水钠锰矿的Mn(Ⅲ)分布及Na_4P_2O_7溶液处理对其铅吸附性能的影响

Characterization of Pb^(2+) Adsorption on the Surface of Birnessite Treatment with Na_4P_2O_7 at Different pH and the Study on the Distribution of Mn(Ⅲ) in the Birnessite

以深入理解水钠锰矿结构中低价锰离子的含量及分布对其铅吸附性能的影响为目的,通过不同pH(pH为2、4、5)的焦磷酸钠溶液络合浸提酸性水钠锰矿结构中的Mn(Ⅱ)和Mn(Ⅲ),研究了浸提锰离子的形态、含量、矿物的锰平均氧化度和Pb2+的吸附量及其伴随Mn2+、H+释放量的变化.结果表明,锰平均氧化度为3.670的酸性水钠锰矿经不同pH焦磷酸钠溶液处理后,层结构边缘的Mn(Ⅲ)和部分层间Mn(Ⅲ)被络合出,结构中Mn(Ⅱ)含量很少,溶解出的Mn(Ⅱ)量只占溶出总锰量的4.70%～7.46%,处理后锰平均氧化度分别增大至3.783(pH=2)、3.786(pH=4)和3.824(pH=5).处理前后水钠锰矿的晶体结构没有发生改变,但是处理后矿物结构中位于八面体空位上下方的Mn(Ⅲ)减少,H+增多,可吸附Pb2+的空位位点数量增加,对Pb2+的最大吸附量增大.另外,探讨了处理前酸性水钠锰矿结构中Mn(Ⅲ)的分布,研究结果表明约有1/6的Mn(Ⅲ)位于层结构边缘区,另外约5/6的Mn(Ⅲ)位于层间和层结构非边缘区.

Acid birnessite was treated with Na4 P2 O7 at pH 2,4,5 respectively.After the treatments,the species and content of manganese ion in the complex solution,and the variation of average oxidation state（AOS） of Mn in birnessite,and the amount of adsorbed Pb2＋ and released Mn2＋,H＋ during the Pb2＋ adsorption were investigated.The results indicate that after acid birnessite,the AOS of Mn is 3.670 which is treated by Na4P2O7 at different pH,Mn（Ⅲ） located in the layer edge and part of Mn（Ⅲ） located in the interlayer are released to the solution through complexation with Na4P2O7.The content of Mn（Ⅱ） in the structure of original birnessite is very low.Small amount of Mn（Ⅱ）,which accounts for 4.70%-7.46% in the molar percentage of total released Mn,is also released simultaneously.The AOS of Mn of birnessites after treatment increases to 3.783（pH 2）,3.786（pH 4）,3.824（pH 5） respectively.While the crystal structure of birnessite does not change after treatment,the amount of Mn（Ⅲ） located above or below vacant cation sites decreases,and the amount of H＋ located above or below vacant cation sites goes up in the structure of birnessites.The amount of vacant cation sites responsible for Pb2＋ adsorption increases,which lead to the increase of the maximum amount of adsorbed Pb2＋.Additionally,the distribution of Mn（Ⅲ） in the structure of acid birnessite is deduced.About one sixth of Mn（Ⅲ） locates in the layer edge,and five sixths of Mn（Ⅲ） locates in the interlayer and the non layer edge.