Study On Preparation Of Biomass Adsorbent And Adsorption Of Heavy Metals

Sargassum Horneri,which is abundant source and low price,has high selectivity and adsorption to metal ions.In this paper,steam-exploed Sargassum Horneri before and after formaldehyde-sulfuric acid heating reflux were used as adsorbent to remove Cr（Ⅵ）in the simulated wastewater.To explore the adsorption mechanism,the conditions of steam explosion,reflux and adsorption were explored;the physical and chemical properties and morphology of steam-exploed Sargassum Horneri before and after refluxing were charecterized and analyzed with the aid of FT-IR,SEM and TG;the different isothermal adsorption models,adsorption kinetics equations and thermodynamic parameter were used to fit the adsorption process.The main conclusions were obtained as follows:（1）Two kinds of different pretreatment methods,microwave digestion and dry digestion,have been adopted to preprocess Sargassum Horneri.The contents of Cu,Fe,Mn and Zn were determined by atomic absorption spectrometer.Results showed that an average over 90%on recovery rate have been achieved by both microwave digestion and dry digestion methods.The microwave research groups had excessed94%while standard deviations of which less than 5%was observed.Compared with dry digestion,the microwave one got a higher recovery rate and precision,which was recognized as a more suitable pathway for the pretreatment of Sagassum Horneri.（2）The simulated wastewater was treated by coaly activated carbon,coconut shell activeted carbon,Sagassum Horneri and carbonized Sagassum Horneri.The results showed that the removal rates of the four adsorbents were high for Cd,Cu,As,Pb and Hg,which could make the wastewater meet the nation industrial wastewater discharge standards,but the removal efficiency of chromium is poor.（3）Steam-exploded Sargassum Horneri was used as the adsorbent to adsorb the Cr（Ⅵ）in simulated wastewater.The results showed that a large number of functional groups containing oxygen,nitrogen and sulfur presented on the surface of steam-exploded Sargassum Horneri.The optimum steam explosion conditions were obtained as:pressure=3.0 MPa,retention time=120 s and particle size=0.83¹.40mm,and the preferable adsorption conditions were pH=2,adsorption time=120 min and adsorbent dosage=20 g×L^-1.The removal rate of Cr（Ⅵ）reached 87.50%under the optimum steam explosion and adsorption conditions.The adsorption kinetics was consistent with the quasi-second-order kinetics model,and the internal diffusion equation showed that the adsorption process was mainly controlled by diffusion within particles.The adsorption isotherm was simulated by Freundlich equation.The adsorption thermodynamic properties indicated that Cr（Ⅵ）adsorption in simulated wastewater was a spontaneous exothermic process.（4）Steam-exploded Sargassum Horneri after formaldehyde-sulfuric acid heating reflux was used as the adsorbent to adsorb the Cr（Ⅵ）in simulated wastewater.The optimum heating reflux conditions was obtained as:temperature=80℃,the ratio of formaldehyde to sulfuric acid（0.1 mol/L）=1:1,the ratio of modifier to steam-exploded Sargassum Horneri=4:1 and heating reflux time=2 h,and the preferable adsorption conditions were pH=2,adsorption time=60 min and adsorbent dosage=25 g×L^-1.The removal rate of Cr（Ⅵ）reached 98.81%under the optimum heating reflux and adsorption conditions.Freundlich model fitted well to the data and the pseudo-second order kinetic model could best describe the biosorption kinetics.According to the adsorption thermodynamic properties improved that the adsorption was a spontaneous,endothermic and entropic process.The modified products were regenereted using H₂SO₄ solution and could be used repeatedly for many time with little loss of adsorption capacity.（5）After modification with formaldehyde-sulfuric acid heating reflux,steam-exploded Sargassum Horneri was used as adsorbent for Cr（Ⅵ）.From the dynamic adsorption breakthrough curve,penetrative point was 482 min,while the failure point was 1882 min.The adsorbent were regenerated using H₂SO₄（0.1 mol/L）solution.