矿物表面基团与表面作用

Surface Function Groups and Surface Reactions of Minerals

矿物的表面或界面过程存在于一切地质过程中 ,并在材料和环境科学领域得到广泛应用。矿物的表面结构、表面基团与表面作用之间存在着一定的内在联系 ,矿物结构的多样性决定了表面基团类型的多种性和表面作用的多样性。本文较系统地介绍了矿物表面功能基、表面配位反应、表面配合反应、表面氧化还原反应、表面异位催化反应和表面离子交换反应的类型及作用机制。

Because the normal lattice is interrupted, there exists exc ess charge density at mineral surface in the 'dangling' bonds, which request the surface at oms to be reconstructed. All cleavage surfaces, which by definition have stoichi ometric numbers of surface anions and cations, are autocompensated. However, at fracture and growth surfaces, which can exhibit many possible stoichiometries, t he excess charge may not be autocompensated. In the latter case we refer to pola r surfaces. The polar surfaces are chemically active which can react with water in wet atmosphere or in solution and form hydroxyl functional groups. The surfac e hydroxyl together with surface permanent charges and Lewis site (or Bronsted s ite) as well as sulfhydryl groups of sulfides or salt groups of salt minerals co nstitute the main kind of surface functional groups of minerals. The surface fun ctional groups, which vary with changes of crystal structure and surface composi tion as well as surface topography of minerals, activate as functional groups of chemical agents and control the mineral surface reactivity with other ions and molecules in media. The major types of surface or interface reactions are coordi nation, complexation, oxidation-reduction and ionic exchange as well as heterog eneous catalysis. The driving force of surface reactions include polarity, charge, Lewis acidity a nd Lewis basicity. The surface coordination is resulted from the electrostatic a ttraction of adions and ionized surface, and depends on charges and radii of ad ions and medium condition as well as mineral surface structure. The functional g roups of organic compounds may form surface complexes with surface hydroxyl grou ps or Lewis site with a variety of arrangements on mineral surfaces. The surface ionic exchange is usually observed on the surfaces of sulfide and carbonate min erals. The sulfur atoms of sulfide minerals are electron donor as they react wit h high oxidation potential ions and may be oxidized to monomorphic sulfur or S 2O 3- 2- and SO 4- 2-. The heterogeneous catalysis is based on abi li ty of electron coupling of Lewis site or proton donor of Bronsted site on minera l surfaces. The mineral surface or interface reactions play an important role in the geoche mical processes of element cycling, for example, mineral dissolution and crystal growth are controlled by surface site concentration. The mineral surface functi onal groups and their reactivity are of great significance in material science a nd environmental science.