First, determine the weight % of solids and the solid particles' characteristic size. Then you must decide whether the pump is to be used for short or long runs, low or high capacities. A tradeoff of pressure drop and solids loadings is one important criterion. Pressure drops are not so simple to estimate because slurries may behave as non-newtonian fluids in different flow regimes.
For a start I can recommend the book by Donald R. Woods "Process design and engineering practice" published by Prentice Hall, chapter 2.