Abstract
The application of dilute nitric acid on the refining of unbleached birch sulfite pulp was studied. Treatments with dilute nitric acid and then a hot alkaline solution were_??_recognized to be effective on the removal of resin without much degradation of cellulose, if the acid concentration is about one percent. Following conditions are recommended: acid concentration 1.0_??_1.2%, temperature 90_??_96°C, time 2_??_3 hours. As the nitric acid treatment makes resin and lignin of pulp easily soluble in a hot alkaline solution, the condition of hot alkaline treatment after the acid treatment may be decided by the degree of refining necessary to the refined pulp. The nitric acid refining is more effective than the ordinary refining in deresination.
