Effect of Electrolytic Manganese Residue in Fly Ash-Based Cementitious Material: Hydration Behavior and Microstructure

Electrolytic manganese residue (EMR) is a solid waste with a main mineralogical composition of gypsum. It is generated in the production of metal manganese by the electrolysis process. In this research, EMR, fly ash, and clinker were blended to make fly ash-based cementitious material (FAC) to investigate the effect of EMR on strength properties, hydration behavior, microstructure, and environmental performance of FAC. XRD, TG, and SEM studied the hydration behavior of FAC. The pore structure and [SiO4] polymerization degree were characterized by MIP and 29Si NMR, respectively. The experimental results indicate that FAC shows excellent mechanical properties when the EMR dosage is 10%. Moderate content of sulfate provided by EMR can promote hydration reaction of FAC, and it shows a denser pore structure and higher [SiO4] polymerization degree in this case. Heavy metal ions derived from EMR can be adsorbed in the hydration products of FAC to obtain better environmental properties. This paper presents an AFt covering model for the case of excessive EMR in FAC, and it importantly provides theoretical support for the recycling of EMR in cementitious materials.

Research Status and Environmental Protection Disposal of Recycled Electrolytic Manganese Residue

Electrolytic manganese residue (EMR) is a common industrial solid waste. The ammonia and manganese components contained in it will pollute the soil environment and have potential risks to human health. Under the premise of investigating the production of electrolytic manganese slag and conventional processes, it is found that the traditional harmless treatment methods of electrolytic manganese slag are still mainly lime solidification, cement solidification, and fly ash solidification, and the resource utilization directions such as cement, concrete, non-sintered bricks, road bases, etc. are mainly used. But, EMR contains ammonia nitrogen, and manganese (prone to leaching) that difficult to meeting environmental protection requirements by using general cement cementitious material solidification. Therefore, this study focused on manufacturing new eco-friendly bricks with EMR using calcination process. Specifically, the physical performance and environmental characterization of the sintered bricks were investigated. Furthermore, the sintering behavior and crystallization of all bricks containing EMR were studied using XRD, FT-IR, and SEM. The results showed the EMR leaching solution contained 1256 mg/L and 8120 mg/L of ammonia nitrogen and manganese, respectively, both of them exceeds Chinese standards (GB 8978-1996). Because of EMR is rich in Fe2O3 and K2O, it greatly promotes particle rearrangement and transfer in the EMR system, reducing the sintering temperature. The compressive strength, leaching performance and radioactivity of sintered bricks with EMR all met the state standard requirement for "sintered common bricks" (GB/T 5101-2017) and (GB 8978). The product can be used as bricks of MU20 grade of Chinese standard. The study provides an effective method for the safe and environmentally friendly disposal of EMR.