Research on Preparation of Silicon–Manganese Organic Composite Fertilizer Using the Electrolytic Manganese Residue

Abstract

Electrolytic manganese residue (EMR), an acidic by-product from manganese production, presents dual challenges of environmental pollution and resource waste. This study developed a silicon–manganese organic compound fertilizer (SMOCF) via the aerobic fermentation of EMR supplemented with bagasse, molasses, and activated sludge. The physicochemical analysis revealed that the EMR’s composition was dominated by silicon (7.1% active Si), calcium, sulfur, and trace elements. Critical parameters during composting—including water-soluble Mn (1.48%), organic matter (8.05%), pH (7.4), moisture (20.28%), and germination index (GI = 87.78%)—met organic fertilizer standards, with the GI exceeding the phytotoxicity threshold (80%). The final SMOCF exhibited favorable agronomic properties: neutral pH, earthy texture, and essential macronutrients (1.36% K, 1.11% N, 0.48% P). Heavy metals (As, Cd, Cr, Pb) in the SMOCF predominantly existed in stable residual forms, with total concentrations complying with China’s organic fertilizer regulations (GB/T 32951-2016). The ecological risk assessment confirmed a minimal mobilization potential (risk assessment code < 5%), ensuring environmental safety. This work demonstrates a circular economy strategy to repurpose hazardous EMRs into agriculturally viable fertilizers, achieving simultaneous pollution mitigation and resource recovery. The optimized SMOCF meets quality benchmarks for organic fertilizers while addressing heavy metal concerns, providing a scalable solution for industrial EMR valorization. Further studies should validate the field performance and long-term ecological impacts to facilitate practical implementation.