Studies On Preparation Of Spherical Geopolymer Using Suspension Solidification And Its Application

Geopolymer is a kind of amorphous gel materials with a 3-dimensional structure,which is consisted of[SiO₄]and[AlO₄]tetrahedra.Ascribe to the advantages of high compressive strength,rapid hardening,resistance to heat and chemical corrosion,broad resource of raw materials,low cost,environment friendly,geopolymer has been well applied in the fields of building materials and refractory materials.The strength and durability performance of geoplymer has been well studied as a cement substitute by researchers.With the deepening research on geopolymer materials,the application studies are gradually diversified.Due to the zeolite-like structure and adjustable pore structure,geopolymer has been used for heavy metal ions adsorption,the dye adsorption,and the results showed a good adsorption performance.But most of current application research on the geopolymer is still mainly concentrated on the compressive strength,durability,adsorption,immobilization of toxic substances and material modification.Besides,the preparation method of geopolymer is simplified,mainly are the traditional injection molding method,which brought a certain limitation for its application.This research is based on the structures and properties of geopolymer,and combined with industrial application demands.By suspension solidification method,geopolymer spheres with the particle size of 75?3000 ?m were synthesized by adjusting the technology parameters.The influence of stirring speed,temperature,viscosity of continuous phase and the shape of reaction kettle on the size distribution of spheres have been studied.The spherical geopolymer includes two kinds of high compressive strength and porous functional spheres.Depending on the properties and the particle size,geopolymer spheres are suitable for the application of four different directions respectively:?1?High compressive strength geopolymer sphere:with slag and sodium silicate as the main raw material,a kinder of high compressive strength geopolymer sphere were synthesized by suspension solidification method using as non-sintering geopolymer proppants?NGP?,with a particle size of 2?3 mm.By using steam curing,adding silicon fume and quartz sand,the compressive strength of NGP had been well improved and finally matched the standard requirements.By the method of Ba²⁺ exchange treatment,a layer of BaSO₄ precipitation is formed on the surface of NGP,and the performance of acid resistance has been greatly improve and the acid solubility reached the standard requirements.By using disperse suspension solidification,NGP with the particle size of 450?800 ?m were obtained and the various performance indexes of NGP reached the standard requirements.?2?Porous P-type zeolites spheres?PZS?:Porous gepolymer spheres were synthesized using metakaolin and sodium silicate as the main raw material,with a particle size of 2?3 mm,by suspension solidification method.Through the hydrothermal treatment,geopolymer spheres transformed into PZS.The influences of the raw material Si/Al,modules of alkali activators,curing condition and hydrothermal conditions on the type of zeolites,morphology and specific area were studied and the crystal mechanism were analyzed.The curing process of geopolymer is equivalent to aging process in the traditional preparation method of zeolites.The generated geopolymer gel contained nano-sized crystal structure and there is genetic relationship between the crystal and resulting zeolites on its composition and structure.Besides,the hydrothermal conditions also have a larger effect on the resulting zeolites.By adding the foaming agent,PZS has more abundant pore structures,and the specific surface area can reach 42.08 m²/g,with density of 1.10 g/cm³,which is conducive to the ion removal in solution.By using sodium silicate and silica sol as alkali activator respectively,using silica sol as alkali excitation agent get P type zeolites with more structured morphology and less mottle crystals.Compared with the self-support geopolymer inorganic membrane and porous geopolymer spheres,PZS presents higher removal ability for Ca²⁺ up to 38.74 mg/g,mainly for the ion exchange function of zeolite and the adsorption of geopolymer.?3?Geopolymer microspheres CO₂ capture?GMCC?:Geopolymer microspheres with particle size of 75?100 ?m were synthesized using slag and water glass as the main raw material by disperse suspension solidification method.Ascribe to the properties of carbonation and adsorption,GMCC was used as CO₂ capturing.The influences of system alkalinity,water content on the capture performance has been studied and it was found that under the condition of suitable alkalinity and water content,GMCC with large specific surface area was obtained,which is helpful to reduce the diffusion resistance of CO₂ gas in microspheres,and to improve the CO₂ capture efficiency finally.On this basis,the appropriate excess alkalinity and water content is beneficial for dissolution of CO₂ in the pore solutions on the surface of the microsphere pore,and promotes further carbonation reaction.Thermo gravimetric analysis results showed that GMCC captured CO₂ with the amount of 1.59 mmol/g?1 atm,25 ??,which is 5 times of the similar material.The kinetics studies showed that the process fitted pseudo second kinetic model well,which indicates chemical adsorption.After adsorption,calcium carbonates crystals were generated on the surface of geopolymer gel after carbonation reaction.By using the calcinations method,the results showed that the chemical adsorption amount accounts for 75%.?4?Porous geopolymer microspheres for heavy metal adsorption?PGM?:with slag and sodium silicate as raw materials,by adding sodium dodecyl sulfate?K12?and hydrogen peroxide?H₂O₂?as foaming agent,porous geopolymer microspheres were synthesized using dispersion suspension solidification method.The particle size of PGM is 75?100 ?m,with specific surface area of 100.99 m/g,and its pore size distribution is concentrated in the 7 nm.The adsorption performance of PGM for Pb²⁺,Cu²⁺ and Cd²⁺ was studied,and it was found that PGM presents adsorption abilities to the three kinds of heavy metal ions,and has a priority on Pb²⁺ adsorption.The adsorption of PGM for Pb²⁺ is efficient and reached adsorption equilibrium in 5 h.The influence of pH,adsorbent dosage and initial concentration on adsorption amount is studied,and the adsorption capacity reached the maximum of 629.21 mg/g under appropriate conditions.Compared with other geopolymer adsorbent,adsorption capacity improved 4?6 times.By using EDTA-2Na as desorption agent,PGM presents good regenerability ratio of 51%.Through the studies of kinetic and isothermal adsorption process,it's shown the adsorption process well fitted with pseudo-second kinetic model,the Langmuir model and D-R model,which respectively indicates for chemical adsorption,monolayer adsorption and favorable adsorption...