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Wholly owned by LKAB (Luossavaara-Kiirunavaara Aktiebolag), Kiruna is the world's largest and most modern underground iron-ore mine. LKAB is a Swedish high-tech mineral products company owned by the Swedish Government. Its primary business is the mining of iron ore and its primary mines are in Kiruna and nearby Malmberget. LKAB supplies highly upgraded iron ore products to the steel industry, custom-adapted mineral products for other industrial sectors and products and technologies for mining.
With an ore body 4km long, 80m thick and reaching a depth of 2km, LKAB has produced over 950Mt of ore, yet only one-third of the original ore body has been extracted in the 100 years since mining began at Kiruna. Since mid-1999, Kiruna's haulage level at a depth of 775m has been replaced by the next level down at 1,045m, which will support production until 2018.
The operation employs 1,800 people, of whom 400 work in the mine. About 90 production people will be hired next year to meet the expected production increase at Kiruna's ore processing plants.
Located in northern Sweden, the city of Kiruna was founded some 100 years ago and is located 145 kilometres north of the Arctic Circle, it has perpetual daylight, or the midnight sun, from approximately May 30th to July 15th. The polar night is a few weeks shorter, lasting from December 13th - January 5th.
The area is great for fishing in the summer. There are more than 6,000 lakes in Kiruna and seven rivers run through the municipality.
When iron ore began to be mined in the area during the late 19th century, the ore was accessible by merely removing layers of soil and rock, but over time it became necessary to follow the huge ore body deeper and deeper underground.
Today the mine remains the backbone of the municipality's business sector, but to enable mining to continue, large portions of the city of Kiruna will have to be moved. Even though the ore is located very deep, the ground above it has settled. Over time, this may damage existing buildings, electrical lines and the city's water supply and wastewater systems.
During the next 30 years, nearly 1,000 apartments and homes will be affected. First affected will be the railroad line, which is located in the most severely threatened zone. The underground crack zone will reach it in less than ten years. Within a further ten years, Kiruna Church and City Hall must be saved. The big remaining question is where to build the new Kiruna.
The Kiruna ore body is approximately 4 km in length, averages 80 m in thickness and reaches a depth of 2 km. It was formed 1.8 billion years ago in an episode of intense volcanic activity and contains a very pure magnetite-apatite mix, which is more than 60% iron and an average of 0.9% phosphorus.
The Lake Ore is not a separate orebody, but an extension of the northern part of the main orebody, and is thus named because it lies beneath the drained Lake South Luossajärvi. Data on the Lake Ore confirms that the ore widens towards the north. At depth, the ore is large, high-grade and contains very little phosphorus. It appears to be twice as wide as at the present mining levels, up to 150-180 meters.
While some of the orebodies contain high levels of hematite, the principal mineral linked with the iron ore is magnetite. The apatite contents of the various ore bodies vary widely, while the average phosphorus levels are lower than 0.8%.
Sublevel caving is the mining method used at Kiruna. Slices of ore are drilled up with remote-controlled production drilling rigs. From their control rooms, the operators (drillers) operate several drill rigs out in the production areas via remote control. The rig drills upwards into the ore, forming a fan-shaped pattern of ten holes, usually about 40-45 m deep each. The holes are straight, so that subsequent charging with explosive and blasting can be done efficiently. When a pattern of holes has been drilled, the rig is moved back three meters, and then drilling of the next pattern begins. About 20 of these patterns will be drilled in an 80-meter drift. Once drilling is completed in the entire drift, the holes can charged with explosive.
A robot injects explosives, manufactured by LKAB, into all the drill holes of one pattern. Blasting is undertaken every night, with each round bringing down approximately 10,000 tonnes of ore. Once the blast has been ventilated, electric wheeled loaders load and carry the ore to vertical shafts (ore passes) located along the orebody. Each loader carries a bucket payload of 17-25 tonnes and tips its load down an orepass. By gravity, the ore falls down to bins located just above the main level.
At Kiruna, the main level is at a depth of 1,045 m below the surface. Ore is tipped via remote control from the bins into railway cars on the main level. Driverless trains, consisting of an engine and 24 cars, haul the ore to one of four discharge stations. When the trains pass the discharge station, the bottom of the train opens up and the ore falls into a crusher bin. The ore is then fed to one of four crushers, where it is crushed to approximately 100 mm diameter chunks. The crushed ore is then carried via conveyor belt then loaded automatically onto ore elevators, capable of carrying 40 tonnes of ore, and hoisted to a processing plant at the surface.
In the ore processing plants at surface level, the crude ore is upgraded to either pellets or fines. After the ore is ground to a fine powder in several stages, undesirable components are removed by magnetic separators.
The concentrate is mixed with water to form a slurry which is pumped to the pelletizing plant. The slurry is then dewatered with large filters, and mixed with binders and additives, depending on the type of pellet to be produced. Olivine, quartzite, limestone and dolomite are examples of additives.
The mixture is fed into gigantic drums and rolled into centimeter-sized spheres called 'green balls'. These are then heated in a large rotary kiln at 1,250°C to become pellets. The red-hot pellets are cooled to about 50°C before they are tipped into an underground storage facility beneath the pelletizing plant. From there, they are automatically loaded to railway cars for further transport.
Unlike pellets, fines must be sintered to larger pieces before the product can be used in blast furnaces. Fines are produced by crushing and then grinding the crude ore to a sand-like consistency.
Currently, there are two operating palletizing plants at Kiruna, with a third plant in the construction phase and expected to be online in 2008. Following the completion of the third palletizing plant, Kiruna will stop producing fines and will solely produce pellets.
Finished products are transported from the ore processing plants to customers by rail and by ship via the shipping ports at Narvik and Luleå. Rail transports are operated under the company's own management. The Narvik ore harbor can accommodate vessels of up to 350 000 dwt.
Environment and Community
For more than a century, Kiruna has remained relatively untouched by the effects of mining, even though some parts of the town have been relocated from time to time.
Now, the next relocation phase is approaching. This will affect not only LKAB's areas, but also the local infrastructure, such as the railway, roads and even residential properties. But not all of Kiruna has to be relocated just yet, at least not because of LKAB. According to estimates, over the long term (some 25-30 years), about 8% of residents or 1,800 people will be affected.
Pellet manufacture at LKAB's mines results in one-seventh the quantity of emissions compared with sintering at the steelmills. This is because thermal energy from the process is utilized in production. The environmental impact must be regarded in a global perspective. Pelletizing and sintering now take place to a greater extent at the mines. This means that some of the emissions have been moved from the steel mills to the mine locations.
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