The present study was designed to prepare the road base material by using electrolytic manganese residue (EMR), red mud (RM) and carbide slag (CS) as main raw materials. The mix was optimized and mechanical properties, durability, strength formation mechanism and environmental behavior were investigated. X-ray diffraction (XRD), Mercury intrusion porosimetry (MIP), 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and electron probe microanalysis method (EPMA) were used for microstructure characterization. The results show that after curing for 7 days, the EMRRM-CS exhibited the highest unconfined compressive strength (UCS), showed the best durability, the best pore diameter distribution and critical pore size. Hydration characteristics reveal that C-A-S-H gel and AFt are generated in EMR-RM-CS, which is positive to the form of UCS and durability. 29Si analysis demonstrates that the synergy of EMR, RM and CS has the best polymerized structure. Al in the hydrated pastes exists in the form of AlIV and AlVI, and one part of the dominant AlIV is activated and another one is converted to AlVI. The leaching results meet the Chinese groundwater standards which indicate that EMRRM-CS system can well solidify the heavy metals. The road base material prepared by EMR not only consumes a significant quantity of solid wastes but also provides a new idea for the synergistic utilization of solid wastes.

Introduction

Electrolytic manganese residue (EMR), red mud (RM) and carbide slag (CS) are three kinds of solid waste which are largely produced and difficult to recycle. EMR is a potentially harmful industrial solid waste, its major hazardous substances are heavy metals and ammonia nitrogen, which are harmful to the environment [1]. China is the largest producer of electrolytic manganese in the world with about 1.66Mt produced in 2018 [2]. Every ton of manganese produced generates 10–۱۲ tons of EMR [3], implying that more than 15.5Mt EMR are produced annually. Red mud is the powder solid residue of bauxite after strong alkali leaching of alumina. For every ton of alumina produced will bring 1.0–۱٫۸ tons of red mud [4,5]. Red mud contains a large number of strong alkaline chemicals with a pH value of more than 12 [6], and the main harmful element in RM is sodium. Carbide slag is an industrial waste produced by calcium carbide hydrolysis to prepare C2H2 gas, PVC, etc. [7,8]. The carbide slag had been identified as an industrial solid waste, which is difficult to be recycled. [9,10].