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Structural determination, identification and removal of Bayer liquor organic poisons
thesisposted on 2022-03-29, 00:45 authored by Regina Elizabeth Maher
Large financial investments are required for the precipitation step of the Bayer Process to ensure moderate yields of gibbsite are recovered. This step is crucial for Al(OH)₃ production but unfortunately is subjected to inhibition caused by the presence of particular organic matter known as 'poisons'. Despite extensive research performed to mitigate these inhibiting effects, they have experienced severe limitation. The structure of the poisons is essential for understanding how inhibition is induced and consequently, how they can be removed. A new extraction and derivatisation method was developed using SPME with a polyacrylate fibre, coupled with MTBSTFA on-fibre derivatisation for analysing Bayerl Liquor OM. As a result, 65 organic compounds were structurally characterised. Importantly, this OM identification process confirmed the absence of model poisons, namely polyhydroxyls, within Bayer Liquor. A comparative study of Bayer Liquor organics, both pre and post gibbsite harvesting was used to identify the poisons. From this, 7 poisons were proposed with the inhibiting functionality identified. To this end, a novel OM removal strategy was investigated which focused on transforming these highly polar poisons into volatiles. This removal strategy presents potential for mitigating inhibiting effect as some OM were successfully removed from the liquor in the form of pyrroles.