Controlling a continuous stirred tank reactor for zinc leaching

This work focuses on the open-loop and closed-loop analysis of a continuous stirred tank reactor for zinc leaching from sphalerite (ZnS) via modeling and simulation approaches. The corresponding process analysis is based on a multi-input multi-output, approach by considering the inlet flows of minerals, acid solution, and aeration as process inputs and dissolved oxygen, ZnS concentrations, and pH as process outputs. An analysis of the relative gain array matrix was performed to determine the best control input pairs. In addition, a bifurcation analysis was carried out considering the process inputs as bifurcation parameters to show adequate operating regions. A local stability analysis of the selected equilibrium points in the chemical reactor under the previously selected operating conditions is presented, employing an eigenvalue analysis. Finally, a class of smooth super twisting sliding-mode controller is proposed to regulate the corresponding dissolved oxygen and pH in the reactor, which leads to increased sphalerite leaching; its performance was compared with a standard super twisting sliding-mode controller. The controllability of the reactor was analyzed via the dynamic behavior of the uncontrolled variables (zero dynamics). Numerical experiments show the satisfactory performance of the proposed controller under the selected operating conditions.