制备方法对锆改性沸石吸附水中磷酸盐的影响

Effect of preparation methods on phosphate adsorption onto zirconium-modified zeolites

采用浸渍法和沉淀法制备了2种锆改性沸石,即浸渍法ZrMZ(I-ZrMZ)和沉淀法ZrMZ(P-ZrMZ),对比分析了这2种不同类型锆改性沸石对水中磷酸盐的吸附特征,进而探讨了制备方法对锆改性沸石吸附水中磷酸盐的影响。结果表明,浸渍法和沉淀法所制备的锆改性沸石对水中磷酸盐的吸附动力学全过程最适合采用Elovich动力学模型加以描述,其次为准二级动力模型,再次为准一级动力学模型。缓慢反应阶段这2种锆改性沸石吸附水中磷酸盐的速率限制步骤为膜扩散和颗粒内扩散。Langmuir、Freundlich和Dubinin-Kaganer-Radushkevic(DKR)模型均可用于描述浸渍法和沉淀法所制备的锆改性沸石对水中磷酸盐的吸附等温数据,且Langmuir模型最优。碱性条件下沉淀法和浸渍法所制备的锆改性沸石对水中磷酸盐的吸附能力劣于酸性和中性条件下。溶液共存的Ca^(2+)和Mg^(2+)会促进浸渍法制备锆改性沸石对水中磷酸盐的吸附,而溶液共存的Cl^(-)、HCO^(-)和SO_(4)^(2-)会抑制浸渍法制备锆改性沸石对水中磷酸盐的吸附。溶液共存的Na^(+)、K^(+)、Ca和Mg会促进沉淀法所制备的锆改性沸石对水中磷酸盐的吸附去除,促进作用从大到小排序为Ca^(2+)、Mg、K^(+)、Na^(+)。沉淀法制备的锆改性沸石对水中磷酸盐的吸附能力强于浸渍法制备的锆改性沸石,但浸渍法锆改性沸石中单位质量ZrO_(2)对水中磷酸盐的吸附容量高于沉淀法。从磷酸盐吸附容量角度看,沉淀法制备的锆改性沸石是一种更有希望的除磷吸附剂。但从性价比和制备便利性角度看,浸渍法制备的锆改性沸石则是一种更有希望的除磷吸附剂。

The main objective of this work is to determine the effect of the preparation methods on phosphate adsorption onto zirconium-modified zeolites.To achieve this aim,two types of zirconium-based zeolites(ZrMZs)were first synthesized,including ZrMZ prepared by the impregnation method(I-ZrMZ)and ZrMZ prepared by the precipitation method(P-ZrMZ),and then the adsorption characteristics of phosphate from aqueous solution on I-ZrMZ and P-ZrMZ were comparatively investigated.It was shown that the Elovich kinetic model was most suitable for describing the kinetic data of phosphate on I-ZrMZ and P-ZrMZ,and both film diffusion and intra-particle diffusion were the rate-limiting steps during the gradual adsorption process after initial rapid surface adsorption.The equilibrium isotherm data were well fitted by the Langmuir,Freundlich,and Dubinin-Kaganer-Radushkevic(DKR)isotherm models.The adsorption of phosphate on I-ZrMZ and P-ZrMZ was more favorable under acidic and neutral conditions than that under alkaline conditions.The presence of Ca^(2+)and Mg^(2+)significantly improved the uptake of phosphate by I-ZrMZ,but the presence of Cl^(-),HCO_(3)^(-)and SO_(4)^(2-)inhibited the uptake of phosphate by I-ZrMZ.Coexisting Na^(+),K^(+),Ca^(2+) and Mg^(2+)greatly enhanced the adsorption of phosphate on P-ZrMZ,and the enhancing effect decreased in the order of Ca^(2+)>Mg^(2+)>K^(+)>Na^(+).The zirconium-modified zeolite prepared by the precipitation method exhibited higher phosphate adsorption capacity than that prepared by the impregnation method.The phosphate adsorption capacity for ZrO_(2)in I-ZrMZ was larger than that for ZrO_(2)in P-ZrMZ.From the point of view of the phosphate adsorption capacity,the zirconium-modified zeolite prepared by the precipitation method is a more promising adsorbent for the removal of phosphate from an aqueous solution.From the point of view of both price/performance ratio and preparation convenience,the zirconium-modified zeolite prepared by the impregnation method is a more promising adsorbent for the elimination of phosphate from aqueous solution.