Applied Centre for Structural and Synchrotron Studies, University of South Australia, Mawson Lakes, SA 5095, Australia.
Langmuir. 2010 Aug 17;26(16):13227-35. doi: 10.1021/la100088n.
The flocculation and solid/liquid separation of four well-characterized kaolinites (2 well, 2 poorly crystallized) have been studied for comparison of surface structure (SEM), aggregate structure during flocculation (cryo-SEM), settling rate, and bed density (with raking). It is shown that major differences in these properties are largely due to crystallinity and consequent surface structure of the extensive (larger dimension "basal") face. Well-crystallized kaolinites, with higher Hinckley indices and lower aspect ratios, have relatively smooth, flat basal surfaces and thicker edge planes promoting both effective initial bridging flocculation (largely edge-edge) and structural rearrangement to face-face during the raking process. This results in faster settling rates and more compact bed structures. Poorly crystallized kaolinites, with low Hinckley indices and high aspect ratios, exhibit ragged, stepped structures of the extensive face with a high proportion of nanosized islands forming cascade-like steps (i.e., multiple edges) contributing up to 30% of the specific surface area and providing flocculant adsorption sites (hydroxyl groups) across this extensive face. This leads to bridging flocculation taking place on both edge and extensive ("basal") planes, producing low-density edge-face structures during flocculation which leads to slow settling rates and poor bed densities. In particular, the complex surface morphology of the poorly crystallized kaolinites resists the transformation of edge-face structures to dense face-face structures under shear force introduced by raking. This results in low sediment density for poorly crystallized kaolinites. The studies suggest that the main influence on settling rates and bed densities of kaolinites in mineral tailings is likely to be related to the crystallinity and surface morphology of the kaolinite. They also suggest that interpretation of kaolinite behavior based on models of a flat (001) basal plane and edge sites only at the particle boundaries is not likely to be adequate for many real, less-crystallized kaolinites.
已对四种特征明确的高岭石（2 种结晶良好，2 种结晶较差）的絮凝和固/液分离进行了研究，以便对其表面结构（SEM）、絮凝过程中的聚集结构（冷冻扫描电镜）、沉降速率和床密度（耙）进行比较。结果表明，这些性质的主要差异主要归因于广泛（较大尺寸“基面”）面的结晶度和由此产生的表面结构。结晶良好的高岭石，具有较高的欣克利指数和较低的纵横比，具有相对光滑、平整的基面和较厚的边缘平面，有利于有效初始桥接絮凝（主要是边缘-边缘）和在耙过程中结构重排为面-面。这导致更快的沉降速率和更紧凑的床结构。结晶较差的高岭石，欣克利指数低，纵横比高，具有广泛面的粗糙、阶梯状结构，纳米级岛屿的比例很高，形成级联状台阶（即多个边缘），占比高达 30%的比表面积，并提供了絮凝剂吸附位点（羟基）跨越这个广泛的表面。这导致在边缘和广泛（“基面”）面都发生桥接絮凝，在絮凝过程中产生低密度的边缘-面结构，导致沉降速率慢和床密度差。特别是，结晶较差的高岭石的复杂表面形态在耙子引入的剪切力作用下，抵抗边缘-面结构向密集的面-面结构的转变。这导致结晶较差的高岭石的沉积物密度低。研究表明，高岭石在矿物尾矿中的沉降速率和床密度的主要影响因素可能与其结晶度和表面形态有关。它们还表明，基于平面（001）基面和平行于颗粒边界的边缘位点的模型来解释高岭石的行为，对于许多实际的、结晶度较低的高岭石来说，可能是不够的。
