Thermal decomposition of frothing agents adsorbed onto activated carbon

Abstract

The thermal decomposition of four frothing agents used in the flotation of gold bearing sulfide minerals was investigated, both alone and when adsorbed on activated carbon. Thermal desorption-pyrolysis-gas chromatography-mass spectrometry (TD-py-GC-MS) was used to determine the gases evolved from the thermal decomposition. Thermogravimetry (TG), coupled to either a mass spectrometer (MS) or a Fourier transform infrared (FTIR) spectroscope, was used to determine the temperature range of decomposition as well as confirm the gaseous products. Three of the frothing agents, polypropylene glycol (PPG), the closely related polypropylene glycol methyl ether (PPGME), and methyl iso-butyl carbinol (MiBC), boiled off unchanged when heated. α-terpineol decomposed by about 20%, of which the major compound was the dehydration product, limonene. When adsorbed on activated carbon and heated, PPG, PPGME and α-terpineol all produced a complex range of gases, which included propanal, 2-ethyl-4-methyl-1,3-dixolane, 3,3-oxybis-2-butanol and dioxanes. MiBC again just boiled off the carbon without appreciable alteration. Since the frothing agents all decomposed below 400°C, the usual process temperature of 650°C for the regeneration of activated carbon should be sufficient to remove any adsorbed frothing agent, although for PPG and PPGME there was evidence that not all the decomposition products were volatile. In addition, the evolved gas profile was very characteristic of the adsorbed frothing agents, and should permit identification of any contamination present on unknown plant samples.