Simultaneous removal of arsenite and fluoride via an integrated electro-oxidation and electrocoagulation process

Abstract

a b s t r a c tAn integrated electro-oxidation and electrocoagulation system was designed and used to remove As(III) and F À ions from water simultaneously. Dimensionally stable anodes (DSA), Fe electrodes, and Al electrodes were combined into an electrochemical system. Two pieces of DSA electrodes were assigned as the outside of the Fe and Al electrodes and were directly connected to the power supply as anode and cathode, respectively. The Fe and Al ions were generated by electro-induced process simultaneously. Subsequently, hydroxides of Fe and Al were formed. Arsenic ions are mainly removed by iron hydroxides and F À ions are mainly removed by the Al oxides. At the initial concentration of 1.0 mg L À1 , most of As(III) was transferred into As(V) within 40 min at current density of 4 mA cm À2 , whereas F À ions can be efficiently removed simultaneously. The effect of the ratio of Fe and Al plate electrodes and current density on the removal of As(III) and F À was investigated. With one piece of Fe plate electrode and three pieces of Al plate electrodes, it is observed that As(III) with concentration of 1 mg L À1 and F À with concentration of 4.5 mg L À1 can be removed and their final concentrations were below the values of 10 lg L À1 and 1.0 mg L À1 , respectively within 40 min. Removal efficiency of As(III) increases with the increase of solution pH. However, in the pH range of 6-7, removal efficiency of F À is the largest.

Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal

“…The presence of carbonate, phosphate and silicate also reduced the F removal efficiency. Zhao et al (2011) designed an integrated electro-oxidation and electrocoagulation system to simultaneously remove As(III) and F ions from water. By utilizing one Fe plate piece and three parts of Al plate electrodes, which reduced As(III) to less than 10 mg/L compared to its initial level of 1 mg/L and F 1 mg/L when its initial concentration was 4.5 mg/L.…”

“…À Synthetic water À Composition: F ¼ 4.5 mg/L As ¼ 1 mg/L À Current density ¼ mA/cm 2 À Duration ¼ 40 min Zhao et al (2011) Adsorption À Adsorbent prepared through the cross-linking reaction of PANF by hydrazine hydrate and functionalized reaction of hydrazine-modified fiber in mixture of sulfur powder and ethylenediamine À Lab scale research À Synthetic water À Composition: F ¼ 10 mg/L, PO 3 ¼ 30 mg/L As(V) ¼ 38 mg/L (Separately treated) Mixed ions, F ¼ 5 mg/L, PO 3 ¼ 50 mg/ L, and As(V) ¼ 34.23 mg/L treated in another run À Flow rate ¼ 2.5e3.5 ml/min À As(V) adsorption ¼ 97.9% at pH 3.5 to 7 À F adsorption ¼ 90.4% at pH 3 À PO 3 adsorption > 99% at pH 3 to 5.5 À In mixed ions F, As(V) and PO 3 adsorption was~50, 85 and 90% respectively À Equilibrium was reached within 5 min for all the experiments Ruixia et al (2002) À Low to medium cost À Simple to use À Efficient À Commercially available sorbents À Can handle high levels of solids À pH sensitive À Considerable adsorbent regeneration time À Needs standby process during regeneration À Exhausted adsorbent disposal problem À Competing ions reduce efficiency Low to medium À CeeFe adsorbent À Lab scale research À Groundwater À Composition: As(V) ¼ 1.1 mg/L F ¼ 1.59 mg/L À Zhijiliang Village, Inner Mongolia, China À Phosphate seriously affected removal of As(V) while F did not compete with As(V) even at F/As molar ratio as high as 30, suggesting that adsorption sites for As(V) and F were different À Mean As(V) adsorption capacity ¼ 16 mg/g at pH 3-7 À Max As(V) adsorption capacity ¼ 8.3 mg/g at pH 5.5 Zhang et al (2003) À Granular activated carbonbased iron-containing adsorbents (As-GAC) À Lab scale research À Synthetic water À Composition: As ¼ 105 mg/L and 1031 mg/L 90.0 mg solid per 30.0 ml solution À pH ¼ 4.7 À Duration ¼ 24hr À As removal > 98% À Max As adsorption (prepared by NaCl oxidation) ¼ 6572 mg/g À Presence of P and SiO significantly decreased As(V) removal at pH > 8.5 À Effects of Cl, and F were minimal Gu et al (2005) À Synthetic water À F removal ¼ 80% Delorme et al (2007) À Mixed oxides obtained from the moderate thermal treatment of quintinite À Lab scale research À Composition: F ¼ 10 mg/L As(V) ¼ 16 mg/L NO 3 ¼ 100 mg/L À As(V) removal ¼ 100% À NO 3 removal ¼ 15% À CO 3 addition resulted in trapped ion leaching (90% F and 20% As released) À Three types of granular ferric hydroxide materials À Lab scale research À Synthetic water À Composition: As(V) ¼ 0.0133 mmol/L F ¼ 0.0133 mmol/L P ¼ 0.0133 mmol/L À pH ¼ 4e8 À F adsorption capacity ¼ 1.8 mmol/g À As(V) adsorption capacity ¼ 0.9e1 mmol/g À Phosphate adsorption capacity ¼ 0.65e0.75 mmol/g À Being not a triprotic acid, F did not compete for same sites with As Streat et al (2008) À Cow and fish bone char À Lab scale research À Synthetic water À Composition: F ¼ 10 mg/L As(V) ¼ 0.250 mg/L À As(V) showed no significant competition for F À F adsorption capacity ¼ 3.94 ± 0.15 mg/g À As(V) adsorption capacity ¼ 4.41 ± 0.23 mg/g À Bone char showed greater capacity to remove F than As Brunson and Sabatini (2009) À Magnetite-type adsorbent À Lab scale research/Field sample testing À Groundwater À Composition:…”

Development of an integrated electro-coagulation–flotation for semiconductor wastewater treatment

“…More recently, Khelifa et al [20] developed a new integrated electro-chlorinationelectro-flotation reactor allowing simultaneous removal of EDTA and heavy metals together with clarification in a one-step process. Zhao et al [21] used an integrated electro-oxidation and EC system to remove As(III) and F-ions from water simultaneously. Bennajah et al [13] studied an innovative one-compartment system based on aluminium electrodes which ensures EC and EF using an airlift reactor for drinking water.…”

Simultaneous removal of arsenic and fluoride by freshly-prepared aluminum hydroxide

“…As for the removal of arsenic, the Fe-based coagulants and adsorbents showed priority due to their strong affinity towards arsenic [10,11], and the formation of bi-nuclear bidentate and monodentate complexes on the iron hydro (oxide) surfaces has been proposed [10,13,14]. To achieve the simultaneous removal of As and F, the coagulation by the combined use of iron (Fe) and aluminum (Al) salts works well [6,15], and the electro-coagulation with Fe and Al plates also exhibits promising efficiency [15]. Comparatively, Al hydro (oxide) is more effective than that of Fe in terms of the simultaneous removal of As and F, owing to the weak affinity of iron hydro (oxide) towards fluoride [6].…”