The presence of arsenic (As) in drinking water is of serious concern due to its negative impact on human health. This work reports on the kinetics of nanoscale zero-valent iron (Fe⁰) supported by activated carbon (NZVI/AC) for the removal of As (V) species from aqueous solutions. To better understand the factors affecting this process, we investigated the effects of various experimental parameters including initial As (V) concentration, adsorbent dosage, pH, temperature, and coexisting ions on the adsorption kinetics using a batch-adsorption method. The optimum conditions for As (V) removal by NZVI/AC were found to be: 318 K, pH 3.5, an adsorbent dosage of 1.5 g/L, and an equilibrium time of 72 h. A greater mass of NZVI/AC, lower concentration of As (V) and lower pH positively promoted adsorption kinetics. The presence of phosphate (${\mathrm{PO}}_4^{3-}$) and silicate (${\mathrm{SiO}}_4^{2-}$) markedly inhibited As (V) removal kinetics. However, in the presence of 4.5 g/L NZVI/AC, ≥99.9% of As (V) was removed from raw groundwater.

Traces of Molybdenum (Mo) in drinking water pose potent dangers owing to its harmful effects on the health of humans. This study used nanoscale zero-valent iron (Fe⁰) supported by activated carbon (NZVI/AC) for removing Mo(VI) from raw water. In an attempt to gain an understanding of the various factors that affect the process, we designed the study to look into the impact of various experimental parameters including pH, adsorption kinetics, and coexisting ions on the Mo(VI) removal using fixed-bed column runs and a batch-adsorption method and for Mo(VI) removal using NZVI/AC. The optimum conditions were found to be pH 4.5 and an equilibrium time of 9 h and 72 h for simulation water (SW) and raw water (RW), respectively. The removal of Mo(VI) was remarkably inhibited by the presence of silicate (${\mathrm{SiO}}_4^{2-}$) and phosphate (${\mathrm{PO}}_4^{3-}$), while the impact of humic acid and some other anions was insignificant. Metal cations such as Fe³⁺, Al³⁺, Zn²⁺, and Ni²⁺ enhanced the adsorption of Mo(VI). The influent contaminant concentration Mo(VI) in raw water was found to be 0.1603 mg/L, the empty-bed contact time (EBCT) was 3 and 6 min, whereas the breakthrough empty-bed volumes were 800 and 1100 and at the value of 70 μg/L provided by WHO provisional guidelines, respectively.

Antimony (Sb) traces in water pose a serious threat to human health due to their negative effects. In this work, nanoscale zero-valent iron (Fe⁰) supported on activated carbon (nZVI) was employed for eliminating Sb(V) from the drinking water. To better understand the overall process, the effects of several experimental variables, including pH, dissolved oxygen (DO), coexisting ions, and adsorption kinetics on the removal of Sb(V) from the SW were investigated by employing fixed-bed column runs or batch-adsorption methods. A pH of 4.5 and 72 h of equilibrium time were found to be the ideal conditions for drinking water. The presence of phosphate (${\mathrm{PO}}_4^{3-}$), silicate (${\mathrm{SiO}}_4^{2-}$), chromate (${\mathrm{CrO}}_4^{2-}$) and arsenate (${\mathrm{AsO}}_4^{3-}$) significantly decreased the rate of Sb(V) removal, while humic acid and other anions exhibited a negligible effect. The capacity for Sb(V) uptake decreased from 6.665 to 2.433 mg when the flow rate was increased from 5 to 10 mL·min⁻¹. The dynamic adsorption penetration curves of Sb(V) were 116.4% and 144.1% with the weak magnetic field (WMF) in fixed-bed column runs. Considering the removal rate of Sb(V), reusability, operability, no release of Sb(V) after being incorporated into the iron (hydr)oxides structure, it can be concluded that WMF coupled with ZVI would be an effective Sb(V) immobilization technology for drinking water.

