RECOVERY OF RARE METALS FROM STEELMAKING DUST

A process was studied for recovery and isolation of rare metals such a s B, V and Ga from steelmaking dust in which they exist at very low co ncentration. Two-stage leaching was employed, depending on the propert ies of the metal ions. First, of the boron contained in the dust, 72% can be leached with 3 mol/dm3 sodium hydroxide solution. Most of the i mpurity metals were precipitated as their hydroxides by adjusting the solution pH to 10 and were removed by filtration. The selective concen tration of B was done using a chelating resin column with a functional group of glucamine type, and eluate containing 4.7 g/dm3 of B was obt ained. This liquor was further treated to give a B solution with minim um purity of 99.9% by a solvent extraction technique, employing EHD (2 -ethyl -1, 3-hexanediol) as an extractant. Second, 2.25 mol/dm3 sulfur ic acid was used for leaching V and Ga from the solid residue of the f irst-stage leaching. The leach liquor contained 0.038 g/dm3 Ga and 0.0 28 g/dm3 V in about 1000 times more Fe and Zn. Ga and V were then conc entrated by use of a chelating resin column with a functional group of aminocarboxylic acid type after reduction of ferric ion to ferrous io n and pH adjustment. The eluate was conditioned and passed again throu gh the column. V was concentrated to 8.5 g/dm3 and Ga to 13 g/dm3 in t he resulting eluate. The liquor was further treated to isolate them by a solvent extraction technique, employing TOMAC (tri- n - octylmethyl ammonium chloride) and D2EHPA (bis (2-ethylhexyl)phosphoric acid) as e xtractants. Stripping solutions of 99% Ga purity and 99% V were finall y obtained.