Preparation Of Coal Based Agglomerated Activated Carbon And Study On Adsorption And Desorption Of Cr(Ⅵ) In Aqueous Solution

Coal-based agglomerated activated carbon is widely used as an adsorbent for drinking water and industrial wastewater treatment,and the market demand is large.At present,the agglomerated activated carbon prepared by using Datong weak sticky coal in China has good adsorption performance and has certain mechanical strength.However,the reserves of weak sticky coal account for only 2.18%of the thermal coal reserves,and the reserves are relatively limited.Moreover,agglomerated activated carbon products produced by a single coal type often have performance defects such as uneven pore structure distribution,which are difficult to use in water treatment.The use of coal blending process to produce agglomerated activated carbon is not only relatively cheap in technical cost,but also not easy to float in the application.Therefore,this thesis attempts to use Datong non-stick coal as raw material,add an appropriate amount of cohesive coal,and improve the adsorption performance of activated carbon while maintaining high strength,so as to solve the problem that the strength and adsorption performance cannot be improved at the same time.The prepared high-quality agglomerated activated carbon was used to adsorb and desorb Cr(Ⅵ)in aqueous solution,and the optimal adsorption conditions for Cr(Ⅵ)and the adsorption and regeneration effect of activated carbon were explored.The specific research content and results are as follows:(1)Datong non-stick coal is used as the main coal,Taoshan coking coal or Yilin fertilizer coal is used as the bonded coal,and an appropriate amount of heavy phase asphalt and water are added for briquetting,and activated carbon is prepared by water vapor activation.The pore structure of activated carbon is regulated by adjusting the coal blending ratio and changing the activation conditions.The results showed that when using Momoyama coking coal as binder coal,the optimal ratio of activated carbon preparation was:55%Datong non-stick coal,25%Momoyama coking coal,10%heavy phase asphalt and 10%water.The raw materials under this ratio condition were kneaded,shaped and carbonized,and then activated at 875°C for 2.5h,and the agglomerated activated carbon(M-AC)strength was 90%,iodine adsorption value was 902mg/g,methylene blue adsorption value was 270mg/g,and specific surface area was 992.60cm~2/g.When Yilin fertilizer coal was used as binder coal,the optimal ratio of activated carbon preparation was:58%Datong non-stick coal,22%Yilin fertilizer coal,10%heavy phase asphalt and 10%water.The raw materials under this ratio condition were kneaded,molded and carbonized,activated at 900°C for 2.5h,and the agglomerated activated carbon(N-AC)strength was 91%,iodine adsorption value was 926mg/g,methylene blue adsorption value was 225mg/g,and specific surface area was 919.75cm~2/g.The above results show that these two activated carbons have high strength and good adsorption performance,and both can meet the index requirements of activated carbon in the field of water treatment.(2)There are currently few reports of the use of KOH as an additive for coal blending.In this thesis,a small amount of KOH was added in the coal blending process,and briquette activated carbon was prepared by kneading and water vapor activation.The experimental results show that the specific surface area of briquetting activated carbon increased from 992.609 and 919.757cm~2/g to 1007.521 and925.436cm~2/g by adding 1%KOH in the above two coal blending schemes,and the pore volume from 0.152 and 0.0927cm~3/g to 0.173 and 0.117cm~3/g,respectively.This shows that adding an appropriate amount of KOH can promote the reasonable evolution of pore structure and improve the mesopore pore volume.(3)In order to evaluate the adsorption performance of the optimized activated carbon prepared above,the adsorption experiment of Cr(Ⅵ)in aqueous solution was carried out.The results showed that the maximum adsorption capacity of Cr(Ⅵ)in aqueous solution of the two agglomerated activated carbons M-AC and N-AC prepared by coal blending process was 27.3mg/g and 24.45mg/g,respectively.The optimal p H value was 3,and all reached adsorption saturation at 12 h adsorption time.Moreover,the removal rate of Cr(Ⅵ)increases with the increase of adsorption temperature,indicating that the adsorption process is endothermic.Through the study of adsorption kinetics and adsorption thermodynamics,it is found that the quasi-secondary kinetic equation and langmuir adsorption isothermal model can better reflect the adsorption process of Cr(Ⅵ)by the two agglomerated activated carbons.(4)In order to explore the regeneration performance of the prepared agglomerated activated carbon,a nitric acid solution with a mass fraction of 5%was used as a regeneration reagent to regenerate two kinds of activated carbon(M-AC,N-AC)that adsorbed Cr(Ⅵ).The results showed that after 5 regeneration times,the mass loss rate of the two activated carbons was less than 21%,the performance recovery rate of M-AC was 70.06%,and the performance recovery rate of N-AC was62.43%.The optimal regeneration time was 8h;The regeneration temperature increased,and the quality loss rate and performance recovery rate of activated carbon increased.