The effectiveness of nanoscale zero-valent iron(nZVI) immobilized on activated carbon (nZVI/AC) in removing antimonite (Sb(III)) from simulated contaminated water was investigated with and without a magnetic fix-bed column reactor. The experiments were all conducted in fixed-bed columns. A weak magnetic field (WMF) was proposed to increase the exclusion of paramagnetic Sb(III) ions by nZVI/AC. The Sb(III) adsorption to the nZVI and AC surfaces, as well as the transformation of Sb(III) to Sb(V) by them, were both increased by using a WMF in nZVI/AC. The increased sequestration of Sb(III) by nZVI/AC in the presence of WMF was followed by faster nZVI corrosion and dissolution. Experiments were conducted as a function of the pH of the feed solution (pH 5.0–9.0), liquid flow rate (5–15 mL·min⁻¹), starting Sb(III) concentration (0.5–1.5 mg·L⁻¹), bed height nZVI/AC (10–40 cm), and starting Sb(III) concentration (0.5–1.5 mg·L⁻¹). By analyzing the breakthrough curves generated by different flow rates, different pH values, different inlet Sb(III) concentrations, and different bed heights, the adsorbed amounts, equilibrium nZVI uptakes, and total Sb(III) removal percentage were calculated in relation to effluent volumes. At pH 5.0, the longest nZVI breakthrough time and maximal Sb(III) adsorption were achieved. The findings revealed that the column performed effectively at the lowest flow rate. With increasing bed height, column bed capacity and exhaustion time increased as well. Increasing the Sb(III) initial concentration from 0.5 to 1.5 mg·L⁻¹ resulted in the rise of adsorption bed capacity from 3.45 to 6.33 mg·g⁻¹.

Due to the large volumes of solid waste produced by the traditional arsenic-rich lime iron salt precipitation method treatment produced during wet-smelting by precious metal workshops, raw As(V)-rich wastewater from a domestic metallurgical enterprise was chosen as the research object. Zero-valent iron (ZVI) was used to remove arsenate (As(V)) from raw wastewater. Factors affecting the adsorption of As(V), such as the ZVI size and adsorption time, were investigated. The As(V) removal percentage was >98.2% when using 40, 100, 250, or 300 mesh ZVI in a 2.8 mg·L⁻¹ As(V) solution at pH 7, with an iron mass–wastewater ratio of 5 g/100 mL, and 12 h reaction time. The As(V) removal percentage was >86.5% when using 40 mesh ZVI after 50 min of reaction. A comprehensive evaluation was performed on the effects of factors such as cost and water head loss. Here, 40 mesh ZVI was used for column-based separation, in which the mass of solid waste was very small. Column experiments indicated that the adsorbent more efficiently eliminated arsenate in comparison to the earlier reported adsorbents. High bed volumes (BV) of 3200 BV, 6300 BV, and 8400 BV up to a breakthrough concentration of 100 μg·L⁻¹ were achieved for arsenate removal in the presence of 2.8 mg·L⁻¹ of arsenic. The empty bed contact times (EBCTs) were 2.6 min, 5.1 min, and 9.8 min, respectively. Furthermore, the concentrations of other pollutants such as Cu²⁺, Zn²⁺, F⁻, Cd²⁺, Cr⁶⁺, Pb²⁺, and F^- met the national discharge standard. The elimination of As(V) and other heavy metals from solutions employing ZVI is efficient, cheap, and produces no secondary environmental pollution, making it an ideal candidate for heavy metal removal from wastewater.

Vanadium (V(V)) removal from simulation water (SW) was successfully accomplished using nanoscale zero-valent iron that was immobilized by activated carbon (NZVI/AC) which was used as an adsorbent. We investigated the effects of different parameters on V(V) removal, such as pH, dissolved oxygen (DO), common ions and adsorption kinetics for SW. The intraparticle diffusion model fits this study well (R² > 0.9) according to the results of the kinetics investigation which showed that the adsorption of vanadium by NZVI/AC was rapid in the first 12 h and that equilibrium was reached in about 72 h. The amount of V(V) that was removed from the solution increased when it was subjected to pH 2 to pH 8, and this decreased after pH 8. While the effects of other anions and humic acid were negligible, the elimination of V(V) was significantly reduced by using phosphate and silicate. Fe²⁺ and Al³⁺, two common metal cations, improved the V(V) adsorption. High oxygen levels impeded the vanadium elimination, while anoxic conditions encouraged it. Elution with 0.1 M NaOH can be used to renew NZVI/AC in an efficient manner.