粉煤灰湿式化学法合成沸石及其对重金属的吸附脱除研究

Study on zeolite synthesis from coal fly ash by wet milling method and adsorption of heavy metals

针对粉煤灰固废的处理/处置问题,采用湿式化学的方法将其合成沸石,探索粉煤灰的资源化高值利用方式。通过设计四因素、三水平的正交合成试验,结合阳离子交换容量的评价,确定湿式化学方法下粉煤灰合成沸石的最佳工况。为了检验合成的沸石对阳离子重金属的吸附脱除效果,进行9种正交工况下合成的沸石对重金属Pb(Ⅱ)的吸附脱除试验,同时研究了合成的沸石对阴离子基团的吸附脱除。采用湿式化学法,粉煤灰合成沸石的最优工况为:NaOH浓度4 mol/L、液固比4 mL/g、研磨时间24 h、转速350 r/min,对沸石合成效果影响较大的因素是研磨时间,其次是液固比、碱液浓度,行星球磨机的转速影响最小。该试验条件下合成的沸石对重金属Pb的吸附脱除结果表明,不同正交工况合成的沸石对Pb(Ⅱ)的吸附以物理吸附为主,其脱除率均达70%以上,最高可达92.5%,主要依赖于合成沸石的阳离子交换容量;对重金属Cr的吸附脱除结果表明,不同正交工况合成的沸石对Cr(Ⅵ)的吸附既有物理吸附也有化学吸附,对Cr(Ⅵ)的吸附脱除率最高可达35.7%,说明湿式化学法合成的沸石对重金属阳离子和阴离子基团均有一定的吸附脱除效果。

In view of the treatment/disposal problem of coal fly ash,which is a solid waste with large output,wet milling method to synthesize zeolite was used to explore the high value utilization of fly ash as resource.Through the design of four factors,three levels orthogonal synthesis experiments,combined with the evaluation of cation exchange capacity,the best condition of synthesis of zeolite from fly ash under wet milling method was determined.In order to test the adsorption and removal effect of cation heavy metals of the zeolite synthesized by this method,the adsorption and removal of heavy metal Pb(Ⅱ)under nine orthogonal conditions were carried out,and the adsorption and removal of anionic groups with less attention under the orthogonal conditions were also studied.According to the average value and range of cation exchange capacity of different factors under different orthogonal conditions,the optimal combination to synthesize zeolite is NaOH concentration of 4 mol/L,liquid-solid ratio of 4 mL/g,grinding time of 24 h and rotating speed of 350 r/min.The range of cation exchange capacity demonstrates that the most important factor for zeolite synthesis is grinding time,followed by liquid-solid ratio and alkali concentration,and the speed of planetary ball mill has the least influence.The results of adsorption and removal of Pb(Ⅱ)by zeolite synthesized under the experimental conditions show that the adsorption of Pb(Ⅱ)is mainly physical adsorption,and the removal rate is more than 70%,up to 92.5%,which mainly depends on the cation exchange capacity of synthetic zeolite.The results of adsorption and removal of heavy metal Cr on the zeolite synthesized under the experimental conditions show that the adsorption and removal of heavy metal Cr is both physical and chemical adsorption.The adsorption and removal rate of Cr(Ⅵ)on the synthesized zeolites is up to 35.7%.The zeolite synthesized by wet milling method has certain adsorption and removal effect on heavy metal cations and anions.