Electrochemical properties of barium sulfate precipitation membranes

Impact of Solution {Ba2+}:{SO42–} on Charge Evolution of Forming and Growing Barite (BaSO4) Crystals: A ζ─Potential Measurement Investigation

“…When r aq < 1, at excess sulfate conditions, the ζ-potential was slightly negative (about −20 mV; Figure a), while the ζ-potential was slightly positive (about +25 mV; Figure e) when r aq > 1, at excess barium. Although this has not been reported previously for nucleation experiments, it has been reported by numerous researchers for barite particles in barium or sulfate-excess conditions near equilibrium. ,,,,− Since the Ba 2+ -ions and SO 4 2– -ions in the solutions can adsorb specifically on the particle surface, their ratio in solution has a large influence on the surface potential and thus the ζ-potential (i.e., these are PDIs). Note that it has been shown previously that BEs such as Na + -ions and Cl – -ions can also interact with the particle surfaces. − Under low ionic strength conditions ( I < 0.1 M), such BE ions only affect the charging of the diffuse double layer and, in that case, are considered to act as indifferent ions, which means that they cannot cause a sign reversal for the surface charge but may affect and even reverse the sign of the ζ-potential ,− (see also Section .).…”

“…This is in agreement with previous work at similar conditions and Gallardo et al (2000) showed that the ζ-potential is approximately +5 mV (at I = 0.02 M, pH ∼ 6, r aq = 1, and with NaCl as BE). Under these conditions, most other investigations reported slightly positive ζ-potential values as well ,, and attributed this to the preferential release of SO 4 2– from the barite crystal structure. Contrastingly, barite crystals in pure water (or with an I up to ∼0.001 M) were reported to carry a slightly negative charge, ,,,, more comparable to our initial observations at r aq = 1.…”

“…Barite formation was slower at extreme sulfate limitation than at equivalent barium-limited conditions. It is well-known that barite particle charge, in terms of zeta potential (ζ-potential), is affected by various physicochemical conditions (i.e., varying pH, ionic strength, chemical composition of solution matrix, temperature, and r aq ) in aqueous solutions at or near equilibrium, − but none have investigated the ζ-potential evolution from nonequilibrium to equilibrium conditions. In addition to the effect of r aq on barite nucleation and growth rates, we expect that r aq also has a significant impact on the surface charge development of Barite crystals during nucleation and growth, altering the crystal’s electrokinetic properties.…”

“…Multitudinous scientific studies have been dedicated to investigating the (rates of) nucleation and growth of barite on both the industrial level as well as from a fundamental perspective. − In both settings, some of that research has been dedicated to the effect of stoichiometry ( r aq ; where r aq = {Ba 2+ }:{SO 4 2– }) on bulk processes, like crystal growth rates, − induction times, and nucleation . It was found that barite nucleation and growth depend strongly and asymmetrically on r aq at a constant degree of supersaturation and pH ∼ 6.…”

Acid‐Base‐Equilibria at Semipermeable Membranes, their Influence on pH‐Triggered Permeabilities

“…The energy well caused by the adsorbed S04--ions is assumed to be less efficient than the energy barrier due to the adsorbed Ba + + ions (cp. [7,8]). A Na + ion crossing the membrane from the left has to surpass the right flank of the well and the left flank of the barrier (both drawn as bold lines).…”