Heavy -metal retention onto Palygorskite clay material

This thesis is devoted to the study of the retention and immobility of heavy metals onto clay material. The low cost of this material can make it very interesting for its potential use in different industrial activities with dumping of metals.;The main aim of this thesis is to know the capacity of a natural clay material for heavy-metal retention. The material studied is mainly composed by palygorskite and it is now a waste product. Both, the chemical and mineralogical composition have been determined in order to characterize it. Its porous texture has also been studied by means of adsorption isotherms of gases, intrusion porosimetry of mercury, thermal analysis, scanning electronic microscopy and zeta potential.;The retention processes of different metals (Cd, Cu, Ni and Zn) have been studied by means of kinetic and isotherm techniques. These techniques have been applied to an individual element or to a combination of different metals. Furthermore, the study was focused on the conditions affecting the retention efficiency: stirring, mixing time, absorbent doses, initial concentration of metals and the presence of different kind of anions. This study is applied to a real industrial dumping. The kinetic study allows one to know the time needed by the system to achieve the equilibrium. The isothermal study permits the knowledge of the different behaviors followed by the different metals. The multicomponent kinetic and isothermal study allows testing the competition among different metals for bonding with the surface centers of the material. Accordingly, multicomponent isotherms show a different shape and lower amount of retained metals than individual isotherms.;Finally, the chemical state of retained metals has been investigated by means of several techniques: x-ray diffraction, scanning electronic microscopy, x-ray fluorescence analysis and x-ray spectroscopy of fine structure (EXAFS). For instance, Cu is retained as atacamite whereas Zn is kept as a kind of oxyhydroxide. We have also studied the immobility conditions in the clay material. Our results show that this material is a good support for retaining heavy metals because it can confine these metals after an adequate thermal process. This process avoids the risk of leaching that could get the metals of the clay and it guarantees the protection of the environment.