Abstract: A Bayer liquor is produced by dissolving bauxite in hot caustic soda. The liquor is cooled so that it is supersaturated, and seed crystals of gibbsite are added to the liquor (16). At the same time at least part of the liquor is subjected to intense ultrasonic irradiation (34) such as to cause cavitation, preferably by passing liquor and seed crystals (28) through a recirculation duct (30). The ultrasound increases the proportion of fines by breaking up any crystal agglomerates and also by generating crystal nuclei, and also removes fouling from crystal surfaces. The precipitation process is consequently more effective. If ultrasound is applied when measurements indicate that there are insufficient fines in the liquor, this improves the consistency of the precipitation process.

Abstract: A sugar coating is formed on a solution multiplicity of items (5) such as confectionery, using a suspension of crystal nuclei in a solution of sugar. This suspension is created by ultrasonic irradiation of a supersaturated solution. For example a saturated solution is cooled, and stored in a tank (16) connected to a recirculation (10) loop (18) containing a pump (24) and an ultrasonic irradiation module (26). Treated suspension (20) is withdrawn to coat items (11), and new supersaturated solution (14) is introduced. The sugar solution is sufficiently viscous to suppress crystal growth.

Abstract: The Bayer process uses hot sodium hydroxide solution to obtain pure alumina from bauxite ore. Alumina dissolves, and is then precipitated, and the remaining caustic Bayer liquor can be recycled for use again. However sodium oxalate tends to build up in the recycled liquor, and causes problems. By removing a stream of the liquor, treating it so as to be supersaturated with sodium oxalate, and then subjecting it to ultrasonic irradiation, crystal nuclei are formed. The resultant crystals can then be separated from the liquor. Surprisingly, other organic compounds in solution do not prevent this crystallisation process from being effective.

Abstract: In the Bayer process for the production of alumina, problems are caused by silica dissolving in the caustic liquor. This silica arises from the presence of kaolin in the bauxite. A process for removing this kaolin comprises contacting the bauxite with sodium hydroxide solution to form a mixture, and subjecting the mixture to intense ultrasonic irradiation to cause cavitation; this can be carried out at temperatures below 100° C. This enhances both the dissolution of kaolin and the precipitation of sodium aluminium silicate. Silica remaining in solution in spent Bayer liquor (after digestion and then precipitation of gibbsite) can be removed by a similar ultrasonic irradiation treatment to cause it to precipitate before it forms scale in heat exchangers.

Abstract: A crystalline material sufficiently pure for use in pharmaceuticals may be made by forming a saturated solution of the material, changing the temperature of the solution so it becomes supersaturated, and subjecting the solution to irradiation by high intensity ultrasound, the frequency of the ultrasound being scanned over a range of frequencies. For example the ultrasound may be varied between 19.5 and 20.5 kHz, and this variation may be sinusoidal. Preferably the ultrasound is provided only briefly, say for less than 5 s, before allowing the solution to cool gradually without further irradiation. The ultrasound may be applied using a vessel with an array of ultrasonic transducers attached to a wall, so each transducer radiates no more than 3 W/cm2 yet the power dissipation within the vessel is between 25 and 150 W/litre. This method can reduce the metastable zone width to less than 10 K. It is applicable in particular to aspartame.

Abstract: Small crystals are made by mixing a solution of a desired substance with an anti-solvent in a fluidic vortex mixer in which the residence time is less than 1s, for example 10 ms. The liquid within the fluidic vortex mixer (12) is subjected to high intensity ultrasound from a transducer (20, 22). The solution very rapidly becomes supersaturated, and the ultrasound can induce a very large number of nuclei for crystal growth. Small crystals, for example less than 5 ?m, are formed. The resulting suspension is treated so as to add or remove ingredients, and then spray dried using an atomizer tuned to create small droplets in such a way that each droplet should contain not more than one crystal. Crystal agglomeration is hence prevented.

Abstract: A crystalline material sufficiently pure for use in pharmaceuticals may be made by forming a saturated solution of the material changing the temperature of the solution so it becomes supersaturated, and briefly subjecting the solution to irradiation by high intensity ultrasound, before allowing the solution to cool gradually without further irradiation. The ultrasound may be applied using a vessel with an array of ultrasonic transducers attached to a wall, so each transducer radiates no more than 3 W/cm2 yet the power dissipation within the vessel is between 25 and 150 W/litre. This method can reduce the metastable zone width to less than 10 K. There is no erosion of the wall and consequently no formation of small particles of metal. It is applicable for example to aspartame, and to amino acids.

Abstract: Proteins may be made by genetically engineered microorganisms, the protein being stored in the form of inclusion bodies (IB). The proteins in the inclusion bodies are in an insoluble and inactive form. They may be dissolved using a solubilization reagent (18), and the resulting solution diluted so that the proteins refold into the active form. This refolding of the protein is enhanced by subjecting a solution or suspension of the protein to low intensity sound waves (25), at a low enough intensity that the protein is not denatured. The intensity may be between 10 and 100 mW/cm2.

Abstract: Small crystals are made by mixing a solution of a desired substance with an anti-solvent in a fluidic vortex mixer in which the residence time is less than 1 s, for example 10 ms. The liquid within the fluidic vortex mixer (12) is subjected to high intensity ultrasound from a transducer (20, 22) in or on the wall of the mixer, or coupled to a pipe supplying liquid to the mixer. The solution very rapidly becomes supersaturated, and the ultrasound can induce a very large number of nuclei for crystal growth. Small crystals, for example less than 5 ?m, are formed that may be of a suitable size for use in inhalers.

Abstract: Small crystals are made by mixing a solution of a desired substance with an anti-solvent in a fluidic vortex mixer in which the residence time is less than 1 s, for example 10 ms. The liquid within the fluidic vortex mixer (12) is subjected to high intensity ultrasound from a transducer (20, 22) in or on the wall of the mixer, or coupled to a pipe supplying liquid to the mixer. The solution very rapidly becomes supersaturated, and the ultrasound can induce a very large number of nuclei for crystal growth. Small crystals, for example less than 5 &mgr;m, are formed that may be of a suitable sise for use in inhalers.

Abstract: In apparatus for decomposing organic waste by oxidation using electrochemically regenerated Ag++, provision is made for preventing unwanted carryover of organic material into recovery streams and into any solid waste produced by the apparatus. Gases formed in the processing are also treated to prevent or minimise any carryover of toxic components in gaseous effluent from the apparatus.