Preparation And Characterization Of Bio-chars Derived From Acidosasa Edulis Shoot Shells And Its Adsorption Properties Of Re(?) From Aqueous Solution

Rhenium(Re)is a rare metal element which has been widely used in the fields of national defense,petrochemical industry,aerospace industry,and the demands of rhenium continue to rise.Rhenium often convert into aqueous solution in the form of Re(?)in the smelting process.Therefore,how to effective separate rhenium from aqueous solutions has drawn extensive attention.In recent years,the adsorption ability of bio-chars for metal ions from aqueous solution has caused wide public concern,due to its has the advantages of the abundant of feedstocks,simple equipment and enriched surface functional group.In this paper,acidosasa edulis shoot shells(AESS)were selected as feedstock to produce bio-chars at different pyrolysis temperature to adsorb Re(?)from aqueous solution.The physicochemical properties of bio-chars produced at different pyrolysis temperature were characterized by Boehm titration,pHpzc values,elemental analyzer,ATR-FTIR,BET and SEM-EDX,and the effect on Re(?)adsorption properties were determined.The factors influencing on Re(?)uptake onto bio-chars were discussed by static adsorption method.The characteristics and mechanisms of Re(?)adsorption by bio-char were investigated by kinetic models,isotherm models,thermodynamic parameters and several characterization methods.The reusability of the adsorbent was also discussed by consecutive adsorption-desorption.The main conclusion were presented as follows:(1)The bio-chars can be used for separating the Re(?)from aqueous solution and the adsorption capacity of bio-chars for Re(?)reached 14.56 mg/g.(2)The adsorption of Re(?)by bio-chars was mainly through electronic attraction and out-sphere complexes involving both hydroxyl and carboxyl groups.(3)As the content of H+ increased,the adsorption capacity of bio-chars for Re(?)increased,the optimal pH was founded to be 1.Considering the recovery rate and adsorption amount of Re(?)by bio-chars,the most suitable adsorbent dosage was determined at 3 g/L.The adsorption equilibrium was obtained at 6 h.The adsorption of Re(?)onto bio-chars is endothermic process and the bio-chars showed a better adsorption property to Re(?)with the increasing of temperature.(4)The pseudo second order kinetics gave a better fit to the experimental date,and the pseudo second order rate constant increased with the increasing of temperature.Both the film diffusion and intra-particle diffusion were the rate-controlling steps of the whole(5)adsorption process.Compared with Langmuir and Temkin isotherm models,the Freundlich isotherm model gave a best fit for the equilibrium date.(6)The ?G0 value for adsorption was negative,indicating that the adsorption process was spontaneous,and the positive ?H0 value suggested adsorption was endothermic.The positive value of ?S0 indicated randomness at the solid/solution interface after Re(VII)adsorption.(7)0.1 mol/L KOH could be used as suitable eluent,after three adsorption-desorption cycles,the desorption rate also remain more than 94%and the adsorption capacity of bio-chars slightly decreased.(8)With the increasing of pyrolysis temperature,the productive rate,total content of H,O and N,the molar ratio of H/C,O/C and(O+N)/C and the content of acidic surface functional groups of bio-chars decreased,meanwhile,the total content of C,ash content,pH and pHpzc of bio-chars increased.The surface area and pore volume of bio-char increased with the increasing pyrolysis temperature and then decreased.The pyrolysis temperature is an important factor affecting the physicochemical properties of bio-chars.Bio-chars produced at the higher temperature showed a greater Re(VII)adsorption efficiency from aqueous solution,due to high temperature bio-chars provided a hydrophobic property to facilitate Re(VII)adsorption onto bio-chars.