Here is a description of Alumina Manufacturing process and why a VSEP would be needed. Aluminum in Bauxite is dissolved chemically, using caustic soda (NaOH in water), in an Alumina refinery. This produces liquor of soluble Aluminum Oxide in caustic water. The dissolved Aluminum Oxide and caustic are recovered and the Aluminum is further processed to pure Aluminum Ingots. Red mud is the reject or waste from this process. The slurry is sent to settling ponds where it is aged. Some caustic water can be decanted and leach lines below collect seepage of caustic water. This caustic water is reused in the processing of the raw ore.
Sub-micron sized particles will take a long time to settle. Silt that is about 10 microns will take 33 minutes to settle. Colloids that are 0.1 microns will take 230 hours. Sub-micron colloidal solids will be problematic if settling is the treatment method. Polymers may help but won’t get it all and would contaminate the caustic water if it were to be reused. I don’t have knowledge about flocculation of Red Mud, if that’s what you’re working on. I do have experience with filtration of Red Mud.
Membranes configured for high solids, (VSEP, Filter Presses, Tubular Membranes), can reject colloidal iron, titanium, and clay and be sized for any flow rate. Typical operating costs are about $15/metric ton of dry solid produced. The justification of membranes is that caustic recovery is enhanced which reduces the ongoing cost of purchasing new caustic for the mining process. The cost of operating membranes for caustic recovery should be less than the cost of buying caustic. Bauxite mines are in remote places and shipping caustic can be quite expensive.
This VSEP process will also greatly Reduce Environmental Impact of the Alumina factory.