Geochemical characteristics determinedby multiple extraction from ion-adsorption type REE ores

Abstract

This article reports results of the multiple six-step extraction and single step extraction experiments conducted on five ion-adsorption ores and three weathered granite samples collected from the Dingnan County in Jiangxi Province, China. The six-step extraction consists of ion-exchangeable (reacted with sodium acetate) fraction, organic-matter (sodium pyrophosphate) fraction, amorphous Fe oxide and Mn oxide (hydroxylamine at 30˚C) fraction, Fe and Mn oxides (hydroxylamine at 60 ˚C) fraction, clays-sulfide (aqua regia) fraction and silicates (mixture acid) fraction. The five ion-adsorption ores from a mining site contained the ion-exchangeable elements by sodium acetate solution ranging from 174 to 388 ppm REY (43 – 68 % relative to whole-rock contents), from 1.1 to 3.5 ppm Th (3.7 – 9.4 %) and from 0.44 to 1.0 ppm U (14 – 25 %). Concentrations of the extracted elements from the ores by ammonium sulfate solution (single step) range from 170 to 346 ppm REY (42 – 64 %), from 0.03 to 0.31 ppm Th (0.1 – 0.8 %) and from 0.25 to 0.71 ppm U (8 – 18 %). The ion-exchangeable fraction is remarkably depleted in Ce relative to the other REY, and is slightly depleted in HREE and Y, compared with the whole-rock compositions. Thorium is dominantly present in the organic-matter fraction, and is moderately contained in the clay-sulfide fraction and in residue. Uranium is extensively present in the residue, silicates fraction, ion-exchangeable fraction, clays-sulfides fraction, and organic-matter fraction. Results of three weathered granite samples outside of a mine are not significantly different although the REY contents or percentages of ion-exchangeable REY are lower than the ores.