On the analysis of fine wet grinding in a batch ball mill

The influence of the slurry density on the fine wet grinding performances of a batch ball mill was examined for an alumina hydrate feed. Irrespective of the operating conditions, the size reduction process proceeds fast in the first period of grinding (20 min); then its rate progressively reduces and after 1-2 h the size of the product approaches a final asymptotic value. The initial grinding rate is higher and the final mean diameter smaller using quite diluted feeds (water content 50%-80%), which represent the optimal operating conditions. When the slurries are dense (20% water), the rate of the grinding process can be enhanced by adding a small amount (2-10 kg m(-3)) of a grinding aid (sodium metaphosphate), which improves the flowability of the suspension. The product size distributions can be adequately described using the Rosin-Rammler expression: an attempt was made to relate the characteristic size of the distribution to the time and to the water content.