Precipitation of potassium aurocyanide from dipolar aprotic solvents using a supercritical antisolvent

Gas antisolvent (GAS) precipitation is considered for the quantitative recovery of potassium aurocyanide (KAu(CN)2) from dipolar aprotic solvents including acetone, dimethylsulfoxide and N-methyl-2-pyrrolidone. Experimental data are reported on the solubility of KAu(CN)2 in the various solvents expanded with carbon dioxide at 308 K. It is shown that carbon dioxide is an effective antisolvent for reducing the solubility of KAu(CN)2 in acetone and N-methyl-2-pyrrolidone. The effect of several process parameters on the GAS process are also discussed in the context of solvent-assisted elution, a process which utilises dipolar aprotic solvents for the desorption of metal-cyanide complexes from activated carbon. The process parameters investigated are the initial solute concentration, the dielectric constant of the solvent and the presence of water in the solvent. It is proposed that the use of mixtures of dipolar aprotic solvents may provide a means of tuning the dielectric constant to satisfy the individual requirements of both processes.