While working with Amira Global, Penny Atkins was part of the team progressing P420. Penny has reviewed the history of this fascinating project series, summarising the outcomes over time. Penny writes that it all began in 1984 with four key projects.
Over the past 38 years, Amira’s gold processing technology research projects have built a major research opus and significantly expanded capacity in the mining sector.
The P420 series (P420 – P420H) has been operating since 1994 and is continuing into 2022.
For operators, the research increases capacity, increases recovery or yield of products, and reduces operating costs.
To date, there have been 27 PhDs awarded for work associated with P420 projects as well as 19 Honours and fourth year project reports. Most of these graduates are employed currently in the resources sector.
The Gold Technology Group (GTG) has been the core group of research participants for all but one project. It is based at the Western Australian School of Mines: Minerals, Energy and Chemical Engineering.
Over the 38 years of activity other individuals/institutions have contributed to the projects. In the early projects, staff at Curtin University and the (then) Mineral Processing Laboratory (Western Australian Department of Mines) made significant contributions. And, in the early years of the P420 series (P420 A, B, C), CSIRO was also a significant partner.
There have also been many other collaborations, mostly notably with the late Professor Andre Laplante at McGill University in Canada, Monash University, University of Western Sydney, Mintek, Laval University, Cape Peninsula University of Technology, JKMRC (University of Queensland), BRGM (France) and others. These collaborations have strengthened the knowledge base of the project, providing enhanced delivery to sponsors.
The foundation projects
This stellar continuum of research rests firmly on the bedrock of the four projects that proceeded the current 420 series, Amira P173/P173A, P277 and P314.
P173 and P173A — Carbon in Pulp (CIP) Technology — considered what was the (then) relatively new technology of CIP, which was not always clearly understood on site.
Amira P173 devised a standard activity test for carbon and gathered information about plant operations through a questionnaire for each sponsor. It was described as “representing the first substantial commitment of the ‘new’ gold industry in Australia to processing R&D”. By P173A there were 22 companies willing to sponsor the research. It was a “practical project targeted at reducing carbon fouling, reducing carbon inventories and, at the end of the project, there was some work done on the leaching itself”!
For Amira P277, Bill Staunton, employed at the (then) Government Chemical Laboratories, at the Western Australian Department of Mines, oversaw a comprehensive review of the research on the chemistry and properties of cyanide compounds, transitional metal cyanide chemistry and on the degradation of cyanide in tailings dams. This study reviewed all the currently available practices used in the analysis of environmental samples and the methodologies for treating cyanide waste.
Of major import was that Amira P277 established that the then current practices for handling cyanide waste in the gold processing industry were safe, that cyanide degraded naturally in the tailings dams and the small percentage which did not degrade was immobilised as an iron cyanide complex, a species not considered as a contaminant in the area around the dams.
These first three projects concerned themselves with processing techniques used at that time, and for the most part, simple free milling ores.
By the time Amira P314 started, the interests of sponsors had turned to the processing of more complex ores (including those with high copper and oxygen consuming minerals, and research was undertaken on processing complex and refractory gold ores using cyanide leaching/CIP.
Interaction with gold processing sites increased dramatically, with 31 ores from multiple sites and sources being studied, to assess the benefits of oxygen addition and other alterations to the traditional cyanidation processes. It was in Amira P314 that the area of Process Control began to be considered.
By the end of P314, the researchers recognised the need for future projects to focus heavily on connecting research with measurable outcomes in industry, noting that, “It was becoming clear in 1993 that in order to optimise plant operation, and further develop Australian gold extraction technology, the emphasis of future research needed to shift in favour of plant operations.”
On that basis the P420 projects were developed, and much of the future work would be outside of the laboratory.
As the cyanide leach process remained the key extraction technology used throughout the gold industry, Amira P420, undertaken by the AJ Parker Cooperative Research Centre for Hydrometallurgy and the CSIRO Division of Minerals, in association with the Julius KRM, South Africa and the University of NSW, concerned itself, in the main, with ways to reduce the cost of cyanide use and to benchmark best practice in the incumbent technologies.
Ideas for alternatives to cyanide/CIP were canvassed. The possibility of assessing whether a plant was operating at maximum efficiency was investigated in 38-hour plant surveys and models refined using USIM PAC software. The surveys established that the mass balancing capability of this software produced realistic results. This marks the first mention of process model development in the project and was achieved through collaboration with scientists from Bureau de Recherche Géologiques et Minières, (BRGM), France and Laval University. This project saw the first development of a database of current plant operating practice and the installation of online measurement devices was shown to have significant benefits for plant control practice.
