Mass balance in the Coulter

The procedures for setting up a mass balance and for mass calibration of the Coulter Counter technique are identical. A weighed amount of sample of known density is suspended in a known volume of electrolyte, a known portion of which is analysed. From these data the total volume of particles in the analysed volume of electrolyte can be calculated and compared with the measured volume of particles. For a mass (or volume) balance this measured volume of particles is calculated by means of a prior calibration, generally with an appropriate latex standard. For mass calibration, on the other-hand the ratio of measured and calculated particle volume is used to correct the prior calibration constant. The following equations can be derived ... 

The normal procedure for determining the number oversize is to carry out a mass balance and present the derived Coulter data graphically as counts/gram against particle size. The problem with using this procedure is that, in some cases, there are only one or two oversize particles in the presence of millions of smaller ones. It is therefore necessary to filter out many of the smaller particles and carry out a count on the oversize residue. This poses problems in that some oversize particles may be lost in the process and, even more likely, large contaminant particles may be introduced in the filtration process. 

Therefore, although the Coulter Counter method allows an accurate evaluation of particle volume diameter in inert media as checked by mass balance evaluation, in some cases it is not suitable to measure particle swelling. In these cases, the Coulter Counter method needs to be integrated with other granulometric techniques. 

As the best model for grade efficiency calculations we applied model 3 in which the catch and probe 2 sample should be known. This model resembles the procedure proposed by Hermann and Leschonski [3], as a correction of the mass balance is applied in this calculation model as well. It appears from our experience that the size analysis of the probe 2 sample must be carried out very accurately. Enough sample should be collected on the filter in order to perform reliable Coulter Counter analysis. 

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