Interpretation of the Ultrasonic Effect on Induction Time During BaSO₄ Heterogeneous Nucleation by a Cluster Coagulation Model

Abstract

The effect of ultrasound on BaSO4 nucleation is studied by measuring the induction time when nucleation is predominantly heterogeneous. In the experiments, barium sulphate is used as the working substance precipitated by mixing aqueous BaCl2 and Na2SO4 solutions with relatively low concentrations compared to the experiments of homogeneous nucleation. It is observed that at a given supersaturation level, the induction time decreases significantly with increasing ultrasonic energy during heterogeneous nucleation. In addition, the effect of ultrasound on nucleation order and the nucleation coefficient in the empirical model of nucleation rate are also investigated and compared with the corresponding effects during homogeneous nucleation.

Solid Barium Sulfate Formation from Aqueous Solution: Re-examination of Key Literature and Kinetics of This Classic System in Search of a Minimum Mechanism of Formation

“…The use of balanced reactions detailing ones chosen set of standard conditions is recommended, as in eq provide herein. Relevant here are the suggestions and insights in Weber et al’s review where they note that a nucleation model needs to take into account rate variations due to stirring rates, ultrasonic energy input, changes in [NaCl], barium-to-sulfate ratio changes, as well as influences from solutes in solution such as additives to delay nucleation and Sr 2+ ions that are known to be included into barite crystals as an impurity . Dust control merits one more mention here as well. ,,, Fortunately, once again all these issues can at least in principle be dealt with via the PEStep approach of A → B (rate constant k 1 ) that has been able to deal with the following, again at least in the case of Ir(0) n particle formation reactions: mass-transfer limitations, the effects of pH, of H 2 O, of acetone solvent impurities, of trace EtOAc as an impurity, of nanocluster stabilizer, , of precursor concentration, , of dust, , and other effects that cause “super-sensitive” kinetics. Fifth, the use of multiple (ideally all), possible complimentary physical methods will help lead to greater mechanistic insights into (BaSO 4 ) n formation.…”

“…149 The use of balanced reactions detailing ones chosen set of standard conditions is recommended, as in eq 2 provide herein. Relevant here are the suggestions and insights in Weber et al's review 60 where they note that a nucleation model needs to take into account rate variations due to stirring rates, 66 ultrasonic energy input, 68 changes in [NaCl], 67 bariumto-sulfate ratio changes, 150 as well as influences from solutes in solution such as additives to delay nucleation 7 and Sr 2+ ions that are known to be included into barite crystals as an impurity. 145 Dust control merits one more mention here as well.…”

“…Weber et al note that BaSO 4 /barite holds potential as a prototype system for developing crystal nucleation, growth, recrystallization, and pore-scale reactive transport models, but state that there is “currently no mechanistic, quantitative predictive model for any mineral that includes nonclassical nucleation that could be scaled up...” (italicized emphasis is ours). Weber et al clearly state the need for the development of a reliable mechanism describing (BaSO 4 ) n formation, one that is based on non-classical nucleation to meet the mounting evidence against CNT in the case of (BaSO 4 ) n formation. , Weber et al further note that “...research has shown that nucleation rates are affected by a variety of chemical and physical processes that have not been incorporated into the classical nucleation theory terms”. − A recent publication from the same laboratory reiterates the importance of linking elementary processes to mineral nucleation when they state “we believe that kinetics expressions that reflect a series of elementary reaction processes by which nucleation reactions occur is necessary”a point we strongly agree with and emphasize as part of the present study. Indeed, many experimental studies of barite nucleation invoke CNT to rationalize results due to the lack of alternative, experimentally supported mechanisms for nucleation. , In short, both we , and Weber et al note the lack of, and therefore call for the development of, a reliable mechanism for BaSO 4 formation, leading to (BaSO 4 ) n particles, precipitates, or crystalline solids. ,, Consistent with this, a key goal of the present contribution is to establish a kinetics-based, PEStep minimum mechanism for the classic, prototype solid (BaSO 4 ) n formation system. ,,− It is hoped that any mechanistic insights extracted from the (BaSO 4 ) n system will serve not only as a working hypothesis going forward for the additional, modern kinetics and mechanistic studies that (BaSO 4 ) n merits, but also as mechanistic hypotheses for the formation mechanism(s) of other precipitation systems as well.…”

Studies of Mineral Nucleation and Growth Across Multiple Scales: Review of the Current State of Research Using the Example of Barite (BaSO4)

“…For example, stirring speed influences homogeneous barite nucleation 75 and induction time is inversely correlated with ultrasonic energy input. 76 As NaCl electrolyte concentration (up to 3 molar) increases, the induction period of barite decreases. 77 Other experimental studies indicate no change in barite nucleation rates in turbulent or laminar flow conditions.…”

“…Most experimental studies of barite indicate homogeneous nucleation occurs via classical nucleation mechanisms, but research has shown that nucleation rates are affected by a variety of chemical and physical processes that have not been incorporated into the classical nucleation theory terms. For example, stirring speed influences homogeneous barite nucleation and induction time is inversely correlated with ultrasonic energy input . As NaCl electrolyte concentration (up to 3 molar) increases, the induction period of barite decreases .…”