改性凹凸棒土制备4A分子筛及其吸附严寒村镇高氨氮水源水性能

Preparation of 4A Molecular Sieve by Modified Attapulgite and Its Adsorption Properties on Source Water Containing High Ammonia Nitrogen in Cold Village and Town

以江苏盱眙凹凸棒原土为原料,采用静水沉降-离心分离法对其提纯,探索提纯土中降低铁含量、提供最大硅源的改性方式,采用碱溶-水热晶化工艺,调整n（Na2O）∶n（SiO2）∶n（Al2O3）∶n（H2O）的配比、晶化温度、晶化时间的因素参数,以X-ray diffraction（XRD）表征、结晶度、产出率与NH4^＋离子交换容量为指标分析4A分子筛的制备条件;考察其吸附NH4^＋性能.结果表明,PA基于3mol/L HCl酸浸除铁-800℃煅烧活化-5mol/L Na OH碱溶处理,滤液添加铝源后水热晶化可合成高结晶度-产出率的4A分子筛ACAPA-4AMS,当n（Na2O）∶n（SiO2）=2.1,n（H2O）∶n（Na2O）=60,n（SiO2）∶n（Al2O3）=1.5,在90℃晶化8h时,NH4^＋交换容量最高,为159mmol/100g,符合工业标准.5℃ACAPA-4AMS饱和吸附量68.04mg/g,吸附符合Freundlich方程且为吸热过程,但温度对低浓度（5mg/L）NH4^＋-N的去除率影响不大.该研究为凹凸棒土在严寒村镇高氨氮水源水的应用提供理论基础.

Original attapulgite from Xuyi in Jiangsu was selected as raw material,it was purified by hydrostatic settlement and centrifugal separation method. The modification ways reducing iron content and providing maximum silicon source for purified attapulgite were explored. Based on alkali extraction and hydrothermal crystallization process,the parameters including ratio of n（ Na2O） ∶ n（ SiO2） ∶ n（ Al2O3） ∶ n（ H2O）,crystallization temperature and time were adjusted.Considering XRD characterization,crystallization degree,output rate and NH4^＋ ion exchange capacity as the indexes,the conditions for 4 A molecular sieve preparation were analyzed. NH4^＋ adsorption properties of 4 A molecular sieve were studied. The results showed that,PA was treated by a series of processes,including iron removal by 3 mol/L HCl acid-leaching,calcined activation at 800℃,alkali extraction by 5 mol/L Na OH solution,respectively. Subsequently,the aluminum source was added into the filtrate of alkali solution,high-purity 4 A molecular sieve named as ACAPA-4 AMS was synthesized by hydrothermal crystallization method. Under the following conditions： the molar ratio of Na2O/SiO2,H2O/Na2O and SiO2/Al2O3 was 2. 1,60,1. 5,respectively,meanwhile,crystallization temperature and time were 90℃,8 h,respectively.NH4^＋ exchange capacity reached the highest of 159 mmol/100 g,which conforming to industrial standard. The maximum adsorption capacity of NH4^＋ at 5℃ was 68. 04 mg/g. The NH4^＋ adsorption process onto ACAPA-4 AMS was in accordance with Freundlich isotherm and endothermic process,but temperature has little effect on the removal rate of NH4^＋ at low concentration（ 5 mg/L）. The study provided a theoretical basis for attapulgite application in source water including high ammonia nitrogen in cold village and town.