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e FeCl3-HCl system was used as a lixiviating impregnant of CrCl2 for the analysis of chromium ions in molten chloride salt.[1,2] If FeCl3-HCl is used as a lixiviating impregnant of CrO, CrCl3 will be formed in the reaction process. CrCl3 is adsorbed and enwrapped on the surface of the sample, resulting in the incompletion of the separation of CrO and Cr2O3. Very often, steel making slags contain CaF2. CaF2 is not soluble in the process of Cr2+ selective lixiviating. Consequently, CaF2 will enwrap Cr2+, leading to incomplete dissolution of Cr2+. The influence of enwrapping Cr2+ by

HUI WANG, Graduate Student, Sub-Institute for Mineral Resource, Beijing General Research Institute of Mining and Metallurgy, is Researcher, Department of Material Science and Engineering, Royal Institute of Technology. YIWU XIAO, Senior Researcher, and KAIXI JIANG, Professor and General Manager, are with the Sub-institute for Mineral Resource, Beijing General Research Institute of Mining and Metallurgy, Beijing 100044, P.R. China. DU SICHEN is with the Department of Material Science and Engineering, Royal Institute of Technology, 100 44, Stockholm, Sweden. Contact e-mail: du@mse. kth.se Manuscript submitted November 22, 2007. Article published online March 7, 2008. 390—VOLUME 39B, APRIL 2008

CaF2 must therefore be considered when Cr2+ is selectively dissolved in an analysis. The present work aims at developing an analytical technique to quantify the fractions of Cr2+ and Cr3+ in metallurgical slag by first separating the ions of the two valences. The chemicals used in the present work along with their purity levels are presented in Table I. A simple experimental setup was employed to make the analysis. It is schematically shown in Figure 1. An Erlenmeyer flask was used as the reaction chamber. A dropping funnel was connected to the flask using ground glass join. The glass join had also one gas inlet and one gas outlet to introduce CO2 gas into the flask and to lead it out. Glass cotton was placed at the bottom of the column of the dropping funnel to support zinc particles. Vanadium hydrochloric solution was also added in the column. Vanadium ions, V5+, would be reduced by Zn through the following reaction: þ 2þ þ 3Zn2þ þ 6H2 O 2VO
3 þ 3Zn þ 12H ¼ 2V

½1

The hydrogen gas generated by Reaction [1] was led out by the gas outlet placed on the top of the dropping funnel. In a typical analysis, a slag sample was crushed into powder. An amount of 0.2 g of the powder was mixed with a few milliliters of FeCl3-HCl-NH4Cl solution in an agate mortar. The addition of NH4Cl was to provide enough supply of Cl- to convert Al2O3 into AlCl3. Hence, CaF2 could be fully dissolved by AlCl3. An agate pestle was used to grind the powder-liquid mixture. During the grinding, the following reaction took place: Fe3þ þ CrO þ 2Hþ ¼ Fe2þ þ Cr3þ þ H2 O

½2

A certain length of grinding time was found necessary to ensure the completion of the reaction. After grinding, the mixture was kept still for some minutes to allow the separation of the solid and liquid. The liquid w