含Ni六方水钠锰矿的表征及其对Pb^(2+)(Zn^(2+))环境行为的影响

CHARACTERIZATION OF Ni-RICH HEXAGONAL BIRNESSITE AND ITS EFFECT ON BEHAVIOR OF AQUEOUS Pb^(2+)(Zn^(2+)) IN ENVIRONMENT

六方水钠锰矿是土壤中普遍存在、活性最强的氧化锰矿物。它常常富集各种过渡金属如Ni等,对其地球化学行为具有重要影响。在六方水钠锰矿形成过程中加入Ni2+,Ni以+2价存在于矿物中。进入水钠锰矿结构中的Ni大部分以[NiO6]八面体形式存在于层内;部分Ni存在于八面体空位上下方。含Ni水钠锰矿沿c轴方向堆叠锰氧八面体层数逐渐减小,而a-b板面晶体大小没有明显变化,即层片状晶体逐渐变薄,比表面积显著增大。随着Ni含量的增加,水钠锰矿结构中锰氧八面体空位数减少,而层边面吸附位点数基本保持不变,其对重金属离子(Pb2+/Zn2+)吸附去除能力逐渐降低。本文为明确过渡金属离子(Ni)对土壤中氧化锰矿物的形貌、结构及其性质的影响提供了参考。

Hexagonal birnessite,ubiquitous in soils,is the most reactive manganese oxide,which often enriches itself with various transition metals,such as Ni,etc.thus significantly affecting its own geochemical behavior.Ni2＋ is added when birnessite is being formed,and stays in the mineral in the form of positive bivalence.Part of the Ni ions that have entered into the structure of birnessite exist in the layers as [Ni（Ⅱ）O6]octahedra,and the other portion above or below the octahedra vacant sites.For these Ni-containing birnessite crystals,the number of octahedron layers that are stacked coherently along the c axis gradually decreases,while the size of the a-b plane does not change much,that is to say,the crystals become thinner,thus making their surface areas larger.With the increase in Ni content,the number of vacant sites decreases,while that of binding sites along the edges of the layers remains almost constant.Consequently,Pb2＋/Zn2＋ adsorption capacity of the birnessite attenuates.These findings may provide some insights into the effect of some transition metals,like Ni on the morphology,structure and properties of manganese oxide mineral in the soil.