Process for preparing pulp using potassium-based alkaline solution

A process for the preparation of chemical pulp from a cellulose raw material comprising:

• contacting the cellulose raw material, in succession, with an acidic solution and with a potassium-based alkaline solution to extract siliceous materials from the cellulose raw material thereby forming a siliceous extract liquor;
• mixing said siliceous extract liquor with an alkaline earth metal and calcining the resulting mixture to produce a potash fertilizer having citric solubility and comprising glass-like materials containing potassium, alkaline earth meal and silica;
• cooking the cellulose raw material, from which siliceous materials have been extracted, at 130.degree. C. to 200.degree. C. in a cooking liquor containing a potassium compound, hydrogen peroxide, a chelating agent, an anthraquinone and water to produce a digestion product;
• separating said digestion product into a pulp waste liquor and an unbleached pulp;
• concentration and burning said pulp waste liquor to recover the potassium compound;
• forming an aqueous solution of the recovered potassium compound and adding calcium oxide to said aqueous solution for causticization;
• and
• adding hydrogen peroxide, said chelating agent and said anthraquinone to the causticized aqueous solution to regenerate the cooking liquor.