Efficient Removal Of Hexavalent Chromium From Water By Bone Char Supported Nanoscale Zero-valent Iron

Heavy metal chromium（Cr）is a common water pollutant.Due to human activities such as mining,metallurgy,electroplating,and chemical industry,heavy metal chromium is inevitably discharged into the natural environment,resulting in serious pollution of groundwater and agricultural irrigation water,affecting the safety of agricultural products.Cr mainly exists in hexavalent and trivalent in water,and hexavalent chromium Cr（VI）is more toxic than trivalent chromium Cr（III）,which is more serious to the environment and human health.Therefore,in this paper,a new type of bone carbon-loaded nano-zero-valent iron（BC-NZVI）composite material was prepared by chemically loading nano-zero-valent iron（NZVI）on the surface of bone charcoal（BC）with high specific surface area,using X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）,infrared spectroscopy FTIR)solid phase characterization analysis of BC-NZVI materials.Under anaerobic conditions,the effects of different NZVI loading and carbon-based materials for the adsorption kinetics and adsorption isotherms of Cr（VI）,and the effects of different p H values and different interfering ions on the removal of Cr（VI）were also discussed.Finally,the XPS and XRD characterization of BC-NZVI after the reaction revealed the reaction mechanism of Cr（VI）removal by BC-NZVI.The specific research results are as follows:（1）Bone charcoal（BC）obtained by bovine bone meal as raw material and pyrolyzed at 950°C and treated with HCl has a high specific surface area（1002.6 m²/g）,a porous structure,and low cost.The prepared bone charcoal loaded with nano-zero-valent iron（BC-NZVI）,XRD analysis showed that NZVI was successfully loaded on the BC surface.It can be seen from the SEM image that NZVI loaded on the surface of bone charcoal can effectively improve the dispersion and stability of NZVI.（2）Studies on Cr（VI）adsorption kinetics show that BC-NZVI can efficiently remove Cr（VI）under anaerobic conditions,and as the load of NZVI increases,the removal rate of Cr（VI）by BC-NZVI also follows increase,but because the removal rate of Cr（VI）by BC alone is almost 0,so the removal amount of Cr（VI）can be normalized to NZVI,after normalization,when the loading of NZVI is 15%,the adsorption of Cr（VI）is the largest amount.In addition,the amount of Cr（VI）removed by BC-NZVI after normalization was significantly higher than the sum of NZVI and BC alone,indicating that the removal of Cr（VI）by BC loaded NZVI showed a significant synergistic effect.BC can significantly improve the dispersion of NZVI;on the other hand,the XRD results of bone charcoal show that it has high graphitization,which can promote electron transfer,improve the NZVI reactivity and contact with Cr（VI）,and thus improve Cr（VI）removal effectiveness.（3）The results of comparative studies on different carbon-based materials show that the removal rate of Cr（VI）by BC-NZVI15 is significantly higher than that of biochar（B-NZVI）and activated carbon（AC-NZVI）,indicating that the synergistic effect of Cr（VI）removal is significantly greater than that of biochar（B）and activated carbon（AC）;when the loading of NZVI is 15%,the maximum adsorption of Cr（VI）by BC-NZVI15 is 77.43 mg/g by adsorption isotherm fitting,normalized to NZVI is516.2mg/g.（4）The experimental results of key environmental factors show that as the p H of the reaction solution increases,the removal rate of Cr（VI）by BC-NZVI15 shows a gradual downward trend,and the p H value of the solution is increased after the reaction;In the presence of humic acid（HA）,PO₄^3-,CO₃^2-in the reaction system,the removal of Cr（VI）by BC-NZVI15 is inhibited,and as its concentration inhibitory effect also increases,therefore it needs to be considered the influence of HA、PO₄^3-、CO₃^2-in the actual application process.（5）The XRD,FITR,XPS solid phase characterization analysis of the corresponding BC-NZVI15 revealed that there are two processes for the removal of Cr（VI）by BC-NZVI15.It can directly fix Cr（VI）,on the other hand,NZVI can reduce Cr（VI）to Cr（III）,which is due to iron precipitation and the formation of crystal Cr₂Fe O₄.The summary shows that a new type of BC-NZVI is prepared in this paper,which can quickly and efficiently remove and reduce Cr（VI）in water under anaerobic conditions,and reveal its reaction mechanism.At the same time,BC-NZVI is also an environmentally friendly new material,so this study provides an effective environmentally friendly material for the anaerobic Cr（VI）pollution remediation.