Published: June 28, 2023

Hannukainen Mining and Tapojärvi are testing new materials to manage the environmental impacts of wall rock formed from mining operations. The activity is related to the TYPKI project, the goal of which is to develop solutions for the stabilisation of nitrogen- and sulfate-rich mine waters by means of concrete or cover structures based on side streams.

In Hannukainen Mining Oy’s mine planned at Hannukainen Kolari, wall rock will be composed which cannot be used in the operation and will be spread on top of the compact foundation structures in the mining waste dumpsite. Wall rock is potentially acid-forming and requires a tight covering structure that does not let water or oxygen through.

‘Tapojärvi is developing materials in which industrial by-products could be used for the dense covering structure of the layered wall rock. In this test operation, belite cement is being tested as a covering material for the wall rock, the production of which uses soda ash and fly ash produced in the forest industry,’ says Jaana Koivumaa, Hannukainen Mining’s Project Manager.

In the test operation, no acid-forming wall rock is used, but the functionality and buildability of the compaction structure is tested with earth and stone materials that come from operators in the field.

The goal of the experimental operation is to test technical work methods and the functionality of the structure in practice in covering the wall rock area.

‘Alternative materials aim to replace membrane structures commonly used in covering structures. Our goal is to develop new, sustainable solutions for the management of environmental impacts from mining,’ Ms Koivumaa explains.

For the actual implementation of the experiment, the water and oxygen permeability, consolidation, stability, weather resistance and workability of the material, as well as other work-based technical aspects, will be tested.

In addition, the effect of the covering structure on emissions from the wall rock area will be tested by monitoring the amount of oxygen passing through the test structures in addition to the water that filters through the structures and travels as surface runoff.

Five-year follow-up

The test operation will take place in the old soil extraction area located in the area designated in Hannukainen Mining Oy’s mining licence application, on the west side of the Laurinoja open pit.

The area to be built for the new test operation will be connected to the test structure previously built in the area. The connection will be made in such a way that the edge of the currently existing structure is demolished and the embankment is extended to the area required by the new structures. The test area is to be built from moraine available in the test area.

‘The functionality of the test structure in terms of oxygen and water permeability, as well as possible emissions, will be monitored directly from the structure with sensors separate from the structure, as well as from the surface runoff waters of the test areas from the sampling wells, discharge ditch and the water passing through the compaction structure from the lysimeters.’

The experimental activity will be started in August 2023. The test structures are to be completed no later than the end of October 2023.

They will be removed during the first stage of building and production of the future Hannukainen mine, at which point the experimental activity will come to an end.

‘Monitoring is to be continued in the area for about five years from the completion of the test structure.’

Tentative results from the first test structure positive

The previous test structure for the mining area planned for Kolari was completed one year ago. According to Ms Koivumaa, the monitoring results obtained have been good, so for this reason there is a wish to continue the testing activity.

Synthetic water similar to mine water was prepared for the first test structure, which will be used in the production of belite cement for the new test structure. Belite cement will be utilised in the production of concrete, which will be used to seal the surface of the layered wall rock.

‘In using mine water, it binds to the belite cement during the process,’ Ms Koivumaa states.

Tapojärvi is a Kolari-based family business that specialises in mining and mill services as well as circular economy solutions. Tapojärvi operates as part of an industrial-scale circular economy that is constantly processing industrial by-products and innovating new solutions for the mining industry.

The Tapojärvi Group is comprised of Tapojärvi Oy, Tapojärvi Italia S.r.l, Tapojärvi Sverige Ab and Hannukainen Mining Oy. The companies together employ 800 people, and the Group’s turnover in 2022 totalled EUR 163.6 million.