At the end of 2013, the mine company LKAB decided to interrupt the drilling operations in one of its mines in Kiruna, Sweden, owing to the increased wear of the pumps and water powered percussion hammers caused by the poor quality water. The introduction of Wassara’s water handling system complemented by a customized flocculation unit resulted in an increase of hammer life time by a factor of four, as well as the disappearance of all pump related issues, ultimately allowing LKAB to re-start its drilling operations.
LKAB’s Kiruna sub-level caving mine
The Kiruna mne is the largest and most modern underground iron ore mine in the world. Owned by Luossavaara-Kiirunavaara AB (LKAB), the world leading producer of processed iron ore products for steelmaking, the Kiruna mine relies on LKAB Wassara water-powered down-the-hole hammers to drill long, straight blast holes. A centralized water system supplies the drill sites with water of the required quality.
The Konsuln site
The remotely located Konsuln drill site was not connected to the main water supply system. Water was instead drawn from a local reservoir, located 360 m underground, and then delivered to the drill rigs after an additional sedimentation stage. The high water demand from the rigs, together with the limited sedimentation time, however, resulted in the inability of the suspended material to settle either in the reservoir or in the sedimentation container, thus resulting in an excessive amount of particles entering the Wassara hammers, shortening their life span. This also led to increased wear of the water pumps.
At the end of 2013, when LKAB contacted LKAB Wassara, the average service interval of the hammers had reduced to about 20% of its nominal value, and several pump maintenance interventions had been required, leading LKAB to a costly temporary shutdown of its drilling operations in the Konsuln site.
Water clarification system
The remote location of the Konsuln iron ore body called for a compact and portable solution. Wassara devised a water clarification system consisting of Wassara’s own water handling system, a lamella-based water sedimentation unit, complemented by a flocculation unit. The lamella system maximizes the settling area while minimizing the footprint, and is therefore optimal for operations in tight and narrow areas. By mixing a flocculating polymer to the water, the suspended particles bond into aggregates, thus settling faster.
The overall water clarification system was placed near the reservoir. Drill water was channelled to the WHS through a concrete collector, which also acted as a pre-sedimentation unit. The flocculant was mixed to the water prior to the WHS, leading to an accelerated settling of the suspended particles. Both the concrete collector and the WHS could easily be emptied by means of a sludge removal truck.
Independent analysis confirmed the increase in water quality due to the introduction of the water clarification system. The amount of suspended particles per liter per sample in the water supplied to the drill rigs decreased from over 700 mg/l to below the threshold of 150 mg/l specified for the Wassara hammers. As a consequence, the average service interval of the Wassara hammers increased past its nominal value, with several hammers surviving over 2000 m. This allowed LKAB to re-start its drilling operation at the Konsuln site.
No additional damage to the pumps occurred after the introduction of the Wassara system, which led to considerable savings for LKAB.
Statement from a pleased customer
“We had to replace a number of pumps, both in the mine and on the rigs, because of the low water quality, and the hammers stopped after just 150 drilled meters. Together with Wassara we built a system channelling the drill water to Wassara’s water handling system. Thanks to this solution, our problems with the pumps in the mine disappeared, and the hammers survive longer than 1000 meters.”
(Roger Tillstam, construction manager for the Konsuln site)