Finnish Mines Showcase Technology Advances

The challenge of meeting profitability targets with complex, often intractable ores, while minimizing environmental effects requires close cooperation among mine operators, technology suppliers and researchers. Here are examples from three Finnish mines – Talvivaara (Talvivaara Mining plc), Kittilä (Agnico-Eagle Mines Ltd) and Pyhäsalmi (Inmet Mining Corp.) and Nordic technology suppliers.

TALVIVAARA NICKEL MINE

Europe’s largest nickel mine, the Talvivaara mine, began production in 2008. Talvivaara uses bacteria occurring naturally in the local environment to extract nickel, copper, zinc and cobalt. I It is the first mine ever to apply bioheapleaching in sub-Arctic conditions. GTK’s Mineral Processing Laboratory helped identify potential hydrometallurgical routes for metal recovery.

A thin overburden over the two main ore bodies with total classified ore resources of approximately one billion tons readily permits open-pit mining of about 22 million tons a year. The ore consists of finely disseminated sulfides and quartz-sulfide veins. After crushing in four stages to sizes below 8 mm, the ore goes to agglomeration drums for mixing with the acid-bacteria solution. Finally it is stacked on 400m x 2,400m leach heaps.

The bacteria used in bioleaching tolerate highly acidic conditions, consume sulfur and excrete metal. Pumping leaching solution over the heap accelerates bacterial action and thus pyrrhotite and pyrite oxidation. Constant circulation maintains temperatures in the heaps well above 60°C even in the depths of winter. Notes Talvivaara mine chief operations officer Lassi Lammassaari, – Essentially we are preparing a giant meal for our bacteria. That means our technology partners are involved in one of two tasks – setting the table or washing the dishes.

Sandvik provided the crushing plant, with twelve screens, eight cone crushers, 26 feeders, 30 in-plant conveyors, an overland conveyor, steel structures and silos. Four Sandvik top hammer drill rigs were ordered later. The local black schist has a high graphite content that makes it slippery to handle, so special modification of the crushing and screening lines was required.

Filter specialists Larox provided a dozen Pannevis horizontal vacuum belt filters (nickel sulfate, zinc sulfate, copper sulfate and neutralization lines), as well as presses and pressure belts. Larox has worked closely with Talvivaara operators to achieve low moisture cake, clean filtrates and good washing results.

Metso provided the agglomeration plant and a limestone crushing facility. Metso Automation supplied the automation package for Talvivaara.

KITTILÄ GOLD MINE

The Kittilä Mine in Lapland achieved commercial production in mid-2009. The ore is mined in 7.5 m benches using buffer blasting. It is loaded selectively to minimize dilution. Hydraulic excavators load trucks that haul ore to a Metso jaw crusher. Some 3,000 tons of ore a day are fed to the processing plant. The operation is on track to produce 150,000 ounces of gold annually from two ore bodies with roughly 110 million tons of reserves.

Gold occurs largely as refractory gold in arsenopyrite (75%) and pyrite (23%). The ore is treated by grinding, flotation and pressure oxidation to convert the refractory gold to a cyanide-soluble form.

Kittilä is Agnico-Eagle’s only refractory gold mine. Prior to the mine’s acquisition from Riddarhyttan, GTK and others extensively studied processing options for the ore. Agnico-Eagle commissioned further studies in 2005 as part of ongoing engineering and environmental design as part of feasibility studies. Bench- and pilot-level tests were conducted in 2006 and 2007 to fine-tune the proposed flotation and pressure oxidation processes.

Pressure oxidation starts with pumping concentrate into a series high acidulation tanks. Acid from the wash circuit is mixed with slurry to react with carbonate minerals and reduce formation of carbon dioxide inside the autoclave. Acidified slurry is then thickened and pumped to an autoclave. The slurry is baked for an hour at 190°C as it passes through six compartments with pressures as high as 1,900 kPa (19 bar). The first compartment is equipped with a 75 kW agitator to provide oxygen dispersion and solids suspension. Slurry exiting the autoclave is cooled to 90°C in a single-stage high flash vessel. Steam produced in the flash vessel goes to a scrubber to recover particulate and acidic vapor.

Treated slurry is pumped to carbon- in-leach circuits, where the gold is stripped from the carbon and recovered from solution by electrowinning. The separated gold is smelted in a furnace and poured into doré bars.

Many of the tanks and the autoclave were fabricated by local Finnish suppliers. Weir supplied the slurry pump and Polar Gas provided the oxygen plant.

PYHÄSALMI COPPER-ZINC MINE

Started as an open pit operation in 1962, Inmet’s Pyhäsalmi copper– zinc–pyrite mine today plunges nearly one-and-a-half kilometers into the earth. The mine is not only Europe’s deepest mine, it is also the most efficient, boasting an excellent safety record and a high degree of automation. Even as annual production now surpasses 1.3 million tons of milled ore, Inmet’s automation push has lowered the mine workforce by about half the level of the 1980s.

As part of the 2001 mine expansion and completion of a new Timo hoisting shaft, Metso supplied the C200 primary jaw crusher for the new crushing plant located at 1,400 meters below ground. The decision was to go for full automation. Notes Pyhäsalmi mine managing director Kimmo Luukkonen when there is a massive system like this operating underground, having a person down there next to the equipment doesn’t make a huge difference.

Thus, the crushing plant is designed for unmanned remote operation and controlled from the control room on the surface. The crusher can be fed from two ore passes or with an LHD, and there is a push feeder to ration the ore into the crusher. The crusher was deliberately oversized to handle the occasional oversize feed without manual intervention and because of a decision to forego scalping before the crusher due to the risk of foreign objects such as rock bolts, wire mesh and cables in the feed. Automation of the crusher station features extensive sensor use, an automatic lubrication system and predictive maintenance software.

A large part of the automation involves Sandvik’s remote production drilling (long-haul) system and the automated loading system, and development of the system continues. Some ore is mucked with remote-operated loaders controlled via video and wireless networks. The automated ore handling system underground is controlled from the mill by by video.

Larox  provided six Ceramec disc filters for copper concentrate and pyrite, and a pressure filter for the zinc concentrate.

Outotec is a leading global provider of process solutions, technologies and services for the mining and metallurgical industries. The company utilizes its extensive experience and advanced process know-how by providing plants, equipment and services based mainly on proprietary technologies. Outotec works in close partnership with its customers and provides proven environmentally sound and energy saving solutions. According to the agreement made with the former parent company Outokumpu Oyj, Outokumpu Technology changed its name to Outotec in April 2007.

Metso is a global supplier of sustainable technology and services for mining, construction, power generation, automation, recycling and the pulp and paper industries. They have about 28,000 employees in more than 50 countries.

Sandvik is a high-technology, engineering group with advanced products and a world-leading position within selected areas. Worldwide business activities are conducted through representation in 130 countries. In 2008 the Group had 50,000 employees.

Larox develops, designs, manufactures and supplies industrial filters and is a leading technology company in its field. Larox is a full service filtration solution provider in solid and liquid separation. Comprehensive aftermarket services throughout the lifespan of the Larox solution form an essential part of the operations. Companies in Mining and Metallurgy, Chemical Processing and related industries benefit from Larox’ high-efficiency process technologies, products and solutions. Since October 2009, Larox is part of the Outotec company.

TEXT Greg Moore