Validity of methods and measurement in alumina trihydrate precipitation
The validity of some of the current research methods used to study supersaturated alumina solutions have been evaluated. In alumina trihydrate crystallisation research, either or both the crystallisation kinetics and crystal population are of interest. Measured liquor concentrations are shown to be sensitive to the length of time before and during analysis and to the pH at which the pH meter is standardised. Solids may be analysed gravimetrically or determined from a particle size distribution (PSD) measurement, with each method having advantages and pitfalls. The population balance may be determined by counting, as with a Coulter Counter or Galai, or indirectly from a simple PSD measurement in conjunction with a mass balance. By gas adsorption measurements, the surface area of alumina trihydrate is shown to correlate well with the surface area calculated from the PSD, indicating that the particles have little porosity.