Preparation Of Circulating Fluidized Bed Fly Ash Base Polymer And Its Adsorption Properties For Pb²⁺

As a new green environmental protection cementitious material,geopolymer has suitable structure and excelent properties of both inorganic mineral and high-molecular polymer.It’s applied to heavy metal ions treatment without seconday pollution,which gradully became a hotspot for both international and domestic researchers.Circulating fluidized bed fly ash（CFB fly ash）,a new solid waste,produced by circulating fluidized bed with coal gangue-burning and desulfurization.The output of CFB fly ash increases sharply with the wide application of clean combustion technology represented by circulating fluidized bed combustion technology,and a large amount of storage is bound to cause many environmental problems.From the perspective of chemical composition and mineral composition,CFB fly ash is good precursor for synthesizing geopolymer with low cost and broad sources.However,the low pozzolanic activity limited its application in geopolymer.Besides,research on heavy metal ions-removal by geopolymer mainly focuses on"solidification",which by adding heavy metal ions during the preparation of geopolymer.However,there are relatively few studies on the adsorption and its mechanism of heavy metal ions in wastewater.In this paper,starting from low pozzolanic activity of CFB flysh,the effect of different sodium silicate modulus,alkali activator dosage,water cement ratio and curing temperature on strength of geopolymer were explored.At the same time,the releation between microstructure and strengh of geopolymer was detected with XRD and SEM.Then the effect of aboved factors on adsorption performance of Pb²⁺by geopolymer was conducted.Subsquently,the effects of adsorption conditions,such as the dosage of geopolymer,p H value of solution,adsorption time,adsorption temperature and initial Pb²⁺concentration,on the adsorption performance were investigated.The adsorption kinetics,adsorption thermodynamics and adsorption isotherm models of Pb2+adsorbtion by CFB ash base polymers were obtained.The adsorption mechanism was preliminarily described.The main results of the study are as follows:（1）The geopolymer was prepared from CFB fly ash with sodium hydroxide and sodium silicate as composite activators.The effects of different sodium silicate modulus,alkali activator dosage,water cement ratio and curing temperature on the compressive strength and adsorption performace of geopolymer were investigated by single factor experiment.The optimum preparation condition is as follows:the modulus of sodium silicate is1.2,the dosage of alkali activator is30%,the water cement ratio is 0.55,and the curing temperature is60℃.Under these conditions,the 28 day compressive strength of geopolymer is 48.6MPa;when p H=5,temperature is 25℃,geopolymer dosage is 0.5g/L,initial concentration of lead ion is 50mg/L and volume is 100 m L,the removal rate of Pb2+from CFB fly ash geopolymer is 92.6%.（2）Pb²⁺adsorbtion by CFB fly ash base polymer was studied by static adsorption method.The experimental results show that the removal rate of Pb²⁺by geopolymer yields increased with an increase in the dose of geopolymer.And the increase in the removal efficiency was not so significant up to 0.5g/L of adsorbent dose,which the removal rate of Pb²⁺is 92.01%.The p H value has a great influence on the adsorption of Pb²⁺by CFB fly ash base polymer,and the greater the p H value is,the better the removal effect is.In this experiment,the maximum adsorption capacity of Pb²⁺is 93.72 mg/g at p H=5.（3）The experiment results of the adsorption data fit well with the pseudo-second order kinetic model,indicating that the adsorption process was mainly chemical adsorption.The adsorption of Pb²⁺by CFB fly ash geopolymer is more consistent with Langmuir isotherm model,which indicates that the adsorption process is dominated by monolayer adsorption.Langmuir and Freundlich isotherm models indicate that the adsorption of Pb²⁺by geopolymer is preferential.Thermodynamic study shows that the adsorption of geopolymer on Pb²⁺is a spontaneous endothermic process,and the removal rate of Pb²⁺by geopolymer from CFB fly ash reaches 98.44% at 55℃.