For tests on the reduction of impurities, three slime samples were selected; one with a relatively high alumina and low iron oxide content (S16: 58.6% Al2O3 and 12.3% Fe2O3), one with both alumina and iron oxide content relatively high (S18: 56.6% Al2O3 and 15.9% Fe2O3) and one with relatively low alumina and high iron oxide content (S26: 37.1% Al2O3 and 17.0% Fe2O3).