Geochemical Effects of Increased Production on Recirculated Process Water at the Kiirunavaara Iron Mine, Northern Sweden

Abstract

Understanding process water characteristics and variations is important for ensuring high quality processing of iron ore. Large amounts of water are used during refinement, and the water is often recirculated to save energy. Water quality is important for processes such as flotation and agglomeration but recirculation of process water and changes in production can alter water quality significantly. This study was undertaken to better understand the origin of dissolved components in the process water and water quality variations in process water geochemistry at the Kiirunavaara magnetite ore mine, based on analyses from 1989 to 2008. Long-term trends at single sampling stations in the process chain, as well as changes along the process chain, were studied. Ca, S, Na, and Cl are the major elements in the process water, accounting for over 80% of the dissolved concentration. Ca has the highest concentrations with a mean of 183 mg/L and a maximum of 303 mg/L in the clarifying pond. At all investigated sampling stations (influent water and water in the sorting plant, concentration plant, pelletizing plant, and clarifying pond), dissolved elemental concentrations increased during the studied time period. This increase was mainly caused by increased production. The high concentrations of Ca and S probably result from sulfide oxidation and calcite buffering in the drainage area. The high N concentrations come from undetonated explosives while the main source of Na and Cl is fluid inclusions. If production continues to increase, higher concentrations in the process water should be anticipated.