Model-based control of Aitik bulk flotation

The Boliden Aitik concentrator in Sweden processes 2,000 t/h (2,200 stph) of low-grade copper ore. The plant consists of five grinding lines that feed four bulk-flotation banks with a scavenger-concentrate regrind mill and a column cleaner circuit with a re grind mill. The authors installed a model-based expert optimizing control system to maximize copper recovery in the bulk-flotation circuit while maintaining an appropriate copper grade in the cleaner feed. The optimizing control system uses on-line assays and calculates and implements set points for cell pulp levels, air rates and reagent-addition rates. It combines the power of a dynamic population-balance model that estimates mineral liberation in each stream, an optimizer that computes appropriate set points and a rule-based module that implements the strategy. The benefits have been evaluated over a period of three months. The model-based expert optimizing control system generates a measurable increase in copper recovery, around 0.5%, and an optimized bulk-concentrate grade. The need to maintain the optimizing control system and other practical aspects are discussed.