| The high fluoride?F?and arsenic?As?contamination in drinking water,especially the co-occurring pollution of F and As have become a worldwide concern due to its severe threat to humans.In particular,due to the serious co-pollution of F and As in groundwater in many areas of China,it is urgent to develop a method for simultaneous removal of F and As from drinking water.In this study,magnesium nitrate and ferric nitrate was used as the raw material with introduction of rare earth metal lanthanum to synthesize an Mg/Fe/La triple-metal hydrotalcite-like compound?Mg/Fe/La HLc?for simultaneous adsorption of fluoride and arsenate?As????.The optimum synthesis conditions of adsorbent were obtained by adjusting the metal ratio and calcination temperature.The fluoride and arsenic adsorption performance on the prepared Mg/Fe/La hydrotalcite-like compound?Mg/Fe/La CHLc?in water have been studied by the adsorption kinetics and isotherms to explore the feasibility of simultaneous adsorption of F and As using the adsorbent.Meanwhile,the effect of contact time,initial pH and co-existing anion on the adsorption of F and As by the calcined Mg/Fe/La CHLc have been investigated.Finally,the adsorption mechanisms of fluoride and arsenic on the Mg/Fe/La CHLc in water have been supported by using SEM,XRD,FTIR and XPS techniques.The conclutions were summarized as follows:?1?The optimum synthesis conditions of the adsorbent Mg/Fe/La CHLc were found when La3+/(Fe3++La3+)molar ratio was 0.1 and the calcination temperature was at 600°C.It was showed the obtained Mg/Fe/La HLc had the typical hydrotalcite characteristics with CO32-as the main anion in the interlayer.After calcination,the surface area was 59.3 m2/g,which was thrice as high asthat of pristine hydrotalcite.?2?For adsorption of F,the experimental data followed the Langmuir isotherm and fitted to the kinetics of pseudo-second-order model at optimum pH 6.8 under35°C,and the maximum adsorption capacity achieved 59.3 mg/g;For adsorption of As???the adsorption performance followed the Freundlich model and fitted to the kinetics of pseudo-second-order model at the optimum pH 6.8 under 35°C,and the maximum adsorption capacity was found to be 65.1 mg/g.?3?It was noted that Mg/Fe/La CHLc can be used to simultaneous removal of F and As???,and the existence of fluoride can promote the adsorption capacity of As???.Furthermore,the effect of pH for simultaneous adsorption efficiency is not interfered by the co-existing of F and As and the adsorption behaviors of simultaneous removal of F and As was consistent with the differential adsorption process.It was showed the maximum adsorption capacity of fluoride and arsenic in the simultaneous adsorption process were 73.5 mg/g and 81.4 mg/g,respectively,which was higher than most of other reported adsorbents.?4?Moreover,0.1 M Na2CO3 and calcination method is a high-efficiency desorption regeneration method for Mg/Fe/La CHLc.After 4 times of desorption-regeneration cycles,the adsorbent still had a high adsorption efficiency for F and As,which can realize the reuse of resources.?5?The adsorption mechanisms of fluoride and arsenic on the Mg/Fe/La CHLc were attributed to the surface adsorption and interlayer adsorption due to the“memory effect”of hydrotalcite.Besides,the complexation of fluoride with the lanthanum,arsenic ligand exchange with hydroxy and complexation with the iron on the surface of Mg/Fe/La CHLc also played an important role for their removal.In conclusion,the Mg/Fe/La CHLc not only has a good performance for individual removal of fluoride and arsenic,but also for simultaneous adsorption of F and As.What's more,the Mg/Fe/La CHLc was a relatively reversible,effectively regenerated and could be potentially attractive adsorbents for fluoride and arsenic removal. |
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