Study On Causticizing Process,Particle Diameter Of Lime Mud And Caustification Ration In Bamboo Pulp Alkali Recovery

The alkali recove(?)lime mud from straw pulping process has a high content of silicon, as a consequence, it is generally dumped or discharged directly, which leads it to become one of the large amount of solid waste in papermaking industry. Refining it as paper filler for recycling is an important way to avoid the second pollution effectively. However, when the refined calcium carbonate is used as paper filler, it makes the AKD sizing efficiency decline, which limit the lime mud’s application scope and utilization as paper filler. Studies have showed that the refined calcium carbonate with regular shape and structure can improve the AKD sizing efficiently. It means changing the causticizing process in alkali recovery, but the adjustment may have a negative impact on the causticizing process. In order to solve the effect of adjustment on the alkali recovery system, this research has studied the influence of causticizing process optimization on the calcium carbonate particle size and causticizing rate, so as to provide the theory basis on the quality control of refined calcium carbonate,limestone and green liquor had great influence on causticizing rate and the particle size of lime mud, and the impact of limestone was higher, the adjustment of causticizing process had a little influence on causticizing rate, but the influence was contrary to the particle size, the variation range was less than 3μm.The mathematical model of refined calcium particle size-causticizing process is:Y=14.2-0.061Z1+0.115Z2-0.039Z3 Y standing for the average particle size of causticizing Calcium carbonate Z1 standing for causticizing temperature Z2 standing for water cement ration Z3 standing for slaking water temperatureThe adding time of green liquor had an obvious influence on the particle size of lime mud and causticizing rate. The longer the adding time was, the bigger particle size and higher causticizing rate were. When the adding time extended to 120min, the variation range of particle size was about 4.5μm, but the causticizing rate was approximately 5%.The size of the calcium hydroxide had significant influence on the particle size of lime mud and causticizing rate. With the increasing size of the calcium hydroxide, the relatively particle size of the calcium carbonate increased, but the causticizing rate decreased. The slaking process of lime had a little influence on the postdigestive particle size of the calcium hydroxide. With the decreasing particle size of lime, the particle size of the calcium hydroxide decreased gradually, meanwhile, the available calcium content of lime had evident influence on the postdigestive particle size of the calcium hydroxide. The higher the available calcium content, the smaller particle size of the calcium hydroxide. The grinding process of lime effectively reduced size of the calcium hydroxide, but the grinding extent should be controled by Solid-Liquid Separation and white liquor turbid degree after causticizing reaction.The size of calcium hydroxide which was obtained by lime and green liquor, could reach relatively above 10μm, but it dramatically influenced causticizing rate. The causticizing rate could be improved by grinding calcium hydroxide. Due to the high brittleness of calcium carbonate, it was easy to form lots of small particles by external force,which seriously influenced normal operation in wet-end. So the case of causticizing rate, the particle size of lime mud and fine particle content should be comprehensively considered to control the grinding extent.In the causticizing process, the feeding rate of Ca2+ had obvious influence on the morphology of lime mud.When the feeding rate was fast, it was easy to generate the calcium carbonate which had big particle size and high inner pores. When the feeding rate was slow, it was contrary to the former. The feeding rate of CO32-had a little effect on the morphology of lime mud.