Thermogravimetric and X-ray powder diffraction analysis of precipitator dust from a rotating lime kiln

Abstract

Precipitator dust was sampled from kilns six and seven of the Lime Acres plant, South Africa, and a mixture analysed for its chemical composition. It mainly consists of Si, Al and Ca compounds, with some Mg compounds also present. The phases were determined to be mainly calcite, with some portlandite, lime, CaSO 4 anhydrite, mullite and a small amount of carbon. Minute amounts of dolomite and magnesian calcite were also observed. Thermogravimetric analysis of the dust indicated a mass loss of between 2 and 3.5 % when heated to 600 °C with a further loss of 26 to 29 % when heated to 800 °C using a heating rate of 5 °C.min −1. Upon treatment with water only a few percent of the available lime reacts with water to form Ca(OH) 2, while some CaSO 4 hemi- and di-hydrate also seem to form. Water treatment of precipitator dust has been shown to be in effective because of the high percentage of lime that still remains in the product. The disposal of the water treated precipitator dust would therefore not satisfy environmental requirements.