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(Latif et al. 2015)

Lime is produced by calcining calcium carbonate at temperatures of approximately 1000ºC, decomposing to release carbon dioxide and form calcium oxide. The material is then cooled and depending on the type of lime produced, often subsequently combined with water to form slaked lime, calcium hydroxide. In the UK, 1.2 million tonnes of lime was produced in 2019 (MPA, 2021).

The main waste generated from the manufacturing of lime is an extremely fine-particle kiln dust, collected by dust control systems and extracted during the calcination process, with an average particle size less than 30 microns (Miller and Callaghan, 2004).

The Environment Agency reports that the fine particle size makes the material unsuitable for direct recycling in the kiln (Environment Agency, 1996), and the composition of the dust to typically be high in calcium carbonate, alongside ash and calcium oxide. The exact composition of the dust depends on a range of factors including the kiln design, fuel and material selection and other studies have characterised the dust as roughly equal parts calcium carbonate and calcium oxide (Miller and Callaghan, 2004).