| The continuous development of the industrial economy gradually enhances people’s live standard,however,the attendant water heavy metals pollution has been become a global environmental issue.Duo to the surge of anthropic production activity and the improper managements,water heavy metal pollution has caused serious threats to the sustainable developments of public health,ecological environment and social economy.Adsorption technology used to treat the heavy metal wastewater has been attracted worldwide attention owing to its efficiency and excellent development prospect.Then the development of adsorbents with excellent adsorption properties and specific selectivity has been become one of the most popular research directions in this field.Generally,water heavy metal pollution is diverse due to the different pollution sources,and heavy metals,with bioaccumulation and biodegradability,are easily taken in human body and have an affinity with various organs,finally lead to the teratogenicity,carcinogenicity and mutagenicity.Based on the above analyses,this paper mainly focuses on the design and construct of the eco-friendly adsorbents with stable chemical property,easy separation,high adsorption capacity,excellent adsorption efficiency,simple preparation,low cost and obvious selectivity to Pb（Ⅱ）.Owning to the special advantages of chitosan in the physicochemical properties and adsorption application,a series of novel spongy composite adsorption materials with excellent structure and adsorption properties were successfully prepared by chitosan which was served as a precursor.The physicochemical properties of the prepared adsorbents were tested and analyzed through SEM,EDX and FTIR.A series of batch adsorption experiments were conducted to investigate the adsorption capacities of the novel spongy adsorbents under the different environmental conditions and to determine the optimal adsorption conditions.The kinetics,isotherm adsorption and thermodynamic models were built to study the rate limiting step and adsorption mechanisms and to evaluate the maximum adsorption capacities.The effects of different eluants on the desorption efficiency were also performed to evaluate the reproductivity of the adsorbents.On the other hand,a column reactor was designed to investigate the effects of the flow rate,column height and influent concentration on the removal of heavy metal ions.Building the mathematical models,analyzing the breakthrough curves and treating the simulated actual industrial wastewaters were used to predict and evaluate the application potential of the novel spongy adsorbents,finally provide the theoretical bases for practical application.The results of this paper were summarized as follows:1.A simple procedure using the eco-friendly and low-cost chitosan as a precursor at room temperature was developed to prepare a xanthate-modified thiourea chitosan sponge（XTCS）by lyophilization.The as-prepared adsorbent was characterized of large volume and light weight,uniform and abundant pores,tunable sharp and dimension as well as high chemical stability,and endowed the potential application value by the properties including remarkable adsorption efficiency,wide pH application range and fast solid-liquid separation ability.Results showed that the pseudo second-order kinetic equation and Langmuir isotherm model were suitable to describe the Pb（Ⅱ）adsorption behavior of XTCS,indicating that the adsorption of Pb（Ⅱ）on XTCS was a chemical adsorption taken placed on the homogenous and single adsorption surface.The analyses of the chemical composition and structural performance of XTCS before and after adsorption were indicated that Pb（Ⅱ）removal mechanism of XTCS was mainly dependent on complexations of sulfur and nitrogen atoms and ion exchange.The optimal p H was 5,and the adsorption process attained equilibrium in 45 min with a maximum adsorption capacity of 188.044 mg g-1 at room temperature.Thus,the removal percentage of Pb（Ⅱ）was more than 90%,when the concentration of Pb（Ⅱ）was lower than 200.00 mg g-1.2.Sponge-like xanthate-modified chitosan with a three-dimensional network macroporous structure was prepared using a facile one-pot approach.The preparation process had less demand of raw materials,moderate reaction conditions and easy operation.The studies showed that cryogenic processing could help to obtain XCTS with attractive appearance,uniform pores and excellent mechanical property.Adsorption properties of Pb（Ⅱ）,Cd（II）,Ni（II）,and Zn（II）on XCTS were systematically investigated in single and multiple systems.The results showed that the adsorption of each heavy metal ion on XCTS was homogenously chemical adsorption.The maximum adsorption capacities of Pb（Ⅱ）,Cd（II）,Ni（II）,and Zn（II）were 216.452,92.854,45.462,and 41.883 mg g-1,respectively,indicating that XCTS had an obviously adsorptive selectivity to Pb（Ⅱ）.The studies in multiple systems indicated that Cd（II）inhibited but Ni（II）and Zn（II）promoted Pb（Ⅱ）adsorption.The inhibitory effect and equilibrium adsorption capacity ratios suggested that the