Influence of particle size distribution on disc vacuum filtration for dry stacking of niobium flotation tailings

The particle size distribution (PSD) of tailings can frequently vary based on ore characteristics. Often, ore requires more intensive grinding to concentrate the valuable mineral. Tailings filtration and dry stacking are significantly influenced by particle size, particularly by the presence of fine particles, which are challenging to filter. Vacuum disc filters are highly productive for coarse particles and are widely used in Brazilian dry stacking operations. This study investigated the influence of PSD on tailings filtration and dry stacking at a niobium mine. Filtering leaf tests and Proctor compaction tests compared the coarse tailings, planned for dry stacking, with finer tailings produced by grinding and the addition of ultra-fine particles. The results indicate that particle size affects both the unit filtration rate and residual moisture. Proctor tests show that finer tailings tend to increase dry density and slightly decrease the optimum moisture content. Small variations in tailings PSD have a low impact on filter cake moisture. However, filtration rates significantly decreased. Finer tailings resulted in a cake with higher moisture, exceeding the optimum compaction moisture. Filtration rates are strongly affected by the presence of ultra-fines particles smaller than 10 µm. To efficiently filter niobium tailings using vacuum filters for dry stacking, the ultra-fines should be limited to 10%.