Abstract: A process for producing alumina is described in which the efficiency of calcination is greatly improved by utilizing a total heat exchange system in which alumina hydrate is heated stepwise in a plurality of heat exchange stages to sequentially higher temperatures approaching calcining temperatures and is then fed to a calciner for final conversion to alumina, and the calcined alumina is cooled in a plurality of heat exchange stages, with sensible heat being transferred from the calcined alumina cooling stages to the alumina hydrate heating stages at a temperature in each stage only slightly higher than the temperature of a heating stage or at which the heat is consumed in that stage. Further efficiency in the system may be obtained by predrying the alumina hydrate to remove superficial moisture using air from the system. Furthermore, exhaust gases from the calciner may be used to preheat combustion and fluidizing air for the calciner.

Abstract: A process is described for removing dissolved silica from process solutions or slurries formed in the Bayer process for producing alumina from bauxite. In the novel process, a Bayer process solution or slurry is contacted with porous agglomerates of a material containing Bayer process desilication product and bonded together by a polymer resin which is resistant to chemical degradation by high concentrations of caustic present in Bayer process liquors. The desilication product is essentially complex hydrated sodium aluminum silicates and typical bonding resins are polyvinylchloride or polypropylene.

Abstract: This invention provides an improved process for increasing the specific gravity of red mud. The process comprises mixing red mud in an acidic solution, such as sulfur dioxide solution, having a pH of between about 1.5 and about 3.0 to form an insoluble red mud residue. The specific gravity of the red mud residue can also be increased by heating the residue in air to a temperature of 250.degree. C. to about 300.degree. C. This process enables recovery of a treated red mud derivative having an increased specific gravity in excess of 4.0, which makes the product particularly useful as a weighting agent for drilling fluid, and as the solid phase of slurries used to fill crevices and fissures exposed by drilling or excavation.

Abstract: A process for the recovery of rare earth elements from Bayer Process red mud includes the following steps: (a) digesting red mud containing rare earth elements with a dilute acid solution, e.g. sulphur dioxide dissolved in water, to selectively dissolve the rare earth elements while leaving iron in the red mud substantially undissolved; (b) separating the solution obtained from the solid residue and (c) recovering the rare earth elements from the solution.

Abstract: A method of transferring heat between process liquor streams such as streams of caustic liquor in the Bayer process for producing alumina from bauxite, utilizing a heat pipe arrangement for heat exchange. The process streams respectively pass in contact with one surface of a first heat-exchange wall and one surface of a second heat-exchange wall while being isolated from the second surfaces of the two walls; these second walls are exposed to a closed volume (also isolated from both process streams) containing a heat transfer fluid that vaporizes below the temperature of the hotter process stream and condenses above the temperature of the cooler process stream. The heat transfer fluid vaporizes at the exposed surface of the wall contacted by the hotter stream, and condenses at the exposed surface of the wall contacted by the cooler stream, thereby transferring heat (as heat of vaporization) from the former stream to the latter.

Abstract: A process is described for the recovery of rare earth elements from a sulphurous acid solution containing them. The rare earth elements can be successfully separated and recovered by solvent extraction from the sulphurous acid solution, being an organo-phosphorus compound as extraction agent. Di-2-ethylhexyl phosphoric acid or 2-ethylhexyl phosphonic acid mono-ethylhexyl ester is preferred as extraction agent.

Abstract: A process for producing alumina from bauxite by the Bayer process. Bauxite slurry is pressure digested in caustic soda solution to dissolve aluminum hydroxides in the bauxite as sodium aluminate while leaving most of the remaining constituents of the bauxite in solid form as red mud. The red mud is separated from the digested slurry to obtain a caustic-aluminate pregnant liquor, alumina hydrate is precipitated from the pregnant liquor and the alumina hydrate is calcined to obtain the alumina. The separation of the red mud from the digested slurry is carried out at a temperature above the boiling atmospheric temperature of the liquor phase of the slurry.