Ultrasonic treatment of high phosphorus Australian iron ore fines.

• Sonication before desliming of high phosphorus iron ore fines was studied. • Ultrafines generation depended on the total ultrasonic energy input. • Pumping the pulp downwards past the ultrasonic probe is more effective than upwards. • Sonication improved the deslimed product increasing Fe and reducing Si and Al grades. • A mild improvement in P assay is due to P being associated with goethite. The trends and efficacy of ultrasonic pre-treatment before desliming high phosphorus Australian iron ore fines was investigated in the presented fundamental study. The −1 mm iron ore fines (57.5 wt% Fe, 2.47 wt% Si, 2.15 wt% Al, 0.132 wt% P) were subjected to sonication while the ultrasonic power, duration and pumping direction were varied. Sonication increased the iron grade and decreased the Si and Al assay in all size fractions except the ultrafines, where the opposite occurred. Ultrasonic treatment was found to depend on the total sonication energy input (up to 68 kJ) with no preference for either power or duration alone. The direction of pulp circulation was important and best results were obtained by pumping the pulp downwards past the ultrasonic probe rather than upwards. Sonication of iron ore fines suspended in water promotes deagglomeration, surface cleaning or disintegration, resulting in substantial deportment of mass from the coarser size fractions to the ultrafines (less than9.9 µm). The iron grade of ultrafines generated by sonication was lower than that of the ultrafines in the head sample, while the corresponding grades of Si, Al and P were higher. Increasing the sonication energy increased the proportion of hematite and decreased the proportion of kaolinite in material that deported to the ultrafines, which was most probably due to the surface action of ultrasonic treatment. A substantial portion of kaolinite (∼33 %) deported to the ultrafines during sonication using 68 kJ, compared with only 8.8 % of the goethite. Desliming of the unsonicated and sonicated samples was evaluated by calculated size classification. The sonication pre-treatments substantially improved the predicted grades of Fe, Si and Al in the deslimed products compared with unsonicated deslimed sample. For experiment using the highest sonication energy (68 kJ) and calculated desliming of < CS5 fraction, the predicted product iron grade improved by 2.8 wt% (1.6 wt% more than unsonicated) after desliming, while the silicon grade decreased relatively by 36.0 % (22.7 % more than unsonicated), the aluminium grade decreased relatively by 39.5 % (25.1 % more than unsonicated) and the predicted phosphorus content decreased relatively by 3.0 % (1.5 % more than unsonicated). The difference in sonication effect between Al, Si and P was due to the association with different minerals. Aluminium and silicon were mainly associated with kaolinite and soft goethite, which were easily disintegrated by ultrasound and deported to the ultrafines, while phosphorus was mainly associated with goethite (mostly of the hard types) present at around 40–48 wt% in most size fractions before and after sonication. [ABSTRACT FROM AUTHOR]