Lesson Learned from Using Column Flotation Cells as Roughers - The Miduk Copper Concentration Plant Case

At the rougher flotation circuit of the Miduk copper concentration plant (Kerman, Iran) five column cells (CISA) have been installed with 4m of diameter and 12m of height using static mixer type (MicrocelTM) spargers. Based on the initial design, columns should accept a feed rate of 625 t/h with 80% passing size of 90 µm and solids concentration of 28% and produce 88% of the plant concentrate (i.e., 22 t/h) containing 32% copper. Due to the mechanical and processing problems this objective was never achieved and theses columns were remained out of operation from the commissioning time (2005). The results of an extensive study indicated that spargers plugging is due to the entrance of small amount (2 kg) of coarse particles (up to 2.5 cm) and it is the main reason of columns non functionality. It was proposed in order to have a stable operation of the columns at the rougher stage the feed rate for each column should be reduced from 125 (design) to 70 t/h. The air superficial rate had to be also reduced from 1.9 (design) to 0.6 cm/s. A period of 10 days of continuous operation showed that the carrying capacity was 0.23 g/min/cm2 which was significantly lower than the design value (i.e., 0.58 g/min/cm2). The gas hold up was found to be lower than 10% beyond which columns started to move to the turbulent state indicated by “boiling” froth. The average life time of spargers was determined to be 20 days. The average recovery and concentrate grade of these columns were found 68 and 32%, respectively. The high wear rates of spargers, high level of maintenance and supervision needed and instability of the operation made the plant managers not to use the column cells as the roughers.