As a renewable non-food resource, lignocellulosic biomass has great potential as an energy source. When pretreated by hydrothermal carbonization, the resulting biochar (or hydrochar) is hydrophobic and of higher energy density. Addition of ionic salts to this high pressure aqueous pretreatment reduces reaction pressure. Ca propionate, Ca acetate, Mg acetate, Ca lactate, Li chloride, Ca chloride, and Ca formate were tested in hydrothermal carbonizations at 260 degrees C for 5 min. Ca chloride and Ca lactate were found to be Ca salts whose addition increases HHV and which decrease the pretreatment pressure. Biomass pretreated with chemical addition of selected salts may have desirable properties when co-fired in existing coal boilers. (C) 2012 Elsevier Ltd. All rights reserved.