Preparation Of Bentonite,diatomite Composite Material And Research On Removal Performance For Heavy Metals In Water

Water heavy metal pollution is an important branch of environmental pollution.With the development of ecological civilization awareness,adsorption materials have been widely used in purifying heavy metal pollution.The preparation of adsorbent materials is a problem that needs to be solved.Electrospinning technology is one of the effective technical means in the field of material preparation.Electrospinning technology has the advantages of simple equipment,low cost,low operation difficulty,and strong combination of multiple technologies.The prepared materials usually have large specific surface areas and many active sites,which can realize the functionalization of material design.At the same time,the materials are easy to collect.These advantages make electrospinning material be widely used in the removal of heavy metals in water.Bentonite(MMT)is a magnesium-calcium-aluminum-silicate-montmorillonite with ion exchange function.Diatomaceous earth(DE)is a natural amorphous siliceous mineral with an orderly pore structure inside which has an adsorption effect.MMT and DE are rich in minerals,low in price,and have a certain removal effect on heavy metal ions in water,but they are in a single function,suspended in aqueous solutions and not easy to separate in water.However,a single inorganic substance is not suitable as a precursor for electrospinning.Polyacrylonitrile(PAN)and sodium alginate(SA)are common raw materials for electrospinning.Therefore,modified polyacrylonitrile/bentonite(AOPAN/MMT)nanofibers were prepared by electrospinning in this thesis.Sodium alginate@Ca²⁺/diatomite(SA@Ca²⁺/DE)microspheres prepared by electrostatic spray were studied for removal performance of Cu²⁺and Pb²⁺in water,and the specific work is as follows:(1)Using MMT and PAN as raw materials,electrospinning to prepare composite nanofibers,and modifying them with hydroxylamine hydrochloride aqueous solution to obtain an amidoximated fiber material(amidoximation rate of 38%).The active site was increased to improve the adsorption of metal ions.The doping of AOPAN and MMT not only avoids the suspension of MMT in aqueous solution,but also improves the thermal stability of the fiber.Scanning electron microscopy(SEM)showed that the prepared fibers had a two-dimensional hemp-like rope shape.Thermogravimetric(TG)analysis showed that the presence of MMT increased the thermal stability of composite nanofibers.Fourier infrared spectroscopy(FTIR)analysis showed that MMT and PAN were successfully combined,and the cyano groups in the modified fibers were converted into amidoxime groups.The water contact angle experiment proved that doping and modification improved the wettability of the fiber,which was beneficial to the adsorption performance of the fiber in aqueous solution.Energy spectrum analysis(EDS)showed that the fiber material with amidoxime group had an adsorption effect on Cu²⁺and Pb²⁺ions.The adsorption capacities(mg·g^-1)of Cu²⁺and Pb²⁺by AOPAN/MMT fiber were 123.99and 105.35,respectively.The study of adsorption kinetics showed that the adsorption process of Cu²⁺and Pb²⁺ions by AOPAN/MMT fiber was more consistent with the quasi-second-order kinetic model,and the equilibrium time was 240 min.In thermodynamic research,the Langmuir isothermal model is superior to the Freundlich model to describe the thermodynamic process of the adsorption of two metal ions.The enthalpy changes(k J·mol^-1)are 29.85 and 13.66,respectively,and the entropy changes(J·mol^-1·K^-1)are 176.1 and 123.4 respectively.The above research shows that the adsorption process of Cu²⁺and Pb²⁺ions by AOPAN/MMT fiber is mainly chemical adsorption.(2)Using DE and hydrophilic SA as raw materials,electrostatic spraying to prepare SA/DE,and receiving with calcium chloride aqueous solution to obtain micro-spherical SA@Ca²⁺/DE,reducing the suspension of diatomaceous earth in aqueous solution and reducing the solubility of hydrophilic SA,so as to improve the stability of microspheres in aqueous solution and enhance the adsorption performance of heavy metals.SEM showed that the flake diatomaceous earth was distributed on the microspheres,and the prepared material had a ridged surface.TG analysis shows that diatomaceous earth improves the thermal stability of the microspheres.FTIR analysis showed that DE and SA@Ca²⁺were successfully recombined.EDS proved that SA@Ca²⁺/DE microspheres containing carboxylate had an adsorption effect on Cu²⁺and Pb²⁺ions.The adsorption capacity(mg·g^-1)of Cu²⁺and Pb²⁺by SA@Ca²⁺/DE were 92.3 and 137.9,respectively.Kinetic studies showed that the adsorption kinetics of Cu²⁺and Pb²⁺ions by the microspheres was more in line with the quasi-second-order kinetic model,with an equilibrium time of 180 min.In the thermodynamic study,the thermodynamic process of the adsorption of Cu²⁺and Pb²⁺ions by the microspheres is more consistent with the Langmuir model.The enthalpy changes(k J·mol^-1)are 26.26 and 23.34,respectively,and the entropy changes(J·mol^-1·K^-1)are 152.1 and 162.0,respectively,which is a spontaneous monolayer adsorption process based on chemical adsorption.In summary,two adsorbent materials were prepared in this thesis,AOPAN/MMT nanofiber and SA@Ca²⁺/DE microspheres,which have a good removal effect on Cu²⁺and Pb²⁺in aqueous solution,and are expected to be adsorbents for removing heavy metals from water.This treatment of heavy metals in water bodies provides theoretical foundation and technical support,and is of great significance to ecological environmental protection and ecological civilization construction.