Experimental Study On Application Of Modified Zeolite To Disposal Of Waste Water Containing Heavy Metal Contamination

The harm of heavy metal pollution wastewater to environment and human beings is widely known nowadays.Therefore it is environmentally significant to deal with wastewater containing heavy metals.Zeolite is a kind of hydrated silicoaluminate mineral with numerous connected holes and frame structures.Because of its special crystal chemical structure,zeolite has the properties of ion-exchange,efficient selective adsorption and catalysis etc.,which enables it to purify all kinds of wastewater.Natural zeolite is abundant in China and its price is low.It is often used as water treatment adsorbent since it has large surface area.However,the adsorption performance of natural zeolite is limited.As a result,scientific researches aiming at improving its adsorption performance have gained extensive attention.The experiment conducted single modification to natural zeolite through NaOH,H2SO4,NaCl solution and then on the basis of this,high temperature roasting composite modification was conducted.The study about modified zeolite's ability of adsorbing heavy metal ions Pb²⁺and Cd²⁺in water under the condition of certain adsorbing time,adsorbing temperature,pH,zeolite amount and the initial concentration of the heavy metal ion solution was conducted.Experimental results show that the modified zeolite,which has been modified through NaOH solution and400?high-temperature roasting,performs the best in removing heavy metal ions Pb²⁺and Cd²⁺.The physicochemical properties of zeolite before and after its modification were analyzed through the following three test methods:surface area measurement,scanning electron microscopy and Fourier transform infrared spectroscopy.The microscopic differences between natural and modified zeolites in all aspects were shown and the exchange adsorption mechanism of the modified zeolite was investigat-ed in this paper.Therefore,a theoretical basis for the development and further processing of natural zeolites can be provided.In the polluted wastewater which was compounded from Jianhu lake,the Pb²⁺concentration is 201.35mg/L,pH is 6.3,adsorption temperature is 25?,and the adsorption time 30 minutes.When the zeolite amount is 1.5g,the removal rate reached 99.89%.The Cd²⁺concentration is 200.15mg/L,PH is 6.7,The adsorption temperature is 25?and the adsorption time is 50 minutes.When the zeolite amount is 2g,the removal rate reached 98.99%.The saturated adsorption amount on heavy metal ion Pb²⁺of composite modified zeolite,NaOH modified zeolite,H2SO4 modified zeolite,NaCl modified zeolite and natural zeolite are 200 mg/g,106.383 mg/g,102.0408 mg/g,82.6446 mg/g and 59.5238mg/g,respectively.Their saturated adsorption amount on heavy metal ions Cd²⁺are 129.8701mg/g,70.9219mg/g,53.1915mg/g,28.9017mg/g and18.2483mg/g,respectively.The adsorption of natural zeolite on heavy metal ions Pb²⁺and Cd²⁺conforms to the first-order kinetics equation.And the adsorption of composite modified zeolite,NaOH modified zeolite,H₂SO₄ modified zeolite and NaCl modified zeolite on heavy metal ions Pb²⁺and Cd²⁺conforms to the second-order kinetic equation.This shows that the modified zeolites are more inclined to chemical adsorption,which proves the effect of modification on zeolites.Elovich equation fitting parameters show that the adsorption processes of zeolites on Pb²⁺and Cd²⁺before and after the modification is heterogeneous adsorption.The particle diffusion model tells that particle diffusion process is not the only control process of the adsorption of two kinds of zeolites on Pb²⁺and Cd²⁺.