Pre-concentration of Low-grade Banded Iron Formation (BIF) by Physical Beneficiation

Abstract The depletion of high-grade iron ore reserves in South Africa has necessitated the exploration of low-grade hematite resources in a bid to extend life of mine and maximize resource utilization, particularly banded iron formations (BIF) material which makes up approximately 66% of future reserves. BIF are sedimentary rocks and consists of alternating layers of silica and iron. It has been observed that for ores with Fe grades below 40%, the concentrate grades and recoveries are compromised. Thus, the aim of the research study involved production of a pre-concentrate grading at approximately 55% Fe with potential for alternative downstream processing such as cationic reverse flotation to further upgrade the pre-concentrates to final concentrates with grades higher than 63% Fe. The industrial benefits of pre-concentration are evident in upfront gangue reduction and ability to improve production capacity and reduce operational costs. With this in mind, the paper investigates the pre-concentration methodology undertaken, namely, magnetic separation versus gravity shaking table on feed material crushed to a fine grind size of − 1.18 mm for effective liberation of hematite from gangue. Comparative SLon testwork and shaking table tests yielded similar overall recoveries at approximately 50% with high Si rejection of approximately 90% at a target pre-concentrate grade of 55% Fe. Increasing the target grade further to 60% and 63% Fe could only be achieved by gravity separation at a significant reduction in recovery of 35–62%, respectively. The feasibility of pre-concentration for this ore type is thus assessed in detail.