Adsorption Of Heavy Metal Ions Of Pb(?) And Cr(?)by Modified Vermiculite

In today's world water environment,pollution caused by heavy metal ions,especially lead,chromium and other heavy metal ions,becomes increasingly severe that causes serious harm to human health.As an important component of the Earth's surface,clay mineral,which has the properties of fine particle size and large surface area,can be used to control the migration and enrichment of heavy metal ions with its variable charge surface of heavy metal ions adsorption,desorption,precipitation,oxidation and reduction,which so as to play a role in the self-purification of heavy metal ion.As a layered silicate clay mineral,the specific surface area and ion exchange capacity of the vermiculite can be improved through modification,then it can be used for lead,chromium and other heavy metal ions adsorption purification in the water.The selected vermiculite was from Hebei Lingshou,whose chemical composition,morphology and crystal structure of vermiculite were characterized by optical microscopy,X-ray diffraction,X-ray fluorescence spectroscopy,scanning electron microscopy.The vermiculite was modified by three methods of high temperature modification,CaCl₂ modification and MnO₂ modification,and then their morphologies were characterized.The adsorption effect of vermiculite on heavy metal ions Pb???and Cr???was detected by ICP-OES and the effect before and after modification was compared with the change of the amount of vermiculite,the time of adsorption and the pH value of the solution.The main conclusions of this paper are as follows:1.Vermiculite is formed by weathering and hydrothermal alteration of biotite and phlogopite,accompanied by hydration,oxidation,and loss of K+ and Fe3+.2.The main mineral phases of vermiculite are vermiculite,biotite,pyroxene,apatite,chlorite.The main chemical composition and content are: w?SiO₂?=44.97%,w?Al₂O₃?=18.34%,w?Fe₂O₃?=14.12%,w?MgO?=12.04%,w?K₂O?=5.80%,w?CaO?=2.38%,w?TiO?=1.54%.3.The vermiculite ground to 100 meshes with specific surface area of 53.48 m2/g and pore size of 10.59 nm,vermiculite has great adsorption property due to its large specific surface area,the layered structure and good cation exchange capacity.4.The order of adsorption rate of vermiculite,expanded vermiculite,MnO₂ modified vermiculite and CaCl₂ modified vermiculite on Pb???is as follows: CaCl₂ modified vermiculite > MnO₂ modified vermiculite > expanded vermiculite >vermiculite.5.It is showed that the best adsorption rate of ore vermiculite to Pb???is 96.066% with dosage of 0.25 g,adsorption time of 60 min,and pH value of 6 while the rate up to 99.428% after modified by CaCl₂.6.The maximum adsorption rate of vermiculite to heavy metal Cr???,mainly determined by pH value,is only 12.54% with dosage of 0.5g,adsorption time of 60 min,and pH value of 2.7.The order of adsorption rate of expanded vermiculite,MnO₂ modified vermiculite and CaCl₂ modified vermiculite on Cr???is as follows: expanded vermiculite > MnO₂ modified vermiculite > CaCl₂ modified vermiculite.The maximum adsorption rate is 67.74%,58.42%,and 7.742% respectively.