Study On The Influence Of Non-process Metals On The Pulp Bleaching System

The development of the paper green-industry depends on promoting clean production. Unfortunately,hydrogen Peroxide can be decomposed under alkaline condition, especially in the situation of the presence of transition metal ions, because of their catalyzing on the decomposition of the hydrogen Peroxide. Thus bleaching efficiency is decreased. It is important to mention that aged NPMES is more suitful in the pulp. To study the different state non-process element enrichment rules in the pulp system and the influence of NPMES on the hydrogen decomposition and find the more effective way to decrease hydrogen's decomposition has become urgent task to solve.The non- process iron not only affects the brightness of pulp, also catalyze the decomposition of hydrogen peroxide. Most of the iron could be removed by washing, the enrichment of aged iron is significantly less than the fresh iron, the addition of alkali can promote the enrichment. The adsorbed iron in the cellulose fibers can be removed effectively by pre-chelator treatment .On the decomposition of hydrogen peroxide, studies show that: in alkaline conditions, free aged iron's capacity of catalytic was significantly weaker than fresh iron. For the free aged iron, DTPA has better stability effect than stabilizer, and if magnesium and sodium are used together, they can prevent hydrogen peroxide from being decomposed., the best ratio of Mg: Si is 1:10; The best dosage of DTPA is 0.04%, The different added order of alkaline will have different effects to the hydrogen peroxide decomposition, and NaOH/NaSiO₃, Na₂SiO₃/NaOH/MgSO₄ is better. The decomposition is also affected by the location of the alkaline. For the adsorbed aged iron, the catalytic decomposition of hydrogen peroxide capacity is two times more than the free aged iron in alkaline conditions. Stabilizer and chelating agents can effectively stabilize adsorbed aging iron catalytic hydrogen peroxide decomposition, but the effect was not as good as on the free-state aged iron, and the compound of stabilizer is better than single use.Among the non-process metals, manganese is most hazardous. the enrichment of aged Mn is less than the fresh Mn, but the alkali has little effect on the enrichment. Mn has not any catalyzing effect on the decomposition of hydrogen peroxide in neutral conditions, but they have sharply catalyzing effect in alkaline conditions, and the absorbed Mn is more serious. Stabilizers have different effect between adsorbed Mn and free-state Mn, and the former has been stabilized better than the last one. DTPA and the mixing of DTPA and stabilizers also have different effect between adsorbed Mn and free-state Mn, DTPA, DTPA-Na₂SiO₃, DTPA-MgSO₄-Na₂SiO₃ can keep free-state Mn more stabilize than free-state Mn, while DTPA-MgSO₄ is opposite, DTPA-MgSO4-Na₂SiO₃ has the best effect.Non-process copper also have serious implications to the decomposition of hydrogen peroxide, but their amount is very low in the raw materials. Enrichment of copper in cellulose fibers are increased with the added amount increase. The addition of alkali can promote the enrichment, and the enrichment of fresh Cu is less than the aged Cu . In neutral conditions, the fresh Cu and aged Cu has different effect on the decomposition of hydrogen peroxide, and it fellows: the free state fresh Cu > free state aged Cu> adsorbed aged Cu; In alkaline conditions, they all have sharply catalyzing effect. Protective agent against aging free state of copper and copper adsorbed aging effects of different stability, DTPA and DTPA- Na₂SiO₃ have better stabilized effect on the free state aged aged Cu and adsorbed aged Cu. But DTPA- MgSO₄ and DTPA-MgSO₄-Na₂SiO₃ have better stabilized effect on both free state aged Cu and adsorbed aged Cu, and the last one can be stabilized more effectively.