Arsenic removal by ferric chloride

Abstract

Source water composition affects removal efficiency. Bench‐scale studies were conducted in model freshwater systems to investigate how various parameters affected arsenic removal during coagulation with ferric chloride and arsenic adsorption onto preformed hydrous ferric oxide. Parameters included arsenic oxidation state and initial concentration, coagulant dosage or adsorbent concentration, pH, and the presence of co‐occurring inorganic solutes. Comparison of coagulation and adsorption experiments and of experimental results with predictions based on surface complexation modeling demonstrated that adsorption is an important (though not the sole) mechanism governing arsenic removal during coagulation. Under comparable conditions, better removal was observed with arsenic(V) [As(V)] than with arsenic(III) [As(III)] in both coagulation and adsorption experiments. Below neutral pH values, As(III) removal–adsorption was significantly decreased in the presence of sulfate, whereas only a slight decrease in As(V) removal–adsorption was observed. At high pH, removal–adsorption of As(V) was increased in the presence of calcium. Removal of As(V) during coagulation with ferric chloride is both more efficient and less sensitive than that of As(III) to variations in source water composition.

Removal of arsenic from water by electrocoagulation

“…As(III) is more mobile in groundwater and 25-60 times more toxic than As(V). The concentration of arsenic species is mainly dependent on redox potentials (Masscheleyn et al, 1991) and pH (Hering et al, 1996). Under low pH and mildly reducing conditions (>100 mV), As(III) is thermodynamically stable and exists as arsenious acid (H 3 AsO 0 3 , H 2 AsO À 3 , HAsO 2À 3 and AsO 3À 3 ).…”

“…The commonly used technologies include coagulation and precipitation with iron and aluminum salts (Edwards, 1994;Hering et al, 1996), adsorption onto activated alumina, activated carbon and activated bauxite (Gupta and Chen, 1978), ion exchange and reverse osmosis (Clifford, 1999). Some recent treatment technologies based on oxidation and adsorption are green sand filtration (Christen, 2000), iron oxide coated sand (Joshi and Chaudhuri, 1996), manganese dioxide coated sand (Bajpai and Chaudhuri, 1999), ferruginous manganese ore (Chakravarty et al, 2002), ferrihydrite (Jain et al, 1999), clay minerals (Manning and Goldberg, 1997) and zero-valent iron (Fendorf et al, 1997;Farrell et al, 2001;Su and Puls, 2001).…”

“…Studies on arsenic indicate that hydrous metal oxides, such as ferric hydroxides, ferrihydrite, and goethite strongly adsorb arsenic (Edwards, 1994;Hering et al, 1996;Fendorf et al, 1997;Ravene et al, 1998;Jain et al, 1999). Recently arsenic removal by zero-valent iron has also been reported (Farrell et al, 2001;Krishna et al, 2001;Su and Puls, 2001).…”

In situ chemical fixation of arsenic-contaminated soils: An experimental study

“…Moreover, studies by other researchers have indicated that precipitation of Fe-As and Mn-As phases is very unlikely. The introduction of ferric ions for removal of arsenic from hydrometallurgical processed solutions and in water treatment has been studied by many researchers (Robins et al, 1987;Edwards, 1994;Cheng et al, 1994;Hering et al, 1996). These studies indicated that coagulation and adsorption are the major mechanisms for arsenic removal.…”

“…Furthermore, ferric ion has been used as an effective coagulation reagent in the treatment of arseniccontaminated wastewater (Cheng et al, 1994;Edwards, 1994;Hering et al, 1996). A study by Krause and Ettel (1988) showed that arsenic can form relatively insoluble ferric iron compounds, which have solubility products on the order of 10−20 to 10−24.…”