Recycling electrolytic manganese residue into sustainable subgrade material with carbide slag pretreatment and ground granulated blast-furnace slag stabilization

Abstract

The large-scale storage and low utilization rate of electrolytic manganese residue (EMR) have caused serious environmental burdens and social problems. This study prepared a sustainable EMR-based subgrade material named GCE, based on carbide slag (CS)-pretreatment and ground granulated blast-furnace slag (GGBS)-stabilization. The optimum mix ratio, mechanical properties, and the durability of GCE were investigated by conducting unconfined compressive strength (UCS) tests. The strength evolution micro-mechanisms under different mix ratios and durability conditions were clarified by performing XRD, SEM, TG-DTG, and MIP tests. Furthermore, the leaching toxicity of GCE was tested to evaluate the environmental risks. The results showed that the optimum pretreatment effect was achieved under the CS-EMR mass ratio of 1:9. The stabilization of CS-pretreated EMR with 10 % GGBS obtained high strength and good durability, exceeding 10 MPa after 7 days of curing. Furthermore, it also exhibited superior dry-wet and freeze-thaw resistance including high strength retention and little mass loss. Thus, the optimum mass ratio of GGBS, CS and EMR inside GCE was determined to be 1:1:9. The main hydration products in GCE are AFt and C-(A)-S-H gel, which contributed to the formation of dense cemented structure, as well as high strength gaining and good durability. The leaching concentrations of heavy metals and ammonia nitrogen in GCE are extremely low, making it unnecessary to consider environmental risks during utilization. This study develops a sustainable subgrade material and promotes the synergistic resource utilization of industrial solid wastes EMR, CS, and GGBS.