Ceramics-Silikáty 59 (2) 169-175 (2015)

LEACHABILITY OF CHROME FROM MAGNESIA-CHROMITE REFRACTORY BRICKS CORRODED BY Cu/CuO-Na2O·2SiO2 SLAGS

The interactions of magnesia-chromite refractory brick with Cu-Na₂O·2SiO₂ and CuO-Na₂O·2SiO₂ melts are studied and the chemical durability of corrosion products in water is evaluated. The corrosion tests confirm intensive infiltration of the slag melts into the tested refractory bricks and formation of Cr(6+) compounds. The molten copper partially oxidizes during corrosion test by air and penetrates into bricks. Interactions among periclase (MgO) and chromite (FeCr₂O₄) grains with the melt Na₂O·2SiO₂ and copper oxides makes possible to form several compounds (e.g. Cu₂MgO₃, CuCrO₄, CaCrO₄, Na₂CrO₄, MgCrO₄). Just the marked yellow spots, which were observed on the corroded brick surface after 30 days of free storage, suggest hydration of the high-temperature corrosion products. The yellow color of spots points out to chromates as Na₂CrO₄ and MgCrO₄, which are well soluble in water. The leaching of corroded bricks in water (batch leaching test of a ratio of S (solid) : W (water) = 0.1 taking up to 28 days) confirmed the Cr, Na, Mg and Ca ions leach-out. The pH value of solution increased up to 9 during leaching mainly as a consequence of elevated Na+ ion concentration. The Cr ion concentration rises in the solution up to 1 mmol·l^-1. The observed moderate decrease of Cr ion concentration in the solution with the length of leaching indicates super-saturation of the solution and precipitation of the products.

Keywords: Environment, Corrosion, Magnesia-chromite refractory, Alkali leaching