Adsorption Capacities of Iron Hydroxide for Arsenate and Arsenite Removal from Water by Chemical Coagulation: Kinetics, Thermodynamics and Equilibrium Studies

Abstract

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 (pHzpc) 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.

Kinetics and Thermodynamics of Adsorption for Aromatic Hydrocarbon Model Systems via a Coagulation Process with a Ferric Sulfate–Lime Softening System

“…Kinetic adsorption equations such as the pseudo-first order (PFO) and pseudo-second order (PSO) models were used to examine the pollutant adsorption profiles [ 17 ]. The non-linear forms of the PFO and PSO kinetic models are expressed by Equations (1) and (2), respectively [ 18 ]: where q t (mg g −1 ) and q e (mg g −1 ) indicate the adsorption capacity of ferric sulfate towards pollutant removal at the time (t) and equilibrium. k 1 (min −1 ) and k 2 (g mg −1 min −1 ) are the respective rate constants for the PFO and PSO models.…”

Composite electrospun membranes based on PET-PAN modified with LDH-hybrid as promising adsorbent for pollutants removal from wastewater

“…With the gradual rise in the pollutant concentration, there was a drop in the efficacy of EBT adsorption; Figure 5(b) shows that the optimum removal performance of EBT was at 10 mg.L -1 . Higher pollutant concentration leads to decrease in percentage of dye elimination at the same adsorption time (Khan et al, 2021;Y. Wu et al, 2013).…”

“…The untreated wastewater discharge of these dyes into the water bodies give serious threats to aquatic life and human being (Manzar, Waheed, Qazi, Blaisi, & Ullah, 2019). Therefore, introducing new effective methods and materials for removing the pollutants and dyes from wastewater is drastically required (Akram et al, 2023;Bano et al, 2024;Inam et al, 2021;Kishore et al, 2023).…”

Arsenic Adsorption on Nanoscale Zerovalent Iron Immobilized on Reduced Graphene Oxide (nZVI/rGO): Experimental and Theoretical Approaches

“…The methods that are currently used for As remediation include ion exchange, − phytoremediation, , adsorption, − chemical precipitation, , electrokinetic, , and electrocoagulation. , Within the adsorption methods, application of affordable iron-based material, such as iron-hydroxide, − zero-valent iron, − iron oxide, , and bimetal oxides, − is noteworthy. In brief, the adsorption process on these materials is associated with electrostatic attraction, ion exchange, and surface complexation, with a further oxidation/reduction reaction over the surface, depending on the material composition and the adsorbing As species. ,, …”