Optimizing inventory stockpiles and mine production: An application of separable and goal programming to phosphate mining using AMPL/Cplex

CIM Bulletin, Vol. 92, No. 1030, 1999

M.L. Smith, Mining Engineering Dept., BRC, University of Queensland, Brisbane, Queensland, Australia

In the Phosporia formation of SE Idaho, ore quality varies by depth, seam and distance along strike; phosphorus recovery is sensitive to these variations. Plant ore feed can be blended over time to minimize this fluctuation by using a combination of mine production and inventory stockpile scheduling. Mixed-integer and goal programming has been used to optimize short-term mine production, but the seasonal nature of mine haulage requires the use of stockpiles both at the mill and the mine. The contents of the stockpiles can also be optimized as part of the production scheduling problem, but introducing inventory control introduces a nonlinear term into the formulation. A solution using a piecewise linear formulation is modelled and solved using AMPL/Cplex, and solution strategies are discussed for similar large-scale problems.

Keywords: AMPL/Cplex, Phosphate mining, Stockpiling, Inventory control.