Preparation Of Hydroxyiron/Hydroalumium And Polyethyleneimine Montmorillonites And Their Adsorption Properties For Hexavalent Chromium From Aqueous Solution

Montmorillonite is widely used as adsorbent for the removal of heavy metal ions in water due to its large specific surface area,good cation exchange,interlayer negative electricity and well water swelling capacity.Hexavalent chromium is one of a highly toxic carcinogen,which widely exists in industrial wastewater such as paint manufacturing,leather tanning,metal polishing and electroplating.With the characteristics of persistence,non-biodegradability and mobility,hexavalent chromium seriously threatens to human health and ecosystem.Therefore,it is of great significance to remove hexavalent chromium effectively from wastewater.In this dissertation,two novel modified montmorillonite adsorbents（Fe/Al-Mt and PEI-Mt）were prepared for the purpose of developing a new efficient and eco-friendly adsorbent,and applied to remove hexavalent chromium in water.The effects of various factors such as contact time,initial concentration of hexavalent chromium,solution pH,coexisting anions and temperature on the adsorption were investigated.The whole adsorption process and mechanism were discussed by analyze relevant adsorption results and characterization,which aim to provide some useful reference for the design of montmorillonite-based adsorbent and their application in water treatment.Two main research works are as follows:Seven kinds of polymeric hydroxyiron/hydroxyaluminum montmorillonite（Fe_xAl_y-Mt）complexes were prepared using ion exchange method.The structure,composition and surface charge of the modified and raw montmorillonite were analyzed by XRD,FT-IR and Zeta potential.The pesudo first-order and second-order kinetics were used to describe the adsorption kinetics,and the whole adsorption process data could be well fitted by pesudo-second-order kinetics model.Under the condition of initial hexavalent concentration of 50mg·L^-1,pH=6.0,adsorbent dosage of 8g·L^-11 and adsorption temperature of 27℃,various modified montmorillonite showed different adsorption capacity.Among them,（5:1）Fe/Al-Mt had the best performance of adsorption on Cr（Ⅵ）and the adsorption capacity reached 4.995mg·g-1,the removal rate of Cr（Ⅵ）was 99.91%,which increased 99.46%in comparison with raw montmorillonite.The following were（15:1）Fe/Al-Mt and Fe-Mt,whose adsorption capacity of Cr（Ⅵ）are 4.7038 mg·g-1 and 4.672 mg·g-1,which increased 90.22%and 90.19%in comparison with raw montmorillonite,respectively.The adsorption capacity of seven modified montmorillonite was ordered as follows:（5:1）Fe/Al-Mt>（15:1）Fe/Al-Mt>Fe-Mt>（1:1）Fe/Al-Mt>（1:15）Fe/Al-Mt>Al-Mt>（1:5）Fe/Al-Mt.It can be summarized that hydroxyl iron/hydroalumium montmorillonite is potentially valuable for removal of hexavalent chromium from aqueous solution.A new adsorbent,Polyethyleneimine-montmorillonite（PEI-Mt）was successfully synthesized via ion exchange method for the removal of hexavalent chromium from aqueous solution.The materials were characterized by SEM,XRD,XPS,BET and Zeta potential.In order to illustrate the whole experiment mechanism clearly,the effects of contact time,initial concentration of hexavalent chromium ions,pH value,coexisting anions and temperature on the adsorption were investigated.The results showed that the adsorption capacity positively correlates with temperature and negatively with the solution pH value.Simultaneously,certain ionic strength was conducive to the adsorption of hexavalent chromium.The adsorption kinetics fitted to a pseudo-second-order kinetic model and the adsorption could by described by Langmuir model.The maximum adsorption capacity of the adsorbent could reach 24.558 mg·g^-11 at the condition of hexavalent chromium initial concentration of300mg·L^-1,pH=3.0 and T=25℃.With the characteristics of convenient preparation and brilliant adsorption capacity,PEI-Mt was expected to be an economical adsorbent for the removal of hexavalent chromium.