Study on the leaching toxicity and performance of manganese slag-based cementitious materials

With the rapid development of electrolytic manganese industry, the environmental problems caused by the storage of electrolytic manganese slag are particularly prominent. It not only occupies land resources, but also easily causes heavy metal pollution in soil, surface water and groundwater. Therefore, it is necessary to treat electrolytic manganese slag safely and effectively. The paper mainly studies the solidification / stabilization of electrolytic manganese slag and its environmental safety for road filling, in order to open up a new way of harmless and resource utilization of electrolytic manganese slag. In this paper, lime and fly ash were used as stabilizers and cement was used as curing agent to stabilize manganese slag, and the stabilization effect of Mn and Pb in manganese slag was studied. The stabilization effect of manganese (Mn) and lead (Pb) in manganese slag was studied. The results show that the dosage of stabilizer quicklime is 2.5%, fly ash is 3%, and the dosage of solidifying agent cement is 12%, the solidification/stabilization effect is the best compared with other ratios, then the leaching concentrations of Mn and Pb meets the requirements of China's surface water environmental quality standards for category III water sources, which can be used as domestic water after treatment. Under the optimal ratio of stabilization effect, the compressive strength and slump are 13.8MPa and 50mm, respectively. The research results of the paper can provide a new way for the harmless treatment of manganese slag and the resource utilization of new materials.

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.

Enhanced Removal of Pb from Electrolytic Manganese Anode Slime by Vacuum Carbothermal Reduction

Electrolytic manganese anode slime (EMAS) is produced during the production of electrolytic manganese metal. In this study, a method based on vacuum carbothermal reduction was used for Pb removal in EMAS. A Pb-removal efficiency of 99.85% and MnO purity in EMAS of 97.34 wt.% was obtained for a reduction temperature of 950°C and a carbon mass ratio of 10% for a holding time of 100 min. The dense structure of the EMAS was destroyed, a large number of multidimensional pores and cracks were formed, and the Pd-containing compound was reduced to elemental Pb by the vacuum carbothermal reduction. A recovery efficiency for chemical MnO2 of 36.6% was obtained via preparation from Pd-removed EMAS through the “roasting-pickling disproportionation” process, with an acid washing time of 100 min, acid washing temperature of 70°C, H2SO4 concentration of 0.8 mol/L, liquid-solid mass ratio of 7 mL/g, calcination temperature of 60°C and calcination time of 2.5 h. Moreover, the crystal form of the prepared chemical MnO2 was found to be basically the same as that of electrolytic MnO2, and its specific surface area, micropore volume and discharge capacity were all higher than that of electrolytic MnO2. This study provides a new method for Pd removal and recycling for EMAS.