Surface Properties Of Diatomites And Their Adsorption Mechanism Of Pb(Ⅱ)

The research on the surface properties of the diatomites and their adsorption mechanism of Pb(II) not only can provide theoretical basis and technical support for the diatomite adsorption of lead and other heavy metal ions, but also better eliminate lead and other heavy metals pollution, protect the environment, develop and utilize the cheap, environmentally friendly diatomite resource.In this thesis, first, the diatomite sample with porous honeycomb structure has a BET specific surface area of 10.21m2/g and large numbers of surface hydroxyl functional groups(≡Si-OH, ≡Fe-OH, and ≡Al-OH) by using nitrogen adsorption/deadsorption isotherms, TG-DSC, FTIR, and XPS. The optimized surface dissociation constants(i.e. log K1, logK2) and their surface site concentration parameter values(i.e. logC) of each surface reactive site of the 600 oC calcinated diatomite have been calculated by the ProtoFit program using continuous acid-base potentiometric titration data, and the surface species distribution calculated by program PHREEQC3.1.2 using the optimizedlogK1, logK2 and logC parameter values were obtained.The second, the adsorption of Pb2+ showed that adsorption was highly pH dependent and the kinetics of the adsorption followed a pseudo-second-order model. The adsorption data of Pb2+ fitted well with the Langmuir and Freundlich isotherm equation. The lead adsorption onto the calcined diatomite is mainly spontaneous physisorptionprocess.Then surface complexation equilibrium constants and surface species distribution of Pb2+ on the calcined diatomite were calculated by the PEST and PHREEQC computer programs, thus, the adsorption behavior and modeling of Pb(II) ions onto the calcined diatomite has been elucidated adequately.To solve the problems of the convenient separation and adsorption selective of Pb2+, the 3-mercaptopropyltrimethoxysilane was use to modify the surface of diatomite and then the Fe3O4 nanoparticles were incorporated on the surface of diatomite. Finally, the new magnetism–diatomite material was obtained. The new sorbent can be easily separated and collected by an external magnetic field within 2min, and the adsorption data of Pb2+fitted well with thepseudo-second-order model.