Influence of semi-batch operation on the precipitation of natrojarosite particles from sulfate solutions

• Published in: Journal of crystal growth Vol. 342; no. 1; pp. 50 - 56
• Main Authors: Sandré, Anne-Laure, Gaunand, Alain
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2012; Elsevier
• Subjects: A1. Computer simulation; A1. Crystal morphology; A1. Nucleation; A1. Supersaturated solution; B1. Minerals; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystals; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Iron; Materials science; Mathematical models; Methods of crystal growth; physics of crystal growth; Nucleation; Physics; Precipitation; Reactors; Solubility, segregation, and mixing; phase separation; Sulfates; Supersaturation; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; A1. Computer simulation; A1. Nucleation; A1. Supersaturated solution; A1. Crystal morphology; B1. Minerals; Particle size; Nucleation; Growth rate; Roughness; Crystal seeds; Computerized simulation; Dispersions; Minerals; Crystallites; Precipitation; Supersaturated solution; Sodium sulfate; Iron additions; Crystal morphology; Crystal structure; Cubic crystals; Secondary nucleation; Habit plane; Iron III; Growth mechanism; Nanostructured materials; Computer simulation
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2011.03.064

The precipitation of natrojarosite from iron sodium sulfate solutions has been investigated at temperatures close to the atmospheric boiling point, in batch and semi-batch conditions. Semi-batch conditions make it possible to maintain a weaker iron concentration in the stirred reactor, leading to lower supersaturations, closer to those in continuous and possibly seeded MSMPRs or tanks—in series units. In these reactors, primary and secondary nucleations are few, allowing the growth of pure mono-crystalline particles of controlled size and size dispersion. Both modi operandi lead to agglomerates made of crystals of cubic habit. The surface of cauliflower-like particles from the batch modus operandi displays overlaying crystals, of size between 100 and 400nm. The particles from the semi-batch mode, with moderate iron addition, are rougher and show bigger intergrown constitutive crystals of size up to a few microns, which denotes lesser secondary nucleation and more growth. A model is developed to characterize iron(III) and sulfate speciation with non-ideal behavior in the mother solution. It is used to compare the variations of supersaturation in the reactor between the batch and the semi-batch conditions. During the first 500min, the supersaturation resulting from a moderate addition of iron is 10,000–10 times lower than during batch kinetics, which agrees with the reduction of secondary nucleation suggested by scanning electron micrographs. The semi-batch technique, which can be combined with the addition of support particles, is worth further work, aiming to reduce secondary nucleation and to determine the crystallite growth rate expression of natrojarosite as a function of supersaturation, using the model of solution developed in this work. ► Formation of natrojarosite in batch and semi-batch reactors. ► Control of size and morphology of natrojarosite. ► Model for iron(III) and sulfate speciation with non-ideal behavior in the solutions.