Abstract
The effects of pretreatments on the zeta potential characteristics of hematite were investigated on a number of hematite samples. The bulk of the test work was conducted on a sample of naturally occurring hematite from the Iron Prince deposit in the Middleback Range area of South Australia. The iep of the ROM ore was measured as 2.6, which was only slightly raised by ultrasonic cleaning. When the ore was contacted with dilute acid over a prolonged period the iep was raised to 6.7, the value commonly quoted for natural hematites. Contact of the hematite ore with HCl solutions for only 1 hour did not increase the iep to this value. Removing the slimes from the ore gave an iep value of 3.5, which was only slightly raised with contact with HCl. The value of 3.5 may be close to the true value of the iep for this ore. Slimes removed from the ore plus assay residue where the iron has been removed gave iep values typical for silica. The iep for a high grade hematite sample from Iron Knob was 5.3 and this was not changed by contact with HCl. Washing the Iron Prince ore with NaOH and HCl followed by NaOH had little influence on the iep of the ore, and still reflected the presence of silica. The iep of freshly precipitated ferrihydrate was 7.5, typical of values obtained for synthetic hematites. The zeta potential characteristics of silica activated by ferric ions gave similar characteristics to that of the acid washed hematite ore. This suggests that the major species under test in the microelectrophoresis cell after prolonged acid washing of the hematite ore is in fact ferric-activated silica from the fine particles removed by centrifugation prior to testing since it is known that the silica is concentrated in the fine fractions of the hematite ore. This finding is further complicated by the fact that both ferrihydrate and AR ferric oxide have iep values in a similar range. These three species could co-exist under the conditions of the microelectrophoresis testing.
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