Interfering ions in the flotation of a phosphate ore in a batch column

Abstract

The “Barreiro” carbonatite complex is located in Araxá, MG, Brazil. The production of apatite concentrate from this ore started in 1978 and the current production capacity is 800,000 tonnes. The ore is subjected to the following unit operations in the concentrator: grinding, classification, low field magnetic separation, desliming, apatite and barite flotation, high field magnetic separation, filtration and drying. Barite and apatite flotations were performed in 300 ft 3 (8.5 m 3) Wemco mechanical cells until 1992. The replacement of the mechanical cells by flotation columns occurred in two stages: fine fraction flotation circuit in 1993 and coarse fraction flotation circuit in 1994. All the 66 mechanical cells were replaced by 6 flotation columns (3.0 m × 4.5 m × 14.5m), resulting in improved selectivity and recovery and significant reductions in the consumption of the collectors for barite and, mainly, for apatite. The flotation process control monitoring in laboratory bench scale mechanical cells was then inadequate due to the discrepancy with the industrial practice. A specific methodology was developed for batch column flotation testing. The technique was checked by means of comparison with the industrial plant practice of apatite and barite flotation, showing its reproducibility and reliability for process development testwork. The batch flotation column was utilised to evaluate the effect of ions (dosed in the conditioning stage) on the flotation of barite and apatite. Flotation tolerance limits were established for the ions calcium, magnesium, phosphate, fluoride and rice bran oil soaps. Due to the fact that these ions were dosed as sodium salts (in the case of anions) or as chlorides (in the case of cations), the effect of sodium and chloride ions was also assessed (tests with the addition of sodium chloride). The results led to the environmental benefit of a full process of water recirculation in the concentrator without impairing the flotation performance.