(205c) Cyanide Recovery from Barren Solution Using UV Photodissociation and Gas-Filled Membrane Technology

A process was developed to recover cyanide from barren solution containing simple and metal cyanide complex. The technology includes pretreatment of metals and oxyanions, UV-light-aided photodissociation of metal-cyanide complex, and Gas Filled Membrane (GFM). Using a 200w medium pressure UV light at 254nm wave length, more than 85% cyanide ions (CN^-) were recovered from soluble iron cyanide complex at pH between 10.0 and 10.5 within one hour of reaction. The effluent from the UV reactor was filtered and pH was adjusted between 5.0 and 5.5 in a leak proof container, prior to pumping to the GFM that separated hydrocyanic acid (HCN⁰) from water. Liquid solutions were pumped on both sides of the membrane. One side contained hydrocyanic acid solution, and 1.0 N sodium hydroxide solution was recirculated on the other side of the membrane. Within one hour, more than 95% of the cyanide was recovered in the sodium hydroxide solution. The impacts of pH, UV dosage, sequestering agent dosage, and reaction time on the photodissociation efficiency will be presented. Furthermore, the impact of membrane flux rate on cyanide recovery will be discussed.