Removal of Cyanide in Solution Using Electrodeionization

Toxic and harmful gases such as HCN are emitted during the polyacrylonitrile-based carbon fiber production process. Electrodeionization(EDI) was applied to remove the CN^-in the solution which obtained after the absorption by NaOH from the waste gas stream, meanwhile regenerate NaOH solution back to the absorption process.

A modified three-chambers EDI device was applied. There were three chambers from the cathode to the anode in proper order: negative electrode chamber 1 which was fed in the CN^- solution from the bottom to the top, resin chamber 2 filled up with anion exchange resin, and the positive electrode chamber 3 flowing NaCl solution. There were anion-exchange membranes dividing the chambers between the chambers. CN^- in chamber1 transferred into the resin chamber, and part of OH^- produced by ionization under the DC power would regenerate the resin and make the CN^- going through into chamber 3 continuously. Also, Cl2 was produced on the anode electrode in chamber 3 by electrolytic action which would oxidize the CN^- to harmless substance. And, the main OH^- stayed in chamber 1 so thatNaOH was regenerated. Effects of the configurations like the sizes, and operation conditions such as the current density and the flow rate were investigated to examine the feasibility of device. With the optimization of operation conditions, the effluent water of chamber 3 can reach below 0.5mg/L which meets the requirement of cyanide discharge standard.