| In this study, rice husk-based activated carbon(RAC)was produced by ZnCl2-CuCl2 composite activator from rice husks. The preparation conditions and mechanism were investageted. The surfacial chemistry and porous structure of the RAC were analyzed through nitrogen adsorption/desorption isotherm, porous size distribution, Fourier Transform Infrared Spectrometer(FTIR), scanning electron microscope(SEM), X-ray Photoelectron Spectroscopy(XPS), point zero charge(pHPZC) and X-ray Diffraction(XRD). Based on property of RAC, the adsorption propertities to fuchsine and methyl orange(MO) was studied through static adsorption and dynamic adsorption, and the desorption of spent RAC was also investigated. In addition, regeneration and producing silica from spent RAC was preliminarily studied.The optimum prepation conditions were determined through single factor experiment and orthogonal array experiment. The optimal conditions were at the ZnCl2 concentration of 5 mol/L, the CuCl2 concentration of 0.4 mol/L, activation temperature of 500 °C and activation time of 1.5 h. The iodine number, methonl blue, BET surface area and total pore volume were 1041 mg/g, 188 mg/g, 1924 m2/g and 1.493 cm3/g, respectively. It was indicated that there were mainly micropore and mesopore existing in the RAC, which was good for adsorption of organic and volatile. The suface functional groups of RAC were mainly oxygen-containing groups(hydrixy and carbonyl groups). The pHPZC was 5.67. When the solution pH was less than 5.67, the high concentration of H+ ions promoted the protonation of functional groups, and thus the adsorbent became more positively charged and easy to adsorb anions. When the solution pH was higher than 5.67, the adsorbent was negatively charged and benefifial to adsorb cation.In static experiments, the removal efficiency was improved by increasing the adsorbent dosage and decreasing the initial concentration. The removal efficiency of fuchsine was increased with increasing pH value, but the removal efficiency of MO was decreased with increasing pH value. The adsorption capacity of RAC was decreased with temperature increasing, indicating the adsorption process was exothermic. In dynamics study, the adsorption of fuchsine and MO followed the pseudo-second-order kinetic model, and the desorption ratio of them in different pH value solution was less than 10 percent, indicating the adsorption is probably effected by chemisorption.The spent RAC was regenerated through thermal regeneration. After regeneration for one time, the BET surface area and pore volume of RAC still remained high quality and it was also effective to decolorize high concentration dye, while the surface area and removal efficiency decreased faster beyond one times. This indicated that heat treatment was effective to regenerate the used RAC for one time.In dynamic experiments, the fixed-bed adsorption system was found to perform better with lower dye concentration, lower flow rate, smaller particle size and higher adsorbent mass, while the breakthrough time and adsorption capacity were longer and larger.Silica was also prepared from the spent RAC with various temperature, which denoted that the high purity silica was produced above 700 °C.The purity was improved by increasing the preparation temperature and the polymorphs were changed with the temperature increasing.The shape of silica was nanoscale and spherical. |
