Effective treatment of cadmium–cyanide complex by a reagent with combined function of oxidation and coagulation

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.