10 13 13

(Whiteley et al., 2015)

Cement is produced by combining limestone with a smaller proportion of aluminosilicates such as clay, mudstone or shale and calcining them together in a rotary kiln, to temperatures of 1450°C before grinding the resulting clinker into a fine powder, blended with a small proportion of gypsum. There are 11 cement works in the UK, producing around 10 million tonnes per year of cement (MPA, 2019). The production of cement for concrete-based construction materials is a significant contributor to the UK's industrial CO2 emissions.

Depending on the type of production process used, the primary waste stream that occurs from cement production is either cement kiln dust or cement bypass dust. Due to its hazardous nature, cement bypass dust is not considered here.

Cement kiln dust contains a mixture of raw and partially calcined feed materials, dust and ash, containing additional alkali sulphates, halides and other volatile materials.

The waste stream typically varies over time and between facilities, depending on the kiln temperature and design, the raw materials and the fuels used. The material can be recycled in cement production, but the quantity that can be incorporated is restricted, with too high a proportion creating an inferior product due to the high concentration of alkalis and unwanted minerals. The primary alternative use is an agricultural fertiliser, as an economic substitute to lime.