Design,Preparation And Adsorption Properties Of Porous Geopolymer Materials

In recent years,with the rise of clean coal combustion technology in a circulating fluidized bed（CFB）,the massive emission of its product,circulating fluidized bed（CFB）fly ash,has also caused serious environmental pollution.The characters of CFB fly ash is different from OP fly ash（from ordinary pulverized coal boiler）in many aspects,such as high water demand,self hardening,and late expansion,which seriously restricts the widespread application of existing comprehensive utilization technology of fly ash.The massive discharge of Pb²⁺,Cd²⁺and NH₄⁺-N has led to serious pollution of the water body.CFB fly ash is rich in silicon and aluminum elements and has high amorphous content,rough particle surfaceand loose structure,which can provide raw materials for the preparation of porous geopolymer materials.With high adsorption activity,CFB based porous geopolymer materials for adsorbing Pb²⁺,Cd²⁺and NH₄⁺-N in waste water can achieve the sustainable development goal of"treating waste with waste".In this paper,CFB fly ash based porous geopolymer materials were prepared using CFB fly ash as raw material by adding an appropriate amount of alkali activator,foaming agent,and foam stabilizer.Combined with optical microscopy,FT-IR,XRD,BET,and other analytical tests,the effects of water glass modulus,water cement ratio,activator content,curing temperature,H₂O₂addition,type and amount of foam stabilizer on the compressive strength and pore structure of porous geopolymer materials were studied to obtain the optimal process conditions for CFB fly ash based porous geopolymer materials.And under the optimal preparation process conditions,by adding plant protein or animal protein to interfere with the foaming property of H₂O₂foaming agent,a porous geopolymer material is prepared.The effects of protein type and content on the rheological properties of porous geopolymer paste and the stability of foam were studied;Combined with optical microscopy,BET,rheometer,Zeta potential,and other analysis tests,the effect of protein intervention in H₂O₂foaming on the pore structure and mechanical properties of porous geopolymer materials was investigated.A porous geopolymer material with high porosity and uniform pore size distribution was obtained.Porous geopolymer materials were applied to the adsorption of Pb²⁺,Cd²⁺and NH₄⁺-N.The effects of solution p H,adsorption time,adsorbent dosage,and initial concentration of solution Pb²⁺,Cd²⁺and NH₄⁺-N on the adsorption efficiency of porous geopolymer materials were investigated,and the adsorption isotherms and kinetic model analysis were used to explore the adsorption laws of porous geopolymer materials on Pb²⁺,Cd²⁺and NH₄⁺-N;a dynamic adsorption system was constructed using porous geopolymer materials as fillers to comprehensively evaluate the adsorption laws of Pb²⁺,Cd²⁺and NH₄⁺-N.The main research conclusions was follows:（1）The compressive strength and pore structure of porous geopolymer materials prepared with sodium dodecylbenzene sulfonate as a foam stabilizer are better than those prepared with oleic acid and triethanolamine as foam stabilizers.Using sodium dodecyl-benzene sulfonate as a foam stabilizer with a content of 7 wt%,a water glass modulus of1.6,a water cement ratio of 0.65,a base activator content of 35%,and a H₂O₂content of 1wt%,the prepared porous geopolymer material exhibited good performance after being cured for 24 hours in a curing box at 80℃.After 28 days of curing in a room temperature curing box,the compressive strength reached 1.93 MPa,the apparent density was 363.44kg/m³,the porosity was 82.29%,and the S_BETwas 30.80 m²/g,V_tis 0.171 g/cm³,and the average mesoporous aperture is 15.29 nm.（2）By comparing the compressive strength and pore structure of the porous geopolymer material prepared after the intervention of plant protein and animal protein in H₂O₂foaming,it was found that when the content of plant protein was 20%,the porous geopolymer material had good compressive strength and pore structure,with a compressive strength of 1.40 MPa,a porosity of 91.94%,an apparent density of 346.02kg/m³,S_BETis 60.90 m²/g,an average pore diameter of 12.19 nm,and V_tis 0.265 cm³/g;By fitting the rheological curve of the porous geopolymer slurry with the rheological model,it was found that it conforms to the Herschel Bulkley model;Due to the intervention of proteins in the foaming performance of H₂O₂,the foaming performance and stability of the foaming agent are enhanced,and the hardened porous geopolymer material also has high compressive strength under high porosity conditions;（3）The optimal conditions for porous geopolymer materials to adsorb Pb²⁺,Cd²⁺,and NH₄⁺-N are as follows:the initial concentration of the solution is 180 mg/L,140 mg/L and 100 mg/L,the p H is 5.0,7.0 and 7.0,the dosage is 2.0 g/L,4.0 g/L and 3.0 g/L,the adsorption time is 150 min,the oscillation temperature is 25℃,and the frequency is 150rpm.At this time,the removal rates of Pb²⁺,Cd²⁺,and NH₄⁺-N by porous geopolymer materials can reach 90.13%,74.63%,and 48.63%,respectively,and the adsorption amounts are 81.12 mg/g,26.12 mg/g,4.86 mg/g.The adsorption of Pb²⁺,Cd²⁺by porous geopolymer materials is a single molecular layer homogeneous chemical adsorption reaction,which conforms to Langmuir and quasi second order kinetic models.The adsorption of NH₄⁺-N is mainly the physical adsorption of heterogeneous reactions in multiple molecular layers,which conforms to the Freundlich and quasi first order kinetic model.（4）The affinity order of adsorption of porous geopolymer materials in a multicomponent system of Pb²⁺,Cd²⁺,and NH₄⁺-N is Pb²⁺>Cd²⁺>NH₄⁺-N.In the dynamic adsorption experiment,the optimal inflow flow rate of the adsorption column is 5m L/min.With the increase of adsorption time,the removal rates of various pollutants gradually decreased.At 60 days,the removal rates of Pb²⁺,Cd²⁺and NH₄⁺-N decreased to73.12%、53.64%、41.51%.