Gold cyanidation with potassium persulfate in the presence of a thallium (I) salt

The use of potassium persulfate as oxidant in gold cyanidation is proposed at pH values between 10 and 11. The addition of thallium (I) ions enables h igh cyanidation rates to be maintained at pH values higher than 11, as it a cts as a catalyst of the process. When gold cyanidation is performed in the simultaneous presence of 10 mM persulfate and 0.5 mM thallium (I) the diss olution rate is eight times higher than that obtained by conventional cyani dation, and the working pH can achieve values near 13, The kinetics of the process have been studied, and the results compared with those obtained by conventional cyanidation, The process is shown to be diffusion-controlled w ith an activation energy of 19.2 kJ mol(-1). Finally, an equation of the re action rate that describes the kinetics of the overall process for gold cya nidation with potassium persulfate and thallium (I) is presented, and the [ CN-]/[S2O82-] ratio at which the dissolution rate reaches its limiting valu e is shown to be 2.5. (C) 2000 Elsevier Science B.V. All rights reserved.