The utilization of red gypsum waste for glazes

Red gypsum (RG) is a by-product during the extraction of titanium(IV) oxide from the ilmenite ores and it causes problems such as storing and environmental pollution. In this study red gypsum, a reddish brown semi-solid mud, which is the industrial waste of a local company in Malaysia, was investigated for use in the making of glazes for the ceramic industry. The major constituents of RG are hydrated CaSO4 (70 wt %), Fe2O3 (30 wt %) and small amount of Al2O3. The total accumulation of RG in Malaysia is at least 340,000 tons per year. It was found that the addition of up to 36 % of the RG waste was possible in the production of glazes. The glazes which contain different compositions were examined for their surface hardness properties, chemical strengths in 5 % HNO3 and 5% NaOH solutions and crazing behaviour at 180 oC under 5 bars of pressure for 2 hours