Experimental Study on Surface Reactions of Heavy Metal Ions With Quartz—Aqueous Ion Concentration Dependence

Adsorption of divalent metal ions, including Cu\+\{2+\}, Pb\+\{2+\}, Zn\+\{2+\}, Cd\+\{2+\} and Ni\+\{2+\}, on quartz surface was measured as a function of metal ion concentration at 30℃ under conditions of solution pH=6.5 and ion strength I=0.1mol/L. Results of the experimental measurements can be described very well by adsorption isotherm equations of Freudlich. The correlation coefficients (r) of adsorption isotherm lines are >0.96. Moreover, the experimental data were interpreted on the basis of surface complexation model. The experimental results showed that the monodentate coordinated metal ion surface complex species (SOM\++) are predominant over the bidentate coordinated metal ion surface complex species \ formed only by the ions Cu\+\{2+\}, Zn\+\{2+\} and Ni\+\{2+\}. And the relevant apparent surface complexation constants are lgK\-M=2.2-3.3 in order of K\-\{Cd\}≥K\-\{Pb\}>K\-\{Zn\}>K\-\{Ni\}≥K\-\{Cu\}, and lgβ\-M=5.9-6.8 in order of β\-\{Ni\}>β\-\{Zn\}>β\-\{Cu\}. Therefore, the reactive ability of the ions onto mineral surface of quartz follows the order of Cd>Pb>Zn>Ni>Cu under the above mentioned solution conditions. The apparent surface complexation constants, influenced by the surface potential, surface species and hydrolysis of metal ions, depend mainly on the Born solvation coefficient of the metal ions.