Consolidation of phosphorus tailings and soluble fluorine & phosphorus with calcium carbide residue-mirabilite waste as a green alkali activator

Two alkalis of industrial solid wastes, calcium carbide residue-mirabilite (CCRM), were used as a green combined activator to consolidate phosphorus tailings and soluble phosphorus as well as fluorine through the alkaline activation process. The results based on XRD, FTIR, 29Si NMR and SEM indicated that most of the blast furnace slag (BFS) forms gels to consolidate phosphorus tailings, and the calcium silicate hydrate (C-S-H) gel dominated mechanical properties and immobilization of soluble phosphorus and fluorine. Comparing with the classical alkaline activators Na2SiO3 and NaOH, the CCRM activated materials displayed great competitiveness in mechanical properties with the order of NaOH < CCRM < Na2SiO3. Its maximum compressive strength reached to 10.9 MPa, and the compressive strength increased greatly with certain increasing content of BFS. In addition, the toxicity characteristic leaching procedure (TCLP) tests found the consolidation of risky soluble fluorine and phosphorus ions in the alkaline activation materials (AAMs) presented in the trend of CCRM > NaSiO3 > NaOH, and the tendency enlarges with increasing BFS addition, over 93.1% and 98.9% of soluble fluorine and phosphorus ions could be well fixed. Considering on the environmental and economic efficiency, mechanical properties, soluble phosphorus and fluorine immobilization, the CCRM is found a quite potential solid waste alkali activator for phosphorus tailings and soluble fluorine & phosphorus solidification.