Hou Lei, Liang Qibin, Wang Fang
College of Ecology and Environment, Southwest Forestry University Kunming 650024 China.
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University Tianjin 300387 China
RSC Adv. 2020 Jan 13;10(4):2378-2388. doi: 10.1039/c9ra08517c. eCollection 2020 Jan 8.
Eutrophication caused by excessive phosphate discharge into surface water has raised wide concern, and the efficient removal of phosphates from wastewater using sorption methods is very important. In our study, magnetite particles with two different sizes and different surface characteristics were chosen as the sorbents to examine their adsorption and desorption behavior toward phosphate. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and N adsorption-desorption methods were used to characterize the morphological and surface chemical properties of the two differently sized magnetite particles. Adsorption kinetics and isotherm models (including the pseudo-first-order, Freundlich, Langmuir and Temkin models) were used to fit the experimental data, and to help with the mechanistic discussions. It was found that the nanometer-sized magnetite (nFeO) has a much higher surface area, larger pore volume, higher amounts of surface functional groups, and a lower point of zero charge (pH) value than the micrometer-sized magnetite (FeO). The adsorption kinetics show that reaching adsorption equilibrium in the case of nFeO is much slower, and the particle size or surface characteristics of the magnetite may become the main factor determining the adsorption rate of the phosphate to magnetite in the rapid or slow adsorption step, respectively. nFeO shows much stronger adsorption of phosphate compared to FeO, which may be attributed to the larger surface area of the magnetite with a smaller particle size. In addition, the amount of functional groups and the surface electrical properties may also affect the adsorption of phosphate to magnetite by influencing the formation of the outer-sphere and/or inner-sphere complexes. The adsorption/desorption of phosphate to/from the magnetite decreases/increases with increasing pH, and the extent of change is more marked for nFeO. Increasing the ionic strength of the solution increases the adsorption of phosphate to the two differently sized magnetite particles, whereas the presence of humic acid only increases the adsorption of phosphate to FeO. These trends may be caused by the different extents of change of the surface properties or the dispersion state of the two differently sized magnetite particles under different solution chemistry conditions. The results imply that when the synthesis of magnetite-based materials for phosphate sorption is performed, both the particle size and surface properties should be considered in order to realize the efficient and economical removal of phosphate from wastewater.
向地表水过量排放磷酸盐导致的富营养化已引起广泛关注，利用吸附法从废水中高效去除磷酸盐非常重要。在我们的研究中，选择了两种不同尺寸和不同表面特性的磁铁矿颗粒作为吸附剂，以研究它们对磷酸盐的吸附和解吸行为。使用扫描电子显微镜（SEM）、X射线光电子能谱（XPS）和N吸附-脱附方法来表征两种不同尺寸磁铁矿颗粒的形态和表面化学性质。吸附动力学和等温线模型（包括伪一级、弗伦德里希、朗缪尔和坦金模型）用于拟合实验数据，并辅助进行机理讨论。结果发现，与微米级磁铁矿（FeO）相比，纳米级磁铁矿（nFeO）具有更高的表面积、更大的孔体积、更多的表面官能团和更低的零电荷点（pH）值。吸附动力学表明，nFeO达到吸附平衡的速度要慢得多，磁铁矿的粒径或表面特性可能分别成为快速或慢速吸附步骤中决定磷酸盐对磁铁矿吸附速率的主要因素。与FeO相比，nFeO对磷酸盐的吸附要强得多，这可能归因于粒径较小的磁铁矿具有更大的表面积。此外，官能团的数量和表面电学性质也可能通过影响外层和/或内层配合物的形成来影响磷酸盐对磁铁矿的吸附。磷酸盐在磁铁矿上的吸附/解吸随pH升高而降低/增加，且nFeO的变化程度更为明显。增加溶液的离子强度会增加磷酸盐对两种不同尺寸磁铁矿颗粒的吸附，而腐殖酸的存在仅会增加磷酸盐对FeO的吸附。这些趋势可能是由两种不同尺寸磁铁矿颗粒在不同溶液化学条件下表面性质变化程度或分散状态的不同引起的。结果表明，在合成用于吸附磷酸盐的磁铁矿基材料时，应同时考虑粒径和表面性质，以实现从废水中高效且经济地去除磷酸盐。
