Preparation And Application Of Steel Slag-blast Furnace Slag-zeolitecomposite Cementitious Material

Cement solidification/stabilization technology is one of the commonly used methods for the treatment of solid wastes and sludges containing heavy metals at present.However,the application of this technology is limited by the high cost and high energy consumption of cement.In this paper,steel slag,blast furnace slag and low-cost zeolite are used as the main raw materials,and activators is used to strengthen the hydration process,to prepare the low-cost steel slag-blast furnace slag-zeolite cementitious materials with low environmental load and excellent solidification/stabilization performance.Firstly,a combination of chemical and physical activation is used to promote the dissociation of Si-O tetrahedron,and Al-O tetrahedron in steel slag and blast furnace slag,to strengthen the hydration process.The effects of various additives on the mechanical strength of cementitious materials were investigated,and the material ratio of Type I cementitious materials was determined through response surface optimization tests:steel slag 34.14%,blast furnace slag 34.14%,zeolite 10%,modified desulfurized gypsum 10%,polysilicon waste slag 8%,cement clinker 3%,and anhydrous sodium sulfate 0.72%.The specific surface area of the steel slag and blast furnace slag is 420 m²/kg.The result show that Type I cementing material can effectively solidify heavy metals lead(Pb²⁺)and chromium(Cr⁶⁺).Compared with ordinary Portland cement,the solidification effect is better,and the cost is lower.Secondly,using steel slag,blast furnace slag and zeolite as raw materials,and adding aluminosilicate-based activator to improve the early strength of steel slag-blast furnace slag-zeolite cementitious materials,and to solve the problem of solidification of sludge with high water content.Orthogonal test and optimization adjustment test were used to determine the appropriate ratio of type II cementitious material:steel slag 31.14%,blast furnace slag 31.14%,zeolite 10%,dihydrate gypsum 1%,anhydrous gypsum 9%,cement clinker 3%,anhydrous sodium sulfate 0.72%,silica fume 6%,activator C 5%,activator D2%,and seed crystal 1%.In this case,the strength of type II cementitious materials met the strength requirements of ordinary Portland cement 42.5R（GB175-2007）.Type II cementitious material has obvious advantages in solidification of sludge with high moisture content.The hydration products of type I and II cementitious materials at various ages were investigated by using XRD,and the hydration mechanism and solidification mechanism were studied.The results show that the hydration products of the system are hydrated calcium silicate,ettringite,and some amorphous substances,and the synergistic effect between the hydrated calcium silicate gel and ettringite helps to improve mechanical strength of cemented materials.Hydrated calcium silicate,ettringite,and zeolite materials solidify heavy metals through chemical bonding,physical adsorption,and ion exchange.By controlling the proportioning of materials,additives and the composition of hydration products,the mechanical strength and application performance of the products are adjusted.The hydration product ettringite plays an important role in the solidification for sludge of high moisture content.Economic analysis and environmental impact of type I and II cementitious materials were carried out.The results show that the cementitious material has greater advantages in production costs and significant economic benefits over ordinary Portland cement.In the production of the cementitious materials,a large amount of solid waste is used,and carbon dioxide emission is reduced,thus the environmental benefits are significant.