Electrolytic manganese residue amendment improved the suitability of lead-zinc tailings for plant growth

Revegetation is urgently needed for the ecological restoration of lead-zinc tailings ponds. However, the harsh properties of lead-zinc tailings-including poor aggregation, nutrient deficiency, and low water retention capacity-severely hinder plant colonization and growth. This study effectively improved the physical structure and nutrient status of lead-zinc tailings using electrolytic manganese residue (EMR), a solid waste characterized by strong cohesiveness and high ammonium nitrogen content. Moreover, lead-zinc tailings amended with 1 % EMR had low leaching of toxic elements, indicating low environmental risk. X-ray computed tomography and nuclear magnetic resonance analyses revealed that EMR amendment significantly reduced total porosity of lead-zinc tailings while enhancing their water retention capacity (p < 0.05). The improvements likely resulted from the filling of interparticle voids by EMR clay particles and the formation of Ca₂(AlFe)(Si₂O₇)(SiO₄)O(OH), a hydrated gel similar to the hydrated calcium silicate gel. The hydrated gel formed by the reaction between Ca²⁺ from EMR and silicates on tailing surfaces may increase interparticle cohesion. A pot experiment showed that 1 % EMR amendment significantly promoted ryegrass growth in tailings, increasing fresh biomass by 13.7 % (p < 0.05). Overall, these findings indicate that EMR amendment is a promising strategy to enhance plant colonization and growth in the revegetation of lead-zinc tailings ponds.