Thickening followed by vacuum or pressure filtration is usually applied for both, products (concentrates) and wastes (mine tailings) in huge quantities in the mining industry. While all three unit operations are long known and well understood, the scale but also the abrasiveness of the material still provides huge challenges.
Conventional, high rate and so-called paste thickening (or deep cone thickening) are all applied to separate the majority of the water added to ground rock for beneficiation, in particular froth flotation. Pre-treatment of the slurry by coagulation and/or flocculation aids in the thickening process and also helps with variable flow rates. As dewatering is the final process step in mineral beneficiation flowsheets, the thickener and filter have to accommodate the changing flow rate coming from the beneficiation plant, which often fluctuates considerably. Thus, thickener control is of upmost importance to achieve a constant thickener underflow product in regards to solids concentration but often more importantly in regards to yield stress to enable pumping of paste. Scale-up of paste thickening has its own challenges due to the drastic change in flow behaviour with only minor changes in solids content.
Tailings dewatering is becoming more and more important due to environmental constrains and also due to public pressure after recent dam failures and resulting loss of life and property. Another important reason for tailings dewatering is water recovery, especially in arid areas such as South Amerika but also Australia. Thus, disposing thickened tailings in ponds is more and more replaced by back-fill of dewatered tailings into underground mines or dry stacked tailings, the thickening, filtration and stacking of huge quantities of mine tailings. This requires vacuum filtration for well filtering tailings but more commonly pressure filtration for fine liberated and finely ground tailings that require higher driving force for dewatering to achieve a solid cake. The large quantities of tailings generated in the alumina, coal, gold, base metals and other mines makes optimising this more than appropriate.
Concentrates - also produced in million of tonnes per annum - are either shipped overseas or directly fed into smelters or other refining processes; often require certain low moisture content. Shipment of concentrates require a moisture content below the TML (transportable moisture limit) to avoid shipment tragedies. Pelletising, smelting or other refining processes also have their own moisture requirements for concentrate filter cakes. With resources becoming rarer, finer liberation produces more difficult to thicken and filter concentrates (and tailings). Thus, higher and higher dewatering forces and more deliberate filtration needs to be applied, increasing the design requirements, operating costs and maintenance requirements. The abrasiveness and with this the wear and tear occurring in filters but also in pumps provide every day maintenance challenges which can be tackled by intelligent and partly simpler designs. Operations also have to account for human factors such as variability and lack of training and skills which is more challenging in boom-and-bust type industries such as the mining industry...
Session: K4 - Keynote Lecture IV
Day: 23 October 2019
Time: 13:00 - 14:15 h