常压下Mn(Ⅲ)在Na-布塞尔矿向钙锰矿转化中的作用

Mn(Ⅲ) AVAILABILITY ON THE PHASE TRANSFORMATION FROM Na-BUSERITE TO TODOROKITE

隧道构造的钙锰矿以其特殊的结构和理化性质在催化、吸附、二次电池正极材料等领域有广泛的应用,常以层状Na-布塞尔矿(Na-buserite)为前驱物进行人工合成。焦磷酸盐(pH=1～8)对Mn(Ⅲ)有很强的络合作用,经焦磷酸盐处理的Na-布塞尔矿向钙锰矿转化的特点可表征Mn(Ⅲ)在层状向隧道构造转化中的重要作用。常压回流条件下Na-布塞尔矿向钙锰矿的转化程度随着焦磷酸盐处理浓度的增加和处理时间的延长而逐渐减小,直至不能向钙锰矿转化。钙锰矿形成的难易与Na-布塞尔矿结构中Mn(Ⅲ)被络合数量成反比,用对Mn(Ⅲ)络合作用很弱的焦磷酸盐溶液(pH=10)处理的Na-布塞尔矿可在常压回流条件下完全转化形成钙锰矿。

The todorokite-type manganese oxide molecular sieve materials have been found to have a wide variety of applications as catalysts, absorbents, and battery materials due to their unique structures and physical and chemical properties, and are commonly synthesized from layered Na-buserite. Pyrophosphate, which is known to form strong complexes with Mn（ Ⅲ） at a pH range of 1 - 8, was added in the suspension of Na-buserite in order to sequester available Mn（ Ⅲ ） of Na-buserite. Thus, the Mn（ Ⅲ ） availability is critical for the transformation from layered to tunnel structure of manganese oxide at atmospheric pressure. Significant transformation reductions were observed for pyrophosphate concentrations between 0 and 0. 05 moL/L at pH = 7. The Na-buserite treated with 0. 10 mol/L pyrophosphate at pH = 7, was hardly converted to todorokite at atmospheric pressure. The transformation from Na-buserite to todorokite decreased gradually with increasing treatment time from 1 hour to 24 hours when treated with 0. 05 mol/L pyrophosphate solution at pH = 7. However, no Mn（ II ） -pyrophosphate complex was formed in the solutions at pH = 10, instead the treated Na-buserites were completely converted to todorokite. The results showed that Mn（ Ⅲ ） complexes with the ligand pyrophosphate interrupted the transformation, and Mn（ Ⅲ ） played a key role in the transformation of layered Na-buserite to todorokite with tunnel structure at atmospheric pressure.