Comprehensive evaluation on magnesium potassium phosphate cement-mineral additive stabilized waste sludge

To ameliorate the physic-mechanical behavior of waste sludge at reasonable costs, fly ash and silica fume are incorporated in MKPC-based solidification, and the impact of MKPC-mineral additive is comprehensively examined from the multi-viewpoint of compaction, strength, permeability and compressibility. The micromorphology of solidified sludge is identified by SEM tests. The results show MKPC-mineral additive has an excellent ability to improve the strength and deformation property of sludge under the influence of MKPC content, mineral additive content, curing age and compaction degree. MKPC content and mineral additive content have a slight impact on the maximum dry density of solidified sludge. The optimum water content tends to increase with mineral additive content and to decrease with MKPC content. The compressive strength and yielding stress have an ascending trend with an extension in curing age and an increase in MKPC content and compaction degree, and the compressibility and permeability presents a descending tendency. The SEM analysis reveals that struvite-k crystals play a dominant role in cementing fine grains to form an interconnected network, and a tiny amount of Mg(OH)2 is generated as secondary phase. It should be noted C-S-H gel and MgSiO3 are respectively produced for MKPC-fly ash and MKPC-silica fume solidified sludge.