Kinetic And Thermodynamic Studies On The Adsorption Of Heavy Metal Ions Onto Silica-supported Chitosan Composite Materials

With the rapid development of the global industry, the pollution of heavy metal ionsbecomes more and more serious gradually. Because of the improper deal of large quantity ofindustrial waste water, a large number of heavy metal ions flow into the food chain, whichbrings great bad effect to human health and survivals. As a result, it’s necessary to find anefficient, simple and inexpensive method to deal with the heavy metal ions. Scientists havealways been very concerned about the problems of pollution and treatment of heavy metalions. Now the methods which are commonly used for the treatment of heavy metal ions are asflows: chemical precipitation, oxidation and reduction, ion exchange and adsorption,electrolysis and so on. The method of adsorption is widely used because of its advantagessuch as low prices, a wide source of simple, high efficiency and no secondary pollution, etc.Chitosan founded widely in nature contains a lot of lively amino and hydroxyl ligandwhich can occur with some heavy metal ions, and it is non-toxic, readily biodegradable anddoes not bring secondary pollution. So the chitosan is attracting more attention in the field ofwastewater handling which contains heavy metal ions. However, chitosan is insoluble inwater, easy to swell and easily influenced by the pH, which results in the limits of its wideapplication. When chitosan is loaded on silica gel to generate silica-supported chitosancomposite materials, it can increase the proportion of chitosan microspheres and the specificsurface area, accelerate its settling velocity, while overcoming the single use of chitosan assome of the shortcomings in the adsorbent.This paper studied the adsorption of Ni²⁺, Co²⁺, and Zn²⁺in aqueous solution ontochitosan-silicone composite materials and the influence of physical and chemical parameterssuch as pH value, reaction time, temperature and initial concentration on the adsorptionprocess. It determined the optimal adsorption conditions. Kinetics and thermodynamics of theadsorption were also studied. In thermodynamics, the adsorption process was simulated withthe Langmuir isotherm balance model and Freundlich isotherm balance model. The resultsshowed that adsorption process of Ni²⁺and of Zn²⁺in aqueous solution is more applicable to Langmuir isotherm equilibrium model and Co²⁺is more applicable to the Freundlich isothermequilibrium model. In this way we can get the corresponding adsorption equilibrium constant,according to Van’t Hoff equation calculated the adsorption process thermodynamic parametersof G, H and S. In Dynamics, the adsorption process was simulated with pseudo-firstorder kinetics equation and pseudo-second order kinetics equation, and the result showed thatthe adsorption process of Ni²⁺, Co²⁺and Zn²⁺are in line with the pseudo-second order kineticsequation. With this model it calculates the apparent rate constant k and the equilibriumadsorption capacity Qeq, and then calculates the apparent activation energy Ea.