BST has capacity to process 110Ktpa of Electric Arc Furnace Dust (EAFD), which can produce 50-60 Mlbpa of payable zinc concentrate
via the Waelz process. The Waelz process is a method to recover zinc from metallurgical waste, using a long, slightly inclined and
refractory-lined rotary kiln.
The kiln is fed with pellets containing a mixture of EAF dust (c.25% average zinc), carbon
(coke and athracite) and lime at a temperature of c.1200°C. As the feed material slowly moves down the kiln, volatile elements,
mainly zinc, are transformed to gas and elements are oxidised to form a so-called Waelz oxide (WOX). WOX is captured and
cooled and further processed with soda-ash to produce double-washed WOX, which is sold as a zinc concentrate
(with a 65-70% zinc concentration) to smelters.