天然沸石结构对合成分子筛吸附脱氮性能影响

针对污水厂尾水深度脱氨问题，从国内几个典型的天然沸石矿床中选取了4种天然沸石（记为A、B、C、D），运用直接碱溶-水热晶化合成工艺制备分子筛，测定了各自的氨氮吸附性能；并采用XRF、XRD等表征方法，对比分析了4种天然沸石在元素组成及矿物含量方面的差异，结合4种合成产物的晶体结构、元素组成、表面形貌分析结果，探讨了天然沸石材料特性对合成产物吸附性能的影响.结果表明：与沸石原料相比，4种合成产物的氨氮吸附性能均得到明显提升，其中C和A沸石合成产物的氨氮吸附量较高，均达到15mg/g以上；合成产物的氨氮吸附性能与沸石原料的碱溶性硅溶出量有正相关关系；碱溶性硅主要来自于天然沸石原料中的方石英、斜发沸石、丝光沸石、透长石等矿物组分，而结构稳定的石英不易被碱溶活化利用.合成产物为含有不同类型分子筛及其它矿物成分的混合物，碱溶性硅溶出量高的C和A沸石均合成了A型、X型分子筛，氨氮吸附性能较好；而B和D沸石合成产物主要为孔径小于铵根离子粒径的方钠石分子筛，其氨氮吸附性能较差.因此，利用天然沸石合成分子筛用于污水脱氨时，应尽量选择石英矿物含量少、碱溶性矿物占比高的沸石原料.

Influence of natural zeolite structure on the adsorption and denitrification performance of synthetic molecular sieve

In response to the problem of deep denitrification of sewage plant effluent, four types of natural zeolites (denoted as A, B, C, D) selected from several typical domestic natural zeolite deposits, were used to produce molecular sieves through a direct alkali dissolution-hydrothermal crystallization synthesis process. Their respective ammonia nitrogen adsorption properties were investigated. Using XRF, XRD and other material characterization methods, the differences in element composition and mineral content of the four natural zeolites were compared and analyzed. The influence of material characteristics of natural zeolites on the adsorption performance of their synthetic products was examined based on the crystal structure, elemental composition and surface morphology of the synthetic products. The results illustrated that compared with raw zeolite materials, the ammonia nitrogen adsorption performance of the four synthetic products was significantly improved, among which the synthetic products from zeolite C and A had relatively higher adsorption capacity, all reaching more than 15mg/g. A positive correlation existed between the synthetic product’s adsorption performance and its raw zeolite material’s alkali-soluble silicon dissolution amount. The alkali-soluble silicon mainly came from the cristobalite, clinoptilolite, mordenite, feldspar and other mineral components in the natural zeolite raw material, while the quartz with stable structure was not easy to be activated and utilized by alkali dissolution. The synthetic product was a mixture containing different types of molecular sieves and other mineral components. Zeolites C and A with high amount of alkali-soluble silica were synthesized into type A and type X molecular sieves which had good ammonia nitrogen adsorption performance. The synthetic products of zeolites B and D were mainly sodalite molecular sieves with pore diameter smaller than the particle size of ammonium ion, and thus they had poor adsorption performance. Therefore, it is better to select raw zeolite materials with less quartz mineral content and high proportion of alkali-soluble minerals to produce synthetic molecular sieves for sewage denitrification.