Table of Contents
Basic things to remember in plant design for cold and remote areas are, everything in these areas is more expensive due to long and difficult supply lines. Fuel is expensive and would be a major cost item even if it were not expensive, due to the extended periods of low temperatures. Building volumes should therefore be kept to an acceptable minimum. Service areas on the other hand must be adequate, because maintenance generally has to be conducted inside in a heated area. Supply vehicles for instance have to get completely inside the building to unload. If you try to unload a supply vehicle with the door open at -50° F, you won’t he able to find the vehicle for fog and if you take more than 5 minutes half the water lines in the plant will freeze up.
Concentrator Layout
Starting with ore storage these facilities will vary depending on whether it is an open pit or an underground operation. It is practical with an open pit to store ore in an open stockpile outside. Depending on the amount of snow fall however a roof is usually required otherwise the plant may end up with very wet feed, and the high handling costs associated with wet feed.
Secondary and tertiary crushers on an underground operation can be grounded in the same building and under the same crane as the grinding circuit. By using heavy rubber chute liners the noise can be reduced to an acceptable level. This configuration is not recommended in an open pit operation largely due to the dryness of the ore and hence the dust problem.
Dust collection and ventilation in a cold area is a much more serious problem that it is in a warmer climate. In normal plant planning dust collection is pushed into some left over area that no one can think of anything else to do with. This normally results in dust collection pipes that are too long and have too many elbows. With very efficient collectors, dust collector exhausts have been recirculated back to the plant to conserve heat. In the author’s opinion however it is better to design for no recirculation. If when the plant is in operation you discover that under certain conditions the heating plant is inadequate then some partial recirculation in areas of low personnel occupancy may be possible.
The next big event was when during the investigation to determine how rotten the building really was someone fell through the roof into the primary cyanide thickener. In our innocence we actually considered putting another wall on top of the existing wall, and another roof on top of the existing roof, before some wise man from the Fast pointed out that our problem was really a ventilation problem. This was not actually a badly designed building.
This is an area in which we finally have large volume space saving machines. They were long in coming; the author is still at a loss to understand why the industry was so long in demanding these machines.
After years of trying to utilize, and economically justify, various patented and readily available variable speed drives, the author is now of the opinion that all concentrate pumps should be driven by an hydraulic motor. The concentrate pumps should be closely grouped to cut down the length of the hydraulic lines.
Dewatering and Concentrate Load Out
Specially designed thickeners have been operated outside in very severe climates. The temperature and volume of the thickener feed is probably the crux of this calculation. Dryers are normally operated inside, if you have to use rappers they are noisy. Dryers however do generate a lot of waste heat that is useful in heating the plant area.
Loading concentrate under the best of conditions is a dirty business. In the author’s opinion if you are loading dried concentrate, it should not be dried below 6% moisture, otherwise dust losses become exhorbitant. On a long haul operation across the Canadian prairies, despite some literature to the contrary, concentrate dried to 6% moisture will freeze. Concentrate at 6% moisture in an open gondola car will freeze hard enough to be very difficult to unload with a grade-all or back-hoe.
Services
You may be in an area so remote, and so unattractive that even a tailings poind would improve it. As soon as you want to do something useful with this area however, it will develop a strange and haunting beauty to some ecological expert who has never been more than 100 miles north of the Canadian American border. The first thing that must be done therefore on a new project is to establish with the government department concerned what your water and tailings disposal rights are to be. In extreme cases this has taken from 3-5 years of litigation, and is such a major cost item that it may turn a good ore body into a mineralized zone.
Tailings disposal costs even in a remote area are a real cost item, and probably take more long range planning than any other production function. Government legislation in some provinces in Canada is already requiring that we spill no effluent at all. In cold areas where the evaporation season is extremely short, this legislation may be almost impossible to meet. Fortunately government departments are forced to face economic facts that ecological experts are not.
Tailings disposal problems vary from one location to another so much that the author again retreats to his own experience and observations. In making tailings pond capacity calculations in very cold climates one must remember that even in a six foot deep pool of water you may get four feet of ice.
