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 Al13 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 Al13 polymer. Two stages 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 Cl2/Al in PACC is 2. This study presents a novel reagent and method to remove heavy metal–cyanide complexes from wastewater.
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