The treatment of paper mill black liquor by using fresh MnO_2

摘要

In this paper, a new effective adsorbent-fresh MnO_2 synthesized was determined by XRD, BET and TEM and was used to treat the black liquor from alkaline straw paper-making. The effect of treatment was evaluated by the removal of COD_(cr) and color. The results showed that: the fresh MnO_2 was δ-MnO_2, quasi globe particle shape, average grain size 250nm, BET area 94.22m~2/g. The COD_(Cr) removal and the color removal, which were dominated by the pH of the solution before adsorption, were very good on fresh MnO_2. For example, when initial color of black liquor was less than 1500 times, keeping the dosage of fresh MnO_2 added 500ppm, the contact time 1 hour, the color removal increased from 88% to 93.1% in the range of pH < 1.5. With pH rising to 2.0, it decreased rapidly. Furthermore, at pH 4.0 the color removal was almost down to zero. At the same pH value, the more the MnO_2 was added, the better of the color was removed. Similar to the decolorization efficiency, the removal of COD_(Cr) varied from 57.3% to 61.4% at pH ≤ 1.5. The different was that the COD_(Cr) removal decreased remarkably but not down to zero at pH > 1.5. At the same pH value, with the increasing amount of MnO_2 added, the removal of COD_(Cr) kept almost constant. Moreover, high temperature was favorable for the removal efficiency. It can be conclude that manganese dioxide may be used for the pretreatment of black liquor.