The Efficiency And Mechanism Of U(?)Removal From Acidic Wastewater By Sewage Sludge-derived Biochar

As a radioactive element,uranium(U)is highly toxic and carcinogenic.With the development of nuclear energy,a large amount of U(?)radioactive wastewater will be generated,which will cause serious harm to the natural environment and organisms.In this paper,sewage sludge(SS)was used as raw material to prepare sewage sludge-derived biochar under anoxic conditions of 300 ?,450 ? and 600?,and then modified by acidification and magnetization.The characteristics of sewage sludge-derived biochar and modified biochar were analyzed,and the effectiveness of treating U(?)with sewage sludge-derived biochar and modified biochar was investigated.The mechanism of adsorption removal of U(?)was discussed by fourier infrared spectroscopy(FTIR),X-ray crystal diffraction(XRD),and X-ray electron diffraction(XPS).The main conclusions are as follows:(1)Sewage sludge-derived biochar(SSB)was prepared at 300 ?,450 ?,600 by slow oxygen limiting method.? The specific surface area and pore volume of sludge and biochar increased with pyrolysis temperature,and the pore size decreased,but the specific surface area,pore volume and pore size of biochar decreased after acidification and magnetization.As the pyrolysis temperature increases,the oxygen-containing functional groups such as hydroxyl(-OH)and carboxyl(-COOH)in sewage sludge-derived biochar decreased,and the content of hydroxyl and carboxyl in biochar increases after acidification,indicating the effective of acidification can increase the number of oxygen-containing functional groups in sewage sludge-derived biochar.The main structures in sewage sludge-derived biochar were Si O2 and Ca CO3.The main crystal structure of nitric acid-modified sewage sludge-derived biochar(SSB-AO)was Si O2,while the crystal plane of Ca CO3 disappeared.The main structures in the magnetic sewage sludge-derived biochar(MSSB)were Si O2 and Ca CO3,and the Fe3O4 structure appeared.(2)The adsorption process of U(?)removal by SSB,SSB-AO and MSSB can be better fitted by the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model,indicating that the removal of U(?)by these materials belonged to chemical adsorption and monolayer adsorption.In addition,the maximum adsorption capacity of SSB300,SSB450,SSB600,SSB-AO and MSSB to U(?)at a temperature of 30? was 34.51 mg/g,41.62 mg/g,44.84 mg/g,80.34 mg/g and 145.13 mg/g,respectively.It indicateed that acidification and magnetization effectively increased the maximum adsorption capacity of U(?)by sewage sludge-derived biochar,but the adsorption capacity of U(?)by magnetized sewage sludge-derived biochar was stronger.(3)The removal mechanisms of SSB,SSB-AO and MSSB included coordination complexing of U(?)with oxygen-containing functional groups(-OH and-COOH,etc.),ion exchange and electrostatic attraction.However,Fe(II)in MSSB can reduce U(?)to low-toxicity U(IV)that was easier to remove.After five adsorption-desorption experiments,the removal rate of U(?)by MSSB(over 90%)was higher than that of SSB and SSB-AO(80 ~ 90%).It was easy to perform solid-liquid separation and had a larger adsorption capacity,so MSSB was better applied to the treatment of acidic radioactive wastewater containing U(?).(4)After comprehensive comparison,it was found that SSB and the modified products(SSB-AO and MSSB)had a good uranium treatment effect,but the modified adsorption capacity was greater,especially MSSB.Therefore,this article provided a reference for the application of sewage sludge-derived biochar and its modified products in the treatment of acidic U(?)-containing wastewater,and also provided a new idea for the utilization of urban sludge resources.