Kinetics of the crystallization of barium chromate

Antonious, M. S.; Ramsis, M. N.; Youssef, A.M.

doi:10.1007/bf00807405

Cited by 3 publications

(4 citation statements)

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“…The adsorption of polymer mainly inhibits the crystal growth of barium chromate, which can be shown by SEM and particle size measurements of bare and covered barium chromate particles, where at sufficiently high polyelectrolyte concentration, polyelectrolyte is able to retard or to block the crystallization process by adsorption at active growth sites of the crystal surface, 16 leading to smaller barium chromate particles in the presence of QUAT. Since the mechanism of the barium chromate crystallization is a surface-controlled growth mechanism, 20 the decrease in the particle size resulted from the inhibition of particle growth rather than the lack of aggregation of primary particles. Polymer adsorption on barium chromate particles can enhance the dispersion stability through electrostatic and/ or steric stabilization mechanisms, leading to a slower sedimentation rate due to repulsive forces.…”

Section: Discussionmentioning

confidence: 99%

“…It has been reported that the barium chromate crystallization occurs by a surface-controlled growth mechanism. 20 The study of the adsorption behavior of polyelectrolytes in relation to the crystal growth kinetics of barium sulfate indicate that the adsorption of poly(phosphinoacrylate), poly(acrylic acid), poly(styrenesulfonic acid), poly(vinylsulfonic acid), and a copolymer of maleic acid and vinylsulfonic acid disturbs the growth rate of barium sulfate. 7,8,15,16 Williams et al 9 described the adsorption of an amphoteric polymer, a copolymer of diallyldimethylammonium chloride (QUAT) and acrylic acid, on barium sulfate crystals and demonstrated its ability to greatly enhance the colloid stability of a barium sulfate dispersion.…”

Section: Introductionmentioning

confidence: 99%

“…Polyelectrolytes can have the tendency to adsorb at the surface of solid dispersed particles, the level of adsorption depending on factors such as the nature of the particle surface, the concentration and chemical structure of polymer, and the solvent quality of the dispersion medium . The effect of additives, including sodium tripolyphosphate (STP), ethylenediaminetetramethylenephosphonic acid (ENTMP), and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), on the crystallization of barium chromate was studied conductometrically, where stoichiometric concentrations of barium and chromate were present at 298 K. , Increasing the additive concentration decreases the growth rate due to the blocking of the active sites for crystallization on the crystal surface through adsorption, which could be interpreted in terms of a Langmuir type adsorption isotherm. It has been reported that the barium chromate crystallization occurs by a surface-controlled growth mechanism .…”

Section: Introductionmentioning

confidence: 99%

“…The effect of additives, including sodium tripolyphosphate (STP), ethylenediaminetetramethylenephosphonic acid (ENTMP), and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), on the crystallization of barium chromate was studied conductometrically, where stoichiometric concentrations of barium and chromate were present at 298 K. , Increasing the additive concentration decreases the growth rate due to the blocking of the active sites for crystallization on the crystal surface through adsorption, which could be interpreted in terms of a Langmuir type adsorption isotherm. It has been reported that the barium chromate crystallization occurs by a surface-controlled growth mechanism . The study of the adsorption behavior of polyelectrolytes in relation to the crystal growth kinetics of barium sulfate indicate that the adsorption of poly(phosphinoacrylate), poly(acrylic acid), poly(styrenesulfonic acid), poly(vinylsulfonic acid), and a copolymer of maleic acid and vinylsulfonic acid disturbs the growth rate of barium sulfate. ,,, Williams et al described the adsorption of an amphoteric polymer, a copolymer of diallyldimethylammonium chloride (QUAT) and acrylic acid, on barium sulfate crystals and demonstrated its ability to greatly enhance the colloid stability of a barium sulfate dispersion.…”

Section: Introductionmentioning

confidence: 99%

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Aqueous Dispersion Behavior of Barium Chromate Crystals: Effect of Cationic Polyelectrolyte

Soponvuttikul

Saiwan

2003

Langmuir

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In polyelectrolyte-enhanced ultrafiltration (PEUF), a cationic polyelectrolyte binds to chromate and is ultrafiltered from solution. The permeate passing through the membrane can contain a very low chromate concentration; the retentate solution not passing through the membrane must be treated to recover a large fraction of the polymer for reuse for economical operation. In the regeneration step, barium chloride can be added to the retentate to precipitate chromate anion as a compact barium chromate solid waste. The solution containing the polymer can be directly recycled after the solid barium chromate is separated from the solution. Gravity settling is much less expensive than filtration or centrifugation, so this investigation studies the ability to separate solid from solution in a settling unit. Unfortunately, the polyelectrolyte can act as a dispersing agent that stabilizes the dispersion of barium chromate particles, resulting in poor separation efficiency in the settler. The adsorption of cationic polyelectrolyte on barium chromate particles increases with increasing polymer concentration, increasing ionic strength, and decreasing barium-to-chromate ratio. In addition, adsorption of the polyelectrolyte onto the barium chromate particles inhibits the growth of crystals and affects the crystal morphology. The average particle size of barium chromate crystals formed in the presence of the polymer is less than in the absence of the polymer. As a consequence, slower settling of the smaller particles occurs in the presence of polymer. The sedimentation rate of barium chromate increases with decreasing polymer concentration, increasing temperature, and increasing electrolyte concentration and reaches a maximum when there is a stoichiometric ratio of barium to chromate present. At this stoichiometric ratio in the absence of polymer, the zeta potential is zero, confirming that the rapid settling is due to the absence of electrostatic repulsion between the particles. Even though the barium chromate settles rapidly in the absence of polymer, the polymer adsorbs on the crystals and acts like a dispersant as well as causing a solution viscosity increase, resulting in slow settling rates in the PEUF process where the polyelectrolyte must be present.

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Section: Discussionmentioning

confidence: 99%