(Zografou, 2015)

In the UK, china clay, or kaolin, occurs in Cornwall and Devon in deposits of global significance. The UK china clay deposits derive from the residual decomposition of granite moors and the clay is typically extracted through a ‘wet process’ by which the decomposed clay is washed from the rock it originated from, generating nine tonnes of waste for every one tonne of pure china clay extracted (Thurlow, 2005).

Stent is the term used to describe the coarse granite removed in this process and typically accounts for 50% of the waste generated.

Following washing, crushing and grading, stent is suitable to be used as a construction aggregate. This process is important to remove clay fines material which can adversely affect its performance as a construction aggregate, and results in a secondary waste, Stent washing residue.

Whilst china clay waste derived sand and aggregates are well used in the South West, their wider use is hindered by the transport costs associated with getting the materials to the main aggregate markets in the UK. As such, the proportion of china waste re-used as aggregate typically only represents about 20-25% of the total quantity of waste produced. As such, there are ever-growing stockpiles of china clay waste, estimated at more than 230 million tonnes in the St Austell area alone (SWAWP, 2018)

(Zografou, 2015)
(SWAWP, 2018)
(BGS, 2009)
(Thurlow, 2005)