Preparation Of High Specific Surface Area Rice Husk-based Activated Carbon And Its Application Research On Wastewater Treatment

With the increasing serious pollution of wastewater, the application of activated carbon adsorbent (especially with the high specific surface area) is becoming more and more widespread. But the traditional raw material of non-renewable coal showed relatively high cost, so the cheap and abundant rice husk was selected as raw material in this study. Currently, the application problem was that its high ash content (mainly SiO2) blocked the pore structure in activated carbon. However, the commonly activators like ZnCl2and H3PO4can not remove the ash; and there was an impregnation treatment before activation. In view of this, the novel dry activation with NaOH was used to prepare carbon. Besides, the effects of carbonization temperature (400-700℃), activation temperature (600-900℃), mass ratio of NaOH/precursor (1-4) and activation method (dry activation and impregnation) on surface area were also studied. Meanwhile, the typical wastewater pollutant, such as phenol (organic small molecule), methylene blue (organic large molecule), nitrate (inorganic ion) and mercury ion (heavy metal ion), were selected as the adsorbate in the systematic research for adsorption, studying the adsorption mechanism and model.Activated carbons were characterized by N2adsorption-desorption, thermal analysis, X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The mechanism of pore development showed that when the formation and deformation rates of micropores were equal, material exhibited the maximum surface area. As a result, at carbonization temperature of600℃and subsequent activation temperature of800℃with the mass ratio of3, samples prepared by dry activation possessed the much higher surface area of2841m2/g than933m2/g for impregnation. Moreover, the economic evaluation revealed that the price of product (40.00￥/kg) was much higher than its total cost (25.78Y/kg) with a gross profit margin of35.6%. Therefore, the results signify that the dry activation is a convenient and effective method to obtain low cost activated carbon with high surface area.In the adsorption experiments of pollution, the data were well explained by the Langmuir and pseudo second-order equations, implying the dominant monolayer adsorption. At temperature of15℃, the maximum adsorption capacities of phenol, methylene blue, nitrate and mercuric ion were found as271.0、822.8、66.0、342.Omg/g, respectively. Additionally, it indicated that the adsorption mechanism of phenol was mainly physical (71.0%) and partly chemical (29.0%) in nature. On this basis, a monolayer liquid adsorption model of organic matter into effective pores in activated carbon was built in this work. According to the comparison between theoretical calculation and experimental data, it was found that this model displayed a suitable correlation.The results showed that the novel dry activation was used to prepare activated carbons with large surface area and low cost in this work; and the subsequent adsorption of pollutants showed the outstanding activity, exhibiting the great practical value and application prospect.