Study on pollution release characteristics, substrate amendment and ecological restoration of electrolytic manganese residue under combined application of red mud and phosphogypsum

This study investigated pollution release control, substrate amendment and phytoremediation of electrolytic manganese residue (EMR) via combined red mud (RM) and phosphogypsum (PG) amendments. A pot trial with gradient EMR-RM/EMR-PG ratios using Pennisetum giganteum explored substrate properties, enzyme activities, plant growth and metal accumulation, with principal component analysis distinguishing RM and PG functions. RM and PG lowered substrate conductivity and buffered pH to weak alkalinity. ERM35 (EMR:RM = 3:5) and EPG35 (EMR:PG = 3:5) were optimal, with total fresh weights of 90.07 and 93.30 g versus 13.27 g in ERM62. ERM35 boosted urease and sucrase; ERM53 raised phosphatase by 1381%, and EPG35 increased urease by 130.60%. The total substrate Mn concentration decreased greatly with increasing RM or PG proportion. Such reduction originates partly from material dilution effect; meanwhile, pH and Eh modulation by solid-waste mixtures further alters Mn environmental behavior. EPG35 achieved a 71.90% reduction in total Mn content. RM elevated substrate Fe, while PG promoted Cu accumulation. Mn, Fe and Zn mainly accumulated in plant roots. RM governed plant growth and metal enrichment, whereas PG regulated substrate properties and suppressed Mn release. This work offers theoretical and technical guidance for multi-source solid waste recycling, heavy metal pollution control and rapid soilless restoration of EMR yards.