AMIRA International is an independent member-based global organisation of mining, exploration and minerals industry service companies, which develops and brokers collaborative research projects with industry-wide relevance. AMIRA International has responded to the industry need to develop improved processing methods for economic recovery of low grade copper, by initiating the development of a number projects within its Low Grade Copper portfolio. This action was motivated by a number of factors including: the large, and growing, inventory of low grade copper resources that fall below the cut-off grade for conventional concentrate production, and the significant economic impact successfully implemented new technology would have on low grade copper resources.
The operating costs for most conventional processing methods increase exponentially with a reduction in grade, with the highest proportion of operating costs incurred through mining and milling unit operations. Using the conventional processing paradigms, copper ore grades of <0.8% and <0.5% for Greenfield and Brownfield applications respectively, are generally uneconomic. The vast majority of discovered copper resources, however, fall within this low grade category.
Although heap and dump leaching technologies are utilised for low grade ores, metal recoveries are generally poor, variable and unpredictable. Importantly, the current methods available for low grade processing are ineffective for recovery of primary copper sulfide ores, most notably chalcopyrite, the predominant form of copper mineralization.
The AMIRA International Low Grade Copper Portfolio comprises a number of related projects aimed at significantly changing the economic viability of the large inventory of ore resources that are just below the economic cut-off grade for conventional processing. The projects range from those with immediate operational application, to those with longer term industry-changing potential. Although each project has its own specific objective, there is considerable synergy between the various projects. While the program has an initial copper focus, the projects also applicable to other commodities including nickel, uranium and gold.
The projects in the Low Grade Copper project are:
- P1134 - Heap Leach Scale-up for Liquid and Gas Dispersion
- P1135 - Continuous Saturated Coarse Particle (Vat) Leaching
- P1136 - In Situ Fracture Stimulation and Leaching
- P1129 - Micro-Capsule Leaching
For further information please contact Chris du Plessis at tel +61 8 9216 0451 email@example.com
P1134 - Heap Leach Scale-up for Liquid and Gas Dispersion
The aim of the project is to develop a robust heap leaching scale-up methodology, where laboratory-determinable parameters reliably translate into full-scale heap performance. The scale-up methodology will focus specifically on liquid distribution, as hydraulic characteristics are most critical to improved heap leaching performance.
Sub-optimal heap leaching performance can often be attributed to inadequate determination and understanding of the fundamental parameters governing solution percolation. This leads to over-reliance on generic rules-of-thumb, empirical testing methods and extrapolation of design parameters from one project to another. Optimal scale-up design can be informed through geomechanical testing procedures to determine permeability and percolation characteristics relevant to liquid and gas dispersion, combined with appropriate and validated predictive models. The purpose of this project is to provide robust and operationally validated methods for process optimization and design. A "reverse-engineering" approach will be used to match ore types, ore preparation and stacking procedures and the resulting externally observed leaching kinetics obtained on commercial-scale, to laboratory measured parameters of geomechanics and leaching kinetics on samples of the same and similarly prepared ores, and to use a mathematical dispersion models to establish the fundamental basis for the correlation.
P1135 - Continuous Saturated Coarse Particle (Vat) Leaching
In many instances heap leaching is not an appropriate or viable treatment option for low grade ore, even when optimized for hydraulic and gas dispersion properties. Heap leaching is not effective for applications with inherent unfavourable hydraulic properties, where copper occurs mainly as chalcopyrite, or where extended heap leach times lead to high acid consumption. An important reason for low rates and recoveries in heap leaching is because solution access to most of the target mineral surfaces is via capillary diffusion rather than bulk solution flow. This results in solution chemistry gradient effects that preclude effective chalcopyrite leaching. Diffusion-related limitations can be overcome by using a saturated continuous leaching reactor in which coarse particles are minimally and intermittently mobilized (not agitated) to alter the pore space arrangement. This strategy eliminates the occurrence of stagnant pore spaces (and thus diffusion-controlled solution gradient effects) and facilitates high solution throughputs, improving control of the leach solution chemistry and increased metal recovery. The aim of the project is to develop a viable alternative option for low grade ore, based on high rate leaching kinetics (approximately two orders of magnitude greater than for heap leaching) in continuous coarse particle (3 - 6 mm) saturated leach reactors (new generation, vat-style reactors). Reactor development for this project will draw upon technology advances in dredging, slurry conveying and stirring, as well as thickener technologies.
