Comparison of methods of calculating particle size from hindered settling results and its application to inorganic oxysalt precipitates

Abstract

The methods of calculating particle size from the results of hindered settling determinations are critically compared and a simple and rapid method of determining the particle size is given.

The systems studied, copper carbonate, calcium carbonate and nickel carbonate, are used to demonstrate the use of hindered settling for investigating precipitation processes and sizing particles. In the precipitation of basic copper carbonate the results of hindered settling measurements are compared with those from the use of a Coulter counter and from wet sieving.

From a study of calcium carbonate precipitates an analysis has been made of the conditions affecting particle size in precipitation processes and the mechanism of precipitation from saturated solutions. Further information has been obtained about the amount of immobile liquid carried down by the precipitate as it settles.

The addition of flocculating agents to decrease the settling time of precipitates is shown to be of practical application in the preparation of basic nickel carbonate, which is an important intermediate in the preparation of nickel catalysts. The mechanism of flocculation is explained on the basis of hydrogen bonding between the flocculating agent and hydroxyl groups on the surface.

A comparison of the particle size and the settled volume after precipitation can, for particular samples, be correlated. When a direct relationship occurs this enables information to be obtained about the attractive forces between the particles and the variation of this force with the precipitation conditions.