Selective And Effective Removal Of Heavy Metals From Contaminated Wastewater By Modified Carbonaceous Materials

Heavy metal pollution has drawn the attention of scholarly circles as a global environmental problem that requires immediate attention.Given the fact that safety regulations are progressively stronger in most areas around the world,metal ions pollution control continue to gained social and academic attentions,and in some places the situation of heavy metal wastewater pollution has substantially improved.Presently,the latest information on mercury and chromium pollution remains severe.A wide range of methods have been used for removing Hg²⁺ and hexavalent Cr⁶⁺ from wastewater.Adsorption method is recognized as the most effective and economic method for the removal of heavy metals from wastewater,to obtain satisfactory heavy metal removal from wastewater.However,the disadvantages of this method are mostly based slow adsorption rate,low removal efficiency,and low adsorption capacity.Therefore,developing of high adsorbent performance is of great importance.In this research,we propose an idea on the modification of new adsorbents,using environmentally friendly carbonaceous materials that could selectively and effectively adsorb Hg²⁺ and Cr⁶⁺ ions from the wastewater obtaining higher removal efficiencies and large adsorption capacities.Therefore,to address this problem,we modified chitosan with thiol（SH-CNTs）for the adsorption of Hg²⁺,Synthesized Polymellitic dianhydride almond shell powder（PMDA-MAS）for Cr⁶⁺ adsorption.SH-functional groups have high infinity for mercury adsorption while polymetallic dianhydride could introduce more carboxyl and hydroxide groups for the adsorption of Cr⁶⁺.The experimental effects of the adsorbents are based on the results and the main conclusions as follows:Chitosan flakes were synthesized using grafting surface modification technique using thiol as the modifier.By modification,the surface area of chitosan increased from 110.2 to 168.04 m² g^-1.X-ray petroleum spectroscopy（XPS）and FTIR results showed that the surface of chitosan was combined with-SH groups.Adsorption performances of Hg²⁺ was investigated.Maximum Hg²⁺ removal efficiency of 98.8% at pH 6.SH-CNTs demonstrate a better absorption performance.Besides,SH-CNTs had a strong selectivity for Hg²⁺ over Zn²⁺,Cd²⁺,Mg²⁺,Pb²⁺.SH-CNTs show loss in adsorption capacity of 0.5 mg/g for Hg²⁺ after five cycles in the regeneration and reusability experiments;removal efficiency was > 90%,indicating an excellent capacity for the adsorbent to treat solutions containing mercury ions.kinetic and isotherm studies showed that the adsorption on SH-CNTs belongs to Pseudo-second-order kinetic model（R² = 0.972）and Freundlich isotherm model（R² = 0.99）.The maximum adsorption of capacity SH-CNTs for removal was achieved at 175.5 mg/g by Langmuir isotherm model fitting.XPS results after absorption showed that the high Hg²⁺ removal was attributed to the enhanced surface affinity due to the adequate-SH functional group on the material.PMDA was used for the modification of wooden almond shell powder using hydrothermal carbonization method for the adsorption of Cr⁶⁺ ions from the wastewater.PMDA-MAS the surface area increased from 126.2 to 148.6 m² g^-1.X-ray petroleum spectroscopy（XPS）and FTIR results showed that the surface of wooden almond shell powder was combined with PMDA functional groups.From the adsorption Performance results,PMDA-MAS promoted the removal of chromium ions from the wastewater at pH 2 attaining over all maximum removal efficiency of 98.6%.Results from the kinetics studies shows that Pseudo-secondorder kinetic model had a better fit with regression correlation coefficient R² > 0.9.Freundlich isotherm model also fitted the adsorption isotherm data（R² = 0.972）,The maximum adsorption capacity of PMDA-MAS for Cr⁶⁺ removal was achieved at 434.3 mg/g by Langmuir isotherm model fitting.Besides,PMDAMAS was partially selective for Cr⁶⁺ in the solution matrix for Zn²⁺,Cd²⁺,Mg²⁺,Pb²⁺.PMDA-MAS show loss in adsorption capacity of 0.42 mg/g for Cr⁶⁺ after five cycles in the regeneration and reusability experiments;removal efficiency was > 80%,indicating an excellent capacity for the adsorbent to treat solutions containing chromium ions.# of Figures 22,# of Tables 21,and # of References 299...