Developing Apparatus For On-line Electro-chemical Preparation Of Ferrate(Ⅵ) For Treating Wastewater Containing Cyanide

Ferrate(Ⅵ), is a new type of green water treatment agent, has shown a great potential in environmental remediation. This work dealt with the synthesis, the characteristics, and the application of ferrate(Ⅵ) for water treatment. An on-line electro-chemical equipment was made in lab to assess the factors influencing the formation of ferrate(Ⅵ), its efficacy in treating electroplating-wastewater and petrochemical-wastewater containing cyanide. The main conclusions are summarized as follows:(1) On-line synthetic parameters were examined to discuss the effects of electrode combinations, NaOH concentrations, electrode distance, current density and concentrations of ions on the formation of ferrate(Ⅵ) in an electro-chemical device(a volume of 10 L) with a commercial cast iron plate as anode, NaOH solution as electrolyte. The results showed that the optimum conditions for the on-line electro-chemical production of ferrate(Ⅵ) were as follows: electrode combination as dual cathode, NaOH concentration as 250 g/L, electrode distance as d=2 cm, current density as Id=31.25 mA·cm-2, and the optimum concentration of NaCl as 100 g/L. Under the above optimum conditions, the maximum current efficiency for ferrate(Ⅵ) production is 22%. An electro-chemical device based optimized conditions was designed as a technological support for industrial production and application of ferrate(Ⅵ).(2) A study on simultaneous removal of total cyanide, Cu2+ and Ni2+ in electroplating-wastewater by ferrate(Ⅵ) was conducted under various pH values and different ferrate(Ⅵ) dosage. The results showed that the removal of cyanide by ferrate(Ⅵ) in electroplating-wastewater was fast and efficient, and that adsorption and flocculation of the reaction products of ferrate(Ⅵ) further removed Cu2+ and Ni2+, achieving the simultaneous removal of cyanide and heavy metals. The removal efficiency of total cyanide, Cu2+ and Ni2+ in electroplating-wastewater by ferrate(Ⅵ) is above 90% when the solution pH is 9~10 and the ferrate dosage is 0.024~0.048mmol/L.(3) The removal of SCN- by ferrate(Ⅵ) in cyanide-containing petrochemical-wastewater under various pH values and different ferrate(Ⅵ) dosages were investigated. The results showed that ferrate can be efficiently oxidized SCN- in petrochemical-wastewater, without bringing secondary pollution, and that the removal efficiency of SCN- by ferrate(Ⅵ) at solution pH is 7~9, and ferrate(Ⅵ) dosage of 0.032~0.064 mmol/L is above 90%.