Recovery of rare earth elements minerals from iron oxide-silicate rich tailings - Part 2: Froth flotation separation

摘要

This study is the second part of an ongoing investigation to recover and upgrade rare earth elements (REE) minerals from iron oxide-silicate rich tailings (IST) generated at a South Australian mining operation. Previous work (Part 1) has shown that REE minerals are preconcentrated in a high-intensity magnetic concentrate and non-magnetic tails along with iron oxides and silicate minerals, respectively. As a part of the overall beneficiation and enhanced REE minerals recovery strategy, complementary studies involving downstream froth flotation of the magnetic preconcentrates were conducted and the results presented in this paper. Froth flotation of the preconcentrates was carried out using sodium oleate and hydroxamic acid as collectors in the presence of sodium silicate and starch as depressants. A comparison of rougher flotation of the preconcentrates indicated that hydroxamic acid produced higher total rare earth oxides (TREO) recoveries (91-93%) with enrichment ratio ranging 1.03-1.30, whereas sodium oleate produced relatively higher upgrade (1.50-1.55 ratios) with significantly lower recoveries (12-36%). Scavenger and cleaner flotation tests were conducted on selected concentrates and tails, where further upgrade was achieved at the expense of recovery. Two process flowsheets for recovering REE minerals were then developed. Flowsheet 1 includes magnetic preconcentration followed by flotation using both collectors, whilst Flowsheet 2 includes magnetic preconcentration prior to hydroxamic acid flotation. Typical metallurgical results indicated Flowsheet 1 produced a final concentrate grade of 1.55% at 55% TREO recovery, whilst rejecting 47% Fe and 74% Si, whereas a final concentrate grade of 1.67% at 72% TREO recovery, with 39% Fe and 59% Si removed using Flowsheet 2. The REE minerals, in combination with mainly silicates in the non-magnetic tails, allows better upgrade, with 2.5 times enrichment through hydroxamic acid flotation, compared to 1.93 times enrichment from the REE iron oxides magnetic preconcentrate. Florencite, which was not recovered and upgraded by magnetic separation, was successfully recovered and upgraded along with bastnasite and monazite by froth flotation. The study has revealed that froth flotation can be used to complement the recovery of REE minerals by magnetic separation, suggesting the IST could be exploited for REE beneficiation. However, it is obvious that minerals liberation and particle size distribution are critical in achieving enhanced REE minerals recovery and upgrade.