Membrane separation of cyanide species

The aim of the thesis research was to identify a membrane technique that would allow for fractionation of metal-cyanide species. Such separation of the cyanide complexes of precious metals from other complexes of heavy metals would have numerous advantages and could significantly improve the environmental footprint, efficiency and the cost of gold processing. Experiments were performed using spiral-wound and flat-sheet membrane filtration systems with reverse osmosis, nanofiltration, ultrafiltration, and microfiltration membranes. Research Philosophy; was based upon size considerations. First, all the membrane types were examined for the filtration of NaCN from solution. Solutions of selected metal-cyanide complexes were used in the second part of the research. It was established that the best-suited membrane was the ultrafiltration membrane JW. Analyses of speciation and MDS showed that heavy metals were present as highly hydrated, large complexes, while gold and silver formed dicyano ions, characterized by a smaller hydration shell. Contact angle measurements proved that the JW membrane was hydrophobic; thus, it was capable of rejecting 30% of heavy metals. It is believed that a truly hydrophobic membrane could achieve higher rejection of cyanide complexes of heavy metals, while sustaining low rejection of precious metal cyanide complexes due to size considerations. However, due to the lack of applications, hydrophobic membranes with the pore size in the range of 100-500 A are not commercially available.