A comprehensive review of the state of developments in gold processing was published.
The research program was divided into five modules covering benchmarking/best practice, cyanide management, alternatives to cyanide/CIP, carbon management and oxygen transfer. Six sites were visited and five conferences/symposia were organised, demonstrating the increasing emphasis on maintaining the knowledge base, on transferring knowledge and on increasing understanding of the processes within the gold processing industry. The Gold on Line Database (later called the Gold Knowledgebase), accessible to all sponsors, was developed. This searchable online tool comprehensively encompasses the outputs of Amira sponsored gold processing technology projects. A review of the potential of resin-based processes, as alternatives to carbon in pulp, was made through collaboration with Mintek in South Africa.
The recovery of gold thiosulfate from solution using resins was investigated.
In 1998, the SIMCIL modelling program was released to sponsors. This is now a free online simulation tool for gold leach, carbon in leach and carbon in pulp absorption circuits and was developed by Mike Nicol during Amira P420A. This was the first of a series of online process models that would be developed over succeeding years.
In this new project, The AJ Parker CRC for Hydrometallurgy and CSIRO extended the research program to include the impact of gravity recovery on overall gold recovery in a circuit, through a deep collaboration developed with Andre Laplante of McGill University, a recognised expert in the field. The SIMCIL platform was converted to an online modelling and simulation software, and its capability further expanded. The project developed a process model for modelling gravity circuits containing batch centrifugal concentrators. An increasing interest from sponsors in alternatives to cyanide meant that research in the use of thiosulfate was expanded, making it the largest area of research in P420B.
Following the completion of Amira P420B, the Parker Centre commissioned an evaluation of the effectiveness of the project in transferring research outputs into useful outcomes for industry sponsors and of the financial value derived by end users was commissioned. In 2004, the identified financial drivers for sponsors were increasing recovery or yield of product, increasing capacity and reducing operating costs. At that time, two operator sponsors expected to obtain increased recovery of $7 million. Of the outcomes from the process optimisation module, the most important was the maintenance of a core expertise to be available to the industry and the training and education of technical staff.
Process optimisation, as the first of the four research modules, continued as the key focus in P420C. After audits of five gravity circuits, the project developed an initial model for the recovery of sulfide and gold using in-line pressure jigs. It became apparent that the data provided by a supplier sponsor was invaluable in this exercise. Detailed recommendations to individual sites were made on the basis of the plant surveys.
Another new development included a first-generation model for flash flotation of gravity recoverable gold (GRG), integrated with a gravity simulator. And SIMCIL was further expanded to include a carousel adsorption circuit modelling option and both silver/gold and copper/gold co-loading options.
In Module 2, thiosulfate process development, work focussed on all aspects of a potential new process where iron(III) – EDTA is used as the oxidant and a trace of thiourea as an anodic catalyst.
In Module 3, a model was developed to describe “the deportment and flux of cyanide within a mining lease” and the Total Cyanide Balance (TCB) model was delivered. The database of information on the use and disposal of cyanide was expanded further.
Module 4, which considered complex and refractory ores, delivered a comprehensive review of treatment options for copper-gold ores and preliminary mineralogical studies on the deportment of gold in copper-gold and preg-robbing ores. The research team believed that the “overall impact of the research module had been to inform the site metallurgist of important issues related to complex gold ore processing.”
First launched during P420A, the website was further developed during the 420C project. The following resources could now be accessed on-line:
- Process Modelling: Gravity and SIMCIL simulators
- Environmental Modelling – HCN volatilisation model, and the Total Cyanide Balance Model
- The Industry Survey Database from P420A, The Gold On Line Database continued to expand in content. The database is a searchable on-line knowledge base containing useful information in all areas of gold processing technology, including: references to published articles, reports of the current and previous Amira gold projects, public reports from the Parker Centre’s other gold R&D projects and links to useful sites on the web. During the life of Amira P420C the database continued to be expanded and by the end of the project contained more than 4,000 entries”.
The structure of the research work was reformed into a “theme” based, rather than a “modules” based, approach and in that project a “Roadmap for the Processing of difficult Gold Ores“, was developed. The themes addressed were: capturing and preserving industry knowledge; predicting and improving ore processing; protecting the license to operate, and processing difficult ores. The website had the Industry Survey Database for 2012 added to it in 2013 following P420D.
The ease of use of SIMCIL was greatly enhanced.
Under the “protecting the license to operate” theme, activities were mainly desktop exercises due to a shortfall in the project’s budget: the Total Cyanide Balance model was further refined, a database was constructed around the effect of minor metals such as As, Sb, Hg, Te, Se and Cd on gold processing and several reviews on minor metals in gold processing were compiled.
