Study On The Gentle Preparation Of Millimeter-scale Hydrothermal Carbon Ball And Its Cr(?) Adsorption Performance

Cr???was specified as one of the top 16 toxic pollutants,and its treatment has received wide attention.Chitosan is a common Cr adsorbent.Based on the common existence of chitosan in powder and easily soluble under acidic conditions,one-step mild hydrothermal method was used to prepare millimeter-sized hydrothermal carbon beads?HCB?in this paper,which solved the problems of difficult separation and poor acid resistance of chitosan powder adsorbent.Furthermore,metal precipitates were introduced in situ as templates,and millimeter porous hydrothermal carbon beads?PHCB?were prepared by acid dissolution,which can increase the specific surface area of chitosan beads and improve their adsorption performance for Cr???.The main findings are as follows:?1?The prepared chitosan beads?CSB?were carbonized at different temperatures,and the HCB-120?particle diameter of about 4.0 mm?,HCB-180?particle diameter of about 3.5mm?and HCB-240?particle diameter of about 1.0 mm?were obtained.Raman spectroscopy,FT-IR,elemental composition analysis and acidic resistance test results show that with the increase of hydrothermal temperature,the higher carbonization degree of CSB,the better its corresponding acid resistance stability;SEM analysis showed that HCB-180 and HCB-240have more pronounced wrinkles and pores than CSB and HCB-120.N₂ adsorption-desorption analysis showed that the specific surface area of HCB increases with the increase of hydrothermal temperature,and the specific surface area of HCB-180 is 4.81 m² g^-1.The results of static adsorption show that HCB-180 can reduce Cr???from 20 to 0.3 mg L^-1(which is less than 0.5 mg L^-1 of the Chinese chromium discharge standard in industrial wastewater).In contrast,the residual Cr???concentrations are 4.7 mg L^-1 for CSB,4.2 mg L^-1 for HCB-120 and 0.8 mg L^-1 for HCB-240,respectively,which indicates that hydrothermal treatment is beneficial to"expose"the adsorption active sites on the CSB surface;In addition,the adsorption kinetics and adsorption isotherms of HCB for Cr???was fitted with the pseudo-second-order model and Langmuir model,indicating that these adsorption processes are dependent on the chemisorption and monolayers.The dynamic adsorption results show that HCB-180 has the prospect of being used in practical chromium-containing wastewater treatment,and the Yoon-Nelson model can fit its breakthrough curve in the dynamic adsorption process well.?2?Based on the preparation of HCB,Al?OH?₃ precipitate was introduced in situ as a template,and PHCB was successfully prepared by acid dissolution.XRD and FT-IR analysis showed that Al?OH?₃ was successfully deposited on CSB,CSB-Al?OH?₃ and HCB-Al?OH?₃was obtained.SEM and N₂ adsorption-desorption analysis showed that PHCB has more abundant pores and larger specific surface area,and its specific surface area(23.7 m² g^-1)is larger than CSB(1.81 m² g^-1),CSB-Al?OH?₃(1.54 m² g^-1),HCB-180(4.81 m² g^-1)and HCB-Al?OH?₃(3.96 m² g^-1).The static adsorption results show that the adsorption effect of CSB-Al?OH?₃ for Cr???is similar to CSB,and the HCB-Al?OH?₃ is little different from that of HCB-180,while the adsorption capacity of Cr???on the PHCB can reach 111.1 mg g^-1.Besides,the corresponding adsorption kinetics and adsorption isotherms are also in accordance with the pseudo-second-order model and Langmuir model,indicating that these adsorption processes are dependent on the chemisorption and monolayers.PHCB was applied to the treatment of actual chromium-containing wastewater?the main components are Cr,Mn,Fe?,and it showed excellent selective absorption for Cr???,the adsorption efficiency can reach 91.7%,indicating that PHCB shows good application prospects for the treatment of chromium-containing industrial wastewater.