During acid leaching of bauxite residue (red mud), the increase in dissolution of rare-earth elements (REEs) is associated with a substantial co-dissolution of iron; this poses problems in the downstream processing (i.e. solvent extraction or ion exchange). Six different slags generated by reductive smelting of the same bauxite residue sample were treated by high-pressure acid leaching (HPAL) with HCl and H 2 SO 4 to selectively extract REEs. Thus, up to 90 wt% of scandium was extracted from the slags using H 2 SO 4 at 150°C, while with HCl the extraction of scandium reached up to 80 wt% at 120°C. The extraction of yttrium, lanthanum and neodymium was above 95 wt% when HCl was used as a reagent, but it was much lower (< 20 wt%) with H 2 SO 4 , presumably due to the formation of a double sulfate (NaLn(SO 4 ) 2 ⋅nH 2 O) and/or due to the adsorption on the surface of silicon/aluminium-oxides compounds. In addition, HPAL of bauxite residue slags led to a significant co-dissolution of aluminium (> 90 wt%, 18 g L −1 ), while the concentration of the remaining iron (> 60 wt%) was of 3 g L −1 in the leachate. The co-dissolution of silicon and titanium was lower than 5 wt%.
Highlights High CO2 concentrations reduce the bauxite residue alkalinity. Cancrinite forms upon decomposition of sodalite with high CO2 concentration. High stability of aluminosilicate compounds with high sodium dissolution. Silica dissolution limits the recovery of metals by acidic leaching. The recovery of scandium is restricted by its chemical association to major elements.
Due to their high metal content, printed circuit board (PCBs) are an attractive resource for metal recovery. Until now, the dissolution and subsequent recovery of metals from PCBs considers either...
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