Reed Pulp Black Liquor To Deal With New Technology Research, The Three-dimensional Electrode Method

In China, the pulp and paper making industry is one of the oldest and a core industrial sector. Black liquor from pulping and paper making industry is one of the main industry pollutants in the environment. China lacks of forest resources, but the non-wood fiber materials, including reed and straw, etc. are quite rich. Noticeably, a sizable number of small paper mills are non-wood fiber as raw materials.The drainage badly pollutes our natural environment so seriously that it was considered as a very important issue. Traditional alkaline recovery technique is available to those large-scale pulping corporations in which the raw material is wood. However, there are many unconquerable problems on economy or technique when it is used in those small and medium-sized corporations in which the raw material is non-wood.In this study, a novel process has been proposed based on the current researches to treat reed black liquor:desilicationâ†'acidificationâ†'three-dimensional electrolysisâ†'causticizationâ†'reused to pulp making. The conclusions are shown as following:Precipitation method was used to remove silicon by adding Ca(OH)2. The effects of material ratio, reaction temperature and time were discussed, and the optimal technical parameters was demonstrated as:at 65℃, material ratio was 6:1, precipitation time was 60 min, and disposable feeding, while the residual concentration of silicon decreased from 6.68 g/L to 0.12 g/L and the removal ratio maintained 98.2%.Lignin was recovered by acidulation-precipitation after adding sulfuric acid. The effects of pH value, reaction temperature, reaction time, heat preservation temperature, heat preservation time and standing time on residual concentration of CODcr were examined in detail respectively through the single factor experiments and orthogonal design experiments. With the membrane, the optimum conditions were obtained:pH value was 2.5, the reaction temperature was 25℃, reaction time was 30 min, heat preservation temperature was 60℃, heat preservation time was 30 min and standing time was 24 h. Under the above conditions, the CODcr recovery in the black liquor was best, while the residual concentration of CODcr can be reduced to 54000 mg/L from 220648.7 mg/L and the removal efficiency maintained 75%. The range analysis showed that the important order of relevant factors was:heat preservation time>standing time>pH value> heat preservation temperature.8.5 g lignin can be got at last from 100 ml black liquor. The lignin was characterized by FTIR, EDX and SEM, which showed that the main structures of lignin were syringyl monomers and hydroxyl groups and lignin particles were not fibrous but granular.The electrochemical degradation of reed pulp black liquor containing lignin pretreated by acidification method was investigated using a three-dimensional electrode reactor. Using activated carbon as particle electrode, the effects of pH value, reaction temperature, electrolysis time, and current on residual concentration of total organic carbon (TOC) were discussed in detail. The optimal conditions were obtained:pH value of 2.5,200 mL/min of influent flow rate,25℃,300 mA and 2 h of electrolysis time, while the removal efficiency of TOC maintained 35.57% and the residual concentration of CODcr can be reduced to 36761.26 mg/LAfter electrolysis, causticization was adopted to regenerate alkali from the wastewater and the solution with the pH value of 13.28 can be reused in the paper mill. The technical parameters was demonstrated as: 70℃, the excessive amount of lime≤3%,1 h of causticization time, while the concentration of effective alkali was 8.3 g/L and the causticization rate of the solution was about 78%. Under the above conditions, the residual concentration of CODcr was further reduced to 33085.4 mg/L and the removal efficiency of TOC was nearly 10%.The electrochemical experiments were carried out to analyze the mechanism of oxygen evolution on the activated carbon electrode. The results revealed the process of oxygen evolution on activated carbon anode in Na2SO4 solution system with pH value of 2.5, which is different from the law of oxygen evolution on metal electrode in acidic solution system. The reaction equations are as follows: Among of these, the second reaction is considered as rate determined step. Simultaneously, based on the polarized curves and electrochemical impedance spectroscopy (EIS), the Tafel equations fitting the reaction equations were got and the equivalent circuit model for three-dimensional electrode on activated carbon anode was built.The results of the electrochemical method also indicated that OH radicals were produced on activated carbon anode in the electrolysis process and then adsorbed on the activated carbon surface. Microcell consisted of the absorbed·OH radicals and the absorbed lignin. With the microcell reaction, the lignin was degraded, while the anodic polarized curve illustrated that the lignin was obviously oxidized in the anode. The contributions to TOC removal ratio were about 50% respectively. The micro-battery mechanism can be used to reasonably explain the results of three-dimensional electrolysis experiments, which conversely further proved the correctness of the micro-battery mechanism.