Speciation of chromium in steelmaking solid wastes by selective retention on ion-exchange media and determination by isotope dilution inductively coupled plasma mass spectrometry

Abstract

The separation and determination of CrVI and CrIII were carried out by using a combination of ion-exchange resins and inductively coupled plasma mass spectrometry (ICP-MS). Once in solution the species were retained on Dowex 1-X8 and Dowex 50W-X8 resins, for CrVI and CrIII, respectively. Following elution of the CrVI with HNO3 and of the CrIII with HCl, and after elimination of chloride ions, chromium contents were determined by ICP-MS. The sample dissolution and preparation method was developed using CrO3 (CrVI) and Cr2O3 (CrIII) mixtures. A general method was established, consisting in the leaching of the soluble chromium species (CrVI and any soluble CrIII compound) with a NaOH–Na2CO3 solution, and in digesting the residue (insoluble CrIII compounds and Cr metal) by fusion with NaHSO4 and extracting the melt with HCl. The obtained solutions were submitted to the ion-exchange speciation processes. The scope of the method was investigated by analysing two electric arc furnace flue dust samples: MS-2 (carbon steel flue dust) and MS-3 (stainless-steel flue dust). The determination limits (10s), considering test samples of 10 mg, were 0.1 µg g−1 for both CrVI and CrIII. Validation of the proposed method was carried out by analysis of BCR CRM 544 and by standard additions of CRM 544 to CrO3–Cr2O3 mixtures; recoveries of both chromium species (CrVI and CrIII) close to 100%, with precision values better than 3%, were achieved. External calibration and isotope dilution (ID) were applied for ICP-MS measurements; the latter system (ID) was developed for application to Cr measurements in steelmaking solid wastes, to overcome any possible interference from the complex sample matrix.