Study of microscopic properties and heavy metal solidification mechanism of electrolytic manganese residue-based cementitious materials

• Published in: Environmental science and pollution research international 2023-10, Vol.30 (48), p.105056-105071
• Main Authors: Tang, Liang, He, Zhaoyi, Chen, Kefan, Wang, Xiaoli, Xiao, Yixun, Yu, Zhou, Xiao, Haixin
• Format: Article
• Language: English
• Subjects: Ammonia; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Blast furnace slags; Calcium hydroxide; Clinker; Crystals; Earth and Environmental Science; Ecotoxicology; Electrolytes - chemistry; Electron microscopes; Emission standards; Environment; Environmental Chemistry; Environmental Health; Ettringite; Ferromanganese; Fourier transforms; Granulation; Heavy metals; Humans; Hydration; Inductively coupled plasma mass spectrometry; Infrared spectrometers; Infrared spectroscopy; Ions; Iron; Leaching; Manganese; Manganese - chemistry; Mechanical properties; Mechanical tests; Metals, Heavy; Mortars (material); Nitrogen; Portland cement; Portland cements; Residues; Review Article; Scanning electron microscopy; Slag; Slaked lime; Sodium hydroxide; Solid wastes; Solidification; Sulfur trioxide; Toxicity; Toxicity testing; Waste Water Technology; Water Management; Water Pollution Control; X-ray diffraction
• ISSN: 1614-7499; 0944-1344; 1614-7499
• DOI: 10.1007/s11356-023-29772-3

Electrolytic manganese residue (EMR) is a solid waste that contains a significant amount of soluble manganese and ammonia nitrogen, which can pose risks to human health if improperly disposed of. This study aimed to prepare cementitious materials containing abundant ettringite crystals by mixing EMR with various proportions of granulated blast furnace slag (GBFS) and alkaline activators (CaO, Ca(OH) 2 , clinker, NaOH). The resulting cementitious material not only utilized a substantial amount of EMR but also exhibited comparable strength to ordinary Portland cement. The optimal ratios were determined through mechanical testing. Additionally, the leaching toxicity of cementitious materials was assessed using ICP-MS (inductively coupled plasma mass spectrometer) tests. The microscopic properties, hydration, and mechanism of heavy metal solidification in the cementitious materials were evaluated using XRD (X-ray diffraction), SEM (scanning electron microscope), EDS (energy-dispersive spectrometer), FTIR (Fourier transform infrared spectroscopy), and TG (thermogravimetric) techniques. The results showed that the optimal ratio for the cementitious materials was 60% EMR, 36% GBFS, and 4% Ca(OH) 2 . The hardened mortar exhibited compressive strengths of 34.43 MPa, 41.3 MPa, and 50.89 MPa at 3 days, 7 days, and 28 days, respectively, with an EMR utilization rate of 60%. The hydration products of EMR-based cementitious materials were C-(A)-S-H, AFt, and ferromanganese compounds, which contribute to the mechanical strength. The Mn 2+ and NH 4 + -N contents of raw EMR were 1220 and 149 mg/L, respectively. Nonetheless, the leaching of Mn 2+ and NH 4 + -N in the alkali-EMR-GBFS system was significantly below the limits set by the Chinese emission standard GB8978-1996. Within this system, C-(A)-S-H and AFt could physically adsorb and displace heavy metals, Ca 6 Mn 2 (SO 4 ) 2 (SO 3 ) 2 (OH) 12 · 24H 2 O could replace Al ions with Mn ions, and ferromanganese compounds Fe 2 Mn(PO 4 ) 2 (OH) 2 · (H 2 O) 8 and MnFe 2 O 4 could chemically precipitate Mn 2+ .