Decomposition of Bayer process organics: Low-molecular-weight carboxylates

Abstract

The degradation of twenty-one low-molecular-weight organic carboxylates has been studied at 90 and 180 °C in a synthetic Bayer liquor consisting of 6 mol kg -1 aqueous NaOH solution for periods of up to 36 days. The reactions were monitored and the major degradation products identified by HPLC and NMR spectroscopy. The carboxylates chosen for study either could be intermediates, or occur as a result of decomposition of organic matter in the Bayer process. Aliphatic carboxylates without hydroxyl substituents were stable at 90 °C but decomposed at 180 °C, except for formate, acetate, oxalate and succinate. The corresponding aromatic carboxylates were stable even at 180 °C. Both aliphatic and aromatic carboxylates with hydroxyl substituents were unstable at 90 °C, except for lactate and 4-hydroxybenzoate. The most frequently detected decomposition products for both aliphatic and aromatic carboxylates were formate, acetate, oxalate, succinate and lactate. Phenolate was also observed for some aromatic carboxylates. These products are briefly discussed with reference to possible mechanisms for the degradation reactions.

Some highs and lows (and in-betweens) of solubility measurements of solid electrolytes

“…Such ores inevitably contain a certain amount of organic matter (humic material, cellulose, etc. ), which reacts with the NaOH solution, producing a variety of sodium carboxylate salts [25]: NaOH(aq) Organic matter ---~ NaOOCR(aq) -200 °C Some of these carboxylate salts have significant impacts on Bayer process operations, and so their properties are of considerable industrial interest. For modeling purposes [24] these properties need to be measured to very high concentrations (say, up to 6 or 8 M).…”

Solubility and related properties in hydrometallurgy

“…The primary low-molecular-weight products are benzenecarboxylates, phenolates, and aliphatic carboxylates; however, polymeric carbon backbones enriched in aromatic groups have also been reported to persist [17]. Although the carbonate ion is the thermo dynamically stable form of carbon under (aerobic) Bayer process conditions, benzoate, succi- nate, acetate, formate, and particularly oxalate are found to be (meta-)stable in 6 mol kg -1 NaOH solution for up to five weeks at temperatures up to 180 °C [21]. The last three of these sodium carboxylates are currently incorporated in our Bayer liquor model [1].…”

Statistical Modeling of the Industrial Sodium Aluminate Solutions Decomposition Process

“…[4] Also, recent investigations indicated that the introduction of certain ions in the aluminate solution influences the crystallization rate and the size of obtained gibbsite crystals. [7][8][9][10][11][12][13] The crystallization mechanism of Al(OH) 3 from sodium aluminate solutions was investigated by Li et al, [4] they indicated that the mineral form of obtained crystals, as well as their size distribution, depends on the concentration of the solution at temperatures ranging between 338 K (65°C) and 343 K (70°C). This was also proved in the investigations published by Dash et al [14] The kinetics of the gibbsite crystallization from the caustic sodium-aluminate solution, as well as size and the shape of obtained particles, depend on the following parameters of the process: temperature, alumina/caustic ratio, amount and size distribution of the crystallization seeds, stirring speed, and the presence of activation ions added to the solution.…”