Solution crystallisation process control and design (liquid-solid separation)
In the mining industry, sequential precipitation is commonly applied to separate valuable elements such as cobalt, nickel and manganese successively from leaching solutions. Operating conditions such as temperature and pH have significant impacts on product quality and operating cost. In addition, some typical crystallisation processes, such as the production of ammonium paratungstate from evaporative crystallisation are energy intensive, and the quality of the ammonium paratungstate is dependent on variables such as the nucleation temperature, evaporation rate, stirring rate and pH. The optimisation of the crystallisation process is essential to reduce the energy cost and obtain a uniform particle size distribution. This research uses in-situ Focused Beam Reflectance Measurement (FBRM®), a laser based process analytical technology, in an integrated workstation (Optimax workstation 1001) with accurate temperature control, stirring speed, anti-solvent dosing rate and pH to develop optimised model-free control strategies for crystallisation processes. This can be achieved through a feedback control strategy that is based on the difference between the set points and the real-time measurements of effects such as concentration/supersaturation, particle counts, temperature or concentration (T/C) control, and direction nucleation control. Additionally, model based control strategies are developed in MATLAB via population balance equations and process analytical technologies (PATs).