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Crystals
Special Issues
Crystallization and Purification
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Crystallization and Purification

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Industrial Crystallization".

Deadline for manuscript submissions: 20 December 2025 | Viewed by 11641

Special Issue Editors

Dr. Kangli Li

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Guest Editor
Institute of Shaoxing, Tianjin University, Shaoxing 312300, China
Interests: polymorphism; nucleation; crystal growth; industrial crystallization; crystal engineering
Special Issues, Collections and Topics in MDPI journals
Dr. Mingyang Chen

E-Mail Website
Guest Editor
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
Interests: crystallization process; spherical crystallization; nucleation; crystal growth; crystal agglomeration; simulation; particle engineering
Special Issues, Collections and Topics in MDPI journals
Dr. Keke Zhang

E-Mail Website
Guest Editor
Biology+ Joint Research Center, School of Chemical Engineering and Technology, Zhengzhou University, Zhengzhou 450001, China
Interests: confinement crystallization; polymorph control

Special Issue Information

Dear Colleagues,

The modern industrial crystallization technology not only emphasizes the chemical purity of crystals, but also focuses on the control of their internal crystal structure and external morphology. With the increasing demand for high-end and high-value crystal products, such as in the electronics and information industries, crystallization technology has demonstrated advantages in separation and purification, as well as in the control of crystal morphologies.

This Special Issue of Crystals serves as a platform for researchers to report on the processes and mechanisms involved in utilizing crystallization technology for the separation, purification, and controlled preparation of high-value crystal products.

Dr. Kangli Li
Dr. Mingyang Chen
Dr. Keke Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • crystallization technology
  • separation and purification
  • polymorph regulation
  • crystal habit

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Published Papers (5 papers)

