When treating plated wastewater mixed with cyanide and ammonia-nitrogen (NH3-N) with alkali chlorine method using NaOCl, there is a problem which NaOCl is injected excessively due to the interference of ammonia-nitrogen (NH3-N). As a countermeasure, ferrate(VI) was used to slectively remove cyanide, a toxic substance in plated wastewater. First, it was compared the amount of NaOCl consumed when treating 70 mg/L of cyanide wastewater manufactured using KCN by the alkali chlorine method with the amount of NaOCl consumed when treating manufactured wastewater which was made by ammonia concentrations of 200, 400, 600, and 800 mg/L using NH4Cl in
same concentration solution of cyanide respectively. As a result, NaOCl''s input increased linearly with the amount of ammonia-nitrogen(NH3-N), and the amount of consumed NaOCl was approximately 7 times at a ammonia-nitrogen(NH3-N) concentration of 800 mg/L than that of ammonia-free wastewater.
To derive optimal reaction conditions for selective elimination of the cyanide using Ferrate (VI), It was investigated the effects of Ferrate (VI) input amount, reaction time, pH, and ammonia-nitrogen (NH3-N) concentrations. As a result, a 30-minute reaction and Fe (VI)/CN = 2/1 mol ratio injection was derived for optimal conditions. And the best removal efficiency was 99.3 % both at pH 3 under acidic conditions and at pH 9 under alkali conditions. it was confirmed that the ammonia-nitrogen (NH3-N) concentration in wastewater does not affect the selective cyanide removal of Ferrate (VI), so that the cyanide, did not compete with ammonia-nitrogen (NH3-N), first reacts selectively with Ferrate (VI).
In order to evaluate the applicability of the actual process, experiments on the removal of cyanide and heavy metals were conducted on actual plated wastewater generated at the I Surface Treatment Center. As a result, the highest cyanide removal efficiency was 98.3 % at pH 3 to actual plated wastewater. Heavy metal removal efficiency was investigated in T-Cr, Cu, Ni, Zn. The highest removal efficiency of Zn, Ni was about 96 % at pH 3. T-Cr showed the highest removal efficiency at pH 5, while Cu showed higher removal efficiency as pH increased.
Application to the plating wastewater treatment process using Ferrate (VI) will require follow-up research to evaluate economic feasibility (chemical cost, maintenance cost, treatment efficiency, etc.) through pilot test and demonstration facilities.