Studies On Preparation Of Composites Based On Melamine-modificated Bentonite And Its Adsorption Properties For Hg(Ⅱ)

Mercury,as a special toxic heavy metal pollutant which is liquid,volatile,migratory,transformable,bio-enriched and difficult to degrade at room temperature,has attracted worldwide attention in recent years.In October 2013,87 countries and regions including China,Japan and Brazil signed the Minamata Convention on Mercury(the Minamata Convention)to prevent mercury from polluting the environment and human health in Kumamoto,Japan.China is the largest country to use and emit mercury.It is considered to be the country most threatened by mercury pollution.At present,the problem of environmental mercury pollution in China is extremely prominent.In order to do a good job in the prevention and control of mercury pollution and the implementation of the mercury convention,our government listed mercury as a key heavy metal pollutant in the 12 th Five-Year Plan for the Comprehensive Prevention and Control of Heavy Metal Pollution,and in the 13 th Five-Year Plan for the Protection In the plan,it is clearly put forward that the control of mercury pollution should be strengthened.In this context,it is of great scientific value and practical significance to seek economical and efficient mercury removal technology and materials.Adsorption is a method to remove pollutant from water or soil by using adsorbent materials.It is considered to be the most promising treatment method for mercury pollution.Bentonite is a kind of clay mineral with abundant reserves and certain ion exchange performance.It is an excellent adsorbent widely used in wastewater treatment.In this study,bentonite was used as raw material to prepare bentonite modified by different acids,bentonite modified by melamine under different acidic conditions and bentonite modified by melamine phosphate.The structure of bentonite modified by different methods was characterized by means of FT-IR,SEM and XRD.The adsorption properties of this series of bentonite on Hg(Ⅱ)ions were compared.The results show that acid modification,melamine modification in acidic system and direct modification of melamine phosphate can increase the interlayer spacing of bentonite.Melamine successfully enters the interlayer of bentonite.The introduction of melamine can significantly enhance the adsorption performance of Bentonite for Hg(Ⅱ)ions.By investigating the effects of pH,adsorption time,concentration of the solution,the amount of the intercalating agent melamine phosphate,and the pH of the solution during the intercalation reaction on the adsorption properties of melamine modified bentonite for Hg(Ⅱ),it was found that: when the pH of the solution is 4-6 and the concentration is lower than 100mg/L,the melamine phosphate modified bentonite has the best adsorption performance for Hg(Ⅱ),and the adsorption reaches equilibrium after about 24 h.When the pH of the solution is 7.92 and the dosage of intercalating agent is 2 times of the cation exchange modulus of the bentonite used,the prepared melamine phosphate intercalated bentonite sample has the best adsorption performance for Hg(Ⅱ).The adsorption behavior of melamine phosphate intercalated bentonite for Hg(Ⅱ)conforms to quasi-secondary kinetics and Langmuir isothermal adsorption model.Comparing the adsorption performance of the sample for other heavy metal ions,it was found that the melamine phosphate intercalated bentonite sample had a certain adsorption selectivity for Hg(Ⅱ).By comparing the adsorption properties of various heavy metal ions,it is found that the melamine phosphate modified bentonite sample has certain adsorption selectivity for Hg(Ⅱ)ions.In order to further develop new and efficient mercury adsorption materials,we have prepared chitosan-gelatin/melamine intercalated bentonite composites by compounding melamine phosphate intercalated bentonite with chitosan and gelatin.The structure of the composites was characterized.It was found that the compounding of melamine phosphate intercalated bentonite with chitosan and gelatin was not a simple physical mixing.The interlayer structure of bentonite was destroyed to a certain extent,and the composited sample appears as a porous layered structure.The adsorption performance of chitosan-gelatin/melamine intercalated bentonite composite on Hg(Ⅱ)was studied.The results showed that the chitosan-gelatin/melamine intercalated bentonite composite has good adsorption performance for Hg(Ⅱ)ions.When the mercury ion concentration in the solution is 200mg/L,the adsorption capacity can reach 98.99mg/g.The adsorption capacity and removal rate can reach a higher level after 2 hours of adsorption.When the mass ratio of gelatin to chitosan in the prepared chitosan-gelatin/melamine intercalated bentonite composite is 1:9,and the content of melamine phosphate intercalated bentonite is 10%,the adsorption performance for Hg(Ⅱ)is the best.The adsorption process of Hg(Ⅱ)ion on chitosan-gelatin/melamine intercalated bentonite composite conforms to quasi-second-order kinetic model and Langmuir adsorption isotherm model.In addition,by comparing the adsorption properties of various heavy metal ions,it was found that chitosan-gelatin/melamine intercalated bentonite composite has good adsorption selectivity for Hg(Ⅱ)ions.