Preparation And Properties Of Niobium Tailings-based Geopolymers

Geopolymer is a new inorganic material with amorphous to semicrystalline threedimensional silicate structure,which has excellent chemical resistance,high temperature resistance and heavy metal ion sealing performance.Tailings,as the end product of beneficiation process,have huge stockpile and cause serious environmental pollution.Niobium tailings contain large amounts of silicon and aluminum,which can be used as raw materials for preparing geological polymers.Therefore,how to use niobium tailings to produce geological polymers is an important research direction for realizing the secondary utilization of the tailings resources.In this study,a niobium ore sorting tailings in Africa was taken as the object,and the niobium tailings were activated by chemical-thermal activation method.Then,the activated tailings and metakaolin were used as the main raw materials,and sodium silicate was used as the alkali activator.Through a series of conditional tests and optimization tests,the optimal preparation process of base polymer from niobium tailings was obtained.Then,a batch of samples were prepared by the optimal process,and their durability and curing properties were studied.The activation effect of niobium tailings was evaluated by alkali leaching test,the dissolution amount of Si and Al.The test results showed that the optimal activation conditions were NaOH dosage of 10 wt%,calcination temperature of 700 ?,and calcination time of 1 h.At this time,the dissolution amounts of Si and Al were 1151.75mg/L and 462.82 mg/L,respectively.The results of microscopic analysis showed that after activation treatment,the phase of niobium tailings changed,and the stable crystal structure in the system was destroyed,resulting in the formation of amorphous substances with high activity.After activation,the surface of the tailings became rough and there were corrosion pits.The performance was that the dissolution of Si and Al increased.Based on the activation test,the effects of metakaolin content,sodium silicate content,liquid-solid ratio and curing conditions on the compressive strength of niobium tailings base polymer were studied by condition test and orthogonal test.The test results show that the influence order of the three factors on the compressive strength of the sample is as follows : sodium silicate dosage > metakaolin dosage > liquid-solid ratio;The best preparation process of geopolymer is metakaolin dosage of 60 wt %,sodium silicate dosage of 20 wt%,liquid-solid ratio of 0.45,wet curing,curing temperature of60 ?,curing time of 18 h.Under this condition,the compressive strength of samples prepared at 3d,7d and 28 d is 57.03 MPa,64.17 MPa and 72.71 MPa,respectively,which meets the national requirements for 62.5 R ordinary Portland cement.The microscopic analysis results show that there are a large number of N-A-S-H gels in the geological polymer,which connect the reaction and unreacted particles in the system to make the internal structure dense,and thus improve the compressive strength of the sample.The niobium tailings base polymer was prepared under the optimum conditions,and the durability and curing properties of water,acid,alkali,salt and high temperature were studied after 7 days of curing.The test results show that the niobium tailings base polymer has good resistance to chemical erosion,high temperature resistance and heavy metal ion curing ability.The experimental results show that niobium tailings after activation can be used as raw materials to prepare geological polymers,and the samples have good mechanical properties,durability and curing properties of heavy metal ions.