氢氧化镧改良沉积物对水中磷的吸附特征

Adsorption characteristics of phosphate in water on lanthanum hydroxide-amended sediments

考察了氢氧化镧改良沉积物对水中磷酸盐的吸附特征,并考察了被改良沉积物所吸附磷酸盐的形态分布特征.结果发现,氢氧化镧改良沉积物对水中低浓度磷酸盐的吸附可以采用线性模型进行描述,而对高浓度磷酸盐的吸附则适合采用Langmuir模型进行描述.准二级动力学比准一级动力学模型更适合用于拟合改良沉积物对水中磷酸盐的吸附动力学过程,膜扩散和颗粒内扩散共同控制了缓慢吸附阶段的速率.强碱性条件不利于改良沉积物对水中磷酸盐的吸附.溶液共存的Cl^-、SO_4^(2-)、HCO^3^-、Na^+、K^+和Mg^(2+)对改良沉积物吸附水中磷酸盐的影响较小,而溶液共存的Ca^(2+)会促进改良沉积物对水中磷酸盐的吸附.改良沉积物对水中磷酸盐的吸附能力明显强于未改良沉积物.改良沉积物的最大磷酸盐单位吸附量明显高于未改良沉积物,并且改良沉积物的最大单位吸附量随着氢氧化镧添加量的增加而增加.改良沉积物的初始吸附速率随着氢氧化镧添加量的增加也随之增加.改良沉积物的磷吸附-解吸平衡浓度(EPC0)明显低于未改良沉积物.被改良沉积物所吸附的磷酸盐中大部分(84%)以较为稳定的NaOH-rP和HCl-P形态存在,仅仅只有16%左右会以容易释放的NH_4Cl-P和BD-P形态存在.以上结果显示,添加氢氧化镧不仅可以增强沉积物对水中磷酸盐的吸附能力,而且可以降低沉积物中磷的释放风险,氢氧化镧是一种有希望的可以用于沉积物内源磷释放的改良剂.

The objectives of the present study were to investigate the characteristics of phosphate adsorption on the La（ OH）3-amended sediment as well as the fractionation of phosphorus in the La（OH）3-amended sediments before and after the phosphate adsorption. The results showed that phosphate adsorption onto the La（OH）3-amended sediment at low initial phosphate concentrations could be described by the linear model,while those at high initial phosphate concentrations could be described by the Langmuir isotherm model. Compared to the pseudo-first-order model,the pseudo-second-order model fitted better to the kinetic data of phosphate adsorption on the unamended and La（ OH）3-amended sediments,and the rate-limiting step during the gradual adsorption stage was both film and intra-particle diffusion. Strongly alkaline condition was unfavorable for phosphate adsorption onto the La（ OH）3-amended sediments. The presence of Cl-,SO4（2-）,HCO3-,Na＋,K＋ and Mg（2＋） in aqueous solutions had negligible influence on the adsorption of phosphate on the La（ OH）3-amended sediments,while coexisting Ca（2＋） enhanced the phosphate adsorption. Under the experimental condition,the La（ OH）3-amended sediment exhibited stronger affinity towards phosphate than the unamended sediment. The maximum phosphorus adsorption capacity for the La（ OH）3-amended sediment was significantly higher than that for the unamended sediment,and it also increased with increasing amount of La（ OH）3 in the amended sediment. The adsorption rate of phosphate also increased with increasing amount of La（ OH）3 in the amended sediment. Most of phosphate adsorbed by La（ OH）3-amended sediment existed in the form of NaOH-rP and HCl-P,and only a very small amount of phosphorus existed in the form of NH4Cl-P and BD-P. Results of this work indicate that the addition of La（ OH）3 significantly enhanced the phosphate adsorption capacity on river sediment,and it may also greatly reduce the releasing of phosphorus from river sediment. Therefore,La（ OH）3 has the potential to be applied as a sediment amendment for the control of internal loading in river sediment.