Mining engineering consultancy IMEC has reported recent success at some mine sites by pursuing a surface dewatering program over an underground one, delivering longer term e ciencies which mitigate more frequent maintenance.

While the company acknowledges that the most e ective option will di er from site to site, IMEC senior dewatering engineer Robert Markoski believes operators should at least entertain the idea of settling pumped water on the surface.

e bigger the surface area that you can do it in, the more settling you have, Markoski explained.

If youre on the surface you can build a huge dam and you get a lot more settling, whereas if you do it underground youre limited for space and every metre you develop is a huge cost.

While settling water underground spoils operators for choice in terms of the availability of various pumps capable of pumping clean water, the capital cost of excavating an underground area can be considerable.

Alternatively, surface settling areas are much cheaper and easier to construct, but the pumps available to transport water with a high solids content from underground to

the surface are limited and can require large amounts of maintenance.

A lot of people at out say it will cost too much to do all this maintenance work, but weve found on a couple of mines that actually know, if you look at the long-term, even though youre replacing the internals of these pumps more o en it is a lot cheaper to do it that way than constantly developing underground and doing your settling there, Markoski said.

ere is that option there and it should be looked at and have a cost bene t analysis done.

According to Markoski, IMEC have had success using centrifugal slurry pumps to pump dirty water to the surface for settling.

e company has found that the robust and simple design of the pumps makes the more frequent maintenance needed, easier to conduct.

By utilising these pumps, we are able to design very e cient pumping systems, which require little or no settling of solids matter underground, Markoski explained.

By comparison, Markoski said, clean water pumps o en needed to be sent back to the supplier for maintenance, which could be costly and time-consuming where the supplier was not present domestically.

Another advantage of settling above

ground is the availability of a wider range of equipment for maintaining a settling system.

In addition to this, using equipment above ground limits tra c underground.

By removing the need for vehicles to transport mud out of the underground settlement ponds to the surface, operators can free up valuable underground real estate for loaders used to transport ore, directly leading to revenue.

e issue is that when youre settling underground, all those solids and materials that do settle you have to get those things out of there, Markoski said.

So youre tying up equipment and it could potentially cause delays in your decline where other vehicles cant pass because youre using this vehicle to remove mud and gunk from underground.

IMEC co-director and senior engineer Martyn Abbott summed up the advantages of a surface settling program rather succinctly.

By implementing a primary dewatering system that can pump unsettled mine water direct to surface, a signi cant operational and capital saving can be realised by the mine by eliminating the need for large underground excavations for settling sumps and utilising larger or more e cient earthmoving equipment for treatment on surface, he said.

Moving the muck and the mire Cost and ef ciency are king in every aspect of a mines operation, and realising these goals quickly is a keen motivator. However, a long-term game plan may be the key to keeping costs down when it comes to the dreaded task of dewatering. By Andrew Snelling

www.miningmonthly.com June 2015 AMM 77

FEATURE FLUID HANDLING

An underground dewatering pumping system.