Preparation And Application Study Of Geopolymers For Phosphoric Acid-based Disused Polishing Liquid As Activator

Guangxi enjoys a fame as hometown of non-ferrous metals,including a large amount of aluminum,manganese and other metal deposits.The annual production of alumina and manganese will cause a lot of polluting waste such as red mud and Electrolytic Manganese Residue(EMR).If not properly processed in time,these wastes will cause serious damage to the local ecological environment.Phosphoric acid-based disused polishing liquid(PADPL)is a kind of industrial effluents during the processing of the aluminum material.Those main components is phosphoric acid,also contains small amounts of sulfuric acid and nitric acid.In addition,PADPL are rich in aluminum,iron and cadmium,arsenic,copper and other heavy metal ions in large quantity.If discharged without any treatment,these effluents will not only pose major pollution to the environment,but also cause a serious waste of valuable resources.Phosphoric acid-based geopolymer is a kind of newly developed material,with advantages of the high strength,fire resistance,acid and alkali resistance,small dielectric constant and low dielectric loss,etc.Based on density functional theory(DFT),this paper studies the mechanism of the geopolymers condensation activated by the phosphoric acid with the DMol3 module in the simulation software of Materials Studio 8.By the depolymerization-condensation method,we prepared the metakaolin-based geopolymer,red mud-based geopolymer and EMR-based geopolymer,which are mainly synthesized with PADP Liquids,metakaolin,red mud and EMR as the main raw material.Meanwhile,we explore the red mud-based porous geopolymer and the EMR-based light fire refractory geopolymer.The main findings are as follows:(1)Based on the density functional theory,after through permutation and combination/theoretical analysis method of[A104]-、[SiO4]-and[PO4]-which produced by phosphoric acid motivating.We determine six possible existing initial state models caculated by optimizing calculation.Twelve final state simulation structures are carried out optimizing calculation based on above and polycondensation reaction mechanism.The calculations results indicate as follows:1)Under the same condition,phosphorus-oxygen tetrahedral will lead to a prioritized combination with silicon-oxygen tetrahedra,and produce condensed structure[—P—Si—Al-]n,which are different from condensed structure conceived traditionally;2)[Al2Si2O4(OH)8]-2(4sr)and[Al2Si2PO6(OH)9]-2(4sr-Si-P)configurations are most posible existing state in geopolymer condensation reaction and next are[Al2Si2PO6(OH)9]-2(4sr-Al-P)structure;3)Besides 2sr and 4sr structure,some other structures such as 2Dr-Si-P、4Dr-Si-P、6sr-Si-P、6Dr-Si-P、2Dr-Al-P、4Dr-Al-P、6sr-Al-P and 6Dr-Al-P may also exist in reactants and products.Which one is the main structure depended on the amount of silicon and aluminum in reactants.(2)Using PADPL to active metakaolin,under the mass ratio of metakaolin:PADPL:water=10:6:3,reaction temperature of 60℃,curing for 5d,geopolymers with high strength,good solidification of metal ions,high temperature,fire resistance and certain resistance to acid and alkali erosion is obtained.The highest compressive strength can reach at 79 MPa;This solidified metal ions have excellent solidification performance,especially to heavy metal ions such as Pb、Cr and so on;It can withstand temperatures up to 1300 ℃;It has good water resistance and can be used as solid acid carrier materials.Besides,it has good corrosion resistance in low concentration(less than 1%)HCl,H2SO4 and NaOH solution respectively.(3)With PADPL as activator,red mud as the main raw materials,adding appropriate amount of the metakaolin,under the optimum mass ratio of red mud:metakaolin:PADPL:water = 8:4:8:2,reaction temperature of 50℃,curing for Id,the red mud-base polymer is synthesized.The red mud-based base polymer maximum compressive strength is nearly 20 MPa;with excellent water resistance(no change in the long-term immersion in water),it could be used as the carrier of solid acid;it has resisitance property in the HCl and H2SO4 solution of low concentration,good resisitance property in NaOH solution.it is corroded seriously in HCl and H2SO4 solution of high concentration;relying on the carbon dioxide produced during the reaction,the porous material of good pore properties could be prepared.The water content have an important effect on the water absorption and volume density;when the porous red mud-base gepolymer is prepared,a suitable amount of metakaolin added can not only significantly improve the compressive strength of the porous red mud-based polymer,but also significantly improve the quality of its pore;it has excellent properties of adsorption and solidification metal ions,especially for heavy metal ions such as Pb,Cd,Cu and other common metal ions like Fe and Al.On this basis,the porous red mud base polymer material is studied.(4)With PADPL as activator,electrolytic manganese slag as the main raw material,and appropriate amount of the metakaolin added,under the optimum condition of manganese slag:metakaolin:PADPL:water =30:9:15:4(mass ratio);reaction temperature of 70℃,curing for Id,the manganese slag-base gepolymer is synthesized.The maximum compressive strength is nearly 51 MPa;it has excellent water resistance,could be used as the carrier of solid acid;it has good corrosion resistance in concentration of about 1%HCl and H2SO4 solution;it has excellent properties of solidifying metal ions,especially for heavy metal ions such as Cr,As,Cu,Cd,but the solidifying ability of Mg and Mn ions is poor.on this basis,the lightweight heat-resisting composite with manganese slag red mud-based geopolymer material is studied.Lightweight composite manganese slag-based geopolymer is synthesized and the mainly properties of materials can meet GB/T 15229-2011 standard for《lightweight aggregate concrete small hollow block》.(5)The experiment studies the effect on depolymerization reaction from depolymerization temperature,time and sulfuric acid,while the influence of the polymerization reaction from sulfuric acid,metal ions and silicon content is also discussed.The results indicate:1)during the depolymerization reaction,low amount of sulfuric acid is beneficial for the dissolution of aluminum and the improvement of the compressive strength of geopolymer,and plays a synergy excitation and catalyst role.However,high amount of sulfuric acid in the preparation of the geopolymer form mainly aluminum sulfate and the compressive strength is decreased;2)Low temperature makes depolymerization process to react more thoroughly.If the depolymerization time is appropriately extended,higher compressive strength geopolymer would be prepared;3)There is a positive correlation between the improvement the compressive strength,heat resistance of geopolymer and metal ion in the phosphoric acid-based disused polishing liquid.