四氧化三铁改性沸石改良底泥对水中磷酸盐的吸附作用

Adsorption of Phosphate from Aqueous Solutions on Sediments Amended with Magnetite-Modified Zeolite

研究了四氧化三铁(Fe_3O_4)改性沸石改良底泥对水中磷酸盐的吸附特征,并通过形态分级提取法研究了改良底泥中Fe_3O_4改性沸石吸附磷后的形态分布特征.结果表明,与准一级和准二级动力学模型相比,Elovich模型更适合用于描述未改良和改良底泥对水中磷酸盐的吸附动力学过程.未改良和改良底泥对水中磷酸盐的等温吸附实验数据可以采用Langmuir、Freundlich和Dubinin-Radushkevic模型进行描述.未改良和改良底泥对水中磷酸盐的吸附能力随着pH值的增加而下降,且水中共存的阳离子会促进底泥对磷酸盐的吸附,促进作用的大小排序为Ca^(2+)> Mg^(2+)> K^+,而水中共存的HCO_3^-会抑制底泥对磷酸盐的吸附.未改良和改良底泥吸附水中磷酸盐的机制包括静电吸引作用和配位体交换作用,而改良底泥中Fe_3O_4改性沸石则主要依靠配位体交换作用吸附去除水中的磷酸盐.改良底泥对水中磷酸盐的吸附能力明显优于未改良底泥,并且前者的磷释放风险低于后者.改良底泥中Fe_3O_4改性沸石吸附磷酸盐后将近49. 4%的磷会以潜在可移动态磷形式存在,需要及时采用外加磁场作用将Fe_3O_4改性沸石从底泥中移出,以消除Fe_3O_4改性沸石上磷发生再次释放的风险.以上的研究结果初步显示,Fe_3O_4改性沸石适合作为一种底泥改良剂用于河道内源磷释放的控制.

Understanding the characteristics of phosphate adsorption onto magnetite-modified zeolite（ MZ）-amended sediment is helpful for knowing the exchange behavior and process of phosphorus at the interface between the overlying water and MZ-amended sediment. Furthermore,it is helpful for the application of MZ as an amendment to control phosphorus release from sediment. To achieve this goal,the adsorption of phosphate on unamended and MZ-amended sediments was comparatively investigated using a series of batch experiments,and the fractionation of phosphorus in the phosphate-adsorbed MZ was studied using a sequential extraction process. The kinetic data of phosphate adsorption onto unamended and MZ-amended sediments were more suitably fitted to the Elovich model than to the pseudo-first-order and pseudo-second-order models. The equilibrium adsorption data of phosphate adsorption onto the unamended and MZ-amended sediments were well described by the Langmuir,Freundlich,and Dubinin-Radushkevic isotherm model.The phosphate adsorption performance of the unamended and MZ-amended sediments decreased with increasing solution pH from 4 to11. The presence of cations,such as K^＋,Mg^2＋,and Ca^2＋,enhanced the adsorption of phosphate on the unamended and MZamended sediments,and the promoting effect decreased in the order of Ca^2＋ Mg^2＋ K^＋,whereas the presence of HCO3^- inhibited the adsorption of phosphate. The mechanisms for phosphate adsorption onto the unamended and MZ-amended sediments involved electrostatic attraction and ligand exchange,while the mechanism for the adsorption of phosphate on MZ in the amended sediment involved ligand exchange. The sequential extraction analysis of phosphate-adsorbed MZ showed that 49. 4% of phosphorus in MZ existed in the mobile form（ NH4 Cl^-P,BD-P,and Na OH-nrP）,which could be easily released from MZ. Therefore,the used MZ should be recovered from sediment using external magnetic fields after its application. The results of this study indicated that MZ is a promising sediment amendment for the control of internal loading in rivers.