Graham Trent R, Gorniak Rafal, Dembowski Mateusz, Zhang Xin, Clark Sue B, Pearce Carolyn I, Clark Aurora E, Rosso Kevin M
Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.
Inorg Chem. 2020 May 18;59(10):6857-6865. doi: 10.1021/acs.inorgchem.0c00258. Epub 2020 Apr 7.
Crystallization of Al-bearing solid phases from highly alkaline NaO:AlO:HO solutions commonly necessitates an Al coordination change from tetrahedral to octahedral, but intermediate coordination states are often difficult to isolate. Here, a similar Al coordination change process is examined during the solid-state recrystallization of monosodium aluminate hydrate (MSA) to nonasodium bis(hexahydroxyaluminate) trihydroxide hexahydrate (NSA) at ambient temperature. While the MSA structure contains solely oxolated tetrahedral Al, the NSA structure is a molecular aluminate salt solely based upon monomeric octahedral Al. Spontaneous recrystallization of MSA and excess sodium hydroxide hydrate into NSA over 3 days of reaction time was clearly evident in X-ray diffractograms and in Raman spectra. single-pulse Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and Al multiple quantum (MQ) MAS NMR spectroscopy showed no evidence of intermediate aluminates, suggesting that transitional states, such as pentacoordinate Al, are short-lived and require spectroscopy with greater time resolution to detect. Such research is advancing upon a detailed mechanistic understanding of Al coordination change mechanisms in these highly alkaline systems, with relevance to aluminum refining, corrosion sciences, and nuclear waste processing.
从高碱性的NaO:AlO:HO溶液中结晶含铝固相通常需要铝的配位从四面体变为八面体，但中间配位态往往难以分离。在此，研究了在室温下单水合偏铝酸钠（MSA）固相重结晶为六水合双（六羟基铝酸）九钠三水合物（NSA）过程中类似的铝配位变化过程。虽然MSA结构仅包含氧配位的四面体铝，但NSA结构是一种仅基于单体八面体铝的分子铝酸盐。在3天的反应时间内，MSA和过量氢氧化钠水合物自发重结晶为NSA，这在X射线衍射图和拉曼光谱中清晰可见。单脉冲铝魔角旋转（MAS）核磁共振（NMR）光谱和铝多量子（MQ）MAS NMR光谱未显示中间铝酸盐的证据，这表明过渡态，如五配位铝，寿命很短，需要具有更高时间分辨率的光谱来检测。此类研究正在推动对这些高碱性体系中铝配位变化机制的详细机理理解，这与铝精炼、腐蚀科学和核废料处理相关。
