Abstract:
Manganese slag is a solid waste produced by the electrolytic manganese metal (EMM) industry. Its large-scale stockpiling not only wastes resources but also poses a threat to the ecological environment due to its heavy metal content. Humic acid (HA) was used as a curing agent to address the limitations associated with the previous over-reliance on alkaline fixatives for \mathrmNH_4^+-N treatment, effectively avoiding secondary pollution issues caused by ammonia emissions. The impacts of HA dosage, curing time, and the synergistic effect of HA and quicklime on the solidification of Mn
2+ and \mathrmNH_4^+-N in manganese slag were investigated by solidification/stabilization technique. Scanning electron microscopy (SEM) and Fourier infrared spectroscopy (FTIR) were used for mechanistic studies. The results showed that when HA was added at a mass fraction of 3.0%, with a water content of 40.0%, and after the solidification for 10 days, the concentrations of Mn
2+ and \mathrmNH_4^+-N in the leaching solution were 4.00 and 0.42 mg/L, respectively. These concentrations were within the limits of 5 mg/L and 10 mg/L specified in
Identification Standards for Hazardous Wastes- Identification for Extraction Toxicity (GB 5085.3-2007). The solidification rates were 65.46% and 97.05%, respectively. The results of synergistic tests using 5.0% quicklime and 3.0% HA showed that when other test conditions remained unchanged, and the solidification rate of Mn
2+ was increased to 99.90%, the solidification rate of \mathrmNH_4^+-N remained unchanged. This indicated that HA had a collaborative solidification ability. The mechanistic studies showed that the HA radical underwent complexation, adsorption, and ammoniation reactions with Mn
2+ and \mathrmNH_4^+-N, generating a relatively stable complex of Mn
2+-HA and ammonium humate.