Gold leaching model studies. Trichloroisocyanuric acid (TCCA) and sodium dichloroisocyanurate (SDIC), were examined for their ability to oxidatively dissolve gold metal in the presence of sodium chloride or sodium bromide (Fig. ). Gold wire (5.00 mg, 25.4 µmol) and an excess of TCCA or SDIC were used (1 mmol) in these model studies. All reactions were run at 25 ºC with magnetic stirring. The concentration of gold leached into solution was monitored by atomic absorption spectroscopy (AAS). In general, both TCCA and SDIC could oxidize and dissolve the gold wire when either sodium bromide or sodium chloride were present. However, the low solubility of the SDIC leach formulations led to poor mixing, so TCCA was selected as the oxidant for subsequent experiments. TCCA alone (without the additional bromide or chloride salts) was not effective at dissolving gold under these conditions. A catalytic amount of the bromide or chloride additive (10 mol%) was sufficient for activating leaching, but the highest rates of leaching were observed when using a TCCA:NaX molar ratio of 1:2 (where X = Br or Cl) (Fig. ). In two examples shown in Fig. , 98% of the gold was dissolved over 3 hours when using the NaBr activator and 90% of gold was dissolved over the same period using the NaCl activator. For the rate-optimized leach formulation, sodium bromide was thought to activate TCCA by nucleophilic attack of one of its chlorine atoms. This would generate bromo monochloride (BrCl), which could hydrolyze to hypobromous acid (HOBr) and hydrochloric acid (HCl). UV-Vis analysis of the reaction between TCCA and sodium bromide in water indicated the formation of a new species with an absorption maximum at 264 nm (Fig. ), which is consistent with the formation of hypobromous acid . The final pH of these model leaching solutions ranged from 1.7 to 5.9, depending on the amount of sodium bromide or sodium chloride activator. While hypobromous acid is thought to be formed in the active leach solution, we note that there will be complex equilibria of hypohalous acids (HOBr and HOCl), molecular chlorine or bromine, and halide and cyanurate salts. Furthermore, while off-gas generation was minimal at this temperature and scale, its formation must be taken into account for larger scales or higher temperatures. Therefore, the leaching vessel was always vented as a precaution and the leaching process was carried out in a fume hood or in an area with suitable ventilation.