Study On The Adsorption And Passivation Of Nickel By K-feldspar Supported MnO₂

In this paper,K-feldspar?Kfs?was chosen as the raw material to prepare the MnO₂ supported Kfs composite?MnO₂/Kfs?.MnO₂/Kfs was applied to adsorb the nickel in wastewater and repair the soil polluted by nickel.The main research contents are as follows:?1?The MnO₂/Kfs has been prepared with MnO₂ as the modifier.The optimum preparation conditions of MnO₂/Kfs were determined by single factor test.The optimum preparation conditions of MnO₂/Kfs are as follows:the mass ratio of MnO₂to Kfs is 1:1,the reaction temperature is 40°C,the stirring time is 2 h,and the aging time is 24 h.Analysis of structural and surface morphology change before and after Kfs modification by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and specific surface area measurement?BET?.The result show that MnO₂ has been successfully loaded on Kfs,the surface morphology become rough and porous,and the specific surface area and total pore volume are increased compared with those before modification.MnO₂/Kfs is more conducive to the adsorption of heavy metal ions than Kfs.?2?This MnO₂/Kfs composite was used as a kind of adsorbing material to remove Ni²⁺from simulation wastewater.The influence of different factors on the adsorption performance of this composite was studied by static adsorption test,and the adsorption kinetics models,thermodynamic models and isotherm models were also discussed.The result showed that the increase of MnO₂/Kfs dosage,initial pH,adsorbed time and reaction temperature are all benefit for the improvement of its adsorption performance for Ni²⁺.With the MnO₂/Kfs dosage of 0.20 g,initial pH of 6,temperature of 25°C and adsorbed time of 10 h,this MnO₂/Kfs presented excellent adsorption performance in 20 mL Ni²⁺solution with the concentration of 100 mg·L^-1,the adsorption rate of Ni²⁺reached 90.68%.Under the above conditions,the adsorption capacity of MnO₂/Kfs on Ni²⁺is more than 7 times that of Kfs.The adsorption of kinetic equations and adsorption isotherm equations are both well fitted with the pseudo-second-order kinetics model and Langmuir adsorption isotherm model respectively.Above results indicated that the adsorption process belongs to monolayer chemisorptions.The maximum adsorption capacities of the MnO₂/Kfs are 14.217,22.114 and 27.217 mg·g^-11 when the temperature are 298,308 and 318 K respectively.The thermodynamic models parameters indicated that this adsorption process is a spontaneous,endothermic and entropy increasing process.Through the 4 adsorption and desorption cycle experiments showed that MnO₂/Kfs had good regeneration performance.?3?The MnO₂/Kfs composites were used as passivators for the repair of nickel-contaminated soil.The effects of the addition of passivating agents on the morphological changes of nickel in soil were studied.The results showed that with the dosage of MnO₂/Kfs,the content of bioavailable nickel in soil decreased gradually.The flexible form of nickel including exchangeable nickel and carbonate binding nickel were trasfored into iron-manganese oxides bounded nickel,organic matter bounded nickel and residual nickel,which were very stable and low bioavailable.The migration ability of nickel in soil is reduced,and the passivation effect of MnO₂/Kfs is more significant than that of raw material Kfs.The bioavailable content of DTPA?DTPA-TEA-CaCl₂?was significantly positively correlated with the exchangeable state,carbonate bound state,iron-manganese oxidation state,organic binding state and residual state.?4?The effects of Kfs and MnO₂/Kfs addition on the nickel content in the Chinese cabbage and the nickel form distribution in the soil were studied by pot experiment.The content of nickel enriched in Chinese cabbage was significantly positively correlated with the content of bioavailable nickel in the soil extracted by Tessier method and the content of bioavailable nickel extracted by DTPA.The addition of MnO₂/Kfs to nickel-contaminated soil can significantly reduce the content of bioavailable nickel in the soil,resulting in a decrease in the absorption and enrichment of nickel in Chinese cabbage.The more the amount of MnO₂/Kfs added,the smaller the bioconcentration factors of nickel in Chinese cabbage.Adding MnO₂/Kfs to the nickel-contaminated soil can reduce the absorption of nickel by plants and passivate the effect of heavy metal nickel in the soil.