The problem of simultaneous decoupling and pole placement without cancelling invariant zeros is important, especially in the case of unstable invariant zeros. An experimental model developed of a primary grinding circuit contains such zeros. The simultaneous decoupling and pole–placement problem without cancelling the unstable invariant zeros of the primary grinding circuit is approached by searching for solutions of the nonlinear system of equations composed of the characteristic equation and the decoupling conditions using ideas of an αBB global optimization approach. The simultaneous steady–state decoupling and pole placement problem is then solved for the primary grinding circuit without cancelling invariant zeros using an eigenvector based approach as well as the steady–state decoupling condition.