Comparison of different iron oxide adsorbents for combined arsenic, vanadium and fluoride removal from drinking water

Abstract

Contamination of groundwater by arsenic due to natural processes is rather common worldwide and hinders its use for drinking water supply. In many cases, arsenic contamination is found together with high levels of vanadium and fluoride. Therefore, more than one type of treatment is required to reduce concentrations of all these contaminants below non-hazardous levels so to make the source drinkable. The present study investigated the uptake capacity of arsenic, vanadium and fluoride by three iron-based adsorbent media differing for particle size, iron content and specific surface. The aim of the treatment was to achieve the maximum allowable concentration set on drinking water by the law. The removal efficiency was evaluated in single and binary contaminated solutions. All the tested adsorbents demonstrated an efficient and rapid removal process of both arsenic and vanadium in the single and binary solutions, with a higher adsorption capacity for vanadium; by contrast, they were unable to achieve an appreciable reduction in fluoride concentration. The particle size showed to have the highest effect on the removal rate. The best kinetic and isotherm models and the related parameters were determined for each condition. In the binary solutions, the presence of vanadium hindered the uptake of arsenic, whereas fluoride did not have any effect. The results obtained showed that the iron-based adsorbents tested in the present study can be successfully applied for the treatment of drinking water contaminated by arsenic and vanadium, whereas a different medium or process needs to be adopted for the removal of fluoride.

Comparison of Adsorptive Removal of Fluoride from Water by Different Adsorbents under Laboratory and Real Conditions

“…31/2001). Among the 6 adsorbents used with the synthetic solution, this series of tests was conducted using only TiO 2 , A33E and GFH, since they are reported to possess a high removal capability versus arsenic in liquid solutions [21,25,[27][28][29][30][31]. Under real conditions of application, there would be the need to reduce both fluoride and arsenic concentrations below the respective limits.…”

“…Then, the mass of contaminant transferred by adsorption per unit weight of adsorbent at equilibrium (i.e., the adsorption capacity), Q e , was calculated by applying Equation (1). The results from the isotherm experiments were fitted by the Freundlich, Langmuir, Brunauer-Emmett-Teller (BET) and Temkin models [21] (Table 5). The best-fitting model was considered as one providing the higher value of the correlation coefficient (R 2 ) between the experimental and model-predicted data using the linearized form of the representative equation.…”

“…Iron-based materials, such as GFH, have been extensively studied for defluoridation, due to the affinity of iron for F − . It has been also widely applied to arsenic removal in the treatment of drinking water sources [19,21]. The adsorption onto GFH is attributed to the interaction of fluoride with singly coordinated FeOH surface groups, with the adsorption mechanism being described as an exchange reaction against OH − of surface groups [33].…”

“…Beside all these factors, the behavior under real operating conditions can differ with respect to the laboratory application because of the more complex composition of the water solution [15]. Furthermore, the co-occurrence of fluoride with other pollutants of concern is quite diffused, e.g., in Italy, Europe and Latin American regions, because they arise from the same natural leaching processes of rocks [19][20][21]. Their presence together in the same solution can hinder the achievement of the required removal of all the contaminants; thus, it can cause more severe health effects [22].…”

Formation of Dense and High-Aspect-Ratio Iron Oxide Nanowires by Water Vapor-Assisted Thermal Oxidation and Their Cr(VI) Adsorption Properties

“…Iron oxide is a compound material, largely found as hematite (α-Fe 2 O 3 ), magnetite (Fe 3 O 4 ), wüstite (Fe 1– x O), and maghemite (γ-Fe 2 O 3 ), which has attracted attention as an adsorbent due to its ability to remove various types of heavy-metal ions. − Recent studies have demonstrated that α-Fe 2 O 3 has a high adsorption capability, which occurs through a chemisorption process involving the hydroxyl group on its surface . Ren et al investigated α-Fe 2 O 3 in a fibrous form for Cr­(VI) ion removal and reported that the porous fiber-like morphology of α-Fe 2 O 3 exhibited excellent adsorption of Cr­(VI) from water, with rapid adsorption kinetics, high adsorption capacity, and good reusability .…”