Preparation Of Open Cell Geopolymer And Hierarchically Structured Zeolite And The Comparative Study On Their Pb²⁺,Cu²⁺ Adsorption Behavior

Heavy metal pollution is hazardous to the environment and living beings,and adsorption is especially effective by using varied adsorbents for the removal of heavy metals from water.It is critical for industry to choose the“right”adsorbents because it deals with the cost and efficiency.Geopolymer is attracting increasing interests because of the effective absorption properties for heavy metals.However,geopolymers are usually dense structured and limit the permeability to liquids.In the adsorption experiments,geopolymers are usually grind to powder,and those powder is difficult to be recycled.It can cause secondary pollution.Therefore,geopolymer foams with interconnected pore structures will be favorable in the absorption process.One important purpose of zeolite is used as adsorbents in the application of adsorption,separation and purification.In industry application,zeolites are usually shaped by binding zeolite powders with various agents.Those binding materials will block zeolite channels,cover active centers,occur side effects and decrease its adsorption properties.Hierarchically structured zeolite prepared without adding any binders will solve those problems.The liquid materials can be transported in the hierarchically structure.Movever,compared with traditional prepared zeolite granules,hierarchically structure zeolite has lowever pressure drop in industry application.Geopolymers are prepared in a similar way as zeolites.They are regarded as zeolite precursor because they are alike in atomic level.Geopolymers are prepared in a low water content system.They can not grow into a well crystallized structure due to the lack of proper situations.In this research,open cell geopolymer is manufactured.On this basis,hierarchically structured zeolite is prepared through adjusting the composition of the geopolymers and the reaction condition.The hierarchically structured zeolite has the micropores from zeolite and the macropores from the open cell geopolymers.In the thesis,we aim to prepare open cell geopolymer and hierarchically structured zeolite using fly ash and metakaolin.Besides,we also investigate and evaluate their efficiencies as sorbents for heavy metal removal from water.Two methods were used in this thesis to manufacture the open cell geopolymer and hierarchically structured zeolite.In the first method,fly ash was used as raw material,and open cell geopolymer was successfully prepared by adding blowing agents and surfactant.On this basis,by changing the components of the geopolymer paste,hierarchically structured zeolite was successfully prepared from the solvent free method.Zeolite prepared in this way can make full use of the industry waste-fly ash and avoid alkline pollution.In the second method,metakaolin was used as raw material.Open cell geopolymer and hierarchically structured zeolite were manufactured using solid template method.PMMA was used as pore forming material and it can be removed by calcination.The efficiencies of open cell geopolymer and hierarchically structured zeolite prepared through two different methods as sorbents for heavy metal removal from water were evaluated.The innovations of this paper are shown as follow:?1?Floatable and highly permeable fly ash-based geopolymer block with 79.52%open porosity,81.59%total porosity and 67.62 m²/g BET surface area was successfully prepared through one-step method.?2?By adjusting the composition of geopolymer pastes,fly ash-based hierarchically structured zeolite with 56.64%open porosity,62.90%total porosity and 41.67 m²/g BET surface area was successfully prepared through one-step solvent free method.?3?Open cell geopolymer membrane and hierarchically structured zeolite membrane was successfully prepared through solid template method.The main research results of this paper are listed as below:?1?For the open cell gepolymer and hierarchically structured zeolite prepared from fly ash.?1?Open cell geopolymer products can be successfully prepared by adding blowing agent,surfactant into geopolymer paste.H₂O₂ solution?0.5⁴.5 wt%?and Al powder?0.02-0.11 wt%?can be used as efficient foaming agents.5-7 wt%is the the optium oleic acid additive amount.H₂O₂ can be used to produce open cell foams with more evenly distributed pores than the one produced with Al powder.Geopolymer foams produced using hydrogen peroxide and Al powder were cured for 10 h and 36 h,respectively.The permeable geopolymer