Experimental study on the beneficiation of a ferruginous rare earth bearing lateritic ore by magnetising roasting and magnetic separation

摘要

The beneficiation of ferruginous rare earth bearing ores derived from lateritic deposits by conventional mineral dressing processes is made difficult by the characteristics of the ore such as fine grain size, complex texture and similar physical characteristics between rare earth minerals and iron oxide gangue. The removal of iron oxides would offer significant advantages with respect to downstream rare earth mineral processing. The purpose of this study was to demonstrate, at bench scale, the feasibility of magnetically separating iron oxides from a ferruginous lateritic rare earth ore after it had been subjected to reduction roasting to convert feebly magnetic iron (III) oxides to magnetite. Bulk roasting of -2.36 mm feed was performed at 650°C for 90 min with the addition of 177 kg coal/tonne of feed; these conditions being optimal with respect to goethite and hematite conversion to magnetite. Char was separated after roasting via a combination of dry screening and gravity separation with total losses of rare earths amounting to 1.3% and carbon rejection amounting to ~93%. Roasting resulted in a slight increase in rare earth oxide grade from 8.51 wt% to 9.11 wt% and bulk mineral phase analysis by QXRD indicated that complete conversion of goethite and hematite to magnetite occurred. Split charges of roasted ore were milled down to varying particle size and the effects of magnetic field strength and feed particle size on the efficiency of low intensity magnetic separation (LIMS) was explored through rougher magnetic separation tests using a Davis tube tester. Subsequent chemical and mineralogical analysis of the rougher magnetic concentrates and tails were performed. Magnetic separation was successful in removing iron (as magnetite) at a minimum field strength of 0.15 T however this was typically accompanied by significant amounts of rare earths and rare earth enriched tails could not be produced at an adequate grade and recovery. It is believed that this may be due to flocculation taking place which has resulted in aggregation and entrapment of magnetite, monazite and gangue components during magnetic separation.