Study On Silica Removal In Green Liquor From Bamboo Pulping And Preparation Of Causticizing Calcium Carbonate

Bamboo materials were widely used in the pulp and paper industry in China.However,the silica content of green liquor from bamboo pulping is high,which brings a series of problems to the process of alkali recovery and recycling of causticizing calcium carbonate?CCC?.Therefore,in order to give full play to the advantages of bamboo materials,the problem of"Silicon influence"must be solved.There were two methods were used in this paper,the impact of reaction conditions on the silicon removal from the green liquor were investigated,at the same time,we studied the characteris of CCC to provide theoretical foundation for searching a better way to the recycling of CCC.Firstly,the effect of pre-causticizing process on the concentration of SiO₃^2-?as SiO₂?in green liquor was studied.The results showed that the silica removal rate increased with the increase of reaction time and the addition of quicklime,but decreased with the increase of reaction temperature.Thus,at 20?,with the reaction time of 60 min,the quicklime added amount of 30%,and stirring rate of 400 rpm,the silica removal rate was as high as 84.62%.After removing silica from green liquor,the CCC was prepared by the reaction between Ca?OH?₂ and Na₂CO₃ from green liquor.The properties of CCC were analyzed by Mastersizer,XRD,FTIR and SEM,The results showed that with the increase of quicklime added amount from 0%to 30%,the average particle size of CCC was reduced from 19.70?m to 14.21?m,which is reduced by about 27.89%,as well as the particle size uniformity of CCC was better and the particle size was smaller.According to XRD results,it is found obviously that the crystals of CCC were not changed with the increase of quicklime added,all of which were calcite and aragonite,while calcium silicate was found in CCC with amorphous form.FTIR showed that,under the same conditions,the silicon content of CCC was lower at 20?than that at 90?.According to SEM results,the morphology of CCC changed gradually from amorphous to pillar-like particles with increasing of pre-causticizing quicklime at 20?.By adding complexing agent into green liquor,the results showed that the silica removal rate increased with the increase of reaction time and the amount of complexing agent added,but didn't change with the increase of reaction temperature.When the amount of complexing agent?the molar ratio of complexing agent and silicon content in green liquor,the same below?was 2:1,the removal rate was up to 91.75%with the reaction time of 15min.The sedimentation rate and the drainability rate of silicon precipitated were improved obviously with the increase of temperature.Under the same reaction conditions,the increase of the amount of adsorbent M had little effect on the desilication rate and pH of green liquor,but the drainability rate of silicon precipitated was improved,and the drainability rate of silicon precipitated at high temperature?90??is obviously better than that under the same condition at low temperature?20??.When the volume of green liquor is 200ml,as well as the amount of adsorbent M?the mass ratio of the adsorbent M to the dry mass of the silicon slag?increased from 0:1 to 5:1,the filtration time decreased from 8.78 min to 7.9 min at 90?,and reduced from 23.067min to 23.008min at 20?.And then,the properties of CCC were analyzed,the results showed that with the increase of the addition of complexing agent,the particle size uniformity of CCC was improved.When the amount of complexing agent increased from 0:1 to 1.5:1,the specific surface area of CCC reduced from 7.28m²/g to 1.95m²/g,which reduced by 73.2%.When the amount of complexing agent increased to 2:1,the specific surface area of CCC increased to 2.91m²/g.The crystals of CCC were not changed with the increase of complexing agent,both were aragonite and calcite,and calcium silicate is found in CCC with amorphous form.FTIR showed that when the amount of complexing agent was 1.5:1 and 2:1,the presence of calcium silicate was not detected.The morphology of CCC changed gradually to spindle-like particles with the increase of the addition of complexing agent,and the amorphous area decreased obviously.