摘要:土壤中流失的磷进入水体容易引起富营养化污染。目前对于铁矿物胶体结合态磷在土壤孔隙介质中的稳定性和迁移能力的认识还存在不足。本研究采用吸附试验，考察水铁矿对磷的吸附特征以及pH、离子强度和胡敏酸对磷在液相、水铁矿胶体和水铁矿固体上分布的影响；通过DLVO理论，预测水铁矿胶体结合态磷的稳定性和迁移能力。结果表明，假二级动力学模型（R2=0.964）更适合用于描述磷在水铁矿上的吸附过程，磷在水铁矿上的吸附受液膜扩散、内部扩散和化学吸附等过程控制。Freundlich模型（R2=0.970）对等温吸附的拟合效果好，说明水铁矿对磷的吸附为多层吸附过程。从Langmuir模型参数可知，水铁矿对磷的最大理论吸附量为22.55 mg?g-1。水铁矿对磷的吸附能力随pH的升高而降低，随离子强度的升高而升高。然而，低离子强度和高pH有利于反应体系中水铁矿胶体的释放。无论胡敏酸是否存在，在碱性且离子强度不高（1~10 mmol?L-1）的条件下，有约5%~20%的磷会与水铁矿胶体结合，且这些磷-水铁矿胶体之间的静电斥力较大。根据DLVO理论计算可知，这些带负电荷的胶体之间稳定性较好，在土壤中有一定迁移能力。在实际农业活动中，磷肥的过量施用可能会使大量的磷酸根离子吸附在铁矿物上，促进土壤孔隙水中形成稳定的、带负电的铁矿物胶体，这种磷-铁矿物复合胶体的迁移很可能成为磷迁移的另一种形式。本研究结果可为胶体促进下磷淋失风险评估提供理论和数据支撑。
关键词:土壤磷/
水铁矿/
吸附/
胶体态磷/
DLVO
Abstract:Losing soil phosphorus to aquatic environments often causes eutrophication; however, the stability and transport of colloidal phosphorus, especially amorphous iron colloid-bound phosphorus in porous soil, is poorly understood. In this study, adsorption experiments were conducted to investigate phosphorus adsorption onto ferrihydrite. The effects of pH, ionic strength, and humic acid (HA) on the dissolved phosphorus distribution and colloidal and solid ferrihydrite adsorbed phosphorus were explored. Ferrihydrite colloid-bound phosphorus stability was calculated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to predict the transport of colloidal complexes. The results showed that the pseudo-second-order kinetic model (R2 = 0.964) best described the phosphorus onto ferrihydrite adsorption process. Adsorption was controlled by liquid film diffusion as well as internal diffusion, and chemisorption. The Freundlich model (R2 = 0.970) was a better fit for isothermal adsorption than the Langmuir model (R2 = 0.842), indicating that phosphorus onto ferrihydrite adsorption was multi-layer; however, the parameters of Langmuir model revealed that the maximum theoretical phosphorus onto ferrihydrite adsorption capacity was 22.55 mg?g-1. Phosphorus adsorption onto ferrihydrite decreased with increasing pH and decreasing ionic strength; low ionic strength and high pH were considered beneficial for releasing ferrihydrite colloids. Approximately 5%–20% phosphorus bound to ferrihydrite colloids in alkaline and low ionic strength conditions (1–10 mmol?L-1) regardless of HA, and the electrostatic repulsion between ferrihydrite-phosphorus colloids was notably. According to the DLVO theory, the colloids were stable and easily transported in the soil pores due to their negative surface charge. Negatively charged ferrihydrite colloids can transport long distances in negatively charged water-bearing media, such as soil or aquifer. In agricultural activities, excessive phosphate fertilizer application may cause large amounts of phosphate ion loading onto iron minerals and promote the formation of stable, negatively charged iron mineral colloids. Ferrihydrite-phosphorus colloid transport is likely to become another form of phosphorus leaching. Thus, this study investigated ferrihydrite-phosphorus colloid generation and stability in variable pH, ionic strength, and HA conditions, qualitatively predicted their transport, and assessed colloid-facilitated phosphorus loss risk. However, in complex soil systems, chelation and precipitation of co-existing ions may alter the fate of ferrihydrite-phosphorus colloids, which needs further investigation.
Key words:Soil phosphorus/
Ferrihydrite/
Adsorption/
Colloid phosphorus/
Derjguin-Landau-Verwey-Overbeek (DLVO)
PDF全文下载地址:
http://www.ecoagri.ac.cn/article/exportPdf?id=d8dc7d83-d3b0-49ce-8749-b030cd14b534
