水钠锰矿(Birnessite)对Mn2+持留机理的研究

本试验研究了一种合成水钠锰矿对Mn²⁺的持留机理和Mn²⁺被吸附后的去向,并进一步探讨了三种锰盐溶液(MnSO₄,MN(NO₃)₂和MnCl₂)对水钠锰矿晶体结构变化的影响。.试验结果表明,水钠锰矿对MN²⁺离子的吸附包括专性吸附和非专性吸附。随着吸附后的老化过程,吸附在矿物表面的锰逐渐扩散到晶格内,其置换性随之降低。.在MnSO₄,Mn(NO₃)₂和MnCl₂溶液中,水钠锰矿最终转化成六方锰矿(Nsutite),一种比水钠锰矿更稳定,结晶更好的晶体。MnSO₄溶液在加入水钠锰矿后pH值比其它两种溶液高,除生成六方锰矿外还形成大量拉锰矿(Ramsdellite)。随着生成新矿物的老化,最初被吸附的Mn被固定在晶格内而失去其置换性和生物有效性。

MECHANISM OF ADSORPTION OF Mn2+ ONTO A SYNTHETIC BIRNESSITE

Adsorption of Mn²⁺ onto birnessite is very rapid and amounts adsorbed are several times higher than its cation exchange capacity. The nature and fate of the adsorption, however, were not well understood. Thus experiments were conducted to investigate the mechanism of adsorption of Mn²⁺ onto a synthetic birnessite and effects of three Mn-salts (MnSO₄, MnCl₂ and Mn(NO₃)₂) on mineralogical alteration of birnessite.The results indicated that adsorption of Mn²⁺ onto birnessite included both specific and non specific adsorption. The adsorbed Mn²⁺ was incorporated into the structure of birnessite and its extrability by salts decreased with time of aging. After reaction of birnessite with MnCl₂ or Mn (NO₃)₂ solution, incorporation of Mn²⁺ into he structure caused transformation of birnessite into nsutite (Mn oxide hydroxide, γ-Mn (O, OH)₂). In the solution of MnSO₄, birnessite was convened into nsutite and a larger quantity of ramsdellite (Mn oxide, MnO₂) . Both newly formed minerals are more stable and better crystallized than birnessite. Thus the Mn²⁺ initially adsorbed onto birnessite became the component of the newly formed minerals and was fixed in the structure after structural conversion of birnessite and finally lost its extractability and availability.