Maurice Jones reports on advantages and disadvantages of long-distance mineral transport.
Considering how long pipelines to transport solids have been existence it is surprising that there are not more of them, or that they are discussed more. They can often represent a viable alternative to other common forms of transport such as road trucks, rail and belt conveyors.
The major areas of possible advantage include:
· Reliability over the other three;
· Ability to handle steep grades with adequate pumping capacity, and other inaccessible areas such as deserts and forests;
· Likely lower energy input than, at least, road transport;
· Less staffing required for operation;
· Less vulnerability to attack, especially if underground.
Possible disadvantages include high capital investment, the need to be dedicated to one operator (difficulty in differentiating contents), and high maintenance unless the best materials are used for all wear parts. In any case, pipelines are not an ‘install and forget’ option since any failures due to neglect can be disastrous for mine productivity and the operation’s public image as well as the environment.
This article concentrates on long-distance mineral transport, but other common uses of solids pipeline transport in mining include process transfer, tailings disposal, dredge mining, drainage sludge and backfill supply.
As indicated above, wear resistance is vital in selecting the components of a solids pipeline transport system, whether it’s the pipes themselves, control valves and, the powerful pumps required. The type of pump chosen depends, of course, on the pumping parameters and whether boosters will be required in a pipeline to overcome elevation, but also on the nature of the solids to be transported including abrasiveness, particle size and density. Dense materials may require large positive displacement pumps, including diaphragm pumps, whereas mixtures such as gravel in water can use large centrifugal pumps. In any case the pumping power input and location, perhaps aided by gravity, has to be matched to the need to keep the slurry mixture moving. Some minerals may not be suitable for standard pipeline transport due to degradation.
Weir Minerals offer heavy-duty pumps dedicated to slurry pipeline transport including Warman centrifugal slurry pumps and Geho piston diaphragm slurry pumps. The Company says that these models have been used to handle the most diverse slurries over distances of more than 300km. This backs the growth of long-distance pipelines, typically to transport partially treated ore from inland mining centres to refineries or loading facilities on the coast, perhaps crossing mountain ranges in between, such as in Chile.
Although water as a medium will be adequate for many duties, as long as the mix can be kept moving, particles of high mass may require a denser medium for transport, such as mud or foam, to keep the material in suspension.
At the delivery end of the pipeline the slurry has to be filtered to remove the required mineral from the medium. Where the production of slurry is a normal part of the mineral concentration process, this just involves transferring filtration from the process centre to the end of the pipeline.
Video 1: Cutaway view of operation of the Geho piston diaphragm pump from Weir Minerals Division for solids handling