Research On The Synthesis Of Bio-adsrption Materials By Mechanical Activation-assisted Solid Phase Reaction And The Adsorption Of Heavy Metal Ions

The situation of heavy metals pollution is grim,which seriously endangers the health and safety of human beings.Traditional treatment methods for the removeal of heavy metals have been unable to meet the increasingly stringent environmental requirements.Therefore,using agricultural wastes to develop low-cost biological adsorbents for removing heavy metals is favored.At present,Preparation methods of lignocellulosic adsorbents are mostly in liquid phase with organic solvent.But the processes are complex,low efficiency,and easy to create secondary contamination.Aiming at overcoming the above problems,this paper adopted mechanical activation(MA)-assisted solid phase reaction(MASPR)for the modification of bagasse pulp(BP)and sugarcane bagasse(SB)without solvent,and sodium alginate(NaAlg)was used to immobilize the modified SB.Then,the preparation and properties of two kinds of biological adsorption materials with different physical forms were studied.The main contents and conclusions are as follows.(1)Modified BP(MBP)was prepared by MASPR with BP as material and succinate acid(SA)as esterifying agent.The influence factors of modification were investigated with the content of carboxyl groups(CCOOH)as the evaluation index.FT-IR,XRD,SEM,BET,DSC,and TGA were used to characterize the characteristics of BP and MBP.Moreover,the mechanism of solid phase esterification of BP assisted by MA was analysized to provide the theoretical basis for the modification of SB.Preparation study showed that the highest value of CCOOH was 5.21 mmol·g-1 when the reaction temperature,reaction time,ratio of SA/BP,and catalyst dosage were 90?,2.0 h,2:1,and 4%,respectively.Characterization analyses showed that the esterification reaction of SA and hydroxyls of cellulose produced new ester groups,and carboxyl groups were introduced.MA could not only increase the specific surface area of products by refined BP into small particles,but also decrease the crystallinity of products by effective destruction of the hydrogen bonds and crystal structure of cellulose,leading to the promotion of esterification reaction.Moreover,the interaction between ester groups and water was enhanced as prolonging reaction time,and the thermal stability of MBP was reduced.(2)Influence factors,kinetics,isotherms,mechanism and order of the absorption of Cd2+ and Pb2+ onto MBP were studied with adsorption capacity as index.The results showed that the adsorption effect of MBP was best with the reaction time of 1.0 h,and the suitable pH for the adsorption of Cd2+and Pb2+was 5.5 and 6,respectively.The order of adsorption was Pb2+>Cd2+.The adsorption kinetics of Cd2+and Pb2+ by MBP fitted well with the pseudo-second order model,and inner diffusion was not the only controlling step.The adsorption of Cd2+and Pb2+ by MBP was well described by the Langmuir isotherm,and the maximum adsorption capacities(Qmax)were 109.41 and 207.90 mg·g-1,respectively.The adsorption energies(E)were all in the range of 8-16 KJ·mol-1.The adsorption mechanism was mainly depended on the complexation of-COO-with heavy metal ions.Besides,partial electrostatic adsorption also existed.(3)Using the same method to directly modify SB which is cheaper than BP to get modified SB(MSB),then MSB was immobilized by NaAlg to prepare spherical adsorbent(MSB-Alg).The effect of embedding ratio on the ballability,mechanical strength and water absorption of MSB-Alg were studied.The results showed that spherical roundness,mechanical strength and water absorption of MSB-Alg were best when embedding ratio was 5.0.FT-IR,XRD,SEM,BET,DSC,and TGA analyses were used to characterize the characteristics of raw materials and products,and the spherulization mechanism of MSB-Alg was investigated.The results showed that MSB had good compatibility with NaAlg,and crosslinking hydrogen bonds were formed during the mixing process of them.MSB could be aggregated by the adhesion of NaAlg,and then NaAlg reacted with calcium ion by crosslinking curing to form MSB-Alg pellets.During the drying process of MSB-Alg,MSB played a supporting role and would reduce the gasification temperature of water,contributing to the generation of abundant micro-porous structure.In addition,the interaction between MSB and NaAlg could decrease the crystallinity of MSB,and improve its thermal stability.(4)Influence factors,kinetics,and isotherms of the absorption of Cd2+ and Pb2+ by MSB-Alg,as well as the differences of adsorption between MSB-Alg and MBP were studied with adsorption capacity as index.The results showed that the adsorption effect of MBP was best when embedding ratio was 5.0.The suitable pH,order of adsorption and adsorption mechanism of Cd2+ and Pb2+ by MSB-Alg were the same as those of MBP.The adsorption kinetics and isotherm were also similar to those of MBP,which were in accordance with the pseudo-second order model and the Langmuir isotherm model.The E values were all in the range of 8-16 KJ·mol-1.However,the Qmax of Cd2+ and Pb2+ onto MSB-Alg were 176.36 and 354.60 mg·g-1,respectively,which was greater than those of MBP.The suitable concentration range of adsorption by MSB-Alg was wider,but the adsorption rate was smaller.