The Adsorption And Desorption Properties Of Thermo-sensitive Calcium Alginate/methyl Cellulose Beads Towards Methylene Blue

As the dyestuff wastewater has the characteristics of large quantity,complex constituent,high chromaticity and high concentration,it is harmful to the environment and people's health.After continuous grope,researchers found the alginate polymers extracted from the seaweed have good adsorption capacity.What's more,these kinds of biomass materials have wide sources and the desorption ability.Therefore,alginate polymers have the broad prospects in the treat of the dyestuff wastewater.In this paper,the thermo-sensitive calcium alginate/methyl cellulose beads(CAMCBs)was made by adding the methyl cellulose(MC)into the calcium alginate beads(CABs).The purpose is to increase the thermo-sensitivity of the CABs and make them have great adsorption capacity at low temperature and good desorption capacity at high temperature.In the adsorption study,the influences of time,solution concentration,temperature and the addition dosage of MC on the adsorption of methylene blue(MB)were investigated.The adsorption mechanism was analyzed by 6 kinds of dynamic models:pseudo-first-order kinetics equation,pseudo-second-order kinetics equation,Elovich equation,two constant equation,exponential equation and intra-particle diffusion equation,and 3 kinds of isothermal adsorption models:Langmuir equation,Freundlich equation and Temkin equation,and thermodynamic equations.The results indicated two adsorbents had the high MB adsorption capacity at low temperature,but the adsorption property of CAMCBs was very low at high temperature.The removal rates of CABs and CAMCBs could reach 75.7%and 70.3%respectively at 20? when the concentration of 200 mL MB solution was 50 mg·L-1,and the removal rates of CABs and CAMCBs were 20.3%and 7.3%respectively at 60?.The adsorption quantity of two adsorbents increased with the increase of solution concentration until reached equilibration.The equilibration adsorption capacities were 895.58 and 288.50 mg·g-1 respectively.The adsorption data were well fitted by the pseudo-second-order kinetics,Elovich equation and intra-particle diffusion equation and the Langmuir equation and Temkin equation could well described the isothermal adsorption behaviors of CABs and CAMCBs.According to negative values of ?G,?H and ?S,and the results above,the adsorption behaviors of CABs and CAMCBs belonged to the monolayer chemical sorption.The adsorptions of MB on CABs and CAMCBs were spontaneous and exothermic,and the freedom degree decreased during the processes.The results of the desorption study showed,the desorption rate of CAMCBs could reach 95.7%and 98.2%respectively under the condition of 200 mL deionized water and 1.72 mL hydrochloric acid at 20? and 60?.When the weak acid of acetic acid was used as the desorbent,the desorption rate of CAMCBs was 98.2%under the condition of 200 mL deionized water and 5 mL acetic acid at 60?,and under the same comdition,the desorption rate of CABs could only reach 51.3%.As the results showed,the adding of thermo-sensitive MC could facilitate the MB desorption from CAMCBs,which could get the same desorption rate under the condition of hydrochloric acid and acetic acid at 60?.The regenerated CAMCBs could be recycled to adsorption MB for they still kept high MB removal rate of 69.8%which was closed to the MB removal rate of 70.3%at the first time adsorption.