KINETICS AND THE MECHANISM OF CHEMICALLY-DEPOSITED CALCIUM CARBONATE GRINDING

Abstract

Conversion calcium carbonate is a by-product of manufacturing mineral fertilizers, i.e. NAP fertilizer. It needs further processing and grinding to be used as a filler for polymeric materials. The choice of equipment and the final degree of grinding depend on the kinetic characteristics of the process. The aim of the work is to study the mechanism and kinetics of chemically-deposited calcium carbonate grinding. The feedstock was ground by means of a laboratory vibratory mill for 30 minutes, a sample was taken every minute to study the fractional composition and the speed of the process. It was determined that the most intensive processing takes place during the first minute of grinding (t = 0-1 min), the maximum grinding speed is reached for fractions of +50-75 μm, +75-100 μm, and +100-150 μm and are 14.5 %/min, 13.5 %/min and 17.5 %/min respectively. Particles predominantly fall into the grade of -5 μm, and, to a lesser extent, into the classes +5-10 μm, +10-20 μm, and +20-30 μm, resulting in a bimodal distribution. With an increase in processing time by more than 5 minutes, the agglomeration of particles occurs, the size of which ranges 10-30 μm. The grinding kinetics of the chemically-deposited calcium carbonate obeys the rules of a first-order equation. A linear relationship is observed between the relative content of the unground fractions ln[Rd(t) / Rd(0)] and the grinding time t. The specific grinding speed of conversion calcium carbonate increases significantly with an increase in particle size.