成核
过饱和度
结晶
方解石
化学工程
纳米颗粒
动态光散射
结块
降水
化学
晶体生长
粒径
粒子(生态学)
材料科学
化学物理
结晶学
物理化学
有机化学
催化作用
沸石
物理
工程类
海洋学
气象学
地质学
作者
Jonas Addai‐Mensah,T.N. Khmeleva,John C. Thomas
摘要
Sodium aluminosilicate (SAS) crystallization from supersaturated caustic liquors is of high industrial significance with regards to intractable heat exchanger precipitation fouling issues in Bayer process alumina refining and high level nuclear waste processing. In the present work, isothermal (65 °C) homogeneous nucleation behavior of nanocolloidal SAS particles in optically clear solutions as a function of time was investigated by dynamic light scattering (DLS). At a high SiO2 relative supersaturation (σ) of 12, the solution was perennially metastable, reflecting a long nucleation induction time of 12 h. Upon ephemeral preheating at 100 °C, and/or a 25–40% increase in σ, the DLS analysis showed that rapid nucleation and moderate particle growth occurred in the optically clear solutions. Furthermore, evolution uni-, bi-, and trimodal particle size distributions in the range of 20–1800 nm with time was observed, accompanied by significant time-dependent distribution broadening effects. For growth mechanisms, both nanoparticle aggregation and surface integration of ionic growth units are revealed, manifesting in polydispersed, low mass density-contrast agglomerates in optically clear liquors. The SAS solid product observed after prolonged crystallization was high carbonate-sodalite crystals, comprising agglomerates of nanoparticles. The pivotal roles played by SiO2 supersaturation and temperature in the early stages of sodalite nucleation and growth are demonstrated by the results.
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