Wet oxidation of precipitation yield inhibitors in sodium aluminate solutions: Effects and proposed degradation mechanisms

Organic compounds in the processing of lateritic bauxites to alumina Part 2: Effects of organics in the Bayer process

“…A number of aliphatic carboxylates with two or more adjacent hydroxyl groups, which are therefore either known or likely to be inhibitors (Bouchard et al, 2005;Loh et al, 2010b;Nikolic et al, 2008;Paulaime et al, 2003;Power, 1991), have been found at low concentrations in at least one Bayer process liquor . Systematic studies of this class of compounds have shown that they generally inhibit precipitation, and that the trends in inhibitor strength tend to correlate with the trends for the corresponding alditols (Watling, 2000).…”

“…Further insight into the mechanisms of hydrogen production has been provided by the recent work of Costine et al (2010Costine et al ( , 2011aCostine et al ( , 2011bCostine et al ( , 2012. The oxidation of complex organic compounds by water leads to hydrogen as the major reduction product, but can also lead to the generation of methane, propane and other volatile hydrocarbons as well as alcohols, aldehydes and ketones, as reduction products (Loh et al, 2010b). Consistent with this, methanol, acetaldehyde, formaldehyde, acetone and methyl-ethyl ketone have all been identified in the vapours from bauxite slurry storage (desilication) tanks, digesters and/or evaporators (Galbally, 2004(Galbally, , 2008Galbally et al, 2012).…”

Understanding Hydrogen in Bayer Process Emissions. 1. Hydrogen Production during the Degradation of Hydroxycarboxylic Acids in Sodium Hydroxide Solutions

“…In the absence of oxygen, an ionic degradation mechanism involving base-catalyzed oxidation by water has been proposed. 27,33 The significance of this mechanism in the current context is that it not only explains the occurrence of oxidative reactions under anaerobic conditions 2,34À36 but also shows how and why hydrogen gas can be produced even in the presence of oxygen.…”

Removal of carbonate and oxalate pollutants in the Bayer process using thermal and chemical techniques

“…Selecting an appropriate method depends on various parameters including operational and economic conditions. Several researches have been conducted on wet oxidation methods using oxygenated compounds such as air oxygen and ozone (Malito, 2006;Loh et al, 2010), filtration, ultrafiltration and reverse osmosis (Mueller and Green , 2000;Marciano et al, 2006), adsorption by resin, active carbon, alumina collected by an electrostatic precipitator (Williams, 1998), washing alumina hydrate (Yamada et al, 1980), evaporation, condensation and precipitation (Conroy and Gloster, 1979 ), evaporation using spray (Carruthers et al, 1977), calcinations of solution (Soucy et al, 2004;Machold et al, 2009), using lime (Matyasi et al, 1982), flocculation by additives such as polydadmac (Poly diallyl dimethyl ammonium chloride) and acrylic polymer (Sommese and Mahoney, 1955), precipitation by germination (sodium oxalate, sodium aluminate, lime, etc.) (Gnyra, 1981), liquid-liquid extraction (Bush and The, 1985), photocausticization of Bayer liquor (Pareek et al, 2003), increasing soda concentration (Donaldson et al, 1984;Akihisa et al, 1972), oxidative photocatalytic degradation (Wang and Adesina, 1997) and using a source of phosphate in the presence of lime (Dunstan et al, 2006).…”