Mining smart in narrow stopes
Using high pressure waterjet technology to mine high grade reef-type ore bodies in short stopes underground by cutting could enhance safety, improve efficiency and minimize costs. This follows a series of successful experiments and growing application in gold mines in South Africa and in other countries globally.
With changing circumstances, to mine operators, simultaneously reducing costs and improving efficiency from mine to mill has become central to fulfilling their respective business mandates. In relation to deep-level mining, one of the ways through which they can achieve this is through utilizing alternative methods to conventional drilling and blasting in the selective mining of high grade ore in statiform ore bodies. If truth be told, considering the current market conditions, drilling and blasting is turning to be a very costly and time-consuming task.
Beyond doubt, there is a strong case for the industry to adopt high-pressure water jet technology in selective mining of high grade reef-type ore bodies (Witwatersrand quartzite material). This is based on findings of a series of experiments that were conducted by in a laboratory at the Department of Geology at the University of the Free State in 2013 and success in mines. The findings demonstrated that high pressure waterjet technology can be used to cut reef-type ore bodies in selective mining of reef-type ore bodies. The conclusion was that water jet technology could be just efficient as drilling and blasting – if not much better. Waterjet cutting involves the application of a water jet with an abrasive agent at ultra-high pressure onto the material to be cut, which results in shattering and cutting of mineral grains and cement.
Stiaan Viljoen, a specialist in high pressure water jet technology, who was part a team that conducted the research, posits mines should serious consider high pressure water jet technology. He is a director of Multicam, a company that specialises in high pressure water jet technology.
“Waterjet technology has been commonly used in cleaning and cutting of materials, including steel, concrete and rock. In fact, on evidence of findings of research, it is more beneficial and economical than machines in an increasing scope of applications, not least selective mining,” says Viljoen.
The conventional method of mining reef-type orebodies is minimum stope heights is drilling and blasting. This often results in large quantities of fines. In addition, all material has to be lifted to the surface for processing and extraction using machinery which needs power.
Why go waterjet?
In contrast, through ultra-high pressure water jet technology, material can be selectively cut off reef portions, conveniently.
Viljoen recommends cutting reef ore bodies using high pressure water jet in short stope heights, when done appropriately, on the the following grounds:
There are immense benefits of high pressure water jetting in terms of efficiency and savings. The following are benefits in terms of cost-savings:
Less use of machinery
There is no requirement for blasting materials and the use of drilling equipment, as well as machinery to lift gangue rock to the surface.
Eliminating the use of machinery would prevent a mine from incurring exorbitant energy costs. There are savings electricity needed for hoisting, locos and batteries etc.
Another cost saving would be in labour costs. While drilling and blasting are very labour-intensive, water jetting does needs lean staff to be executed.
While drilling and blasting would need more manpower, water jet cutting does not need any. As a result, the company significantly reduced potential labour costs.
High mineral retention
Typically, during blasting material is scattered, resulting in loss of minerals. With water jetting, this is eliminated. High quality ore is sent to the recovery plant due to low dilution.
Water jetting increases the life of a mine, as mining activity continues for a longer time.
- Environmentally friendly
There is an obligation from regulators for mines to adopt green technologies in order to reduce their carbon footprint. And waterjet technology can enable them meet that objective in a number of ways.
With no drilling and blasting, water jet leaves minimal footprint on the environment. In addition, as there is less material sent to slime facilities, there is marked reduction in the production of acid mine drainage (AMD).
The most understated advantage of water jetting is the convenience it brings in mining in smaller (shorter heights). There is less need of support due to smaller stopes, in addition to the better containment of stope width. What’s more, there is more capacity to accommodate hoisting systems.
No doubt, the most important benefit of water jetting is enhancing safety. Water jetting increases stability of hanging wall conditions, minimising collapse.
Though, the cost of water jet equipment might initially appear forbidding in short stope mining of reef-type ore bodies. However, when applied on a wider scale, in the long-term, it would turn out to be lower than conventional drilling and blasting methods. In a nutshell, altogether its benefits outweigh conventional methods by far.