Identifying organic foulants on activated carbon from gold processing plants

One of the ways of assessing organic fouling of activated carbon during gold cyanide adsorption is thermogravimetry (TG). Unfortunately TG only gives an overall percentage of organic fouling agents and not the identity of individual compounds. However, previous work with pure reagents adsorbed on activated carbon indicated that when thermally decomposed, the evolved gases are characteristic of a specific fouling agent. This current work reports on the use of this information and three thermal analysis techniques, namely thermal desorption-pyrolysis-gas chromatography-mass spectrometry (TD-py-GC-MS), thermogravimetry-mass spectrometry (TG-MS), and thermogravimetry-Fourier Transform Infrared (TG-FTIR) spectroscopy, to identify the organic fouling agents on activated carbon samples from commercial gold processing plants. Analysis of a suite of samples from one gold processing plant, Plant A, showed that fouling by a xanthate compound had occurred as indicated by the detection of carbonyl sulfide at 360–400 °C. For another gold processing plant, Plant B, the detection of propanal at approximately 370 °C and carbonyl sulfide at 215 to 540 °C indicated fouling due to both frothing agents and xanthates respectively. The thermal analysis of these samples showed many other gases had evolved indicating the presence of other unknown organic fouling agents.