blocks prepared by adding 4.5 wt%H₂O₂ solution,cured at 80?for 10h are floatable in water.Through the FTIR analyses,it is assumed that part of oleate molecules have coated on the foamed geopolymer.The oleate molecules play a role as hydrophobic modifier,and the hydrophobic modification results in the open cell geopolymer block float in water.?2?Foaming agents,surfactants,activator have significant effect on the formation of open cell geopolymer.The average cell size and open pore size increased with the increasing amount of H₂O₂ and Al powder.Liquid oleic acid is more suitable for the formation of interconnected cell structures.By increasing the surfactant content?2-11 wt%?,the cell size of the pores does not show significant difference,and their density and porosity are close.The lower the modulus of the activator,the poorer workability of the geopolymer paste.And the poor workability will hinder the expansion of wet bubbles.Higher modulus activator with excellent workability facilitate the formation of interconnecting structures.The cell sizes of K-based geopolymer foams are larger than the Na-based geopolymer foams,while the compressive strength is lower,and porosity are higher.Two factors should be considered to explain the formation of zeolite phases.?1?The curing time sand the SiO₂/Al₂O₃ ratio,Na₂O/SiO₂ and H₂O/Na₂O ratio.Change the SiO₂/Al₂O₃ ratio of the geopolymer paste.?3?The optimum conditions for synthesizing the well crystallized hierarchically structured faujasite foams are as follows:the addition amount for oleic acid and Al powder with respect to the weight of CFA is 2-7.0 wt%and 0.05 wt%,respectively.The optimum curing temperature is 70°C and the optimum molar ratio of H₂O/Na₂O is 10.?4?The results show that the adsorption efficiency follows the order hierarchically structured faujasite>open cell geopolymer>fly ash.It takes much longer time?240 min?for the raw ash to reach the adsorption equilibrium,while the faujasite and geopolymer sample reach the adsorption equilibrium after 150 min.The Pb²⁺adsorption capacity of fly ash is only 49.8 mg/g,while after geopolymerisation and crystalisation,the Pb²⁺adsorption capacity increase to 137.66mg/g and 114.25 mg/g,respectively.?5?For the raw ash sample,the experimental data fit to the pseudo-first-order model better than the other three model.For the geopolymer and faujasite sample,the experimental data fit the pseudo-second-order model much better than the rest.The adsorption of Pb²⁺on geopolymer and faujasite sample is a chemisorption process while the adsorption of Pb²⁺on fly ash is nearly physisorption process.The adsorption equilibrium data of fly ash,geopolymer and faujasite fit the Langmuir model better than the Freundlich model and Tempkin model.?2?For the open cell gepolymer and hierarchically structured zeolite prepared from metakaolin.?1?Open cell geopolymer films can be fabracted after calcination using PMMA as the template.Hierarchically structured faujasite films can be produced from the geopolymer films through in-situ hydrothermal method.The mole ratio of H₂O/SiO₂,SiO₂/Al₂O₃,H₂O/Na₂O and the content of PMMA,and the calcination temperature have played essential roles in the formation of open cell geopolymer films.The optimal condition for the synthesis of open cell geopolymer films were SiO₂/Al₂O₃=3,Na₂O/SiO₂=0.4,H₂O/Na₂O=12.5,with 60%PMMA and calcine at 600?.The hydrothermal transformation was conducted in 2 mol/L NaOH solution and cured at 80?for 24h.?2?H₂O/SiO₂,SiO₂/Al₂O₃,H₂O/Na₂O mole ratio,PMMA content and calcination temperature have significant effect on the formation of open cell geopolymer.It is not suitable to prepare open cell geopolymer under lowever H₂O/SiO₂ ratios,high concentration of alkali,lower PMMA content and lower calcination temperature conditions.The geopolymer paste has poor workability under lower H₂O/SiO₂ ratios,the PMMA can not be mixed well in that situation.In the high strength geopolymer martrix and lower,PMMA can not be easily removed.?3?The results show that the adsorption efficiency follows the order hierarchically structured faujasite>open cell geopolymer.For the geopolymer and faujasite sample,the experimental data fit the pseudo-second-order model much better than the rest.It takes 240 min for the faujasite and geopolymer to reach the adsorption equilibrium.The Cu²⁺adsorption capacity of faujasite and geopolymer are 36.63 mg/g and 24.25 mg/g,respectively.The values of?G°and H°suggest that the adsorption of Cu²⁺on geopolymer and faujasite is spontaneously endothermic process.