Recovery of REEs as co-products from a Vietnamese sedimentary phosphate ore by flotation - Impact of milling conditions

Vietnamese phosphate deposits are of marine sedimentary origin and one of the largest phosphate rock deposits of Southeast Asia. Lao Cai phosphate reserves have been estimated at about 526 million tonnes with hypothetical reserves of about 2.6 billion tonnes. Phosphate rock has been considered as a secondary rare earth elements (REEs) source due to REEs often found as tracers of geochemical processes in the crystal structure of phosphates via substitution of Ca. Although the content of REEs in apatite is rather low, it is still relevant by total mass due to large tonnages of phosphate rock mined annually.
The impact of milling conditions on particle properties, pulp/ froth properties (Ca2+/ Mg2+ ion concentrations, pulp rheology, froth structure, etc.), which in turn influences on the flotation responses (grade, recovery, flotation kinetics and selectivity between apatite, REEs-bearing apatite and carbonate minerals) are given. With a rougher flotation feed containing about 12 % P2O5 and 200 g/t REEs, the obtained recoveries were 88-93 % for apatite and 75-84 % for REEs. This indicated that REEs can be enriched by froth flotation via co-flotation of the REEs-bearing apatite or true flotation of rare earth bearing minerals. However, there was only 24-29 % of dolomite removed from a feed containing about 7.3 % MgO. Thus, the separation of carbonate from finely disseminated siliceous carbonaceous apatite ores is given to be challenging due to fine intergrowth and a significant amount of dolomite with similar flotation properties like apatite.