Arresting of efflorescence in ceramic tiles developed using caustic alumina industry waste (red mud)

Abstract

Conversion of caustic red mud (RM, Alumina industry waste) into building materials becoming one of the viable solution for its large scale utilization. The building materials developed using RM often results in efflorescence due to its high alkalinity, which is detrimental for the structural integrity of the buildings. The X-ray shielding tiles developed through ceramic route using the mixtures of RM, BaSO₄ and kaolin clay also suffers from severe Na₂SO₄ efflorescence when sintered above 1000 °C. The XRD analysis confirms the formation of Na₂SO₄ through the solid-state reaction that occurs between BaSO_4, Na₂Fe₂Ti₆O₁₆ and NaAlSiO₄ at above 1000 °C. The formation of Na₂SO₄ was reduced by adding KOH with the mixtures, which reacts with RM and BaSO₄ and form stable K₃NaS₂O₈ and KAlSiO₄ phases, as revealed through Rietveld refinement. Eventually, the wt% of Na₂SO₄ was found to decrease from 3.2 % to 0.2 % while adding 8 % of KOH. Subsequently, the efflorescence has decreased from 90 % to 2 %. Moreover, the KOH addition assist to increase the density of the shield from 2.8 g/cc to 3.6 g/cc. It eventually increases both the mechanical strength and X-ray attenuation characteristics of the shield. The flexural strength of the tile has increased from 16.46 N/mm² to 19.46 N/mm² while adding 8 % KOH. The 15 mm thick tile possess the attenuation equivalent to 2 mm lead at 100 kV.