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Paste project at the Laiva mine
In order to deposit the sand at the Laiva mine, a so-called paste method is used. This is the first time the method is used in this type of application. There are several advantages with paste, including that the water in the process can be re-used, that dust and the precipitation of metals is minimised and that there is no need for big dams.
The method has been examined by Leena Harjumaa as part of her examination work at Ouolo university. At the processing plant, the ore is crushed and ground. Sand is a waste products of this process. The majority of the sand (98-99 per cent) is free from harmful substances and becomes so-called inert waste.
Nordic Mines has been granted permission to produce paste from this sand. The paste method means that the sand is de-humidified, resulting in a thick sand paste. This paste is deposited at at nearby bog. When the deposition is finished, the bog can be covered with moraine, for example. This area can be planted with forest. In her examination work aiming at a degree in enviromental engineering, Leena Harjumaa has examined how paste deposited close to the surface will be affected by a Scandinavian climate. The waste products she used in her laboratory studies came from pilot tests at the Laiva mine.
The study was focused at studying how freezing and thawing affected the deposited paste. She simulated the circumstances that for deposit at the future mine. Lena Harjumaa found that the more water the paste contains, the more it shrinks or swells when freezing or thawing. In her study, which took some eight weeks in laboratory to perform and afterwards four months of analyses, evaluation and writing, she also found that the optimal water content for the climate conditions in the Nordic region, a result that will be used at the Laiva mine. The study was granted top grades.
Nordic Mines Nordic Mines also participates in a number of other research projectsin cooperation with other mining companies, governmental organisations and universities, where one of the objects is to develop risk assessment and dealing with environmental hazards in metal mines. In another project, conducted together with other mining companies, universities and goveremental research organisations, the goal is to develop new tools for the mining industry when it comes to handling arsenic.
Footnote: The rest of the sand (1-2 per cent) will contain metal sulphides. Nordic Mines will deposit this sand in a safe way withing the mining area for potential, future extraction.