Enlightening chromium for safe circular material use in metallurgic industry

Purpose and goal:

The purpose of the project was to investigate the chemical forms of Cr in metallurgic slag from full scale production processes, using adsorption spectroscopy - XAS (primarily XANES). Goals of the project were gaining knowledge and data on: a) Cr-oxidation states and the chemical forms of Cr in metallurgic slag, b) impact of changes in processing and aging on the abundance of different chemical forms of Cr.

The methods used proved to work well for the purpose, and all objectives have been fulfilled. Cr appears mainly as Cr(III) in the slag Expected results and effects:

XANES spectra were achieved from all samples and could be compared with reference spectra. Chromium appeared mainly as Cr(III) or with lower oxidation status in all slag samples. A slight change in spectra from aged and washed samples was observed, possibly indicating slight impact of exposure to air and water. Environmental risks with regard to leaching of Cr from recycled slag should be low as long as no oxidation to Cr(VI) occurs in the environment.

Approach and implementation:

During 20 hours at XANES at MAXIV, 27 samples from various metallurgical processes and pre-treatment (fresh, grinded, cut, leached and aged under atmospheric conditions, washed) were analysed. VAAB was responsible for collecting samples, LTU for pre-treatment and complementing analyses of the samples and RISE for conducting the experiments at MAXIV. Spectra were analysed by RISE and LU, and the results were interpreted collectively. LU was responsible for reporting, Afry for project management.