About 800,000 t of BOF slag are generated per year during the steel production process by Austrian steel plants of voestalpine. Austrian legislative authorities restrict the use as recycling construction material in road building to the bituminous binder course, which additionally includes a lifetime responsibility of the producer for possible future contaminants that currently have not been considered.
Alternative routines of recycling of BOF slag are thus addressed in a project of K1-MET within the COMET funding program of the Austrian Research Promotion Agency (FFG), financed by the Austrian government and industry. Selective leaching processes are investigated by the Chair of Mineral Processing, Montanuniversität Leoben to recover the iron bearing oxides contained in the slag (i.e. magnesio wuestite, Ca- and Mg ferrites) with the lowest amount of phosphorous possible, which is contained in larnite (dicalciumsilicate) only.
Common mineral processing methods obtained only poor results due to intergrowth conditions. Selective leaching of P containing larnite by citric acid may provide an alternative.
Systematic tests for optimum leaching conditions concerning optimum mass ratio of agent to industrial slag, volume of eluate, leaching time, leaching temperature, and pH were performed. As the acid consumption is comparatively high, a special effort was spent on the regeneration of citric acid.