As(III) Oxidation by Active Chlorine and Subsequent Removal of As(V) by Al-13 Polymer Coagulation Using a Novel Dual Function Reagent
ABSTRACT An electrochemically prepared water treatment reagent containing a high concentration of Al(13) polymer and active chlorine (PACC) showed promising potential for the removal of As(III) due to the combined function of oxidation and coagulation. The results indicated that PACC was effective for As(III) removal through oxidation by the active chlorine and subsequent removal of As(V) by coagulation with the Al(13) polymer. The As(III) was oxidized to As(V) by active chlorine in PACC, with a stoichiometric rate of 0.99 mg Cl(2)/mg As(III). The Al(13) polymer was the most active Al species responsible for As(V) removal in PACC. To meet As drinking water standards the stoichiometric weight ratio of Cl(2)/Al within PACC was 0.09 for the treatment of As(III). Considering the process of As(III) oxidation and As(V) coagulation together, the optimal pH conditions for the removal of As by PACC was within the neutral range, which facilitated the reaction of As(III) with active chlorine and favored the formation of Al hydroxide flocs. The presence of humic acid reduced the As(III) removal efficiency of PACC due to its negative influence on subsequent As(V) coagulation, and disinfection byproduct yields were very low in the presence of insufficient or stoichiometric active chlorine.
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ABSTRACT: The treatment of heavy metal-cyanide complex in industrial wastewater generally involves various processing units, such as chemical oxidation, hydrolysis precipitation and coagulation. A novel dual function reagent (PACC), which contains high content of active chlorine and Al-13 polymer, shows a promising potential to shorten the process and heighten the treatment efficiency for cadmium-cyanide complex ([Cd(CN)(4)](2-)). The results indicated that PACC is able to simultaneously achieve the complete oxidation of cyanide (CN-) by active chlorine and the subsequent coagulation of cadmium ion (Cd2+) by Al-13 polymer. Two stagek were carried out for complete CN- oxidation and effective Cd2+ coagulation. The first stage involves the conversion of CN- to cyanate (CNO-), and the second stage involves the conversion of CNO- to nitrogen and the coagulation of the liberated Cd2+. The optimum pH values for the first stage and the second stage are pH 11 and pH 8.5, respectively. The two stages for effective treatment of [Cd(CN)4](2-) at the optimal pH condition totally need about 43 min at active chlorine dosage 130% of the theoretical requirement for CN- decomposition. Under the optimal conditions for [Cd(CN)4]2- treatment, the stoichiometric weight ratio of Cl-2/Al in PACC is 2. This study presents a novel reagent and method to remove heavy metal-cyanide complexes from wastewater.Chemical Engineering Journal 02/2015; 262:96–100. DOI:10.1016/j.cej.2014.09.080 · 4.32 Impact Factor