Chlorine dioxide bleaching of soda-anthraquinone jute pulp to a very high brightness.
Bleaching of soda-anthraquinone jute pulp by chlorine dioxide (ClO2) was studied to reach a target brightness of above 88% for the purpose of using less bleaching chemicals. The performance of either chlorine dioxide or peroxide in the final bleaching to boost brightness was also studied. The experimental results revealed that the final brightness depended on ClO2 charge in the Do and D1 stages. The brightness reversion was lower when the final stage brightening was done by peroxide. The use of Mg(OH)2 in the D1 and D2 stages improved the final brightness due to the formation of less chlorate and chlorite during the Mg(OH)2- based ClO2 brightening stages. The strength properties of pulp bleached by peroxide in the final stage was slightly better than that from ClO2 as the final ClO2 bleaching stage.
Investigation of eucalyptus kraft pulp brightness stability
Nous avons evalue la stabilite de la blancheur des pâtes kraft d'eucalyptus hautement blanchies et delignifiees a l'oxygene (90 a 90,5 % ISO) selon les sequences (DC)(PO)DD, (DC)(PO)DP, D(PO)DD, D(PO)DP, D HT (PO)DD, D HT (PO)DP, A HT /D(PO)DD et A HT /D(PO)DP, en effectuant des essais de jaunissement a la chaleur avec 20 repetitions pour chaque sequence. Une etape P finale a permis d'ameliorer la stabilite de la blancheur. Certains groupes reducteurs presents dans les pâtes hautement blanchies sont probablement la cause de la perte de blancheur. La blancheur des pâtes blanchies selon la sequence (DC)(PO)DD etait moins stable, meme si les pâtes ne contenaient que des traces d'acides hexeneuroniques et de lignine. Les etapes acide chaud/dioxyde de chlore chaud ont ameliore la stabilite de la blancheur, mais seulement dans les sequences sans l'etape P finale. Le profil de jaunissement tout au long des sequences de blanchiment a affiche une tendance vers l'accroissement de la stabilite de la blancheur apres les etapes acides.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.