| In the roasting process of extracting vanadium from stone coal, large numbers ofsalts are needs to promote the roasting effect. Hence, the wastewater containing highsalinity is produced in vanadium extraction process. There are two classes ofconventional technologies for treating the high salinity wastewater, evaporation andmembrane method. Both methods possess the drawback of high energy comsumption.In order to further reduce the energy consumption, This study focuses the desalinationof capacitive deionization (CDI), investigates the influence of electroce material onadsorption capacity, and compares the desalination performance of electrodematerials before and after modification in treating vanadium extraction wastewater.By comparing the desalination capacity of different kinds of activated carbons,combined with chemical analysis, physical analysis and electrochemical analysis, thispaper finds out the general characteristics of electrode material with good adsorptionperformance, which can guide the selection of electrode materials for CDI. Theresults show that under the same conditions, the adsorption capacity of mineralactivated carbon (M-AC)electrode is about4times as that of wood activated carbon,and about7.5times as that of coco activated carbon. The reasons for the discrepancybetween M-AC and other two materials are that the former has the less content ofimpurity, more developed pore structure, abundant surface functional groups, whichresults in the high adsorption capacitance and low adsorption resistance. Thus,electrode material for CDI should possess these characteristics.The most optimal processing parameters of CDI in this study are chargingvoltage of2.0V, flow rate of25mL/min, space between polar plates of3mm andbinder content of9%. Kinetic researches show that the pseudo-first-order kineticequation fits the experiment data quite well during desalinating differentconcentration of NaCl solutionsThe study of selective adsorption properties of ions indicates that the main factorthat affects the adsorption capacity is concentration of ions. The higher the charge, thehigher the adsorption capacity. The lower the hydrated ionic radius, the higher theadsorption capacity. The kinetic of different electrolyte solutions show that the adsorption rates follow the order: Fe3+>Al3+> Ca2+> Mg2+> K+> Na+. It indicates thatthe adsorption rate of high valence ion is greater than that of low one. The lower thehydrated ionic radius, the higher the adsorption rate.The wastewater produced invanadium extraction from stone coal was treated by using3step capacitivedeionization, the total ion adsorption capacity reached to87.03mg/g when thevoltage of2.0V, feed flow rate of25mL/min，space between polar plates of3mm.Surface modification was used to improve the adsorption capacity of activatedcarbon. The kinetics results show that nitric acid modification can improve theadsorption rate. It has been found that the modification greatly increased theoxygen-containing functional groups on the surfaces of activated carbon, such ashydroxyl and carboxyl groups, and a new functional group (C-N) is produced, leadingto the decrease of hydrophobicity of electrodes, and the increases of the capacitanceand the reduction of the charging resistance.In order to prove the nitric acid modification in general use, the study ofdesalination performance of original and nitric acid modified multi-walled carbonnanotube was studied. The results indicate that the adsorption capacity increased44.9%after modification. Nitric acid modification not only can improve theperformance of activated carbon electrode, also suitable for multi-walled carbonnanotubes.The electricity consumption analysis of treating vanadium extraction wastewaterby capacitive deionization indicate that: the electricity consumption can decrease22.4%by using nitric acid modified M-AC electrode during the salts content isreduced from30388mg/L to1500mg/L. At the same time, the consumption ofelectrode material and the processing time also can be reduced by modification. |
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