Impact of Solution {Ba²⁺}:{SO₄^2–} on Charge Evolution of Forming and Growing Barite (BaSO₄) Crystals: A ζ─Potential Measurement Investigation

Effect of Solution Stoichiometry on BaSO4 Crystallization from Turbidity Measurements and Modeling

“…The choice of KCl as the background salt was motivated by preliminary experiments at r aq,0 = 1, where it showed faster BaSO 4 formation kinetics than with NaCl. Additional preliminary measurements with NaCl at r aq,0 = 0.001 and r aq,0 = 1000 (see Supporting Information 2) indicated that this effect of background salt is rather small compared to the impact of stoichiometric ratio and supersaturation, in agreement with findings by Seepma et al 23 The growth solutions were filtered using a syringe with a 0.2 μm filter, before the Ba-containing and SO 4 -containing growth solutions were mixed. Hence, the possible presence of dust particles that could induce heterogeneous nucleation was avoided.…”

“…There is also a significant outlier at SI 0 = 2.3 and r aq,0 = 100 possibly due to a shift in crystallization or morphology. 23 For t n , a less consistent trend over r aq,0 is observed, and this varies for SI 0 . To better visualize the different trends depending on SI 0 and r aq,0 , we have included additional plots over SI 0 in Supporting Information 7.…”

“…For r aq,0 ≠ 1, it is expected that some of the surplus ions adsorb to the surface of crystal seeds since a surface charge was measured in these cases. 23 This amount is likely still small compared to the overall material formed.…”

“…Since at r aq,0 ≠ 1, the amount of particles is smaller, it is expected that neglecting aggregation has a smaller impact on our results, and aggregation would not affect the overall trends in J over r aq,0 . Additionally, as a surface charge was measured for r aq,0 ≠ 1, 23 the particles might behave as charge-stabilized colloids preventing aggregation. 49 If aggregation would then only impact r aq,0 = 1, a larger effect of solution stoichiometry is expected as the nucleation rate at r aq,0 = 1 would be higher.…”

“…Previous studies on the effect of solution stoichiometry on BaSO 4 precipitation − indicated that it can influence the particle size, morphology, or induction time (here defined as the time between setting the supersaturation and observing new particles, which can vary depending on the type of measurement). From studying the growth of BaSO 4 on a substrate for a range of ionic ratios using atomic force microscopy, , it was revealed that the growth rate is reduced by orders of magnitude for strongly nonstoichiometric conditions, while growth can be stimulated by a small Ba 2+ surplus.…”