Preparation of non-sintered permeable bricks using electrolytic manganese residue: Environmental and NH₃-N recovery benefits

The present study aims to prepare non-sintered permeable bricks using significant amount of electrolytic manganese residue (EMR), discharged by electrolytic metal manganese industry. Mechanical and environmental properties were investigated. The microstructure was analyzed by means of XRD, FTIR, TG-DSC and SEM-EDS. It was observed that the splitting tensile strength and permeability coefficient of the optimum proportion were 3.53 MPa and 3.2 × 10^-2 cm/s respectively. The main hydration products were found to be ettringite, C-S-H, aluminosilicates and C-A-S-H. The leaching test showed that Mn, Pb, Cd, total Cr and NH₃-N in the non-sintered permeable bricks were solidified up to concentrations lower than groundwater standard. In addition to that, the NH₃-N produced during the process was transformed into ammonia water which was in turn recycled and reused in manganese electrolysis. Besides, non-sintered permeable bricks have been produced at large scale and applied successfully as pavement materials in Songtao, China. Therefore, the use of EMR to produce non-sintered permeable bricks possesses important environmental and economic significance because the process not only utilizes large quantities of EMR and saves EMR disposal cost, but also saves a lot of natural resources and improves the urban environment.