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.

Abstract: In the regeneration of alkaline liquors as used in paper pulping, a mixed oxide compound of an alkali or alkaline earth metal oxide and an oxide of Ti, Fe, Co, Ni, or Mn is formed by burning black liquor. The burning step is carried out in a fluidized bed. The mixed oxide product is washed in cold water and subsequently treated with hot water to precipitate the oxide of Ti, Fe, Co, Ni or Mn and enable recovery of the alkaline solution for recycling.