Mining Mirror June 2019 | Page 41

Cradle to grave Mining and quarrying equipment specialist Osborn has secured a significant order from Petra Diamonds for an apron feeder that will be employed at the diamond mining group’s renowned Cullinan Diamond Mine in Gauteng. Cullinan’s new Osborn apron feeder will be deployed in the mine’s shaft and plant interface project. Eight Osborn apron feeders of the same size were installed underground at the Cullinan Mine as part of a previous order. These are successfully servicing the operation’s underground silos and crushing stations. A further five Osborn apron feeders have since been supplied to the operation’s process plant. With their heavy-duty construction, Osborn apron feeders are designed to handle feed sizes of up to 1 500mm where no fines removal is required or where fines are removed by a separate dribble conveyor. Equipment shines at Cullinan An Osborn apron feeder will be employed at Petra Diamonds’ Cullinan mine in Gauteng. Pumping water at heights Deep opencast mines pose great challenges for the dewatering process. Often, long distances, especially vertical ones, cannot be bridged with conventional submersible pumps. Most pumps can only pump up to a height of about 40m. In practice, they can only lift a small part of the stated maximum pumping capacity to this height, because height and capacity are intricately connected: the higher the height, the less water passes. As a solution, some operators use a series of pumps ‒ two pumps that are operated sequentially in one section. This will almost double the achievable distance, although the pumping capacity remains the same. Usually, hoses are fitted between the aggregates. The problem with this concept is the same core risk associated with all complex systems: (too) many components are involved, some of which might not be in their best condition, are not installed to the optimum, or simply should not have been combined in the first place. The process can be enhanced by using an adapter manufactured by the pump manufacturer Tsurumi, which allows two identical pumps to be directly coupled to create a kind of ‘super pump’. Nevertheless: the limiting factor here is the physics of the speed and impeller, which is why the pump programmes of most manufacturers end at this point. If this is insufficient for the dewatering process, things become difficult for tunnel builders and miners. In contrast to clear water, there are few pumps in the dewatering field that can improve the output noticeably. High-pressure pumps are the best choice. For instance, the LH series by Tsurumi basically covers the pumping height range from 42m to more than 100m. This is where classic pump designs reach their physical limits. Another pump concept is required if you want to go any higher ‒ you need multi- level pumps. From a technological point of view, this means that several impellers are mounted inside the casing. While the pumping capacity remains the same, the pumping height increases with the number of these levels: The pump supplies more pressure and is therefore able to reach a higher head. As simple as the idea sounds, it is very difficult to realise if the pumped water contains solid matter. Tsurumi from Japan is the only supplier of these kinds of dewatering pumps in the world. These models are marked with a ‘W’ in the product catalogue. The LH4110W is the premium model. It is able to pump waste water vertically to a height of 216m. To put this into perspective: this is higher than from the base to the viewing platform of the Berlin Television Tower. The aggregate can move 400ℓ/min. If requirements are lowered, for instance to a pumping height of 170m, the pumping output is increased five-fold to 2 000ℓ/min. The power required for this is generated by a 110kW motor. If two of these 1 825 × 616mm large monsters with a dry weight of 1 270kg were to be combined, a 432m-deep pit could be supplied with the smallest amount of conceptual effort. Geosynthetic materials are of great value for environmental projects on mines, especially during mine closure. Typical applications for geosynthetics include mine tailings facilities, heap leach pads, and water retention ponds. Geosynthetics are used for mine closures, as well as for access roads and other geotechnical structures, says Johnny Oriokot, geotechnical engineer at Fibertex SA. “Fibertex’s highly UV-stabilised 100% virgin polypropylene (PP) geotextiles and geosynthetic solutions take the uncertainty and risk out of the design of crucial applications like landfills, dams, and tailings dams. www.miningmirror.co.za “Geotextiles have advantages in installations where the cost of failure may be extreme, in both financial and environmental terms. Virgin PP offers a high level of chemical stability under a wide pH range and for this reason, Fibertex geotextiles are particularly well suited for installation in areas where the textile may be in contact with alkaline conditions, for example in certain types of slimes dams and waste sites. “Fibertex geotextiles have important functions — for separation, filtration, drainage, protection, and reinforcement. These materials can also act as a stress-relieving waterproofing Geosynthetic value in environmental management Fibertex mining installation. membrane when used with bitumen in road applications.” JUNE 2019 MINING MIRROR [39]