In a surface mine there are currently two zones being exploited of approximately equal grade and...

Transcribed Image Text:

In a surface mine there are currently two zones being exploited of approximately equal grade and recovery potential, but each subject to different costs, and transmitting different residual quantities of mercury into the tailings pond, as summarized in the following table: Zone Processing rate Operating cost (S/t ore) Site remediation 5.9 3.7 I II (t ore/h) 50 35 Drilling and blasting 2.5 3.8 Milling and flotation 37.9 48.8 Tailings treatment 16.4 15.5 Hg in tails. (ppm) 125 90 a) Implement and solve a linear program using Excel Solver, to determine the most cost- effective approach to excavate and process ore from the two zones, a total of 1800 t within 48 hours, considering all of the tabulated operating costs, and maintaining an average Hg in tailings discharge concentration no higher than 100 ppm. Use the variables m and mi to represent the mass of ore processed from zones I and II, respectively. b) Solve the linear program by first applying the substitution mu = 1800-mi and then applying the logic of a one-dimensional version of the Simplex Method. (You should not use Solver in this case). c) Modify the exercise of part b), considering an undetermined Hg discharge concentration limit expressed as LHg.max. Thus obtain expressions for optimal mi" and mu" as a function of LHg.max. d) Following the analysis of part c), create a plot of Optimal Operating Costs Per Tonne versus L.Hg.max, considering the feasible range of LHg.max values, up to 150 ppm. Consider that the permissible mercury transmitted by the tailings stream depends on the current mercury within the pond, e.g. if the current mercury content within the pond is relatively low, then LHg.max can be temporarily increased. Describe how reliable monitoring of mercury levels supports a more cautious and optimal balance between production and environmental management, rather than hamfistedly fixing LHg,max to 100 ppm. Can this be a case for process integration and/or upgrading mercury measurements? Explain. In a surface mine there are currently two zones being exploited of approximately equal grade and recovery potential, but each subject to different costs, and transmitting different residual quantities of mercury into the tailings pond, as summarized in the following table: Zone Processing rate Operating cost (S/t ore) Site remediation 5.9 3.7 I II (t ore/h) 50 35 Drilling and blasting 2.5 3.8 Milling and flotation 37.9 48.8 Tailings treatment 16.4 15.5 Hg in tails. (ppm) 125 90 a) Implement and solve a linear program using Excel Solver, to determine the most cost- effective approach to excavate and process ore from the two zones, a total of 1800 t within 48 hours, considering all of the tabulated operating costs, and maintaining an average Hg in tailings discharge concentration no higher than 100 ppm. Use the variables m and mi to represent the mass of ore processed from zones I and II, respectively. b) Solve the linear program by first applying the substitution mu = 1800-mi and then applying the logic of a one-dimensional version of the Simplex Method. (You should not use Solver in this case). c) Modify the exercise of part b), considering an undetermined Hg discharge concentration limit expressed as LHg.max. Thus obtain expressions for optimal mi" and mu" as a function of LHg.max. d) Following the analysis of part c), create a plot of Optimal Operating Costs Per Tonne versus L.Hg.max, considering the feasible range of LHg.max values, up to 150 ppm. Consider that the permissible mercury transmitted by the tailings stream depends on the current mercury within the pond, e.g. if the current mercury content within the pond is relatively low, then LHg.max can be temporarily increased. Describe how reliable monitoring of mercury levels supports a more cautious and optimal balance between production and environmental management, rather than hamfistedly fixing LHg,max to 100 ppm. Can this be a case for process integration and/or upgrading mercury measurements? Explain.