Abstract: The invention relates to an improvement in a method of regenerating alkaline or alkaline earth metal oxides or hydroxides from solution particularly in delignification processes wherein a suitable transition metal such as ferric oxide is burnt with the solution to produce a mixed oxide that is subsequently treated in hot water to regenerate the alkaline or alkaline earth metal oxide or hydroxide and precipitate the transition metal oxide. The improvement controls the presence of fines in the transition metal oxide to maintain these at an acceptable level in the fluidized bed combustion zone. This is achieved by contacting the fines with spent liquor from a delignification process. The invention also provides for the pelletization of the fine material of the transition metal oxide and spent delignification liquor can be used as a binder in the formation of such pellets.