Determination of optimum heap height from column leach tests: 2. Sensitivity analysis

Abstract

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.

Determination of optimum heap height from column leach tests: 1. Model development and initial results

“…The next paper (Apelt, Forrester, Short and Stefan in press) provides details of a sensitivity analysis of the optimum height estimate and a comparison with a Namibian uranium project with design specifications in the public domain (Bannerman Resources Limited 2012).…”

“…Trading off the lost revenue against the pad cost savings yields an optimum heap lift height and corresponding leach recovery. Figure 6 shows the lost revenue curve and the cost savings curve for the 2014 project conditions (Apelt et al 2014). They intersect at the optimum heap lift height, which is 7•8 m. The leach recovery that corresponds to this heap height is 87•3%.…”

“…In the pursuit of an algebraic solution, the spreadsheet calculation was transcribed into Maxima, 1 GBM Minerals Engineering Consultants Ltd, UK 2 Plateau Uranium Inc, Canada a computer algebra system (CAS). The algebraic problem formulation presented below is a recapitulation of this earlier work (Apelt et al 2014), which is required as the foundation of the new research presented in this paper.…”

“…The method also contends with changes in production rate and grade, which are typical early in a project as further exploration and drilling take place. For example, in 2013 the annual ore processing rate studied was 12·1 Mt year −1 at an average U 3 O 8 grade of 212 ppm (Apelt, Forrester, Short and Stefan 2013), whereas in 2014 the annual ore processing rate was 8·5 Mt year −1 , with an average U 3 O 8 grade of 259 ppm (Apelt, Forrester, Short and Stefan 2014; Macusani Yellowcake Inc 2014). In 2016, with the incorporation of new areas of mineralisation, the annual ore processing rate is 10·9 Mt year −1 , with an average U 3 O 8 grade of 289 ppm (Plateau Uranium Inc 2016b).…”

“…In the pursuit of an algebraic solution, the spreadsheet calculation was transcribed into Maxima, a computer algebra system (CAS). The algebraic problem formulation presented below is a recapitulation of this earlier work (Apelt et al 2014), which is required as the foundation of the new research presented in this paper. After a leach extraction model simplification, an algebraic solution for an estimate of optimum heap height is presented, along with some encouraging initial results.…”