Optimisation of the solids suspension co

The large-scale biooxidation of gold concentrates is usually carried out in continuous stirred tank reactors (CSTR), where achieving homogeneous slurries presents a significant challenge due to solid stratification. This work aims to identify the optimal agitation conditions in a CSTR to enhance solids suspension. A series of experiments were conducted in a 5-liter glass tank containing a 6% w/v slurry, utilizing impellers (pitched blade turbine and marine propeller) positioned at varying heights (6.7 to 13.4 cm) and operating at rotational speeds ranging from 370 to 1040 rpm, alongside aeration rates from 0.3 to 3.7 vvm. A statistical experimental design enabled the derivation of response surface models correlating the exit and mean solids concentration with impeller type, distance from the bottom, and aeration and agitation rates. Results indicated that no solids settled at the bottom during testing, and solids concentration was consistently higher near the bottom than at the top. Under optimal conditions, the marine propeller required 15 to 22% more agitation than the pitched blade turbine; however, it was determined that the marine helix is preferable due to its lower power requirements and ability to produce a more uniform suspension.