Study On Preparation Of One-part Geopolymers Using Vanadium-bearing Shale Leaching Residue

Recently,geopolymer technology becomes popular in utilization of Vanadium-bearing shale leaching residue(VSLR).However,the use of alkali-activated solutions during the geopolymerization limits the bulk application of this technology because of handling difficulties associated with cautious storage for these viscous,corrosive alkali-activated solutions.Also,the alkali content of geopolymeric mixture should be control carefully otherwise there can be a tendency toward efflorescence in service.In this paper,VSLR and activator were combined together to form geopolymer precursor,which could be activated by water instead of alkali solution in field application.This study explored the feasibility of using VSLR to prepare one-part geopolymers and two routes are investigated,including“direct mixing”and“thermal activation”.The response surface methodology(RSM)was used to optimize the preparation process,and the mechanism of thermal activation was also discussed in detail.The results are as follows:(1)The"direct mixing"method can produce one-part geopolymers,and the compressive strength of the geopolymers reached 9.29MPa,11.89MPa and 12.21MPa respectively after 3 days,7 days and 28 days curing.The geopolymer prepared by direct mixing has a low compressive strength and cannot meet engineering application requirements.The geopolymer product obtained after thermal activation of the VSLR can reach 28.9 MPa just after curing 7 days,and it possess the potential to replace Portland cement in engineering application.(2)According to the analysis of the process optimization,the factors that have the greatest impact on the compressive strength of the geopolymer are the alkali consumption,followed by the calcination temperature,then the metakaolin content and the calcination duration.The optimized condition is that the calcination temperature is 431°C,the calcination duration is 60min,the alkali consumption is20%,the metakaolin content is 30%,and the compressive strength of the geopolymer can reach 29.24MPa.The resulting response surface model equation is as follows:Y=28.81–5.51A–1.51B+11.10C+0.64D–1.29AB–3.61AC–3.90AD–1.29BC–0.90BD+1.18CD–9.79A²–7.13B²–7.45C²–7.76D²(3)The formation of Na₂Si O₃ from VSLR particles and Na OH is the main reaction that occurs during the thermal activation process,and the reaction starts at250°C.After the temperature exceeds 600°C,the VSLR further melts and sinters,which negatively affects the thermal activation.After adding water,the Na₂Si O₃ on the surface of the VSLR particles dissolves and releases free silicon components,while creating a strong alkaline solution environment.Then,metakaolin is dissolved in a strongly alkaline solution environment to release free aluminum components,and follow by geopolymerization and form a geopolymeric gel phase.