The dissolution of metals used in the super alloy CMSX-4 by means of aqua regia, with the focus of recovering rhenium by means of molecular imprinted polymers
Creators: name: Ghaleb, Matthew Stewart
Publisher: name: University of Lincoln
Year: 2024
Subjects: F180 - Analytical chemistry

description: Aqua regia, which is an acid solution of hydrochloric acid and nitric acid, was used at threedifferent strengths, over a period of seven days, to see how effective it was at dissolving theindividual metals that are used in the super alloy CMSX-4. Tantalum, Hafnium and Titaniumcould all withstand the corrosive effects and did not dissolve. The strongest strength of aquaregia (not diluted) managed to partially dissolve the other metals, with Molybdenum beingfully dissolved. The two diluted solutions of aqua regia were not as affective, howeverrhenium managed to be fully dissolvedSuper alloys, which are used in industries such as the aviation and energy sectors, are acombination of specific metals which exhibit special characteristics. When the metals arealloyed together, they produce an alloy that can withstand extreme temperatures (over+1000°C) and workloads over an extended period of time, without the integrity of the alloybeing affected. As technologies change different generations of super alloys have beendeveloped. A second generation super alloy, CMSX-4, contains 3% rhenium and rheniumbeing an extremely rare element, is an expensive metal to use (around £2500 per kg).Molecular imprinted polymers are a new separation technique that has become increasinglypopular due to their benefits of, ease of creation; low cost and extremely specific separationabilities. The specific separation is achieved during the polymerisation process, by using atemplate, identical in chemical and structure to the analyte of interest, allowing forseparation of the analyte of interest, even in the presence of similar structural and chemicalcompounds.Five molecular imprinted polymers were made, each with different concentrations of rheniumtemplate. They were tested to not only see if they could successfully trap rhenium, but to alsoinvestigate if the maximum loading of the molecular imprinted polymer would increase as theconcentration of the template increased. Throughout the research, the molecular imprintedpolymers were analysed by X-Ray fluorescence to determine the presence of trappedrhenium. The solutions that were eluted through the polymers were analysed by AtomicAbsorption Spectroscopy to identify how much rhenium was not being trapped by themolecular imprinted polymer during the analyte loading stage and how much rhenium wasbeing removed during the analyte removal stage.The research also investigated to see if a re-useable polymer was produced. The resultsindicated that not only could the molecular imprinted polymer trap rhenium; it could also beremoved and then re-used again at least four times, without the maximum loading capacitydiminishing. The results also confirmed that it was possible to trap 75mg of rhenium using 1gof polymer. Doubling the template from 60mg to 120mg did not increase the loading capacity,identifying that there was a limit to the maximum loading of the polymer, even with increasedconcentration of template.