Study On The Biomass Based Compound Adsorbent And The Interface Mechanism Action On Cr(?) In Aqueous Solution

The pollution of heavy metals in water is one of the threats to human being,and the pollution of Cr(?)in water is serious especially in the leather making and electroplating industry.Cr(?)is a primary carcinogen that can accumulate in plants and cause permanent damage to human and animal through the food chain.Our country have proposed to strengthen the efforts to the prevention and control of heavy metal pollution in China's 13th Five-Year Plan for ecological environment protection.How to effectively control heavy metal pollution needs to start from the aspects of chemical transformation and migration,and the regularity need to be studied systematically.This paper focuses on the problem of Cr(?)in water,in order to study the mechanism of biomass based adsorbent on Cr(?)in aqueous solution,the idea of stripping complex problems is adopted.The regularity between composite iron oxide/biochar,pure biochar and layered metal oxide and Cr(?)is studied.The constituent and structure of modified biomass based adsorbents are characterized by scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),Infrared spectroscopy(IR)and X-ray photoelectron spectroscopy(XPS).It is investigated that the effect of carbonation temperature,initial solution pH and the dosage of adsorbent on adsorption of Cr(?).The experiment data is fit'ted to the kinetics and thermodynamic models.The regularity is sunmmarized based on the analysis results,especially about the chemical bond of Me-O,C-OH,C=O and the microstructure is also compared and analyzed.The main results are listed below:(1)In order to investigate the adsorption performance of metal oxide and biochar complex,iron oxide composite biochar is prepared based on modifying cotton stalk by iron sludge.The main chemical bond is Fe-O,C=C,C=O and C-OH.The BET of Fe-CS-500 is 129.16 m2/g,and the optimum adsorption pH is broaden from 1.0 to 5.0.The adsorption capacity of Fe-cs-500 on Cr(?)is 67.44 mg/g at room temperature.The adsorption kinetics data is well fitted to the pseudo-second-order and Cr(?)removal onto Fe-CS-500 is accelerated and the process is chemical adsorption.The adsorption mechanism between iron oxide/biochar and Cr(?)include the formation of Cr(?)by oxidation-reduction and the coordination fixation of Cr(?)from the results of XPS analysis,and the result of thermodynamic adsorption data fitting show that it is a monomolecular adsorption.(2)In order to investigate the adsorption characteristics of biochar to Cr(?),the carbonized precursor PCC is synthesized based on the concentrated cellulose wastewater,and then carbonized to synthesis adsorbent.The main chemical bond is-COOH,C-O-C and C=C.The maximum adsorption capacity of Cr(?)is 25.87 mg/g.The kinetics data is well fitted to the MSRDC model including the chemical reaction of Cr(?)reduced to Cr(?)and the fixation of Cr(?)onto the surface of biochar.The adsorption isothermal data is well fitted to Sips model,which include both monolayer and multilayer adsorption.XPS analysis results show that 58.9%of Cr(?)is reduced to low toxic Cr(?)after Cr(?)reaction with biochar.(3)In order to investigate the adsorption characteristics of layered metal oxide to Cr(?),the modified precursor SLDH is prepared in sodium alginate system,and then magnesium aluminum oxide is prepared after calcination.The main chemical bond is Mg-O and Al-O,and the BET of C-SLDH-500 is 155.96 m2/g.Cr(?)anion enter the interlayer of magnesium aluminum hydrotalcite anion layer by ion exchange with OH-in order to restore the layered structure.The kinetics results show that the adsorption equilibrium can be reached within 60 minutes and the maximum adsorption capacity of Cr(?)is 69.02 mg/g.The adsorption isotherm data is well fitted to Sips model,which include both monolayer and multilayer adsorption.(4)In order to investigatewhether new Cr(?)adsoption sites were generated after the reaction of biomass with Cr(?),The product CKN is prepared by Cr(?)and kelp through oxidation and reduction reaction.Its specific surface area is as high as 343.20 m2/g,with both mesoporous and microporous structure.The results of XPS analysis show that Cr(?)content in CKN reached 82.70%,containing Cr-O-OH chemical bond.The adsorption experiments show that the amount of adsorption of Cr(?)is less than 2.0 mg/g.In addition,the composition and the interfacial action of Cr(?)are systematically summarized.In acidic condition,the effect mechanism of FeOx/biochar composite adsorbent on Cr(?)includes reduction of Cr(?),coordination fixation of Cr(?)and the synergistic effect of iron-oxygen bond.The effect of biochar on Cr(VI)is not only the reduction of Cr(?),but also the fixation of the electron donor on Cr(?).The adsorption mechanism of layer metal oxide on Cr(?)is ion exchange.CKN has no new adsorption sites for Cr(?).