Crystallization Kinetics of Monosodium Aluminate Hydrate in Concentrated Sodium Aluminate Solutions

Abstract

The nucleation, growth, and agglomeration of monosodium aluminate hydrate (MAH) crystallization in concentrated sodium aluminate solutions were investigated in a steady-state mixed-suspension−mixed-product-removal (MSMPR) crystallizer, and the mechanism was analyzed in detail. The crystal growth was diffusion-and surface-integration-controlled, and the secondary nucleation, as a result of crystal−agitator and crystal−crystallizer collisions, was determined further. The agglomeration kernel, expressed in terms of mean residence time, growth rate, and suspension density, was found to have a positive order of about 0.52 in the suspension density, indicating that the agglomeration kernel increased at higher frequencies of collisions between particles. The growth rate of MAH was found to be higher than that of gibbsite in active NaAl(OH) 4 − NaHCO 3 systems, but the nucleation rate of MAH was lower than that of gibbsite in seeded-hydrolysis processes.

Estimation of Nucleation and Growth Kinetics of Benzoic Acid by Population Balance Modeling of a Continuous Cooling Mixed Suspension, Mixed Product Removal Crystallizer

“…The ability to achieve steady-state conditions coupled with the typical assumptions made in the analysis of MSMPR crystallizers allows the solution to the population balance to be simple and the direct recovery of nucleation and growth rates from experimental CSD data to be straightforward. This, in essence, is the power of the methodology, and the relative simplicity of the analysis has encouraged extensive application of the MSMPR crystallizer in determining and studying crystallization kinetics for a wide variety of systems. ,,,,,,− …”

“…Recently, several MSMPR studies have emerged where the researchers have employed model-based optimization procedures to estimate crystallization kinetic parameters. ,, In all examples, the model predicted size distribution using the kinetic parameters estimated from this approach agreed reasonably well with the experimental equivalent, with growth and nucleation modeled as the principal kinetic mechanisms involved in shaping the CSD. Other kinetic factors of agglomeration and breakage can also be crucial in shaping the CSD, and several studies have also considered inclusion of one or both phenomena in modeling crystallization systems. ,− ,,,− …”

Conversion of Coarse Gibbsite Remaining in Hanford Nuclear Waste Tank Heels to Solid Sodium Aluminate [NaAl(OH)4·1.5H2O]

“…Most previous works have dissolved gibbsite at much lower NaOH concentrations using temperature to accelerate this admittedly very slow reaction to practical time frames. ,− Given the obstacles in temperature control in >50-year-old buried waste tanks at Hanford, this study examines the possibility of using high NaOH concentration rather than temperature to achieve reasonable rates. Similarly, other researchers have crystallized NaAl(OH) 4 ·1.5H 2 O by evaporating sodium aluminate solutions. ,,− This is the first study that crystallizes NaAl(OH) 4 ·1.5H 2 O while simultaneously dissolving gibbsite in concentrated NaOH(aq) and demonstrates that this reaction happens over a reasonable period of time.…”

“…NaOH will eventually be used to dissolve gibbsite and boehmite from the bulk tank waste at elevated temperatures. ,, Gibbsite dissolution, however, is reported to be slow at NaOH concentrations below 5 M at ambient temperatures. , It is hypothesized that reasonable rates can be achieved at ambient temperatures using highly concentrated NaOH(aq), from which sodium aluminate readily precipitates. − It is further hypothesized that gibbsite rapidly dissolves in highly concentrated NaOH(aq) and recrystallizes as sodium aluminate. − If the NaOH concentration were high enough, sodium aluminate might precipitate even as gibbsite was still dissolving through a metathesis reaction. The high water solubility of sodium aluminate suggests that the sodium aluminate solid could be easily redissolved in water after metathesis is complete. , …”

Determination of kinetics in batch cooling crystallization processes—A sequential parameter estimation approach

“…A judicious algebraic manipulation allows the growth and nucleation rates to be determined independently of other crystallization phenomena, even if those phenomena occur in the same experiment . This approach has been broadly applied in academia and industry to sequentially estimate growth and nucleation kinetics, growth, nucleation and agglomeration kinetics, growth and agglomeration kinetics, growth and breakage kinetics, or growth, nucleation, agglomeration and breakage, and to obtain initial estimates of the kinetic parameters before applying optimal model‐based experimental design to simultaneously fit the whole model …”