Within the Roadmap for processing difficult ores, sponsors provided the themes which they believed were high priority for future research and development. “The Processing Difficult Gold Ores Roadmap had as its focus not on the whole of the gold production chain but rather just the winning of gold from the “difficult ores”. And the driver for the P420 theme “Processing difficult ores” was to sustain ore reserves.
The process of developing a Roadmap, with industry experts providing the input and guidance, was found to keep it practical and focused on needs, but the prioritisation was found to be surprising. The lead author of this roadmap noted just how much emphasis was placed on matters other than novel lixiviants for gold. The industry consensus highlighted the things that really mattered to operators at that time.
Again, the organisation of the research project was by theme. Theme 1. Technology Transfer and Professional Development, Theme 2. Models and Optimisation and Theme 3. Future Ores Processing.
Within Theme 1, “A good practice guide to gold ore characterisation” (1st Ed) and “A guide for the treatment of copper/ gold ores and handling of ores with high nuisance copper” (1st Ed) were compiled.
Theme 2. Procedures for ore characterisation and an online modelling method (ILLM) to model the differential and total recovery dependence upon grind variation, gravity circuit operating characteristics and leach/adsorption circuit operating characteristics were developed as was the model to predict the behaviour of combined flash‐flotation gravity circuits drawing from the same recirculating load. Competitive adsorption models were developed for CIL/CIP circuits. Research was undertaken to study the corrosion of various types of grinding media (forged steel, high chromium and ceramic media)
Theme 3. Future ores. Initial work on an alternative lixiviant ended due to an outside grant not being approved but this would be revisited in P420F and the first phase of work on the continuous coarse particle gangue rejection research began.
P420E’s May 2016 report confidently asserted that “The project achieved all the targeted deliverables and also created a solid foundation for research in the next project cycle. The work in preconcentration, flash flotation, polymetallic (silver-gold and copper‐gold), preg-robbing gold ores, grinding media interactions and new lixiviants broadened the delivery of the P420 project series to all aspects of the processing value chain”.
Additional funding was sought from organisations such as MRIWA, ARC CoE on Eco-Efficient Minerals Processing, ARC ITTC on Green Chemistry and CRC ORE. The project again promoted “Themes” rather than a “Modules” organisation and considered, in addition to the immediately technical considerations, such issues as managing the water balance, e.g. using less of it and investigating technology to enable that reduction in water use. Knowledge transfer expanded e.g. plant visits and surveys increased, reagents and consumables became a major theme of the work and, within that thrust, glycine- based lixiviants were investigated for a number of ore types. There were no fewer than 32 sponsor specific visits or technology transfer events. The newly patented technology GlyCat TM to process Cu-Au ore was trialled. Ref May 2019 project report.
Theme 2: Optimising Post‐crush Liberation for Pre‐concentration. Gangue Rejection Optimisation was looked upon as the flagship theme for this project and the research showed that using hydraulic gravity-based techniques, one could obtain a significant upgrade potential.
The proposal for Amira P420G firmly emphasised the research group’s intent to concentrate 50-60% of the projects’ resources on plant optimisation and technology transfer, and also highlighted that supplier organisations would be assisted to position strategically within the industry. There would be an emphasis on professional development and mentoring through courses, site reviews, benchmarking of the best practice for training and training for use of the online models. The processing of gold and the investigation of gold ore metallurgy would utilise 20-25% of the project resources allocated to it.
In Amira P420G, The gold ore mineral processing theme “developed a series of assessment frameworks” to compare new and emerging technologies in the gold industry. (These were surveys and supplementary laboratory test work would be undertaken where gaps in knowledge were identified.)
Extension Projects – P420X
Sponsors of the P420 project, in addition to their sponsorship of the main project modules, are able to request one-on-one analyses of site samples through the P420X projects. The main activity of these projects to date has been assessment of carbon. The P420X projects provide sponsors with the advantage of having issues specific to their operations investigated by the highly experienced Gold Technology Group, at rates far more favourable than existing commercial costs.
Process Models developed throughout the Amira P420 projects and available to sponsors include:
- SIMCIL (gold only)
- SIMCIL (Competitive Adsorption – Ag and Cu)
- Classification models
- Gravity circuit Models (BCC devices and jigs)
- Flash flotation model
- Integrated flash flotation – gravity circuit model
- Integrated liberation Leach Model (ILLM)
Additionally, the Gold Knowledgebase and two industry surveys from P420D and D are available.