Preparation Of Zr-MMT Hierarchical Porous Material And Its Adsorption Of Heavy Metals

Heavy metals in wastewater are difficult to be degraded and easily accumulated in the human body through the food chain,which have great harm to ecological environment and human beings.Sorption method is widely used in heavy metals' treatment.Previous study found that the charge of zirconium modified montmorillonite(Zr-MMT)nano composite adsorbent is negative,which has good adsorption properties to the positively charged heavy metals,such as Cu(?),Pb(?)and Cr(?I).To solve the problem that powder materials are difficult to separate from the aqueous phase in engineering application,zirconium-pillared montmorillonite porous ceramic was developed by gelcasting which required high calcination temperature,which resulted in the collapse of montmorillonite layer structure and the poor mechanical strength of the ceramic.Therefore,it is very important to find a suitable method to prepare porous adsorbent.In this study,Zr-MMT hierarchical porous material was developed from Zr-MMT by dry pressing technique combined with pore-forming agents,and to optimize the forming process.The static and dynamic adsorption properties of Pb(?)and Cu(?)by Zr-MMT hierarchical porous materials were investigated systematically.The important results of this dissertation were summarized as follows:(1)Zr-MMT hierarchical porous material was developed from Zr-MMT by dry pressing technique combined with pore-forming agents.The effect of the ratio of pore forming agent,pore forming dose,pressure on porosity and permeability coefficient,specific surface area(SSA),compressive strength of Zr-MMT hierarchical porous material were studied.The optimum conditions for forming Zr-MMT hierarchical porous material were: m(PMMA):m(AC)= 1:2,w(pore forming agent)=40%,pressure and calcination temperature were 20 MPa and550 ?,respectively.The porosity of Zr-MMT hierarchical porous material was up to 39.85% and have good permeability and compressive strength.The macropore of Zr-MMT hierarchical porous material was interpenetration and the hole wall presented three-dimensional honeycomb structure,which not only is advantageous to the fluid seepage,but also enhanced the Zr-MMT hierarchical porous material SSA.The isoelectric point of Zr-MMT hierarchical porous material was p H=4.3,when p H > 4.3,Zr-MMT hierarchical porous materials with negative charged and easy to absorb positive ions.(2)Static adsorption of Pb(?)and Cu(?)on Zr-MMT hierarchical porous material.The effects of adsorbent dosage,adsorption time,initial concentration and p H value on the adsorption of Pb(?)and Cu(?)and the adsorption kinetics,thermodynamic were investigated systematically.In addition,the competitive adsorption of Pb(?)and Cu(?),and the regeneration of Zr-MMT hierarchical porous materials were also explored.Results showed that Zr-MMT hierarchical porous material had a high adsorption rate for Pb(?)and Cu(?),which was a fast adsorption process.The Langmuir isotherm model and pseudo-second-order model matched the removal process well,indicating the adsorption process existed chemical adsorption,and the maximum adsorption capacity of Pb(?)and Cu(?)were 43.87 mg/g and38.01 mg/g,respectively.The thermodynamic parameters showed that the adsorption of Pb(?)and Cu(?)on Zr-MMT hierarchical porous material was a spontaneous endothermic process,and the increase of temperature was favorable to the adsorption process.The adsorption processes of Pb(?)and Cu(?)on Zr-MMT hierarchical porous materials include surface adsorption,electrostatic adsorption and ion exchange.Na+,K+,Ca2+ had little effect on Zr-MMT hierarchical porous material adsorption of Pb(?)and Cu(?)in natural water.when the Zr-MMThierarchical porous material was regenerated 4 times,the adsorption rate could reach more than 65%.After Zr-MMT hierarchical porous material adsorption(4 times)and desorption(4 times),the specific surface area decreased slightly,and the compressive strength decreased obviously,which still remained at 5~6 Mpa,The results showed that Zr-MMT hierarchical porous material has good application potential and prospect.(3)Fixed bed adsorption column studies were carried out to assess the breakthrough performance of Zr-MMT hierarchical porous material for the removal of Pb(?)and Cu(?)in aqueous solution.The effects of bed depths,flow rate and influent concentrations were evaluated.The Thomas and Adams-Bohart models were used to fit the breakthrough curves of dynamic adsorption and to evaluate the model characteristic parameters of the fixed bed.The research indicated that the effectively removal was achieved at high bed mass,low influent concentration and flow rate.After the dynamic adsorption of Zr-MMT hierarchical porous material,the specific surface area decreased obviously and the compressive strength could be maintained at 8~9 MPa.The Thomas model were found to describe experimental breakthrough curves well under different experimental conditions,while the Adams-Bohart model fairly described only the initial part of the breakthrough curve well.These simulation parameters provide reliable parameters for the industrial application of Zr-MMT hierarchical porous material.