coexisting heavy metal ions had a synergistic promoting effect on Pb（Ⅱ）adsorption,however,Pb（Ⅱ）had a remarkbale antagonistic effect on the adsorption of coexisting heavy metal ions.The competitive adsorption behaviors of Pb（Ⅱ）in multiple systems were successfully described by the Langmuir and Langmuir competitive models.The results indicated that there was a competitive adsorption among these heavy metal ions,and the adsorption capacities of Pb（Ⅱ）in multiple systems were higher than that in single system with the highest adsorption capacity of 248.764 mg g-1.The results of FTIR and XPS suggested that the removal mechanisms of heavy metal ions by XTCS were ion exchange and complex reactions among sulfur/nitrogen atoms and heavy metal ions.The selectivity coefficient and distribution ratio revealed the selective adsorption sequence of the different heavy metal ions on XCTS was as follows: Pb（Ⅱ）> Cd（Ⅱ）> Ni（Ⅱ）> Zn（Ⅱ）.3.Pseudomonas putida I3 and Talaromyces amestolkiae Pb respectively combined with xanthate-modified thiourea chitosan sponge（PXTCS and TXTCS）were prepared and used to investigate the ability of Pb（Ⅱ）removal from solutions.The prepared biosorbents possessed a three-dimensional macroporous structure convenient for separation.The adsorption performances of PXTCS and TXTCS were evaluated under batch mode.Results indicated that the additions of P.putida I3 or T.amestolkiae Pb biomass obviously enhanced the adsorption capacities of composite biosorbents toward Pb（Ⅱ）in comparison with XTCS which was free of biomass addition.The maximum biosorption capacities of PXTCS and TXTCS were 232.033 and 241.611 mg g-1,respectively.It was demonstrated that the optimal additive mass ratios of P.putida I3 and T.amestolkiae Pb to TCTS were 40%（0.40 g）and 15%（0.15 g）,which made the biosorption capacities enhance 39.4% and 44.7%,respectively.The results of kinetics and isotherm models revealed that the chemical adsorption and intraparticle diffusion were the rate limiting steps of Pb（Ⅱ）biosorption on the two biosorbents,and the biosorption occurred on the homogenous surface.For the effects of co-existing metal ions on Pb（Ⅱ）biosorption,Cd（II）played a negative role while Zn（II）had an obviously promoting effect,and for major inorganic ions,the one with low valence had more obviously promoting effect on Pb（Ⅱ）biosorption than the one with high valance.The promoting degree on Pb（Ⅱ）biosorption followed the sequence:Zn（Ⅱ）>Na（I）≈K（Ⅰ）>Ca（Ⅱ）>Mg（Ⅱ）≈Al（Ⅲ）?Cd（Ⅱ）>Fe（Ⅲ）.Moreover,0.5 M HNO3 and 2.0 M HCl both had efficient desorption effect on Pb（Ⅱ）.The results of FTIR and XPS suggested that the removal mechanisms of heavy metal ions by PXTCS-40% and TXTCS-15% were complex reactions among S/N atoms and Pb（Ⅱ）,ion exchange and microprecipitation.Both prepared biosorbents were effective in removing heavy metals from simulated industrial effluent containing various trace-levels heavy metal ions or high concentration Pb（Ⅱ）.4.Titanate nanotubes（TNTs）were firstly synthesized by hydrothermal method and then loaded on sponge-like xanthate-modified chitosan（XCTS）to transform into the composite adsorbent XCTS@TNTs.The adsorption of Pb（Ⅱ）on XCTS@TNTs was systematically investigated through static batch adsorption and dynamic column adsorption experiments.Results of kinetics,isotherm adsorption and thermodynamics indicated that the adsorption behavior of Pb（Ⅱ）on XCTS@TNTs well followed the pseudo-second-order kinetics and Langmuir isotherm model,and the adsorption was spontaneous and exothermic.The solution pH had a significant effect on Pb（Ⅱ）adsorption which was a positive relationship.The maximum adsorption capacities of Pb（Ⅱ）on XCTS@TNTs at the temperature of 25,35 and 45 ℃ were 342.466、335.570 and 324.675 mg g-1,respectively.XCTS@TNTs could be reproduced in 1 M HCl.The effect of ion strength on Pb（Ⅱ）adsorption by XCTS@TNTs was dependent on the valance of cation,Pb（Ⅱ）adsorption capacity of XCTS@TNTs increased with increasing the Na（I）concentration,while Ca（II）concentration had an insignificantly promoting effect on Pb（Ⅱ）adsorption.The results of the effects of co-existing metal ions on Pb（Ⅱ）adsorption indicated that XCTS@TNTs had an obvious preference to Pb（Ⅱ）,and the coexisting heavy metal ions had a synergistic promoting effect on Pb（Ⅱ）adsorption,however,Pb（Ⅱ）had a remarkbale antagonistic effect on the adsorption of coexisting heavy metal ions.Furthermore,the studies of column adsorption experiments showed the flow rate,column height and influent concentration all significantly influenced the removal of Pb（Ⅱ）.Two simulated industrial wastewaters were treated using the fixed-bed.The results indicated when the Pb（Ⅱ）concentration from the uppermost sampling port reached no more than 1.00 mg L-1,which met the Integrated wastewater discharge standard,the processing capacities of the mining and smelting plant wastewater and the acid battery wastewater by XCTS@TNTs were about 49584.00 and 6360.00 mL,respectively,indicating that XCTS@TNTs had an excellent application potential. |
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