Finnish know-how succeeds in treating problem minewastewater

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09/2013

Watermasters pump, excavate, and pile

Based in Säkylä in southwest Finland, Aquamec is a global company and has supplied its Watermaster multipurpose units to over 60 countries around the world. In addition to their suction dredging capabilities, Watermasters are equally

at home excavating, raking and piling. A Watermaster can also be used to power a hydraulic hammer and other hydraulic equipment.

“The unique mobility of the Watermaster makes it very useful for the mining industry, as conventional solutions are difficult to use in shallow mining ponds or when moving between ponds,” says Watermaster Marketing Manager Johannes Karvonen. “In addition to pumping sludge from ponds, Watermasters can also be used for excavation and piling work to strengthen pond walls and secure their long-term integrity. Watermasters are also ideal for cleaning out the various process ponds found at many mines.”

Sami Ojanen, Managing Director of Vesirakennus Ojanen, has used TenCate Geotube® technology and Watermaster equipment on a number of contracts in Finland and elsewhere in the Nordic region. Vesirakennus Ojanen used five Watermasters simultaneously during the Talvivaara project.

The water treatment expertise offered by the Sito-Aquamec-Ojanen ‘team’ has proved its worth in numerous projects for the mining, oil, and pulp & paper industries.

The Watermaster’s built-in propulsion system makes it easy to use in the water. Integrated stabilisers anchor it to the bottom when needed. In addition to dredging, a Watermaster can be used for excavation and piling work in water up to five metres deep or on dry land. No cranes are needed to move a Watermaster from one location to another, and a unit does not need to be dismantled and reassembled when moving it to a new site.

Europe’s largest nickel mine, Talvivaara in northeast Finland, has been operational since 2008. The mine, which makes use of an innovative bioleaching technique, was developed and

opened in record time and soon began supplying international customers.

2012 proved a challenging year for the mine, however. In September, the company was forced to halt mining ore because of high levels of contaminated water that had built up in the deepest section of the opencast site; and in November, a tailings pond containing gypsum sediment began leaking. The majority of the water that leaked from the pond, which contained both metals and sulphate compounds, was recovered and the leak was plugged in a couple of weeks. Around 220,000 cubic metres of effluent escaped, however.

Halting the leak from the tailings pond did not solve the water balance problem affecting the mine, which extends over 61 square kilometres. Record rainfall during the summer and autumn of 2012 meant that millions of cubic metres of water had to be stored across the site, as rainwater became contaminated with water

A highly reliable, all-in-one solution has been developed in Finland for reducing the impact industry has on the environment. The technique – developed by Vesirakennus Ojanen and Sito, and based to a large degree on the use of Watermaster multipurpose dredgers – has already proved its capabilities in a variety of Finnish mining and paper industry applications. A water management project at the Talvivaara nickel mine is one of the latest examples of its success.

Finnish know-how succeeds in treating problem mine wastewater

high in sulphates coming from mining operations. A solution to dealing with this mass of water was urgently needed.

Talvivaara’s environmental and water management specialists wanted an effective solution capable of delivering sufficient treatment capacity without being excessively expensive to implement. Sito, a leading infrastructure and consultancy company, knew of a system that could fit the bill and this was chosen for further investigation.

Trials in Sito’s and Talvivaara’s laboratories showed that the system was suitable for the mine, if it was used with an experienced contractor and efficient and reliable dredging and earthmoving equipment. In addition, the solution would need a series of neutralisation units, dosing equipment for polymer and quicklime, and sludge and water treatment units.

Vesirakennus Ojanen was selected as the contractor for the project, in large part because of its experience in using Watermaster multipurpose dredgers, which were ideal for the job, as they are designed to operate in shallow water no more than five metres deep and can also work on dry land.

Sito and Vesirakennus Ojanen had extensive experience in working on environmental projects for Finnish industry, but now they would

be called on to deal with a particularly demanding site and deliver highly efficient results.

The clean-up operation began in March 2013 with the installation of Geotube® units for treating the sludge and effluent problem. When sludge treatment got under way using these, it proved highly successful from the very start. This success owed much to the customer’s ability to define the nature of the problem facing them in detail, Sito’s insightful input, the choice of the right equipment, and well-managed site operations. The work done to optimise the polymer used to promote the flocculation of the sludge, together with the feed pump solution developed for the site by the contractor, are just two examples of the professionalism called for in dealing with the challenge facing Talvivaara.

The multipurpose nature and high dredging efficiency of the Watermaster proved very useful and underlined its suitability for the project. Using conventional equipment, separate systems would have been needed for individual tasks, which would have increased costs significantly, both for the contractor and indirectly for the customer as well. High-efficiency machinery was also essential as high capacity was necessary for the water treatment process.

The role of the Geoport, as this section is known, is to ensure the integrity of the Geotube® containers where the sludge is fed into them for treatment.

The new technique is suitable for

• Mines• Oil refineries• Pulp & paper mills• Municipal and industrial water treatment plants• Tanning units• Waterway restoration • Environmental projects• Construction projects

Benefits of the technique

• High treatment speed and large capacity• Good cost efficiency• Filling height can be easily regulated• Safe and reliable• Works well regardless of sludge type • Operates year-round in all weather conditions • Good purification results• Excellent sludge treatment and drying performance = high post-process solids content

The treatment of the mining effluent and the heavy metals that it contained also proved successful, even more so than expected in fact, and concentrations of heavy metals fell well below the threshold limits set by the local environmental authorities. As a result, Talvivaara was able to start up ore mining and crushing operations again in May 2013 after water levels in the opencast mining area had fallen sufficiently. Since then, all four of the mine’s production areas have operated normally. The freshly mined ore that has been produced plays an important role in helping manage the site’s water balance, as the 10 million tonnes of new ore that has been transferred to the leaching area binds 1-1.5 million tonnes of water.

Maija VidqvistWater Management Expert, Talvivaara Mining:

“Our biggest challenge in managing the water problem at Talvivaara was to separate the sulphate-contaminated water at the site from the sulphate-free water and deal with them separately. This proved very difficult, as the record-heavy rain in autumn 2012 saw these effluent streams intermix with each other. By summer 2013, however, we had been able to solve the site’s water balance problem and were able to restart ore extraction.”

Kimmo HeikkinenProject Engineer, Talvivaara Mining:

“The water treatment units at Talvivaara use the same neutralisation process as the mine’s metal production plant. Bottom sludge is pumped from the plant to the tailings pond or dried in band filters, while bottom sludge from water treatment areas outside the plant are pumped to the Geotube® units or holding ponds. This gives us a good purification result, as along as the number of basins and the staging used, in other words the reaction and flocculation times, are sufficient.”

The sludge containing the metals problem is purified inside Geotube® units. Four layers of the Geotube® containers capable of being filled to 2.32 metres high each were installed at the site. The size of the Geotube® processing area and the number of containers were carefully dimensioned to meet the capacity needed, the composition of the sludge to be treated, and the mechanical stress imposed on the structures.