Study On Preparation And Adsorption Properties Of Magnetic Activated Carbon From Peanut Shell

As a kind of carbon material, activated carbon has developed pore structure, huge specific surface area and strong adsorption capacity. It has been widely applied in many fields, such as industry, national defense, transportation, medicine, health care and environmental protection, etc. However, the used activated carbon often suffers from serious problems of separation in liquid-solid phase processes. The traditional filtering methods can easily cause the blockage of screen mesh and the loss of activated carbon. Compared with the traditional method, magnetic technology makes it possible to effectively separate and recover the spent activated carbon by a simple magnetic process. Therefore, the preparation and application of magnetic activated carbon （MAC） have been paid more and more attention in recent years. China is a big producer of activated carbon, where a large number of activated carbon is produced from coal. As the energy crisis and environment problem become increasingly serious, the use of industrial waste and agricultural by-products for preparation activated carbon has been paying more and more attention.In this paper, the single-step preparation of magnetic activated carbon from peanut shell （MPSAC） was developed by using potassium carbonate （K₂CO₃） as a activating agent and Fe₃O₄ as a magnetic additive agent. The porosity development and the magnet evolution in the existence of K₂CO₃ and Fe₃O₄ were studied. Meanwhile, the adsorption of heavy metal Pb （Ⅱ） and methylene blue （MB） dye on MAC was done. The main research contents and conclusions of this study are as follows:1. Research on the single-step synthesis of MPSACMPSAC was prepared by a single-step method via using K₂CO₃ as a activating agent and Fe₃O₄ as a magnetic additive agent. The effects of the mixing ratio of peanut shell, K₂CO₃ and Fe₃O₄, carbonization temperature and time, activation temperature and time on the adsorption properties of magnetic peanut shell activated carbon are studied. The rusults show that the optimal conditions are peanut shell:K₂CO₃:Fe₃O₄= 10:5:0.5, carbonization at 300℃ for 1 h and activation at 750 ℃ for 1.5 h, respectively. The obtained MPSAC has an iodine adsorption value of 1228 mg/g and a methylene blue value of 395 mg/g. The BET surface area and total pore volume of MPSAC are 1219 m²/g and 0.5767 cm³/g, respectively. The magnet in MPSAC is Fe₃C.2. Research on the porosity development and the magnet evolution of MPSAC in the existence of K₂CO₃ and Fe₃O₄In order to clarify the porosity development and the magnet evolution of MPSAC, the morphology, pore structure and surface functional groups of impregnated samples, carbonization samples and activation samples obtained before and after K₂CO₃ and Fe₃O₄ added were characterized by using thermo-gravimetric analysis （TG-DTG）, Fourier infrared spectrum （FT-IR）, X-ray diffraction （XRD）, scanning electron microscope （SEM）, specific surface area and pore size distribution, etc. Meanwhile, the K-related species and Fe-containing intermediates formed at different stages including impregnation, carbonization and activation were also detected. The results show that the introduction of K₂CO₃ has damaged the partial structure of peanut shell during the impregnation process. At the pre-carbonization stage, K₂CO₃ greatly modified the carbonization behavior of peanut shell, shifted the weight loss peak from 350℃ to 255℃ and developed primary pore structure. At the activation stage, K₂CO₃ facilitated the conversion of Fe₃O₄ to Fe₃C besides developing abundant micropores. Meanwhile, Fe₃O₄ functioned as an activation promoting agent while providing the Fe source. Finally, a three-step reaction mechanism Fe₃O₄→FeO→Fe→ Fe₃C is proposed for the formation of Fe₃C in the coexistence of Fe₃O₄ and K₂CO₃.3. Research on the adsorption of heavy metal Pb （Ⅱ） and MB on MPSACThe adsorption of heavy metal Pb （Ⅱ） and MB on MPSAC was investigated, respectively. The influence of several operating parameters, such as pH, contact time, adsorbent dose, adsorbate concentration and temperature of solution were investigated in batch mode. The related kinetic and equilibrium data were fitted with different models, and the thermodynamic data were calculated. The results show that:（1） The equilibrium time is 8h for the low concentration of Pb （Ⅱ） and 14h for the high concertration of Pb （Ⅱ）. When pH is over 2, the removal of Pb （Ⅱ） increases dramatically. The adsorption process follows pseudo-second-order reaction kinetics. The equilibrium data were fitted better by Langmuir equation. The adsorption process is spontaneous, and the maximum monolayer adsorption capacity of Pb （Ⅱ） on MPSAC is 143.88 mg/g at 20℃.（2） The initial adsorption rate of MPSAC for MB is fast, and equilibrium time is only 2 hours. At the pH range of 2.0-9.0, the adsorption capacity of MPSAC has a small change. The adsorption process follows pseudo-second-order reaction kinetics. The equilibrium data were fitted better by Langmuir equation. The adsorption process is spontaneous, and the maximum monolayer adsorption capacity of MPSAC for MB is 617.28 mg/g at 25℃.