Modeling the hydrodynamics of heap leaching in sub-zero temperatures

Abstract

Heap leaching involves the application of a leach solution onto stacked low grade ores. Solution percolates through the ore, dissolving metals from various minerals, and is recovered at the base. This process is conceptually a simple one, but quickly becomes complex when considering the sub-processes, such as dissolution chemical reactions, oxidation, precipitation, ore with different leaching characteristics, and multi-lift heaps with dynamically changing irrigation schemes.In addition, changing meteorological conditions, such as heavy rain, evaporation and extreme ambient temperatures have a significant effect on the hydrodynamics. Various factors, such as large variations in ore hydraulic properties, saturated-unsaturated flow, preferential flow pathways, perched water tables, infiltration into dry ore or possible freezing of solution within the heap, can lead to reduced leaching efficiency.This contribution describes the methods employed within a computational fluid dynamics heap leach model to account for freezing climate conditions. Validation of one-dimensional thermal phase change is performed and a theoretical column of coarse and fine ore is partially frozen to illustrate how the preferred flow path can be counter-intuitive. Finally, a three-dimensional heterogeneous gold oxide 'test' heap is simulated assuming non-thermal reactions and sub-zero ambient temperatures. The results demonstrate how recovery can be affected by cold weather changing the hydrodynamics of the heap.

Heap Leaching: Modelling and Forecasting Using CFD Technology

“…Equation (1) requires that pressure-moisture-conductivity relationships be defined to complete the model. The unsaturated soil hydraulic properties θ(h) and K(h) are in general highly nonlinear functions of the pressure head, can be temperature (T) dependent, and are represented in this work by the amended van Genuchten relationship as described by [16]. The saturated hydraulic conductivity is dependent upon the intrinsic permeability of the ore and the fluid properties that are in turn dependent upon temperature.…”

“…In this way, the ore material can be characterized by defining a particle size distribution, with a single heap grade or each particle size class having its own initial head grade. The equations solved are given below and [16] gives details of the shrinking core algorithm and coupling. The equation used to calculate the rate of dissolution of a given mineral is solved explicitly for each particle size at the start of each time step.…”

“…Fluid flow models to capture the hydrodynamic behaviour of the heap have been presented by [10][11][12][13][14][15][16] amongst others. Computational fluid dynamics (CFD) technologies have enabled more complex multi-phase transport in the modelling of the heap leaching process [17][18][19][20][21][22] with much of this work focusing on capturing the kinetics in one-dimensional columns or two-dimensional slices.…”

Hydrometallurgical Processing of Low-Grade Sulfide Ore and Mine Waste in the Arctic Regions: Perspectives and Challenges

“…The world industry has accumulated scientific and production experience that is related to assessment of ore amenability to heap leaching, engineering, and design of heap leach pads, solution irrigation systems, and collection of pregnant solutions, heap leaching schemes optimization, and chemicals regeneration [2,3,31]. Mathematical modeling techniques are being developed [32][33][34][35].…”

Preferential flow behaviour in unsaturated packed beds and heaps: Incorporating into a CFD model

“…Dixon and Petersen (2003) presented a model for column heap leaching using a model based on raffinate diffusing out to reaction sites from discrete channels through the ore and used comparisons to column test results to generate confidence in the model for predictions of behaviour in heaps. Computational Fluid Dynamics (CFD) technologies have enabled more complex multiphase transport in the modelling of the heap leaching process (Leahy et al, 2005(Leahy et al, , 2006(Leahy et al, , 2007Leahy and Schwarz, 2009;Wu et al, 2010;Garcia et al, 2010;Bennett et al, 2012;Gebhardt et al, 2012;McBride et al, 2014McBride et al, , 2016. Cariaga et al (2005) employed a mixed hybrid finite-element approach for two-phase flow in a two-dimensional heap.…”