"5 g of each biochar was heated with 200 ml of 1 M of either H3PO4 or 0.1 M KOH for 1 h at 90 C, then cooled down to room temperature. The solid (treated biochar) was separate from the solution by filtration. The treated biochar, once isolated, was dried at 60 C for 24 h."
They sell this stuff (Niagara-450) which consists of 98-99% KOH, as pipe cleaner for about 6 euros. I plan starting some pot trials as soon as the weather turns a bit warmer.
(1) Y. Lin et al. / Chemosphere 87 (2012) 151–157