Browsing by Subject "Crystallisation"

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    The effect of a morphology modifier on the precipitation behaviour of nickel powder
    (Elsevier, 2006) Ntuli, Freeman; Lewis, Alison Emslie
    The effect of a morphology modifier on the precipitation process of nickel powder was investigated in order to develop an understanding of its mechanism of action. Experiments were conducted on a pilot-plant scale using a 75-L autoclave with modifier dosages in the range of 0.25–5 vol%. Samples were collected from each successive batch reduction within a cycle and the powder was separated from the liquor before being washed and dried for subsequent analysis. The active particle rate processes were identified by transforming the particle size distribution (PSD) data into moments and from the change in surface area as measured by the BET method. Scanning Electron Microscopy (SEM) micrographs of the powder were used to observe the powder morphology and to validate the proposed particle rate processes and mechanism of action of the modifier. Evolution of the first moment (m0) and third moment (m3), equivalent to the total number of particles and volume, respectively, indicated that growth and aggregation were the major particle rate processes at a modifier dosage of 0.25 vol%. Breakage became apparent at dosage levels above 0.25 vol%. A decrease in BET surface area was noted in each cycle, indicating the presence of aggregation. The magnitude of decrease in the surface area indicated that the extent of aggregation decreased with increasing modifier dosage. SEM micrographs revealed that the powder was compact and aggregated at modifier dosages between 0.25 and 3 vol% and that loose porous powder was produced at 5 vol%. The modifier was found to inhibit growth, resulting in the formation of weaker agglomerate bridges leading to shear-induced breakage. This led to an increase in the surface area available for reduction. However, the effect of increased surface area in promoting reduction was outweighed by growth inhibition above a modifier dosage of 1 vol%. Thus, the number of attainable batch reductions increased when the modifier dosage was increased from 0.25 to 1 vol% and decreased with further increases in modifier dosage.
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    Industrial Crystallization: Fundamentals and Applications
    (Cambridge University Press, 2015-07-01) Lewis, Alison Emslie; Seckler, Marcelo; Kramer, Herman; Rosmalen, Gerda
    Bridging the gap between theory and practice, this text provides the reader with a comprehensive overview of industrial crystallization. Newcomers will learn all of the most important topics in industrial crystallization, from key concepts and basic theory to industrial practices. Topics covered include the characterization of a crystalline product and the basic process design for crystallization, as well as batch crystallization, measurement techniques, and details on precipitation, melt crystallization and polymorphism. Each chapter begins with an introduction explaining the importance of the topic, and is supported by homework problems and worked examples. Real world case studies are also provided, as well as new industry-relevant information, making this is an ideal resource for industry practitioners, students, and researchers in the fields of industrial crystallization, separation processes, particle synthesis, and particle technology.
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    Recovery of Na2SO4·10H2O from a reverse osmosis retentate by eutectic freeze crystallisation technology.
    (Elsevier, 2010) Reddy, S T; Lewis, A E; Witkamp, G J; Kramer, H J M; van Spronsen, J
    The increasing amount of waste water and effluent from South Africa’s mining industry forms a growing problem, which processing requires sustainable solutions in which both the water and the dissolved component can be reused. Eutectic freeze crystallisation (EFC) has been identified as a key technology that is not only energy efficient, but also produces ice and salt products of high quality. Unlike reverse osmosis membrane systems, EFC can treat both dilute and concentrated systems minimising waste water volumes. In this paper it is shown that freeze and eutectic freeze crystallisation can be used for the processing of a reverse osmosis retentate stream containing 4% NaSO4 and a number of impurities (F, Cl, K, Li, Mg, Ca, NO3 and NH4), producing both pure water and NaSO4•10H2O crystals. The influence of the impurities on the eutectic point and on the crystal structure of mirabilite was investigated using EFC technology investigated for a pure binary system, for a synthetic reverse osmosis retentate as well as for a concentrated NaCl system. In addition, investigations into the recovery and purity of mirabilite for these streams were conducted.