EFFECT OF SUBSTITUTION OF MG(OH)2 FOR NAOH AS ALKALI SOURCE IN P-RC APMP PROCESS ON OXALATE FORMATION

摘要

The formation of oxalate during pretreatment stages of P-RC APMP process was investigated in this paper, including the NaOH-based P-RC APMP process, the Mg (OH)2-based P-RC APMP process and Mg(0H)2 partially substituted P-RC APMP process. The distribution of oxalate between precipitated form and dissolving form was also included. The results showed that the substitution of NaOH with Mg(0H)2 can lower the formation of oxalate during the pretreatment stages. The Mg(OH)2-based P-RC APMP process gave a lowest total oxalate formation. And the NaOH-based P-RC APMP process gave a highest concentration. The usage of Mg (OH)2 as alkali source in pretreatment stage can reduce the formation of precipitated oxalate. The oxalate concentration has a close relationship with the cationic charge demand. The Mg(OH)2-based peroxide P-RC APMP process produced less anionic trash and lower COD load compared with the conventional NaOH-based P-RC APMP process. Although the total substitution of NaOH with Mg(OH)2 in P-RC APMP process can lower the oxalate formation, the pulp strength - properties (tensile, burst and tear) decrease obviously.