Floatability of synthetic light and heavy rare earth element carbonates and selectivity towards calcite

The fourteen lanthanoid elements, also commonly referred to as rare earth elements (REE) or rare earth metals (REM) and often including lanthanum as well as both Yttrium and Scandium, can be referred to as the vitamins of the periodic systems table. They are used for green and high tech applications such as powerful magnets, batteries, glasses and triband dyes. Commonly they can be found and mined as carbonate minerals, e.g. bastnäsite, synchisite and ankylite or as phosphate minerals, e.g. monazite and xenotim. Usually they all occur as mixed REM carbonates with different proportions of light and heavy rare earth elements. The light rare earth elements LREE (lanthanum through samarium) are less scarce and thus economically becoming less critical (EU list of critical elements from 2014). The heavy rare earths HREE (europium through lutetium plus yttrium) are indeed rare, scarce and thus considered critical elements. The ratio of LREE and HREE depends very much on the deposits. When beneficiating rare earth carbonate minerals flotation is often an important unit process operation especially to reduce content of silicates, calcite and barite. As flotation reagents in principle simple carboxylic acid type collectors are used in combination with silicate and calcite depressants. It has been reported (Nature (2013), 12, 315) that the surface wettability of REE oxides very much is influenced by high ionic radius of the REE cations. The ionic radius is indeed one of the distinguishable properties of the REE amongst one another. Therefore the question is how different synthetic unmixed individual LREE and HREE carbonates behave in terms of floatability.
Results are presented for the REE carbonates of yttrium, lanthanum, cer, neodymium, dysprosium and ytterbium with sodium oleate at different pH values. Lignin sulfonate is investigated as the selective depressant for calcite and barium carbonate and not the REE carbonates.