BacTech’s core technology, bioleaching, uses naturally-occurring bacteria, harmless to both humans and the environment, to oxidize the sulphide materials left behind after years of mining, and separate metal from the difficult-to-process tailings.
The tailings we target contain ores and related materials contaminated by arsenic and other substances that are poisonous to humans and animals, as well as harmful to the local environment. The sulphides in these tailings react (oxidize) with the atmosphere to create an acidic solution called acid rock drainage (“ARD”), which seeps into the surrounding area over time.
BacTech’s bioleaching process can stabilize these toxins from minerals and prevent additional harmful ARD. The technology provides a “Garden of Eden” environment for the bacteria to thrive and multiply and permits them to achieve in 6 days what would normally take 20 years to occur naturally.
The tailings created by bioleaching are benign, and zero environmental damage occurs as a result of the process. An added bonus is its ability to recover valuable metals such as gold, silver, cobalt and nickel that remain in the tailings.
Summary Of Advantages
- Remediation of tailings at no cost to government
- Revenues through the recovery of contained metals — Au, Ag, Cu, Ni, Zn, Co, Pb
- Local opportunities for work, training, development and the start of a new ‘green metal’ industry
- Lower cost than the alternatives (e.g. pressure oxidation) and requires less capital
- Easy to expand to accommodate tailings from many types of mines within a region
- The bacteria are naturally occurring and harmless to the environment and human health
- What is being treated is the actual source of acid generation and not the symptoms
- Prevention of future Acid Mine Drainage through sulphide neutralization
- Toxic heavy metals, like arsenic, are converted into stable, environmentally benign products
- No gaseous emissions (e.g. S02,As203)
- Efficient reuse of water from the process
- Reduction in use of mercury by artisanal miners
- The technology is already commercially proven
- BacTech has “in-house” capacity for the design, construction and operation of the plant
- It is a continuous process which is safe, easy to operate and flexible
- Scalable in a short period of time and capable of processing a wide variety of low to high grade mine tailings
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Bacterial oxidation technology, also known as “bioleaching” or “bio-oxidation”, was originally developed by BacTech Mining Corporation (re-named REBgold Corporation effective December 2, 2010). The technology employs naturally-occurring bacteria, harmless to both humans and the environment, to liberate precious and base metals from difficult to treat ores, concentrates and tailings. This is only one of the benefits of using bioleaching for the remediation of tailings and other mining stockpiles. Through its ability to neutralize the source of Acid Mine Drainage (AMD) and stabilize toxic heavy metals, bioleaching addresses several tailings-related environmental issues at once, while generating revenue that can effectively fund the remediation process
Put simply, bioleaching uses naturally-occurring bacteria in reactors (tanks) to oxidize sulphides. The key is providing the bacteria with optimal operating and living conditions in the reactors. They are capable of oxidizing sulphides in as little as 5-6 days, as opposed to many years in their natural habitat. This is a common residence time in a commercial bioleach plant and the control of this and other parameters, such as the particle size of feed, are relatively simple and readily managed by operators with the correct training.
The registered trademark for REBgold’s bioleaching technology is “BACOX”.
BacTech Environmental Corporation (“BEC”) was created in December 2010 following completion of a Plan of Arrangement originated by BacTech Mining Corporation (now called “REBgold”). Under the Plan of Arrangement, BacTech Mining shareholders were given 1 share of REBgold for each BacTech Mining share they held, and 1/5 of one share of BacTech Environmental; that is how BEC came into existence.
BacTech Environmental was granted a perpetual, exclusive licence by REBgold to use the BACOX technology for the remediation and reclamation of tailings and waste rock left by previous mining operations. Recently, the Company added a second application for bioleaching. Through a professor at the University of British Columbia, we learned of the dangerous use of mercury in artisanal mining in various countries. This uncontrolled use has led to widespread environmental degradation in Peru, Ecuador and Colombia, to name a few. Through the use of flotation, arsenopyrite concentrates are produced that, when processed with bioleaching, produce gold and effectively tie up the arsenic. All this without the use of mercury.
The Cleantech Solution
The historical approach to treating refractory arsenic ores has been to use smelting and/or roasting. This entails subjecting the sulphide ore to intense heat, whereby the sulphides are burned off, leaving the desired metals for recovery. There are strict limits on the amount of arsenic that can be burned through a mineral treatment process, and the general industry rule is that smelters cannot treat base or precious metal concentrates that contain more than 1.5% arsenic. Furthermore, they are also subject to a total tonnage limit that can be produced in a given year.
