As the excessive extraction of high grade iron ore reserves has led to the rapid depletion of these ore bodies, there is a growing need to extract and upgrade low grade iron ores into more economically viable products with an iron content in excess of 50%. The beneficiation of low grade iron ores through the reverse cationic flotation procedure is gradually gaining popularity as a possible processing route of the future for South Africa’s iron industry. Reverse cationic flotation employs a reagent suite consisting of an amine compound which functions as a quartz collector in addition to providing the frothing effect in the flotation system, and hydrolysed starch which serves to depress hematite during flotation. The aim of this project was to investigate the effect of using five amine collectors with different molecular structures on the flotation recovery of quartz and the entrainment of hematite in the flotation of a South African iron ore and a Brazilian iron ore. Laboratory batch flotation tests were conducted on both ore samples and the grade and recovery of hematite were recorded. The collectors were characterised through surface tension measurements and pKa value analysis. An attempt at using different polysaccharides as hematite depressants entailed the use of a CMC and a guar gum in batch flotation tests of the Brazilian iron ore. With regards to the batch flotation of a South African iron ore, results showed that at the grind size of 80% passing 150 μm, there was no selective separation of quartz from hematite. When the most commonly employed collector, an ether monoamine (Flotigam EDA) at a dosage of 125 g/t was used in flotation, the iron grade changed from 39% to 40% whilst the quartz grade dropped from 38% to 36%. This change in grade was insignificant when experimental errors were considered. Flotation of a mill product with a grind size of 80% passing 75 μm using a hybrid flotation cell also exhibited poor flotation results when the same reagent suite was applied. The iron grade changed marginally from 39% before flotation to 41% after flotation. The ether diamine 1 (Flotigam 3135) and a blend of the Flotigam EDA and Flotigam 3135 at a dosage of 125 g/t also failed to selectively float quartz from hematite. The remaining collectors (ether diamine 2, an imidazoline and a quaternary ammonium salt) did not yield any mass recovery to the froth zone, therefore, they were the worst performing collectors in the batch flotation tests of a South African iron ore. QEMSCAN analysis of the South African iron ore revealed that the ore was texturally complex with finely disseminated mineral phases in the sizes of -20 μm. Poor liberation of the quartz and the hematite led to the poor flotation performance. Further milling of the ore merely produced high amounts of slimes which would lead to high losses of hematite through the entrainment of hematite during batch flotation. Batch flotation results from the flotation of a Brazilian iron ore at the standard grind size of 80% passing 150 μm yielded good flotation results for all five collectors that were investigated. Surprisingly, the ether diamine 2 (Flotigam 2835-2L) performed best as a collector for the Brazilian iron ore although it failed to perform in the flotation of the South African iron ore. A hematite concentrate with an iron grade of 65% and a quartz grade less of 1.5% was attained. At the same collector dosage of 125 g/t, the superiority of alky ether amines over the quaternary ammonium salt and the imidazoline was evident in the final iron grade and recovery. QEMSCAN analysis of the ore sample revealed that both quartz and hematite were above 90% liberated explaining the good response to reverse flotation using cationic collectors. In both mineral systems, entrainment of hematite was influenced by the type of collector employed as they differed in frothing strength. The use of a collector with a strong froth stabilising effect resulted in a higher degree of entrainment as seen when ether diamine 1 (Flotigam 3135) was utilised in flotation. The addition of an alcohol frother in systems employing the quaternary ammonium salt and the imidazoline salt as quartz collectors introduced a strong frothing effect to the system as well as an enhancement in quartz recovery to the froth zone. The presence of a neutral species in a flotation system either through the addition of an alcohol or the manipulation of chemical conditions i.e. the pH such that the alkyl ether amines generate neutral molecular species and ion-molecule complexes is necessary in order to achieve good flotation results. The neutral species and the ion-molecule complexes assist with frothing and adsorption of cationic collectors onto the quartz surface. Batch flotation using a CMC and a guar gum as hematite depressants showed that starch remains a superior hematite depressant. At the same depressant dosage of 1500 g/t a system using starch as a depressant yielded a hematite concentrate with an iron grade and recovery of 65% and 97%, respectively. The CMC and guar gum yielded a hematite concentrate with iron grades of 51% and 66% respectively and iron recoveries of 88% and 80%, respectively. The CMC, employed at a dosage of 1500 g/t, had a dispersive effect which resulted in more hematite reporting to the froth phase hence the lower iron recovery after flotation. At lower depressant dosages i.e. 250 g/t and 500 g/t, the system using a guar gum attained a higher iron grade of 63%. The results confirmed the strong flocculation effect of a guar gum in higher concentrations which results in the agglomeration of quartz causing it to remain in the pulp zone. In general, the study showed that the South African iron ore under investigation was not amenable to flotation. Further studies into the processing of ultrafine ore will be required if the desired iron grade is to be attained. Another key finding is that the collectors’ molecular chemistry alone does not accurately determine their flotation performance as their flotation behaviour can differ depending on the mineral system.

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