| Recent years,with the rapid boost of industry,a large amount of industrial sewage containing heavy metal ions was emitted,leading to different levels of pollution to our country's main rivers,lakes and reservoir.These heavy metal ions will eventually be enriched into human body through the food chain,leading to various symptoms that will endanger human health.At present various techniques and methods were employed to remove heavy metal ions from water,such as chemical precipitation,ion exchange,membrane separation,biological method and adsorption method,among which adsorption was the most effective and promising one.The cellulose composition enriched in cassava dregs belongs to Polysaccharide polymer compounds.The hydroxyl groups on the polysaccharide were easy to modify and connects functional group,which makes adsorption properties of heavy metal ions on polysaccharide fundamental changes.Based on this,the preparation research of heavy metal adsorbent that uses agricultural waste as raw material has become one of the hot spots.This paper used the local cassava dregs as raw materials.After extraction of cellulose through optimizing the method of purification,then conduct chemical modification based on reactive hydroxyl groups of cellulose on cassava dregs to prepare three kinds of adsorption materials containing carboxyl and amino functional groups.The obtained three kinds of materials were characterized by Fourier transform infrared spectrometer(FTIR)and scanning electron microscope(SEM).The adsorption properties of materials were evaluated by kinetic study,effect of pH,adsorption isotherms and regeneration studies.The main research contents and results were as follows:(1)Using cassava dregs as raw materials,cellulose was extracted from cassava dregs by a method combing enzyme with alkali.Through single factor discussion and orthogonal experiment to optimizate extraction process conditions,the best extraction conditions will be obtained.The results showed that the best extraction conditions were:105 W ultrasonic power,0.8%alpha amylase concentration,60 min enzymatic hydrolysis time,6%sodium hydroxide solution concentration,90 min alkaline hydrolysis time,under which the purified cellulose content of cassava dregs was 63.84%.(2)Succinic anhydride,ethylenediamine and triethylenetetramine were as modifier to conduct chemical modification for the purified cellulose of cassava dregs.The carboxyl and amino groups were introduced into the cellulose structure of cassava dregs in the preparation of three kinds of new type adsorption materials of heavy metal ions(MCCW 2,MCCW 3 and MCCW 4).The materials before and after the modification were characterized by Fourier transform infrared spectrometer(FTIR)and scanning electron microscope(SEM).Infrared spectra results showed that the carboxyl and amino functional groups were successfully introduced to the cellulose of cassava dregs.Besides,through scanning electron microscopy(SEM)analysis,the three kinds of adsorption materials(MCCW 2,MCCW 3 and MCCW 4)appeared a lot of wrinkle and became rough with increases of specific surface compared to pre-modification,which would be conducive to adsorption materials to adsorb heavy metal ions.(3)Three kinds of adsorption materials were applied to adsorption properties study of heavy metal ions(Pb2+and Cd2+)in water.The adsorption laws of materials were discuss from the influence factors of adsorption(pH),kinetics and isotherm,etc.The results showed that the three kinds of adsorption materials could be applied in a wide range environment of pH to deal with the heavy metal ions in water.The adsorption process was described well by Pseudo-second-order.The adsorption properties of MCCW 2 were the best from three kinds of adsorption materials.The Langmuir isotherm model was more appropriate than Freundlich isotherm to fit the adsorption process.The maximum adsorption capacity,which was calculated by Langmuir model,was extremely close to the corresponding experimental data.The maximum adsorption capacity of MCCW 2 was 476.19 mg g-1 for Pb2+ and 289.02 mg g-1 for Cd2+,respectively.Compared with raw material of cassava dregs,the maximum adsorption capacity of MCCW 2 increased to 15.6 times for Pb2+ and 20.9 times for Cd2+ in water,respectively.The concentrations of heavy metal ions(Pb2+ and Cd2+)in water were determined by an atomic absorption spectrophotometer,of which the standard addition recovery rates for Pb2+ and Cd2+ were 106.02%and 108.84%,respectively.And the relative standard deviation(RSD)of measurement datum were less than 5%.Therefore,the measurement datum were accurate and reliable.(4)In desorption regeneration experiments,0.5mol/L hydrochloric acid was used as desorption reagent of adsorption materials.Saturated sodium hydrogen carbonate was rarely reported as a detergent in regeneration studies.And the regenerated washing effect of Saturated sodium hydrogen carbonate and ultrapure water were compared.The results showed that the adsorption efficiencies of MCCW 2,which was eluted with ultrapure water,decreased from 98.72%to 35.49%for Pb2+ and from 94.14%to 11.98%for Cd2+,respectively,after three cycles of adsorption-desorption.However,the adsorption efficiencies of MCCW 2,which was eluted with saturated NaHCO3 solution,could still be maintained at 97.40%level for Pb2+ and 93.16%level for Cd2+ even after three cycles.Therefore,using different regeneration detergents,regeneration effect of adsorption materials was very different.Saturated sodium bicarbonate as regeneration detergent of MCCW 2 has achieved a good effect of regeneration. |
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