US 6,555,076 B1 · Bauxite ore digestion in the bayer process

Abstract

The process according to the invention to raise simultaneously to an optimum level the temperature and concentration of an aqueous medium intended for use in bauxite ore digestion in an alumina production plant according to the Bayer process, which includes successive phases (a) to (f) in which: a) the aqueous medium coming from digestion containing pregnant liquor is cooled and evaporated in a multiple staged flash evaporation zone; b) the sterile residue is separated, the aluminium trihydroxide is precipitated and the aqueous medium, consisting of spent liquor, intended for use in digestion is recovered; c) if need be, the required quantity of water, additional to that already evaporated in phase (a) is eliminated by evaporation in a specific evaporation section; d) the aqueous medium intended for use in digestion is heated in several stages; e) the flash vapour generated in each of the stages of the evaporation phase (a) is used in each of the stages of the heating phase (d); f) the aqueous medium intended for use in digestion coming from the heating phase (d) is heated by live steam. is characterised in that, in addition to all these phases, a simultaneous heating and evaporation phase is carried out on the aqueous medium intended for use in digestion.

Claims41

Dependent claims

A process line for use in a Bayer process installation for the treatment of bauxite wherein a slurry of bauxite ore in an alkaline aqueous medium is digested at temperature and pressure values to dissolve alumina as sodium aluminate and separated into solids and a pregnant liquor stream from which aluminum hydroxide is precipitated leaving aqueous medium, the process line to raise simultaneously the temperature and concentration of the aqueous medium for use in the bauxite ore digestion, including:

a section of interconnected evaporator-flash tanks FT1 to FTn installed in series and through which circulates an aqueous medium coming from the bauxite ore digestion in a digester D;
a section of interconnected heaters H0, H1 to Hn installed in series through which circulates the aqueous medium for use in the bauxite ore digestion, each evaporator FT1 to FTn flash tank being connected with each heater H1 to Hn directly associated with each flash tank FT1 to FTn between the flash tanks and the heaters for obtaining vapor circulation;
an optional specific evaporation section P for eliminating by evaporation a quantity of water, additional to that removed in the evaporator-flash tank FT1 to FTn;
at least one heater H0 connected to a source of live steam installed at the inlet of a mixing device and/or bauxite ore digester by means of the aqueous medium to raise the temperature of the aqueous medium coming from the outlet of the first heater H1 in the heater section H0, H1 to Hn to the temperature required for digestion;
and
a simultaneous heating and evaporation section for the aqueous medium used in the digestion.

3 more elements

In a Bayer process treatment of bauxite where a slurry of bauxite in an alkaline aqueous medium is digested at high temperature and pressure values required to dissolve alumina as sodium aluminate and separated into solids and a pregnant liquor stream from which aluminum hydroxide is precipitated leaving aqueous medium, the improvement for raising simultaneously the temperature and concentration of said alkaline aqueous medium from which aluminum hydroxide has been separated for its use in the further digestion of bauxite, comprising the steps of

a) cooling and evaporating the aqueous medium in a section of interconnected flash evaporators FT1 to FTn installed in series;
b) separating a the sterile impurities residue from the pregnant liquor, precipitating the aluminum hydroxide from the sodium aluminate present in the aqueous medium, separating out the aluminum hydroxide and recovering the remaining aqueous medium for use in the further digestion of bauxite;
c) evaporating a quantity of water in addition to that removed in the flash evaporators FT1 to FTn in an evaporation section P inserted between the section for the precipitation and separation of aluminum hydroxide from the pregnant liquor and recovery of spent liquor in order to further concentrate the aqueous medium for further digestion of bauxite;
d) heating the aqueous medium in a section of interconnected heaters H0, H1 to Hn installed in series with each flash evaporator FT1 to FTn directly associated with each heater H0, H1 to Hn;
e) using the flash vapor generated in each flash evaporator FT1 to FTn to concentrate the aqueous medium recovered in step b) and forming the aqueous medium to be used in the digestion of bauxite, in the heaters H0, H1 to Hn;
f) utilizing live steam supplied to a heater H0 to raise the temperature of the aqueous medium coming from the heaters to the temperature required for digestion;
and
g) carrying out a simultaneous heating and evaporation of the aqueous medium for use in the digestion of bauxite in a simultaneous heating and evaporation section.

5 more elements

Dependencies are inferred from the claim text.

Bauxite ore digestion in the bayer process

Life of this patent

Bauxite ore digestion in the bayer process

Life of this patent

Abstract

Claims41