Swiss Tower Mills Minerals AG

Kevitsa – Finland, Boliden

Kevitsa is a multimetal mine and concentrating plant in northern Finland, the 700 kW vertical stirred, HIGmill™ from STM was installed into the existing plant and commissioned in February 2015 in a regrind duty of the copper rougher and scavenger concentrate.

The improvements were significant: 

  • The average copper grade increased from 22.5 to 25% while also increasing the recovery from 70% to 80%, an impressive 10% increase. 
  • The grade improved by reducing Nickel in the Copper concentrate from 0.85% to 0.7%. this improvement in purity of the concentrate further increases value. 

Operational Precision 
STM mills have multiple operating modes, the Kevitsa mill operated in the most sophisticated “P80 control mode”. This utilises the installed online particle size analyzer: the target P80 from the mill can be set by the operator. The mill operates in a closed loop control mode, and despite the feed size and feed rate fluctuating significantly, the control automatically varies the mill speed, in order to achieve the target P80. This produces very consistent grinding results minimising wasted energy on overgrinding. 

Steep Product Particle Distribution
The mill produces a large amount of particles within the required product size range. The internal selective grinding mechanism minimises overgrinding of fine particles, minimising ultrafine particles, and produces large amounts of desired 20-40µm particles. The grinding performance achieves precise results on a single pass through the mill, allowing open circuit flowsheet, without any recirculating through the mill.

High Performance Recoveries 
The impact of the HIGmillTM on the final copper grade and copper recovery is outstanding. Interesting is also that the finer grind resulted into less nickel reporting to the final copper concentrate product. 

Not only did recovery and grade increase, but the finer grind resulted into less nickel reporting to the final copper concentrate product.

Read more in the technical paper