A method to determine optimum heap leach height has resulted from design work for a uranium heap leach project on the Macusani Plateau in south-eastern Peru. An analysis of the optimum heap height estimate details its sensitivity to the constituent variables algebraically, graphically, and, in contour plot format. A comparison is drawn against a Namibian uranium project with design details in the public domain and agreement is found to be reasonable. The leach extraction model and dynamics are analysed in terms of solution to ore ratio (SOR), reaction extent and acid consumption efficiency to address model time dependence loss in the model simplification step. The rate of change in the acid efficiency is used to specify the target extraction and determine leach SOR and leach time. The validity of the optimum height estimate equation is supported by favourable comparison against the spreadsheet calculation results and data from another uranium heap leach project. The estimate is dependent on recovery discount and pad maintenance costs but is independent of theoretical recovery and pad capital costs.

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The Taiwan Kobin Bottom Ash Processing & Recycle Plant (Kobin-BAPRP) processes approximately one quarter million metric tons of bottom ashes from several municipal solid wastes the incinerators annually, generating fine aggregate finished products and ferrous recovery. The results from USEPA Method 1311 Toxicity Characteristic Leaching Procedure (TCLP) for un-treated bottom ash indicate that about 5% of the time that lead and less than 0.5% of the time, copper or cadmium may fail to meet leaching standards (i.e. 5 mg/L for Pb, 15 mg/L for Cu, and 1 mg/L for Cd ). Previously, Kobin applied phosphoric acid solution for stabilization, which caused strong odor problem, increased moisture content, and still about 1% of the time that TCLP-Pb failed to pass the standard, hence, required reprocessing. Recently, Kobin-BAPRP has switched its stabilization agent from the phosphoric acid solution to dry chemical dosage. In addition to having a better stabilized byproduct, the use of dry chemical further ensures worker safety. Dry chemical is water insoluble and fine calcium phosphate particles, with different combinations of buffers and complexing agents, such as Fe+2, Fe+3, Al+3, or chloride. It took about 8 months for laboratory tests and plant trials to identify the optimum dosage as well as the best mixing point. Long term operation has demonstrated that dry chemical spread and mixing is safe to communities and workers, non-reactive with storage and handling materials, generates no toxic gases or odor, and most importantly, provides for effective and consistent Pb stabilization. The final stable family of mineral crystals includes complexed hydroxyapatite and chlorapatite minerals.

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A method to determine optimum heap leach height has resulted from design work for a uranium heap leach project on the Macusani Plateau in south-eastern Peru. The on-off/racetrack heap leach process, the base case design parameters and the relevant column leach test results are described. In the problem development, a maximum leach extraction versus grade relationship, the leach extraction model, a recovery discount model, the financial parameters utilised and the calculation sequence are described before a spreadsheet solution for optimum heap height is presented. Equations used in the spreadsheet solution are detailed in the algebraic optimisation problem formulation. Symbolic solution proved too challenging for the computer algebra system utilised (Maxima). The subsequent algebraic simplification to the leach extraction model yields a succinct solution for an optimum heap height estimate. The estimate is affected by recovery discount and pad maintenance costs but is independent of theoretical recovery and pad capital costs. The initial results were approximately 50% of the spreadsheet calculation results. A correction factor is required to compensate.

This research was performed under the auspices of the U.S. Department of Enerry under Contract No. DE-4C02-76CHffi016. DISCIAIMER _ This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor atry agelcy ihereof, nor any of thei¡ employees, nor any of thei¡ contra€tors, subcontractors, or their employees makei any warranty, express or implied, or assumes any legal liability or responsibility for the |9?1a9t completeness, or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. Reierence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recoÍunendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily stãtJor ieflect those of the United States Government or any agençy, contractor, or subcontractor the¡eof.