Weir Minerals is a good advice but their pumps are way too big and much too expensive because they are rated for 400 psi minimum. My guess is around 200 k$ for such a pump. The problem is that 120 psi is not really a high pressure but 250 m³/h is a rather high flow for a PD pump. 10 mm particles can be a challenge but more important is the density of the solids and the solids concentration. Why do you think that a centrifugal pump cannot do that, Rob821?