Calcium pyrophosphate dihydrate (CPPD) crystallization was investigated in a mixed‐suspension mixed‐product removal (MSMPR)‐type crystallizer in the presence of the amino acids L‐serine and L‐proline as additives. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential analysis were applied for characterization of the crystals obtained. CPPD crystals obtained in pure media consisted of aggregated particles which included plate‐like structures and rod‐shaped crystals. However, it was observed that agglomeration and breakage tendency on CPPD crystals obtained in the presence of amino acids were remarkable. The population balance equation for CPPD crystals was resolved with numerical analysis considering aggregation and breakage steps. The predominant mechanism was the breakage for CPPD crystallization in the presence of amino acids.
A multidimensional population balance model was applied to elaborate the effects of amino acids on the crystallization mechanisms of calcium pyrophosphate dihydrate crystals. Breakage and growth terms defined in the model were expressed in two dimensions depending on the sizes. The exponential hyperbolic function based on the particle sizes was selected for expressing the growth. The model was resolved by using the finite differences method. It was detected that in the nonadditive media, the growth along the length-1 is extremely dominant against both the growth along the length-2 and the breakage. However, it was discovered that the amino acids made the crystals more fragile, and the breakage at certain size ranges and certain concentrations of amino acids was the dominant mechanism. In any case, it was proven that both growth and breakage are suppressed considerably in the amino acid-containing media.
The solubility of calcium sulfate dihydrate (gypsum) was measured in HCl solutions in the presence of Cr 3+ and Fe 3+ ions at various temperatures. The results indicate that the solubility of gypsum is fairly dependent on the concentrations of HCl and impurities, i.e., Cr 3+ and Fe 3+ ions. The experimental data were analyzed by applying the Buchowski-Kiazczak (lh) model and the modified Apelblat model. Some thermodynamic parameters, such as the standard molar dissolution enthalpy, the standard molar Gibbs energy, and the entropy of solutions, were calculated by Van't Hoff analysis and Gibbs equation. The influences of the concentrations of both HCl and impurities, i.e., Cr 3+ and Fe 3+ ions, and temperature on the gypsum solubility were examined by applying the central composite design.
Diamonyum hidrojen fosfat kristallerinin büyüme ve çözünme hızları akışkan yataklı kristalizörde incelenmiştir. Deneyler, saf ortamda ve amino asitlerin farklı derişimlerde kullanıldığı koşullarda yapılmıştır. Amino asit katkısı olarak L-prolin ve L-asparajin kullanılmıştır. Büyüme hızı, aşırı doygunluk seviyelerine göre değerlendirilmiştir. Elde edilen sonuçlar incelendiğinde, L-prolin ve L-asparajin varlığında diamonyum hidrojen fosfat kristallerinin büyüme hızlarının saf ortama göre az da olsa bastırıldığı, buna karşılık çözünme hızlarının belirgin bir şekilde azaldığı tespit edilmiştir. Difüzyon ve entegrasyon olarak iki direncin kristal büyümesi üzerindeki bağıl etkinliğini değerlendirmek üzere, büyüme hızı verileri kullanılarak Damköhler sayıları ve etkinlik faktörleri hesaplanmıştır. Etkinlik faktörü sonuçlarına göre, hem saf ortamda hem de amino asit katkılı ortamlarda diamonyum hidrojen fosfat kristallerinin büyümesini kontrol eden mekanizmaya difüzyon ve entegrasyon adımlarının birlikte katkı sağladığı görülmüştür. Ancak saf ortamda entegrasyonun biraz daha yüksek etkiye sahip olduğu saptanmıştır. Bununla birlikte amino asitlerin varlığında, difüzyon basamağının etkinliğinin saf ortamdakine göre biraz daha arttığı görülmüştür. Bu artış, L-prolin amino asitinin en yüksek konsantrasyonunda en belirgin şekilde olmuştur. Ayrıca, ışık mikroskopunda çekilen görüntülerden, amino asitlerin varlığında büyüyen diamonyum hidrojen fosfat kristallerinin morfolojisinin saf ortama göre belirgin şekilde değiştiği görülmüştür.
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