Study On Adsorption Of Ni(?) From Electroplating Wastewater By Modified Peanut Shell Biochar

In recent years,nickel-containing wastewater discharged from electroplating industry has become an important pollutant in the ecological environment,which is directly or indirectly harmful to human health.It is imminent to develop technologies with highly efficiency and low cost in treating nickel ion?Ni????in electroplating wastewater.As the major producer of peanuts,China discards and burns a large number of peanut shell,which not only pollutes the environment,but also causes the great waste of resources.Biochar is one kind of carbon-rich product produced via pyrolysis of biomass under anoxic circumstances.Because of its excellent surface area,pore structure and other properties,biochar has a good adsorption capacity for heavy metals and is expected to be a cheap and efficient adsorbing material for the treatment of nickel-containing wastewater.In this study,biochar derived from waste peanut shell was produced and modified.The pyrolysis chemical modification method was used to optimize modification conditions for the adsorption of Ni???on peanut shell biochar for which to obtain the modified peanut shell biochar with efficient removal of Ni???in electroplating wastewater.The morphology,specific surface area and Zeta potential of the non-modified and modified peanut shell biochar were characterized by modern analysis and detection techniques for which to compare and analyze the changes in the structure and surfacing characteristics.The effects of non-modified and modified peanut shell biochar on the adsorption of Ni???were investigated under the conditions of different dosage,pH and ionic strength.The adsorption thermodynamics and kinetic behavior were studied and combined with the analysis of physicochemical properties about non-modified and modified peanut shell biochar for which to investigated the corresponding adsorption mechanism of Ni???.Eventually,the reasonable desorption conditions and the service life of materials were further analyzed through the desorption and re-adsorption experiments.The achievements in this study were given in this following:1)Modified peanut shell biochar was prepared and modified through pyrolysis,heat treatments accompanied by the addition of potassium permanganate?KMnO₄?and potassium hydroxide?KOH?.It was found the optimum modifying conditions of the peanut shell biochar to adsorb Ni???were including the temperature of 361?C,the mass ratio of KOH to biochar of 2.5:1?w:w?,and 0.76%KMnO₄.After modification,the physicochemical properties of the material changed significantly.For instance,it altered to the smaller particle size and coarser surface.The specific surface area and average pore volume increased,however,the average pore size decreased.Besides,its absolute value of Zeta potential increased,and the species of functional groups also considerably changed.2)The results of batch study exhibited that the adsorption capacity of modified and non-modified peanut shell biochar to Ni???reduced when increasing their dosage,and raised while an increase of pH.Before modification,the best adsorbing effect of peanut shell biochar to Ni???was appeared under the circumstance of pH 7.0.It was slightly different that modified peanut shell biochar performed better at the adsorption of Ni???when the pH was set as 6.0 or 7.0.The ionic strength had little effect on the adsorption of Ni???before and after the modification,which indicated that the main reaction process was the formation of inner complexes.The competitive Cu???obviously affected the adsorption of Ni???on both of modified and non-modified adsorbents,which meant the adsorption capacity declined dramatically.3)The results of isothermal experiment showed that the Langmuir equation could better describe the adsorption equilibrium of both adsorbents.Moreover,the maximum adsorption capacities of non-modified and modified peanut shell biochar of Ni???at298 K were 5.79 mg/g and 87.92 mg/g,respectively.There was no doubt that modification had significantly improved the adsorption capacity of Ni???by pristine biochar.For these two adsorbents,their values of?G were negative,on the contrary,values of?H and?S were positive.These results revealed the adsorption of Ni???by both adsorbents might be spontaneous and endothermic.FTIR and XPS found that the adsorption of Ni???by peanut shell biochar mainly relied on the-CO₃ and?-conjugated aromatic structure That's to say,Ni???adhered to the peanut shell biochar via the form of NiCO₃.Nevertheless,the?-conjugated aromatic structure,-OH and-NH₂ exerted a vital function in Ni???sorption by modified biochar which in the form of R-Ni?OH?₂,R-O-NiONi-O-R and R-NNi.4)According to studying the effects of desorbent types,concentration,temperature and time on desorption of Ni???,reasonable conditions of desorption were obtained.Desorption studies showed that 0.15 mol/L HCl had the strongest desorption effect on desorbing peanut shell biochar-Ni???,while 0.05 mol/L HCl considerably desorbed the modified peanut shell biochar-Ni???.During desorption,non-modified and modified absorbent respectively spent 12 hours and 5 hours reaching the equilibrium,whereas the effect of temperature was insignificant.5)Service life of both non-modified and modified peanut shell biochar was analyzed by the re-adsorption experiments.In re-adsorption studies,the non-modified peanut shell biochar had the adsorption capacity decreasing from 5.14 mg/g to 0.05mg/g within five adsorption periods,which finally had almost no adsorption of Ni???and a transient service life.In the same re-adsorption periods,the amount of Ni???adsorbed by the modified peanut shell biochar changed from 80.23 mg/g to 18.77 mg/g.Compared with not only the non-modified absorbent but also other materials,the modified peanut shell biochar had competitive adsorbed amount of Ni???and longer adsorption life.