Removal of Arsenic Oxyanions from Water by Ferric Chloride—Optimization of Process Conditions and Implications for Improving Coagulation Performance

Abstract

The chronic ingestion of arsenic (As) contaminated water has raised significant health concerns worldwide. Iron-based coagulants have been widely used to remove As oxyanions from drinking water sources. In addition, the system’s ability to lower As within the maximum acceptable contamination level (MCL) is critical for protecting human health from its detrimental effects. Accordingly, the current study comprehensively investigates the performance of As removal under various influencing factors including pH, contact time, temperature, As (III, V) concentration, ferric chloride (FC) dose, and interfering ions. The optimum pH for As (V) removal with FC was found to be pH 6–7, and it gradually decreased as the pH increased. In contrast, As (III) removal increased with an increase in pH with an optimum pH range of 7–10. The adsorption of As on precipitated iron hydroxide (FHO) was better fitted with pseudo-second order and modified Langmuir–Freundlich models. The antagonistic effect of temperature on As removal with FC was observed, with optimum temperature of 15–25 °C. After critically evaluating the optimum operating conditions, the uptake indices of both As species were developed to select appropriate an FC dose for achieving the MCL level. The results show that the relationship between residual concentration, FC dose, and adsorption affinity of the system was well represented by uptake indices. The higher FC dose was required for suspensions containing greater concentration of As species to achieve MCL level. The As (V) species with a greater adsorption affinity towards FHO require a relatively smaller FC dose than As (III) ions. Moreover, the significant influence of interfering species on As removal was observed in simulated natural water. The author hopes that this study may help researchers and the drinking water industry to develop uptake indices of other targeted pollutants in achieving MCL level during water treatment operations in order to ensure public health safety.

Coagulation removal of nickel (II) ions by ferric chloride: Efficiency and mechanism

“…As can be seen from Figure 7a, the zeta potential of the iron (III) hydroxide precipitate particles formed in our experiments in the absence of nickel ions in the model solution is positive at pH < 5.4 and becomes negative at pH > 5.4 (Figure 7a, curve 1). The point of zero charge corresponds to pH = 5.4, which significantly differs from the data of works (Inam et al, 2021;Liu et al, 2021;Villalobos & Antelo, 2011), where the pH of the point of zero charge for ferrihydrite was 8.8, 8.4 and 7.5, respectively. We ascribe the observed difference to the presence of sulfate ions in the model solution in our experiments, as well as to a small possible admixture of iron (III) hydroxycarbonate FeOHCO 3 in the formed precipitates.…”

Impact of Temperature and Coagulants on Sludge Dewaterability

“…Although the comparison was made repeatedly using different types and shapes of mixers, findings still indicate that the performance of ferric chloride is not impacted by temperature. In contrast, other investigations have shown that ferric chloride as a coagulant was influenced by temperature (Duan & Gregory, 2003;Inam et al, 2021).…”

“…Temperature and type of coagulant are equally effective on the coagulation efficiency (Duan & Gregory, 2003;Rodrigues et al, 2008). Temperature can affect the metal ion hydrolysis reaction rate (Inam et al, 2021). A higher temperature causes an enhanced reaction rate and vice versa.…”

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

“…The residual As(III, V) and Fe(III) concentrations were analyzed after filtering the supernatant using a 0.45µm glass filter. For all chemical coagulation experiments, the sequential experimental strategy was as follows: 3 min fast agitation (coagulation); 20 min slow mixing; 30 min quiescent settling; and aliquot collection [20]. However, only slow mixing for 25 min was done for kinetic experiments, with the rest of the experimental protocol remaining same.…”

“…However, how the sorption properties of FHO for As(III, V) species vary with temperature needs significant attention. Several studies have also focused on the sorption potential and removal mechanism of As oxyanions onto and from FHO by coagulation [10,20]. Still, the literature comparing the sorption capacity and rate of FHO for trivalent and pentavalent As oxyanions in complex waters seems scarce.…”