Optimization On The Preparation Of Calcium-rich Shaped Activated Carbon Based On Lime Mud Of Paper Mill And Its Application

Lime mud is a solid waste that results from the causticization reaction in alkali recycling process of paper manufacture industry,mainly composing calcium carbonate.In this work,calcium-rich activated carbon powder(Ca-ACP)with high specific surface area derived from Chinese fir sawdust from timber processing plants was prepared by physical activation effect of CO2 gas released via lime mud decomposition.Next,shaped activated carbon(SAC)cemented by lime-based mortar with high compression strength was prepared using sticky rice flour or carboxymethyl cellulose(CMC)aqueous solution as adhesives.The effects of activation 'process including activation temperature,activation time,impregnation ratio(the weight ratio of lime mud to Chinese fir sawdust powder)and molding conditions on the mechanical strength,specific surface area,iodine and methylene blue adsorption capacities were investigated.The mechanical strength,pore structure characteristics and morphology of SAC were characterized by universal testing machine,pore structure auto analyzer,scanning electron microscope(SEM),fourier transform infrared(FTIR)and thermogravimetry analysis(TGA).The preparation mechanism as well as the desulfuration and dechlorination performance of the as-prepared SAC were investigated.The experimental data in this paper are valuable for the industrialization of calcium-rich SAC,and some significant observed results are listed as follows:1.Calcium-based activated carbon can be successfully prepared from Chinese fir sawdust powder by lime mud activation.The result showed that CO2 gas derived from the decomposition of calcium carbonate of lime mud under high temperature is an effective gaseous activate agent to give rise to substantial miro-and mesopores in charcoal to produce developed pore structure.2.The calcium-based shaped activated carbon has been successfully prepared using sticky rice-lime mortar as adhesive.Column-shaped calcium-based activated carbon(CCAC)with high compressive strength was achieved by low-pressure compression molding technique.The observed results displayed that the sticky rice slurry could provide a biomimetic mineralization regulation effect during the carbonation process of caustic lime under ambient conditions.As a result,the mechanical strength of the calcium-based SAC was remarkably improved due to the biomimetic carbonation of caustic lime to generate calcite lattice with excellent stability.3.Bar-type calcium-based activated carbon(BCAC)can be readily fabricated by kneading-extrusion technique when CMC is used as adhesive.The abrasion performance of the bar-type calcium-based activated is superior than the commercial activated carbon used in this work.The crystal lattice of the limestone phase in the BCAC is typical of calcite.4.The calcium-based shaped activated carbon showed undesirable dechlorination performance as compared to the commercial activated carbon used in this work,as a consequence of the transformation of caustic lime in SAC into limestone,which show poor reactivity with free chlorine.When treated under 500 ?for 1h,the dechlorination efficiency of SAC was greatly recovered to display better dechlorination performance as compared to that of commercial activated carbon.5.The as-prepared calcium-based shaped activated carbon exhibits superior desulfuration performance by comparison with that of the commercial activated carbon used in this work.The results showed that the desulfuration efficiency of the calcium-based SAC increased with CaCO3/CaO content increasing in the calcium-based SAC.However,the increase of CaCO3/CaO content in the samples would be apt to scale formation resulting in saturation adsorption.On the other hand,the increase of carbon content is favorable for recycling.