Influence of pH and Contaminant Redox Form on the Competitive Removal of Arsenic and Antimony from Aqueous Media by Coagulation

Abstract

In most countries, arsenic (As) and antimony (Sb) are regulated pollutants, due to their significant impacts on the environment and human health. Iron-based (Fe) coagulants play a fundamental role in the removal of both elements from aqueous media. This study aims to investigate the competitive removal of As and Sb in relation to Fe solubility. Coagulation experiments were conducted in synthetic water under various pH and contaminant loading, using ferric chloride (FC) as a coagulant. In the single system, the pentavalent species significantly reduced the Fe solubility and thereby enhanced the mobility of As and Sb under these environmental conditions. The coexistence of pentavalent and trivalent species in the binary system considerably decreases the Fe solubility at acidic conditions while enhancing the dissolution under alkaline conditions, thus affecting the overall removal of both species. The presence of four redox species in the quaternary system decreases the Fe solubility remarkably over a wide pH range, with better Sb removal, as compared to As under similar conditions. The adsorption study of the single system showed a decrease in As(V) adsorption capacity at higher concentration, while in the binary system, the Sb(III) showed strong adsorption potential, compared to other species. In the quaternary system, the presence of all four redox species has a synergistic effect on total Sb adsorption, in comparison to the total As. Furthermore, the results of Fourier transform infrared (FT-IR) analysis of FC composite contaminant flocs confirm that the combined effect of charge neutralization and inner sphere complexation might be a possible removal mechanism. These findings may facilitate the fate, transport and comparative removal of redox species in the heterogeneous aquatic environment.

Complexation of Antimony with Natural Organic Matter: Performance Evaluation during Coagulation-Flocculation Process

“…The presence of a peak around ~1400 cm −1 in each NOM further suggests the formation of a Sb-NOM complex through C=C stretching in the aromatic ring and OH bending in phenols [37]. The peaks at ~472 cm −1 in Figure 1B and ~490 cm −1 in Figure 1C indicate the attachments of Sb(III) and Sb(V) species, respectively [29], after the interaction of organic matter with each Sb species. It is worth noting that the interaction of hydrophilic ligands with Sb(III) species did not oxidize the Sb(III) species to Sb(V).…”

“…In addition, the complexation behavior may also depend upon the speciation of Sb(III, V) species. For the pH of interest (7 ± 0.1), the Sb(III) and Sb(V) species exist as Sb(OH) 3 and Sb(OH) 6 ¯, respectively [29]. The presence of carboxylic, phenolic, and amine groups in HA and SA may be responsible for complexation with Sb(III) via a ligand exchange reaction at the Sb center, and thereby, the release of OH − radicals in solution [17].…”

“…Prior to the experiments, a 100 mL solution was added to the beaker and had its pH adjusted to 7.0 ± 0.1 using 0.1 M HCl or 0.1 M NaOH. The coagulation experiments followed three sequential steps as reported in our previous studies [28,29]: (a) rapid mixing at 140 rpm for 3 min; (b) slow mixing at 40 rpm for 20 min, and (c) settling for 30 min. The aliquot was then collected for total organic carbon (TOC) analysis; meanwhile, some volume of the aliquot was filtered using a 0.45 µm glass fiber filter to evaluate the residual concentrations of Fe and Sb species.…”

Release Behaviors of Arsenic and Heavy Metals from Arsenic Sulfide Sludge during Simulated Storage

“…The toxicity and carcinogenicity of arsenic and heavy metals have caused serious environmental concerns throughout the world [1,2]. Arsenic pollution in the environment occurs mostly due to anthropogenic processes such as agriculture, mining and mineral processing operations [3][4][5].…”

Selective Separation of Arsenic from Lead Smelter Flue Dust by Alkaline Pressure Oxidative Leaching

“…The high content of arsenic not only effectively reduces the economic value of lead smelter flue dust due to requirements for further operations of hazardous emissions, but also creates great risks to the environment and the human body [4,5]. Arsenic has been classified as a Group 1 human carcinogen by the international agency for research on cancer, and arsenic exposure is associated with an increased incidence of human malignancies in skin, lungs, bladder, and liver [6][7][8]. As mentioned above, although arsenic in nature has many negative effects, there is still value and necessity in recycling it due to its current uses, where it is applied in the manufacture of glasses, lead additives in car batteries, anti-friction agents in bearings and Gallium-Arsenide (GaAs) semiconductors [9,10].…”