Barite nucleation - Measuring effects of solution stoichiometry on crystal population and critical nuclei size

Abstract

Crystal growth is ubiquitous in natural and anthropogenic systems. Comprehension of the effects of solution stoichiometry on crystal growth is very limited. Barite is chosen as a model crystal due to its relevance in the hydrocarbon and geothermal industry and the effects of solution stoichiometry (raq {Ba2+}/{SO2−4}) varying between raq = 0.01 and raq = 100 on crystal nucleation are researched. The development is explored at different supersaturations. Supersaturation is defined as Ω = IAP/KSP where IAP is the ion activity product and KSP the solubility product. Ω = 100 and Ω = 500 in regards to barite are measured. A synergistic approach of dynamic light scattering(DLS), scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS) is used to determine the size of stable populations at different stoichiometries, the critical nucleus size and crystal shape. The dominant crystal size is 400nm (equivalent sphere) at all stoichiometries and supersaturation. At Ω = 100, the largest crystals are observed at raq > 1 and at Ω = 500 at raq = 1. Barium desolvation seems to be a limiting step in crystal growth. Critical nucleus size generally slightly decreases with increasing barium activity. There is a strong stoichiometric effect on crystal morphology, with a high shape variation at Ω = 500 and raq = 0.1 and raq = 10 and very limited effects at other measured stoichiometries. Varying stoichiometry is a promising solution to scale formation in geo-industry by inhibiting crystal nucleation through application of extreme stoichiometries modifying growing and nucleation behaviour.