A low-waste process was developed to convert all the KCl involved in the making of K2CO3 (cf. preceding paper) into chlorine or HCl by the reaction of KCl with V2O5 in the presence of H2O or O-2. The resulting KVO3 is finally converted into K2CO3. Solubility isotherms were determined in the KVO3 -NH4VO3-H2O, KHCO3-KVO3-H2O, NH4HCO3-NH4VO3-H2O and KHCO3-NH4HCO3-H2O systems over 293-323 K. These data enabled a Janecke equilibrium diagram to be constructed for the KVO3-NH4HCO3-H2O system. No double salts were found to form in the systems studied.