Study On The Removal Of Heavy Metal Ions In Aqueous Solution By Modified Wheat Straw And Its Application

In recent years,a large number of heavy metal pollutants have entered the water environment with the development of industry and the rapid expansion of urbanization,which has caused a series of safety problems.The traditional treatments will alleviate the pollution of heavy metals to a certain extent,however,these treatments have many problems,such as high cost,low efficiency and even more serious,these treatments will produce a lot of difficult to deal with chemical sludge during processing,which will cause subsequent disposal problems.At present,the research of natural and modified cellulose materials has attracted wide attention.Wheat straw is a by-product of agriculture rich in cellulose resources.It contains a large number of functional groups such as hydroxyl,carboxyl,amino and phenolic resin,so that it has potential adsorption capacity for heavy metals.The application of wheat straw on the adsorption of heavy metal ions has opened up a new idea to treat waste,save energy and protect the environment.The adsorption characteristics of natural wheat straw?NS?on heavy metal Pb²⁺and Cu²⁺were studied in this paper.On this basis,the NS was modified by lactic acid?0.3LANS?or polyglutamic acid?0.1PANS?,and it was applied to the adsorption of heavy metals Pb²⁺and Cu²⁺.The effect of lactic acid and polyglutamic acid modified wheat straw on the adsorption of Pb²⁺and Cu²⁺was similar.They achieved the best condition at pH 5-5.5,the adsorption rate and removal of organic acid modifier on Pb²⁺were higher than that of Cu²⁺.The maximum removal rate of 0.1PANS to Pb²⁺was 99%in 30min,to Cu²⁺was 75%in 90min and the maximum removal rate of 0.3LANS to Pb²⁺was 96%in 60min,to Cu²⁺was 73%in 120min,respectively.The adsorption of Pb²⁺and Cu²⁺ions by two kinds of modified adsorbents was suitable for interpretation by Langmuir model.The maximum adsorption capacity calculated respectively was:for Pb²⁺,0.3LANS—51.493mg/g,0.1PANS—52.083mg/g;for Cu²⁺,0.3LANS—49.358mg/g,0.1PANS—50.651mg/g.They all reached the best state at 35?,indicating that the adsorption of Pb²⁺and Cu²⁺ions on the modified wheat straw was an endothermic reaction,and the increase of temperature was beneficial to the reaction.The kinetic equation results showed that the adsorption of the two kinds of modified adsorbents on Pb²⁺and Cu²⁺wasfitted with the pseudo-second order kinetic,which proved that the adsorption was mainly chemical adsorption.The results of FTIR spectra showed that the strength increased significantly and the morphology broadened at 3418cm^-1,1633cm^-1 and 1383cm^-1after modified by the organic acids,indicating that carboxyl and hydroxyl groups were successfully introduced into wheat straw to promote adsorption.In this paper,NS was pyrolyzed and carbonized at 300?to make wheat straw biochar?CS?and study the adsorption of heavy metal Pb²⁺and Cu²⁺.The results showed that CS could reach the adsorption equilibrium when the dosage was 0.5g?half of the dosage of organic acid modifier?,and the removal rate of Pb²⁺reached 99%,Cu²⁺was 85%.The adsorption of CS on heavy metals Pb²⁺and Cu²⁺still accords with Langmuir and pseudo-second order kinetic model,but its isothermal adsorption process for Cu²⁺was also suitable for analysis with Freundlich model.From the data of isothermal equation,it is known that the adsorption capacity of CS to two kinds of ions was obviously higher than that of organic acid modifiers.CS adsorption on copper was 1.7 times of that of 0.3LANS and 0.1PANS,and that on lead is 3times.The changes of functional groups before and after CS adsorption of lead ions were analyzed by FTIR.The results showed that carboxyl and hydroxyl have had certain deviation after adsorption,and the transmittance changed,means these oxygen-containing functional groups play a major role in the adsorption process.In order to adapt to the actual situation of industrial wastewater,this paper studied the influence of competitive adsorption in the coexistence of Pb²⁺and Cu²⁺.The results showed that the selectivity of three modifiers to Pb²⁺was greater than Cu²⁺.