals anchored by biochar. The synergy of biochar and hyperaccumulators enhances their individual effectiveness, showing promise for remediating polluted mining areas.