System and pump charecteristic determines the operating point of your slurry pump. If there is a significant static head in your system. Pump efficiency may decrease. I will not advice VFD because you will be loosing 4-5% to cover the VFD losses.
If your pump has VHS (vertical hollow shaft) motor, you will not experience any problem, except removing or temporarily reversing the discharge check valve.
All VHS motors has non reverse rachets. motor will not rotate backwards and impellers will not come loose.
Regards
A. Ozden Ertoz