Institute of Environmental Sciences and Engineering (IESE), School of Civil and Environmental Engineering (SCEE), National University of Sciences and Technology (NUST) H-12 Campus, Islamabad 44000, Pakistan.
Department of Chemical Engineering, Quaid-e-Awam University of Engineering, Science and Technology (QUEST), Nawabshah 67480, Pakistan.
Molecules. 2021 Nov 22;26(22):7046. doi: 10.3390/molecules26227046.
Arsenic (As)-laden wastewater may pose a threat to biodiversity when released into soil and water bodies without treatment. The current study investigated the sorption properties of both As(III, V) oxyanions onto iron hydroxide (FHO) by chemical coagulation. The potential mechanisms were identified using the adsorption models, ζ-potential, X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometry (FT-IR) analysis. The results indicate that the sorption kinetics of pentavalent and trivalent As species closely followed the pseudo-second-order model, and the adsorption rates of both toxicants were remarkably governed by pH as well as the quantity of FHO in suspension. Notably, the FHO formation was directly related to the amount of ferric chloride (FC) coagulant added in the solution. The sorption isotherm results show a better maximum sorption capacity for pentavalent As ions than trivalent species, with the same amount of FHO in the suspensions. The thermodynamic study suggests that the sorption process was spontaneously exothermic with increased randomness. The ζ-potential, FT-IR and XRD analyses confirm that a strong Fe-O bond with As(V) and the closeness of the surface potential of the bonded complex to the point of zero charge (pH) resulted in the higher adsorption affinity of pentavalent As species than trivalent ions in most aquatic conditions. Moreover, the presence of sulfates, phosphates, and humic and salicylic acid significantly affected the As(III, V) sorption performance by altering the surface properties of Fe precipitates. The combined effect of charge neutralization, complexation, oxidation and multilayer chemisorption was identified as a major removal mechanism. These findings may provide some understanding regarding the fate, transport and adsorption properties onto FHO of As oxyanions in a complex water environment.
含砷废水未经处理排入土壤和水体，可能会对生物多样性造成威胁。本研究通过化学混凝考察了砷（III、V）两种含氧阴离子在氢氧化铁（FHO）上的吸附特性。利用吸附模型、ζ-电位、X 射线衍射（XRD）和傅里叶变换红外光谱（FT-IR）分析，确定了潜在的机制。结果表明，五价和三价砷物种的吸附动力学均较好地遵循准二级模型，且两种毒物的吸附速率均明显受 pH 值和悬浮液中 FHO 数量的影响。值得注意的是，FHO 的形成与溶液中添加的三氯化铁（FC）混凝剂的量直接相关。吸附等温线结果表明，对于相同量的悬浮 FHO，五价砷离子的最大吸附容量优于三价砷物种。热力学研究表明，吸附过程是自发的放热过程，且随着无序度的增加而增加。ζ-电位、FT-IR 和 XRD 分析证实，与三价砷离子相比，FHO 表面上形成的 Fe-O 键与 As(V)的键合紧密，且键合络合物的表面电位接近零电荷点（pH），这导致五价砷物种具有更高的吸附亲和力。此外，硫酸盐、磷酸盐、腐殖质和水杨酸的存在通过改变 Fe 沉淀物的表面性质，显著影响了 As(III、V)的吸附性能。电荷中和、络合、氧化和多层化学吸附的综合效应被确定为主要的去除机制。这些发现可能有助于理解复杂水环境中砷含氧阴离子的归宿、迁移和在 FHO 上的吸附特性。
