A Descriptive Model for Microbial Population Dynamics in a Copper Sulphide Bioleaching Heap with Spatial and Physicochemical Considerations

Abstract

A descriptive mathematical model is a valuable tool that can help understand the relationship between the heap leaching process at the Escondida mine in Chile, the microbial community that participates in the process, and the physical characteristics of the heap, such as the arrangement and the mineral composition of the individual leaching strips. However, the bioleaching process at Escondida is a system, which presents many challenges to modelling. The main challenges relate to heap's design and mineral characteristics, the complex interactions between biological and physicochemical parameters, and the unexpected changes in the heap's operational conditions. The heap is sampled periodically and more than 20 variables, including 16S rRNA gene copy number for 16 different microorganisms, are recorded. The data exhibit complex behaviour, including variable dynamics between strips, systematic differences between lifts of the heap, and spatial and temporal correlations. In this work, we develop a non-linear descriptive model for the microbial population trajectory along the leaching cycle and across the different strips. The parameterisation of the model considers the different dynamics between lifts, and strip specific parameters characterise the behaviour of data from individual strips. The parameterisation also allows for spatial correlation by incorporating the effect of adjacent strips on the microbial population trajectory. The model is found to provide a good fit to the data and captures its behaviour across strips. Residuals showed no systematic patterns of departure between the observed and modelled response. The R2 values ranged from 0.53 to 0.71, indicating a reasonable level of predictive power.