Since bioleaching works in the absence of direct heat, there are no arsenic trioxide (As203) gases produced through the process. In fact, bioleaching can treat concentrates with much higher levels of arsenic than what would be allowed using a pyrometallurgical process. Precious metal concentrates produced from tailings in a region of Northern Ontario regularly return readings for arsenic of over 10%, thereby eliminating them from consideration for smelting.
Bioleaching, given access to a ready supply of iron, either internally generated or through the addition of pyrite from external tailings, can handle much higher levels of arsenic for neutralization. Bioleaching converts the arsenic present in the tailings into ferric arsenate, which is a stable and environmentally benign end product (EPA).
Previous testing of bioleaching precipitate residues using the Toxicity Characteristic Leaching Procedure (“TCLP”) has been undertaken in conformance with US Environmental Protection Agency (“EPA”) standards, which are recognized internationally as the test method for environmental stability of such materials. The results serve to confirm the environmental suitability of the precipitates for disposal. The EPA TCLP is the procedure used by Ontario Regulation 558 to determine the suitability of a byproduct for land disposal.
Bioleach plants built by REBgold in the gold industry treat multiple types of arsenical concentrates and readily achieve the EPA TCLP criteria. Staff also routinely monitors any ferric arsenate produced according to the TCLP protocol to ensure the material remains stable.
In addition to the avoidance of S02 airborne emissions, bioleaching can be an effective method for treating Acid Rock Drainage (“ARD”) through the oxidation of sulphides, which are responsible for leaching metals into surrounding areas. As opposed to “band-aid” solutions that treat contaminated water and/or soils indefinitely, bioleaching acts as a “cure” by targeting the source, the sulphides in tailings, and thus preventing future acid generation from occurring.
There are numerous technologies that are being developed using a hydromet process, but only REBgold and Gold Fields have successfully commercialized their gold bioleach processing technologies to date. BacTech Environmental intends to apply this proven technology on tailings for gold and base metal extraction, ARD remediation, arsenic stabilization and mercury reduction.
The Case for Bioleaching
A common query for any arsenic treatment process relates to the stability of the final arsenic product and its fate over time in the environment. The stability of the final ferric arsenate product has never been an issue at the REBgold arsenical gold projects nor, to the best of our knowledge, has it been a concern at any of our competitor’s sites, resulting in over 20 successful projects worldwide since 1986.
Over this time, a variety of sources of published literature have confirmed the stability of the final products from commercial bioleach plants. One such reference entitled “Neutralization of Bioleach Liquors” by Nyombolo et al. of Mintek South Africa (a high-quality, accredited, world class research facility) tested the stability of ferric arsenate precipitates over a 7 year period and concluded the following:
“For all of the tests, the very long-term trend is for an improvement in arsenic stability. Precipitates that are stable initially tend to remain stable, and those that exhibit some instability in the first few years appear to gain in stability after about two years. This is a very encouraging finding, and indicates that fears of a decrease in stability could occur over the long term are unfounded.”
We believe that a majority of the tailings could be processed in a commercial facility that will adopt a broad design envelope to cater to variations in tails characteristics. The REBgold plant in Laizhou, China was designed using a similar strategy for being able to treat “unknown” arsenical gold ores from a variety of origins. Bioleaching lends itself to this type of strategy and copes with greater fluctuations in feed types than smelting or pressure leaching processes.
In the commercial treatment scenario, each of the tailings piles would be sampled and tested in the laboratory prior to reclamation and processing in the commercial facility to ensure that the arsenic can be extracted/stabilized and the metal values recovered. This is similar to the strategy currently employed in the REBgold-built plant in China where samples are sent for testing prior to establishment of contracts for treatment. In the nine years of operation of the plant in China, it has been very rare for a concentrate to be rejected as not amenable to processing.
The History of Bioleaching
Intellectual Property: Patents & Expertise
BacTech has always protected its intellectual property through the application of process patents in countries where deemed necessary. Since bacteria are naturally occurring, we cannot apply for any protection on them as entities, but can apply for patents relating to their application. We will continue to advance our base metal bioleach technology and we will apply for patents as appropriate. However, we have found that the art of bioleaching is made up of 50% process patent and 50% know-how, which can only be acquired through a lengthy commercial track record.