Applications of CO2 in CO2-responsive foams and pyrochlore froth flotation
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Reduction of auxiliary substances which reduces waste is a main principle of green chemistry that this thesis deals with in two projects by using CO2: (1) CO2-switchable additives for controlled foam dissipation, and (2) the use of CO2 as a pH modifier in pyrochlore flotation. The first project is a study of foams generated with the conventional surfactant tetradecyltrimethylammonium bromide C14TAB in the presence of the CO2-switchable additive N,N,-dimethylethanolamine (DMEA) or N,N,N’,N’-tetramethyl-1,4-butanediamine (TMBDA). The properties of foams generated with N2 and different additive-to-surfactant molar ratios were only influenced at a high additive-to-surfactant ratio of 10:1 for the additive TMBDA. Foams generated with CO2 are inherently less stable due to the higher solubility of CO2 and therefore faster coarsening, but even more so when the protonated additive was present. To determine if it is possible to induce a controlled foam decay through CO2, foams generated with N2 were subjected to CO2 after foam generation. Introducing CO2 from the top led to a fast foam decay even with a small additive-to-surfactant ratio of 1:1, compared to when no additive was present. The additive TMBDA contains two amine groups that can be protonated through the addition of CO2 and therefore disturbed the close packing of the surfactant which led to film rupture. The second project compares the effect of CO2 used as an acid instead of HCl or oxalic acid in pyrochlore mineral flotation. In micro-flotation testing it was found that at a pH of 4, the use of CO2 led to recoveries of pyrochlore and the gangue minerals quartz and microcline that are comparable with the recovery achieved when oxalic acid or HCl are used. The promising outcome of the micro-flotation tests were replicated in a batch flotation setup with real ore. Results of the first rougher stage at a pH of 5.9 revealed that CO2 and HCl led to comparable concentrate compositions and recovery yields, whereas oxalic acid led to a higher pyrochlore grade in the concentrate. The use of CO2 in pyrochlore flotation was therefore possible, but the gangue mineral depressing effect of oxalic acid was not achieved with CO2.