#Disrupt Mining: Integrated Extraction and Recovery System for Complex. Ores and Wastes"

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1 #Disrupt Mining: Integrated Extraction and Recovery System for Complex Ores and Wastes" The Process. Supplemental Information The proposed integrated process covers both extraction and recovery of many of the most economically important base and precious metals. The key to making the system practical is the simple removal of the leached metals from the leach solution, allowing high recovery of values and allowing the bulk of the leach solution to be recycled repeatedly. The precise chemical formulations for the salt-based leaching process cannot be published in detail at this time to protect the patentability, but information on the sulphide precipitation step and our proprietary biological sulphide generation system are available. Highlights of the integrated process include the following: The leach is carried out at a neutral to alkaline ph (no acid). It can be carried out at low temperature and at atmospheric pressure to minimize costs. This means that many potential problems of leaching processes are avoided, such as high Fe and Al in process solutions, and formation of clay slimes through break down of silicates. The leach reagents used are not consumed in the process. They can be fully regenerated by sulphide precipitation to remove the metals. The reagents used are all low cost and readily available in most locations. Leached metals are precipitated into high grade sulphide concentrates. Separate metals can be selectively removed to a high degree (e.g. CuS separate from ZnS).

2 Our preferred option is to use our proprietary bio-based process to further upgrade products and regenerate sulphide. The dewatering of leach tails is enhanced by the process chemistry, and thorough dewatering allows high leachate recovery and reuse, thus minimizing costs. This part of the process is expected to lead to reduced tailings footprints, allow dry-stacking of tailings and make zerodischarge minesites more likely. If necessary, the water balance can be maintained by membrane separation to produce clean water and upgrade brine solutions, or by removal of bleed streams to the bioreactor, where they are treated and used to provide nutrients. The overall system flowsheet is shown in the Figure 1

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4 Biometals Technology. Kemetco Research has been developing an in-house technology based on biological generation of sulphide from various sulphur sources and its use for selective metal recovery from waste streams and process solutions. This is an advancement of previous biological sulphate reduction technology that has already seen limited commercial application. Kemetco s advances relate mainly to biological efficiency and reduced energy use. Expertise around selective metal removal from solutions using sulphide precipitation is also an important aspect of the technology. Selective use of sulphide precipitation for metal recovery is a key to the economic potential for the overall extraction system. The sulphide does not need to be biologically generated, but there are a number of important advantages over use of a chemical reagent: Recycling of sulphur within the system results in improved metal product quality and allows energy recovery. With the use of a low cost energy source to the bioreactor, the cost of sulphide can be significantly lower than chemical reagent sulphide. It is less hazardous to generate sulphide on demand than to transport and store chemical sulphide. Metal sulphide precipitation using a dilute H 2 S stream (in a carrier gas from the bioreactor) can generate larger precipitate particle sizes, providing better solid-liquid separation. Use of reagent sulphide results in eventual build up of sodium in the recycled leach solution. BioSulphide Process - Doug Warkentin is the principal developer of this extraction technology. He was also one of the principal inventors of the BioSulphide technology, which was patented in This

5 was later successfully commercialized for metal recovery from mine drainage streams. The patent was assigned to another company in 1997, and expired in US Patent # A, issued Dec 24, Biometals Publication Kemetco s advances in developing the Biometals technology have not been published in detail. The work has been advanced in-hose, and with a series of grants from the Canadian Government via the NRC-IRAP program. To date, one paper has been published documenting some of the results obtained in testing the technology on a number of mine drainage applications. The paper is available on-line: An example of results from this paper is shown below, indicating the degree of separation that can be obtained using sulphide precipitation. This example was from a mine drainage stream containing less than 20 ppm each of copper and zinc, but still almost complete separation was obtained. The ability to fully recover metals from low concentrations is also essential to the success of this system, particularly for gold and silver recovery. This means that no pre-concentration is needed and low grade ores tailings and wastes can be successfully treated.

6 The precipitates generated from this process can be very high grade. Typically the raw sulphide precipitates generated can be above 60% copper, or 50% zinc prior to any upgrading that may be added as part of the sulphide regeneration stage. Applications. The initial concept is to apply the technology to low grade ores containing both precious metals and base metals, particularly where a significant portion of the base metals occur as oxides. These ores are difficult to process as gold ores due to the high cyanide consumption and high cyanide destruction costs that can result from conventional cyanide leaching. These processes generally also do not recover significant base metal values. Depending on the ultimate efficiency and operating cost levels that can be achieved, there are also a wide range of other possible applications that the technology could be adapted to: Reprocessing of tailings deposits. This may be especially applicable to site remediation, for example where a wet tailings impoundment is to be converted to a dry stack. Low-grade base metal oxides. Copper, Nickel and zinc are readily leached, and more importantly are easily recovered from the leach solution. Conventional acid leaching needs high solution metal concentrations to make the solvent extraction (SX) recovery method work economically. Refractory gold ores. Because of the different leaching chemistry, the technology is likely to give better recoveries than cyanide without pre-treatment for certain refractory ores where gold is subject to preg-robbing or is locked in sulphide minerals such as arsenopyrite.

7 Metal-contaminated industrial wastes. This technology was derived from work aimed at removing heavy metals (e.g. cadmium) from municipal waste by-products. This is also an important use, particularly where the waste also contain significant metal values. Environmental Aspects. Several of the potential environmental advantages of this technology are noted above. The most important potential benefits to the environment may be summarized as follows: Closed-loop extraction and recovery. There is relatively little reagent loss or consumption, and there is also relatively little build-up of unwanted components in the recirculating leach solution, meaning low inputs and little or no discharge beyond the solid tailings. Improved dewatering. The process minimizes the generation of unwanted components such as iron or aluminum hydroxides, clay slimes, etc. The salt component also tends to act as a coagulant for fines, resulting in easy dewatering. This further adds to the potential for closedloop, zero-discharge operations. Heavy metal containment. Certain hazardous heavy metals, such as lead and cadmium, can be extracted from wastes or ores and concentrated into either sellable products or high grade concentrates for small-scale containment or recycling. Using sulphide precipitation, these can be readily removed from solutions to very low levels. Cyanide replacement. In cases where this technology can provide economic gold and silver recovery it would eliminate the need for cyanide use, and the need to destroy the resulting cyanide complexes in the discharge solution.