The UCC process
The UCC process has parallels with the Bayer process for refining
bauxite into alumina. A two step (caustic/acid) process produces UCC with ash
levels typically in the range of 0.5 to 1%. A third process step can reduce
this further to around 0.2 to 0.5%, if required.
Silica species such as quartz in the incoming coal are converted to soluble
forms via a caustic digestion process operating at elevated temperature. The
modified clays are dissolved via a subsequent acid washing process.
The dissolved minerals from both steps are then precipitated as gypsum and
aluminium silicates by reaction with lime. The precipitates are suitable
for commercial application in the building and ceramics industries, or
alternatively, they are environmentally safe for disposal.
The principal reagents required are sulphuric acid and lime. Caustic soda is
recycled within the process.