麦草原料矿质元素在碱法制浆过程中的转移(Ⅰ)

Removal Behavior of Mineral Elements of Wheat Straw in Alkaline Pulping(PartⅠ)

用原子吸收光谱法、SEM-EDAX法研究了麦草原料灰分及矿质元素在碱法制浆过程中的脱除规律。结果表明,麦草原料灰分含量高达8.12%。在实验条件下,随温度升高、时间延长,原料相关成分的溶解,浆得率下降,黑液的固形物及其灰分含量均呈逐渐增加的趋势,保温后期则基本保持平衡;浆中的灰分含量及Ca、Mg、K、Si、Al、Fe等元素的含量则呈先降低而后稍有增加至基本稳定的趋势;上述元素大量转移至黑液中,将对黑液碱回收产生严重干扰。麦草Si的转移率仅为60%～70%,明显低于芦苇、竹子等原料Si的转移率,预示着麦草中Si的某些特殊性;也说明从预处理去除Si等矿质元素的角度来看,采用较低的用碱量、温度及较短时间较为合适。

The removal of the mineral elements in wheat straw during alkaline pulping and the effect of those mineral elements on the alkali recovery process were researched by means of SEM-EDXA and atomic absorption spectrometer. The results show that a large number of mineral elements in wheat straw, such as Si, Al, Mg, Fe and K will be removed and transferred to the black liquor to a great extent during pulping and washing, e.g. the transferring rate of Si element is 60% to 70%. As a result, the alkali recovery of black liquor will be interfered seriously. At causticizing stage, the existence of the above mineral elements will bring about a very high residue of soda in white mud and become impossible of mud recovery. On the other hand, a great quantity of K element in black liquor will always cause a grave scale on the water-cooling wall of the alkali recovery boiler. An enhanced pretreatment of straw material used, the development of new technologies and equipment, resulting in a substantial decrease of the mineral elements in material, will be of key importance for the improvement of alkali recovery rate of straw pulp black liquor and the realization of cleaner production of alkaline straw pulp.