| Animal bone biochar has rich pores and sufficient adsorption space,and the surface hydroxyl group which has strong affinity,so it is feasible to use it as a fluorine removal adsorbent.In this study,the four common defluoridation materials,activated alumina,bovine bone biochar,pig bone biochar and chicken bone biochar i.e.were used for dynamic adsorption and isothermal adsorption experiments to screen bovine bone biochar with better fluorine adsorption effect.The selected bovine bone biochar was used as the basic skeleton,and the composite modified bovine bone biochar was prepared by adding aluminum salt and iron salt.The adsorption capacity,regeneration ability and influencing factors of fluorine were studied.The modified bovine bone biochar before and after adsorption were characterized by scanning electron microscope,automatic adsorption instrument,Fourier transform infrared spectroscopy,Zeta potential and X-ray diffractometer to determine adsorption mechanism.The main results are shown as follows:?1?The adsorption of fluorine by activated alumina,bovine bone biochar,pig bone biochar and chicken bone biochar are fitted with quasi-secondary kinetics which belongs to chemical adsorption.The adsorption capacity and affinity of bone biochar for fluorine are much larger than that of activated alumina and the affinity of bovine bone biochar is the strongest.The procedure of the bovine bone biochar modified by Al2?SO4?3 and Fe2?SO4?3 is shown as following:firstly,the Fe2?SO4?3 mass fraction is4%,the soaking time is 0.5h and the solid-liquid ratio is 1:5,then the Al2?SO4?3 mass fraction 8%,soaking time 1h,the ratio of solid to liquid is 1:5.Bovine bone biochar modified by Al2?SO4?3 and Fe2?SO4?3 composite had the highest adsorption capacity for fluorine(45.46 mg·g-1),which was 8.5 times of the pre-modification adsorption(5.34 mg·g-1).The adsorption capacity of biochar modified by Fe2?SO4?3 and Al2?SO4?3 are 13.33mg·g-11 and 34.48mg·g-1,respectively.?2?The bovine bone biochar modified by iron-aluminum composite has a relatively large adsorption capacity for fluorine,which was related with structural group hydroxyl groups OH-,CO32-,PO43-and HPO42-and large pore size.After modification of bovine bone charcoal with aluminum and iron salts,the complexation of F-with Fe3+and Al3+entering the pores enhances the chemisorption capacity of the modified bone biochar.XRD showed that the superimposed peak of CaHPO4?H2O?2appeared after modification,the modified bovine bone biochar had better crystallinity and the XRD diffraction ability was enhanced.And the pHpzczc of the modified bovine biochar is shifted to the right and the pH range of the fluorine removal is wider.?3?In the dynamic experiment,the continuous adsorption fluoride effect of Al2?SO4?3-Fe2?SO4?3-bovine bone biochar is greatly affected by the height of the adsorption column,the residence time,the flow rate of the solution and the concentration of the original solution.When the raw water fluoride ion concentration>15mL·min-1,the flow rate<3.75mL·min-1,the height of adsorption column>6cm and the residence time is about 5.03min,the effective utilization rate of the modified bovine bone char can reach more than 50%.?4?Al2?SO4?3-Fe2?SO4?3-bovine bone biochar has good recyclability when the NaOH solution with a concentration of 1%was used as the regenerating liquid and soaked with Al2?SO4?3-Fe2?SO4?3-bovine bone biochar at a solid-liquid ratio of 1:30 for 9 h. |
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