:: AMIRA's Heap Bioleaching Research Project Begins 2nd Phase

An innovative project enlisting bacteria for minerals recovery has drawn praise from researchers as it begins its second phase.

AMIRA International's project P768, Improving Heap Bioleaching, is a three-phase project designed to increase understanding of the microbial, chemical and physical processes underlying heap bioleaching.

Heap bioleaching is a mine site leaching technology that uses selected bacteria to assist in the dissolution of valuable metals from sulphide mineral ores. The technology is currently most commonly used in copper recovery, but there are applications across many other metals including gold, zinc and nickel.

This project proposes to address current limitations with the process by investigating the fundamental aspects of heap bioleaching. The research strategy involves a combination of laboratory and pilot scale test work, modelling, and practical demonstration of the approach at full scale. Critical model parameters will be determined, and the model will be refined and validated against laboratory and test heap data.

In particular, the project aims to deliver:

• A suite of methods and tools, including a comprehensive computer model, for the effective design, monitoring and management of heap bioleaching operations
• A comprehensive and qualitative description of the microbial, chemical and physical sub-processes occurring in sulphide bioleach heaps
• A protocol for assessing the amenability of an ore to heap bioleaching
• Strategies for improved rate and recovery of target metals in bioleach heaps
• Demonstration of these tools and strategies through improved chalcocite and chalcopyrite heap bioleaching on an industrial scale
• An expert multi-disciplinary team in heap bioleaching offering ongoing preferential service to project sponsors.

The first stage of the project was launched on 1 May 2003 with a six month duration. It was sponsored by seven companies located in Australia, North and South America and South Africa, and utilised the skills of research teams at the A.J.Parker Cooperative Research Centre for Hydrometallurgy and the CSIRO Land and Water Division in Perth, Australia; the University of British Columbia, Canada; and the University of Cape Town, South Africa.

Specific deliverables of stage one included:

• A comprehensive review of existing rate laws and microbial growth models
• Determination of cardinal growth temperatures for mesophiles, moderate thermophiles and thermophiles
• Value of pre-inoculation
• Molecular methods and data bases for quantifying biomass and community structure
• Description and demonstration of a respirometric method for measuring biological activity and a test procedure for measuring gas-liquid mass transfer rates
• Isopotential batch leaching tests to establish intrinsic rate laws for chalcocite
• Development and coding of a two-dimensional heap bioleaching model.
• Provision of an interactive current version of the HeapSim model

Dr Peter Franzmann, from the CSIRO Land and Water Division, said being involved with the first phase of P768 provided numerous benefits: "The project provides good linkage to the major companies involved (or potentially involved) in mining biotechnology. It has helped us understand their R&D needs and to tune our work to those needs. It is great to be able to get their feedback on the work program, and a challenge for us to respond to that feedback.

"The project has also enabled the formation of an excellent interdisciplinary international team that can focus a broad skill set to the task of improving our understanding of heap bioleaching. The hydrologists, chemists, microbiologists and modellers involved will influence each other's perceptions and understanding of the process, and provide new insights.

Launched on 1 March, 2004, the second stage of project P768 will build on the achievements of the stage one, and focus more on suiting the needs of specific sponsors. It will have funding worth A$2million, representing a significant increase on the funding levels of stage one.

Rio Tinto is one of five companies to have agreed to sponsor the second stage. Manager for Technology Transfer, Lucy Esdaile, said the P768 project "provides industry with the opportunity to collaborate and share the cost of improving our understanding of the fundamental reactions that occur in heap bioleaching."

"Through the project we gain access to the unique skills of research groups on three continents. Running the project through AMIRA enables the logistics of this geographically dispersed project to be managed with ease for the sponsors," she said.

Other sponsor companies include Anglo American, BHP Billiton, Phelps Dodge and WMC Resources. To individually service sponsoring companies, stage two of the project has been sub-divided into four separate modules to suit the needs of specific sponsors.

The scope of stage two, encompassed in the above modules, includes:

• Quantification and prediction of solution and gaseous transport phenomena in the mineral heap
• Validation of the hydrological component of the HeapSim model developed in Phase 1, using a sponsor's ore heap as a test site
• Leaching kinetics and its quantitative understanding in terms of the ore characterisation with particular reference to chalcocite, pyrite and chalcopyrite
• Iron chemistry within the heap environment
• The influence of the operating window with respect to environmental conditions within the heap on the kinetics of key microbial sub-processes in the heap leaching environment

In addition, stage two of P768 will benefit sponsors by providing tools to assist them in their development of ore-specific processes. These include: a methodology through which to characterise ore bodies with respect to key parameters required to describe the hydrology; procedures for characterising gas-liquid mass transfer in particulate beds; a protocol for characterising ores and their leaching performance; and a set of tools for the characterisation of the bio-phase and its functional understanding.

It is envisaged that the further understanding of key mechanisms in the heap bioleaching process, as well as enhanced validation of the predictive model through large scale columns, cribs or test heaps will be conducted in Phase 3. While a strong focus will be placed on chalcopyrite in Phase 3, it is envisaged that the validation may extend to other ore bodies, based on the requirements of sponsors.

Additional comments on the benefits of P768 stage one:
Dr Helen Watling, A.J.Parker CRC: "The expanded group brings together a broad range of skills and resources in bioleaching chemistry and kinetics and heap modelling. Outcomes are expected to include a suite of methods and research tools, including a comprehensive mathematical model, for the design, monitoring and management of heap bioleaching operations. These tools and strategies will be demonstrated through improved chalcocite and chalcopyrite heap bioleaching on an industrial scale."

Professor Dave Dixon, University of British Columbia: "Benefits included developing a fundamental understanding of the heap bioleaching process at all levels - physical, chemical, biological; gaining access to a state-of-the-art, validated mathematical model of heap bioleaching for use in design and diagnosis; and being on the cutting edge of developments towards a viable heap bioleaching process for low-grade primary copper ores."