The Effect Of Dissolved Organic Matter On The Adsorption Of Cd(?) On Magnetic Nano-hydroxyapatite And Its Mechanism

Cadmium Cd???,was highly toxic among all heavy metal ions in wastewater,and did a great deal of harm to the human health and environment.In the treatment of wastewater,the adsorption was generally utilized to remove heavy metal ions in water with magnetic hydroxyapatite nanoparticles?HAP/?-Fe₂O₃?as the adsorbent.Dissolved Organic Matter?DOM?also widely spread in real water,including humic acid?HA?,fulvic acid?FA?and tannic acid?TA?.DOM could not only affect the solubility and mobility of metal ions in aqueous solutions,but also even generate a complexation with heavy metal ions.Due to that,that HAP/?-Fe2O3 was applied to the adsorption of heavy metal ions in water was inevitab ly influenced by DOM.However,there was a lack of thorough research on how DOM exerted an impact on the process where HAP/?-Fe₂O₃adsorbed heavy metal ions in water.In this thesis,with HAP/?-Fe₂O₃as the adsorbent and Cd???in aqueous solutions as the targeted pollutant,the writer systematically studied the impact exerted by three kinds of DOM?HA/FA/TA?on the adsorption efficiency,as well as the influence mechanism.Furthermore,with DOM as the modifier to modify HAP/?-Fe₂O₃,the writer compared and analyzed the adsorption efficiency before and after the modification,and preliminarily discussed its process mechanism.The main conclusions were as follows:?1?The adsorption efficiency of the three common kinds of DOM?HA/FA/TA?performed by HAP/?-Fe₂O₃ and the related adsorption mechanism were firstly studied.The study showed that,according to the X–ray Diffraction?XRD?Analysis,an electrostatic interaction occurred between Ca²⁺in HAP/?-Fe₂O₃ and HA,FA,and TA;according to the Fourier Transform Infrared Spectroscopy?FT-IR?Analysis,a hydrogen-bond interaction occurred between a large number of functional groups?oxygen-containing groups?in HAP/?-Fe₂O₃ and HA,FA,and TA;the increase of p H value led to an increase of the adsorption efficiency of HA,FA,and TA performed by HAP/?-Fe₂O₃ in the beginning and then a decrease.When the p H value rose from 2.0 to 11.0,the adsorption capacity changed from 38.07mg/g to 43.80mg/g and then to 27.80mg/g,from 45.44mg/g to 47.34mg/g and then to 42.89mg/g,from 33.00mg/g to 49.14mg/g and then to 2.96mg/g respectively.Other coexisting cations inhibited the adsorption efficiency of HA,FA,and TA by HAP/?-Fe₂O₃.The adsorption of HA,FA,and TA by HAP/?-Fe₂O₃ totally followed the pseudo-second order model,with the isotherm conforming to Langmuir and Temkin models.According to Thermodynamic Analysis,the adsorption process of HA,FA,and TA by HAP/?-Fe₂O₃ was spontaneous and endothermic,also an increase of entropy.?2?The influence exerted by HA,FA,and TA on the adsorption efficiency of Cd???by HAP/?-Fe₂O₃ and the analysis of factors were studied.The result indicated that,at this point,the p H value and other coexisting cations were major elements which affected the adsorption of Cd???by HAP/?-Fe₂O₃.When p H value was from 2.0 to 9.0,the adsorption capacity increased slowly.With HA,FA,and TA,the adsorption capacity climbed respectively from33.68mg/g to 40.94mg/g,from 34.68mg/g to 41.79mg/g,and from 38.80mg/g to 42.60mg/g.without HA,FA,and TA,the adsorption capacity soared from 32.35mg/g to 43.44mg/g,with p H value from 2.0 to 8.0;when p H value continued to increase,the adsorption capacity remained,with adsorption rate reaching 88.75%.In the presence of other coexisting cations,they inhibited the adsorption of Cd???by HAP/?-Fe₂O₃.The higher the concentration of coexisting cations(k⁺?Ca²⁺?Mg²⁺)were,the better the inhibition was.Among these three coexisting cations,Mg²⁺had the strongest inhibition.The main reason might be that Mg²⁺occupied more adsorption sites due to dissolution–precipitation effect.Whether with or without HA,FA,and TA,the adsorption of Cd???by HAP/?-Fe₂O₃totally followed the pseudo-second order model,with the isotherm conforming to Langmuir and Temkin models.According to Thermodynamic Analysis,the adsorption process was spontaneous and endothermic,also an increase of entropy,no matter HA,FA,and TA existed or not.?3?HAP/?-Fe₂O₃was modified by DOM,a modifier,and then was applied to the removal of Cd???in aqueous solutions.After this process,the writer analyzed and compared its adsorption efficiency and related mechanism.According to XRD Analysis in the modified materials,we found that there was no significant change in major phase compositions of HAP/?-Fe₂O₃afterthe modification.FT-IR Analysis showed that the amount of surface functional groups contained in HAP/?-Fe₂O₃increased.The adsorption peak of hydroxyl was found at 620cm^-1,and that of carboxyl was found at 1380cm^-1.According to the analysis of the high-power transmission scanning microscope,after the modification,the surface of HAP/?-Fe₂O₃was smoother and the isoelectric point of HAP/?-Fe₂O₃decreased than before,which was due to that the combination of DOM molecules on the surface of HAP/?-Fe₂O₃brought more negative charges.The adsorption efficiency of Cd???by HAP/?-Fe₂O₃was also enhanced after modification.The adsorption capacity of the modilied adsorbent increased by 1.38mg/g?HA-HAP/?-Fe₂O₃??4.17mg/g?FA-HAP/?-Fe₂O₃?and 6.37mg/g?TA-HAP/?-Fe₂O₃?compared with that of the unmodified adsorbent.Based on the preliminary alysis,the possible reason why the adsorption efficiency was enhanced was due to the electrostatic adsorption and ion exchanges between Cd???and the surface of the modified adsorbent.To sum up,it was very complex when it comes to the effect of DOM in aqueous solutions on the adsorption of Cd???performed by HAP/?-Fe₂O₃ and related mechanism,because that process was influenced by the characteristics of DOM together with various environmental factors?p H value,the kind and concentration of coexisting cations,etc.?;after HAP/?-Fe₂O₃was modified by DOM with many kinds of functional groups,the adsorption efficiency of Cd???by HAP/?-Fe₂O₃was effectively improved.In this thesis,the work of this paper provides basic data for further study on the adsorption and removal of heavy metal lions in real water.