P1136 - In Situ Fracture Stimulation and Leaching
Heap leaching and coarse particle continuous vat leaching, circumvent the high energy cost associated with milling, thereby reducing operating costs. However, neither of these methods circumvent mining costs, which along with milling are typically the main operating costs. For this reason, heap leaching and saturated coarse particle leaching, is most applicable to Brownfield low grade scenarios where the ore has already been mined (and mining costs have been expensed) as part of a higher grade mining operation. Many low grade deposits, however, do not have a high-grade component. Such deposits can only be made economically viable if both the mining and milling costs are circumvented. In-situ leaching provides a potential option to achieve this objective.
The aim of this project is, to enable viable in-situ fracture stimulation and leaching technology for suitable hard rock sulfides mineral deposits. In addition to circumventing mining and milling costs, the in situ leaching also offers the potential to overcome the capital costs of pre-stripping and significantly reduce above-ground processing plant costs.
This project will be conducted by various research disciplines from CSIRO and will apply existing fracture stimulation technology, developed for the petroleum industry, to determine the extent to which target mineral veins can be made accessible to leaching fluids by induced fracturing. The target application would be geological formations in which sulfide minerals are present as late stage veins or in strata bound ore. Laboratory hydraulic fracturing will be conducted on large blocks (400mm in each dimension) of representative ore under stress conditions that simulate the pressures and stresses as they occur, in situ, at the selected field site. Proven modelling methods will then be used to design the field-scale hydraulic fracturing campaign. Proxy methods will be developed to quantify the extent of target mineral exposure to induced fractures without actual leaching. These methods, used in combination, will provide the information required to evaluate the economic attractiveness of the technology, prior to undertaking actual leaching. Comprehensive groundwater modelling will also be undertaken to manage and demonstrate solution management and containment within the fractured zone, again ahead of actual leaching.
The project is designed to overcome the main hurdles to effective deployment of in-situ fracturing and leaching, which include: " Solution containment and hydraulic management to prevent groundwater contamination. " Ore permeability and the extent to which existing or induced fractures can effectively access and intercept target minerals - particularly relevant in the context of hard rock mineralization. " The ability to leach target minerals for economically effective metal recovery.
P1129 - Micro-Capsule Leaching
Economically viable hydrometallurgical metal recovery from low grade ore is dependent upon two criteria: (1) effective recovery and (2) affordability. An important constraint for low grade ore processing is that high potency (effective) leaching reagents are often consumed by gangue mineral interaction, thereby precluding their use. This, in turn, results in the use of low potency leaching reagents and reactor methods, with poor metal extraction outcomes, particularly from low grade chalcopyrite ores.
In this project, micro-capsule technology is proposed as a means to overcome this constraint by facilitating selective interaction of lixiviants with valuable target minerals. Micro-capsule technology can be used to create optimal leaching conditions locally by encapsulating and presenting leaching agents selectively and directly to target minerals, with minimal gangue mineral interaction.
Conventional mineral processing already makes use of selective chemical interaction with sulfide minerals over gangue minerals, in the form of collectors. The most widely used example is the use of xanthate chemicals that selectively interact with sulfide minerals to render them hydrophobic, enabling effective mineral flotation. The proposed concept is that similar selectivity can be achieved through functionalising the outside of the micro-capsule wall with collector-like functional groups so that they selectively bind to valuable sulfide minerals. Once delivered to the target sulfide mineral surface, the capsule discharges its lixiviant cargo in close proximity to the target mineral site. The cargo in the capsule can be tailored to initiate a leaching reaction, prevent passivation or disrupt already-formed passivation layers, deliver oxidants or provide local pH modification at target mineral surfaces. The micro-capsule cargos can be designed either to improve conventional leaching methods (such as heap leaching) and chemistry or to facilitate leaching using unconventional solution chemistry conditions (e.g. in non-acidic bulk solutions). Micro-capsules may also be used to enhance coarse particle saturated leaching kinetics, or for effective metal recovery from in-situ leaching scenarios.