| Biomass-based carbon material is a kind of ideal adsorption material due to the developed porous structure. Besides, agriculture and forestry waste and natural lignocellulosic fiber materials are used to prepare high performance carbon materials is in accordance with green development strategy.Rice husk based activated carbon (RHAC) and sisal based acitivated carbon fiber (ACF) were prepared with zinc chloride assisted by microwave and electric dual-mode heating. Different influencing fators (impregnation ratio, activation temperature, activation time and heating rate) on the porous structure and the influence of adsorption performance of heavy metal ions were studied. Optimum conditions were acquired by single factor experiments. The best conditions for RHAC:activation temperature 600?, activation time 50min, impregnation ratio (zinc chloride:rice husk) 1.5:1, heating rate 15?/min. The optimum conditions for ACF:activation temperature 600?, peroxidation time:1 h, activation time 50 min, impregnation ratio (zinc chloride:rice husk) 1.25:1, heating rate 10?/min. It was found that the specific surface area of RHAC and ACF in the optimal conditions achieved 1719.32 m2/g and 2055.53 m2/g, respectively.The optimum RHAC and ACF were modified by nitric acid assisted by microwave nitric acid (RHAC-O/ACF-O) and vulcanization (RHAC-S/ACF-S). The different factors on the microwave-nitric acid modification (nitric acid concentration, modification temperature, modification time, power) and vulcanized modification (dosage of thionyl chloride, time of thionyl chloride, dosage of TGA, Time of TGA) were explored. Optimum conditions of microwave-nitric acid modification were obtained by orthogonal experiments. The best conditions for RHAC-O:nitric acid concentration 8 mol/L, modification temperature 130?, modification time 5 min, power 800 W; the best conditions for ACF-O:nitric acid concentration 9.5 mol/L, modification temperature 150?, modification time 15 min, power 800 W. Optimum conditions of vulcanized modification were obtained by single factor experiments. The best conditions for RHAC-S:dosage of thionyl chloride 10 mL, time of thionyl chloride 1.5h, dosage of TGA 12 mL, Time of TGA 2 h; The best conditions for ACF-S:dosage of thionyl chloride 12 mL, time of thionyl chloride 1.5h, dosage of TGA 14 mL, Time of TGA 2 h.The porous characteristics, elementary composition, surface chemical properties and crystal structure of six absorbents were characterized by N2 adsorption-desorption test, element analysis, XPS, FTIR, Boehm titration, Zeta potential and XRD. The influence of adsorption time, pH and initial concentration of absorbents were investigated in the study, the results showed that the ACF had shorter equilibrium time than the RHAC. The pH had a greater influence on the adsorption process, the maximum adsorption capacity achieved between pH 2.0-3.0 for hexavalent chromium ions and pH 5.5 for copper ions and lead ions. With the increase of initial concentration, absorbent adsorption capacity increased, while the removal rate was falling. For two kinds of modified absorbent, temperature could promote the adsorption process.Some models were used to analyse the adsorption process. The results showed that the adsorption process was fitted with pseuo second order model; intra-particle diffusion model presented in multi-stages; the HSDM model showed surface diffusion and film diffusion limited the adsorption process. For rice husk activated carbon adsorbed three kinds of heavy metal ions and sisal activated carbon fiber adsorbed copper and chromium ions, Langmuir could better describe the adsorption process. For sisal activated carbon fiber adsorbed lead ions and modified absorbents adsorbed heavy metal ions were more in line with the Freundlich isotherm equations. Adsorption thermodynamics indicated that all the adsorption process could occur spontaneously, enthalpy of modified absorbents were higher than that before, indicating that proportion of chemical adsorption increased.Different influence factors (bed depth, initial concentration, flow rate) on adsorption process were investigated by fixed bed experiments. And the kinetic study on fixed bed was researched on sisal activated carbon fiber. Sisal activated carbon fiber was desorbed by acid and alkali in different conditions (pH, flow rate, temperature), and repeated adsorption experiments were carried out, the results showed that sisal activated carbon fiber has good renewable performance. |
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