粉煤灰提铝中间产物合成4A分子筛对氨氮的吸附行为研究

采用粉煤灰提铝中间产物合成4A分子筛,利用XRD、SEM、热重分析、化学成分分析、阳离子交换容量对4A分子筛进行表征.考察吸附时间、pH、分子筛投加量、氨氮初始浓度、共存阳离子对其吸附性能的影响,研究其对模拟废水中氨氮的吸附效果,并结合准二级动力学方程、吸附等温线研究吸附性能和机理.结果表明,初始浓度为50 mg·L~(-1)、4A分子筛投加量为5 g·L~(-1)、pH值为6~9、吸附时间为80 min时氨氮去除率可达71.34%;随着氨氮初始浓度升高,其去除率降低,吸附容量增加;共存阳离子Na~+、K~+、Ca~(2+)对NH_4~+有强烈的竞争吸附,Mg~(2+)无明显竞争作用.吸附过程符合准二级动力学方程和Freundlich模型.Langmuir吸附等温线显示最大吸附容量为20 mg·g~(-1).

Adsorption of ammonium with 4A zeolite synthesized by using byproducts duringalumina extraction from fly ash

4A zeolite was synthesized by using waste residues which are generated as intermediate products during the alumina extraction process using fly ash. It was characterized by using XRD and SEM. Its thermogravimetric analysis, chemical composition analysis and cation exchange capacity were also tested. The effects of shaking time, initial pH, adsorbent dosage, initial ammonium ion concentration, and competitive cations were investigated by batch experiments. To understand the exchange process of ammonium by the synthesized zeolite, the adsorption process was described with Ho''s pseudo-secondorder kinetic model. Three models including Langmuir, Freundlich and Henry isotherm equilibrium were also used to fit the data in this sutdy. The results show that ammonium removal efficiency was found to be 71.34% with optimal reaction conditions:initial ammonium concentration 50 mg·L^-1, 4A zeolite dosage 5 g·L^-1, pH 6~9, shaking time 80 min, respectively. As the initial concentration of ammonia increased, the removal efficiency of ammonium decreased and the adsorption capacity of 4A zeolite increased. Coexistence cations such as Na⁺, K⁺ and Ca²⁺ obviously affected the adsorption of ammonium, but Mg²⁺ had little effect. The adsorption process followed the quasi second order kinetic equation and Freundlich model. The maximum adsorption capacity was 20 mg·g^-1 according to langmuir adsorption isotherm.