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Research

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16 pages, 6052 KiB  
Article
Crystal Form Investigation and Morphology Control of Salbutamol Sulfate via Spherulitic Growth
by Xinyue Qiu, Hongcheng Li, Yanni Du, Xuan Chen, Shichao Du, Yan Wang and Fumin Xue
Crystals 2025, 15(7), 651; https://doi.org/10.3390/cryst15070651 - 16 Jul 2025
Viewed by 280
Abstract
Salbutamol sulfate is a selective β2-receptor agonist used to treat asthma and chronic obstructive pulmonary disease. The crystals of salbutamol sulfate usually appear as needles with a relatively large aspect ratio, showing poor powder properties. In this study, spherical particles of salbutamol sulfate [...] Read more.
Salbutamol sulfate is a selective β2-receptor agonist used to treat asthma and chronic obstructive pulmonary disease. The crystals of salbutamol sulfate usually appear as needles with a relatively large aspect ratio, showing poor powder properties. In this study, spherical particles of salbutamol sulfate were obtained via antisolvent crystallization. Four different antisolvents, including ethanol, n-propanol, n-butanol, and sec-butanol, were selected, and their effects on crystal form and morphology were compared. Notably, a new solvate of salbutamol sulfate with sec-butanol has been obtained. The novel crystal form was characterized by single-crystal X-ray diffraction, revealing a 1:1 stoichiometric ratio between solvent and salbutamol sulfate in the crystal lattice. In addition, the effects of crystallization temperature, solute concentration, ratio of antisolvent to solvent, feeding rate, and stirring rate on the morphology of spherical particles were investigated in different antisolvents. We have found that crystals grown from the n-butanol–water system at optimal conditions (25 °C, antisolvent/solvent ratio of 9:1, and drug concentration of 0.2 g·mL−1) could be developed into compact and uniform spherulites. The morphological evolution process was also monitored, and the results indicated a spherulitic growth pattern, in which sheaves of plate-like crystals gradually branched into a fully developed spherulite. This work paves a feasible way to develop new crystal forms and prepare spherical particles of pharmaceuticals. Full article
(This article belongs to the Special Issue Crystallization and Purification)
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20 pages, 1786 KiB  
Article
Challenges in Resolubilisation of Rare Earth Oxalate Precipitates Using EDTA
by Mark Stephen Henderson, Laurence Gerald Dyer and Bogale Tadesse
Crystals 2025, 15(2), 103; https://doi.org/10.3390/cryst15020103 - 21 Jan 2025
Viewed by 1405
Abstract
The two-stage process for the treatment of rare earth phosphate minerals, involving an oxalic acid conversion leach and subsequent EDTA dissolution, has been demonstrated as a promising alternative to conventional extraction methods. To underpin a more detailed understanding, this work serves to further [...] Read more.
The two-stage process for the treatment of rare earth phosphate minerals, involving an oxalic acid conversion leach and subsequent EDTA dissolution, has been demonstrated as a promising alternative to conventional extraction methods. To underpin a more detailed understanding, this work serves to further develop knowledge of the linkage between the stages and key practical aspects of the operation of the EDTA dissolution. A more detailed treatment of the phenomena observed in the EDTA treatment, characteristics of the solids, mass loss in dissolution, and the impact of parameter alterations in both stages provide greater holistic knowledge of the proposed flowsheet and considerations that will need to be addressed when increasing scale. Acid production (indicated by a pH decrease) in the EDTA dissolution stage was shown to be a feature of the reaction and not of residual acid associated with the solids from the oxalic acid stage. The consistency with which the rare earths were dissolved with respect to the phosphorus provided greater confidence that Nd and Pr (greater dissolution than P) are recovered at a higher efficiency than Ce and La (poorer dissolution than P). This was only not the case at high solids loading across both tests, leading to both oxalate and EDTA-deficient systems, respectively. Under high conversion conditions, it was demonstrated that Nd and Pr recoveries into solution approaching 70% were achieved. This equated to in excess of 17 gL−1 of total rare earths in solution. Solid/liquid separation was shown to be a significant challenge, created by both the fine particle size distribution of the leached residue and the dispersant nature of EDTA. Full article
(This article belongs to the Special Issue Crystallization and Purification)
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16 pages, 4792 KiB  
Article
Leaching Efficacy of Ethylenediaminetetraacetic Acid (EDTA) to Extract Rare-Earth Elements from Monazite Concentrate
by Ammar S. A. Al Sheidi, Laurence G. Dyer and Bogale Tadesse
Crystals 2024, 14(10), 829; https://doi.org/10.3390/cryst14100829 - 24 Sep 2024
Cited by 1 | Viewed by 2825
Abstract
Alkaline EDTA solution has been previously identified as an effective leaching agent for solubilising rare-earth oxalates. These oxalates are the product of an oxalic acid conversion leach dissolving monazite and redepositing the salt. Pervious work suggested a significant increase in recovery was observed [...] Read more.
Alkaline EDTA solution has been previously identified as an effective leaching agent for solubilising rare-earth oxalates. These oxalates are the product of an oxalic acid conversion leach dissolving monazite and redepositing the salt. Pervious work suggested a significant increase in recovery was observed between pH 8 and 10; we have demonstrated that, in an excess of EDTA, this is not the case, and the dissolution is similar. While demonstrating that, at a nominal solid loading of 100 g/L, 0.2 M EDTA solution produced the highest dissolution, elevated solids require an equivalent increase in lixiviant concentration driven by consumption. Very-high-solution concentrations (>50 g/L dissolved TREEs) were achieved at a high solid loading, indicating both that a solution equilibrium is yet to be reached and that a build-up of oxalate in the system (estimated at ~1 M) does not impact the leach efficiency. We have also demonstrated the recycling of EDTA to use in multiple stages as well as the ability to recover oxalate from this solution. Full article
(This article belongs to the Special Issue Crystallization and Purification)
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12 pages, 4918 KiB  
Article
An Enhanced Deep Learning-Based Pharmaceutical Crystal Detection with Regional Filtering
by Yanlei Kang, Zhenyu Duan, Tianlei Tong, Xiurong Hu, Xiongtao Zhang, Hailong Hu and Zhong Li
Crystals 2024, 14(8), 709; https://doi.org/10.3390/cryst14080709 - 5 Aug 2024
Viewed by 1310
Abstract
In the process of pharmaceutical crystallization, the automatic detection of crystal shapes in images is important since controlling the morphology of the crystals improves the quality of pharmaceutical crystals. In this paper, a novel image detection method called RECDet is proposed. It leverages [...] Read more.
In the process of pharmaceutical crystallization, the automatic detection of crystal shapes in images is important since controlling the morphology of the crystals improves the quality of pharmaceutical crystals. In this paper, a novel image detection method called RECDet is proposed. It leverages an automatically adapted binary image to bypass background regions, thereby reducing the detection field. In addition, the method greatly reduces the training time while improving the detection accuracy by using a specially designed detection box for the crystal shape. The performance of our model is evaluated through experimental analysis on a publicly available glutamate crystal dataset and a self-made entecavir pharmaceutical crystal dataset. Experimental results show that RECDet improves the accuracy of prediction bounding boxes by more than 2% compared to other popular models and achieves a classification accuracy of 98%. It can be used as a promising tool in the application of pharmaceutical crystallization control. Full article
(This article belongs to the Special Issue Crystallization and Purification)
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Review

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20 pages, 3643 KiB  
Review
Prevention of Crystal Agglomeration: Mechanisms, Factors, and Impact of Additives
by Huixiang Zhang, Shichao Du, Yan Wang and Fumin Xue
Crystals 2024, 14(8), 676; https://doi.org/10.3390/cryst14080676 - 24 Jul 2024
Cited by 11 | Viewed by 5218
Abstract
Crystal agglomeration is a common phenomenon for most chemicals and pharmaceuticals. The formation of agglomerates usually lowers product purity and generates a broad particle size distribution. This review focuses on preventing agglomeration in solution crystallization, the storage of crystals, and pharmaceutical preparation processes. [...] Read more.
Crystal agglomeration is a common phenomenon for most chemicals and pharmaceuticals. The formation of agglomerates usually lowers product purity and generates a broad particle size distribution. This review focuses on preventing agglomeration in solution crystallization, the storage of crystals, and pharmaceutical preparation processes. The agglomeration mechanisms in these stages are analyzed and the effects of operating parameters are summarized. Furthermore, effective control means related to the crystallization environment are elaborated, including solvents, ultrasound, and additives. Special attention is paid to the influence of additives in preventing the aggregation of both suspensions and dried powders. Besides additives used in solution crystallization, the roles of anti-caking agents, stabilizers of nanosuspensions, and excipients of solid dispersions are also discussed. The additive type and properties like hydrophilicity, hydrophobicity, ionic strength, viscosity, the steric hindrance effect, and intermolecular interactions between additives and crystals can greatly affect the degree of agglomeration. Full article
(This article belongs to the Special Issue Crystallization and Purification)
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