Potassium Alum Crystals Research Articles

Study of Secondary Nucleation by Attrition of Potassium Alum Crystals Suspended in Different Solvents

Secondary nucleation by attrition was studied in a milliliter-scale reactor, where the effects of different stirring rates and of different solvents were investigated. The experiments in suspension...

Flasking technique with alum crystals for fabricating definitive hollow bulb obturators

Different techniques have been described for fabricating obturators for patients with maxillary defects. The hollow bulb obturator has emerged as the treatment of choice in most patients owing to its light weight, cleanliness, and ease of fabrication. This article presents a simplified flasking technique for fabricating a definitive, closed, hollow bulb obturator by using a potassium alum crystal.

Vanadium Leaching from Vanadium-Bearing Carbonaceous Shale by a Multi-stage Counter-Current Process

This study investigated vanadium leaching from carbonaceous shale by a multi-stage counter-current (MSCC) acid leaching process. Experimental results showed that MSCC leaching can decrease the consumption of acid and enhance the leaching rate of vanadium remarkably compared with the conventional leaching way. The leaching rate of vanadium can reach 86% under optimal conditions. When the leaching stage exceeded 3, two types of precipitation formed in the leaching solution after the solution cooled to below 40°C. One was suspended amorphous silica and the other was potassium alum crystals. The formation of amorphous silica can result in the loss of vanadium by electrostatic adsorption of VO2+ to the surface of the silica and the loss of aluminium was mainly due to the formation of potassium alum crystals. Hence, it was appropriate to decide on the three leaching stages for counter-current acid leaching in this study.

Electrolytic coloration below 100 °C and spectral properties of potassium alum crystals

Potassium alum crystals are colored electrolytically below 100°C and under various voltages using a pointed cathode and a flat anode. SO3−, SO2−, O3−, O2−, O− hole-trapped centers and O0, O2−, H+ radicals are produced in colored potassium alum crystals. No obvious characteristic absorption band in ultraviolet and visible wavelength regions is observed in absorption spectrum of uncolored potassium alum crystal. Characteristic absorption bands of SO3−, SO2− and O3− hole-trapped centers are observed in the absorption spectra of the colored potassium alum crystals. The hole-trapped centers and radicals come from electric- and thermal-induced decomposition of SO42− radicals and crystalline water molecules. Current–time curve for electrolytic coloration of potassium alum crystal is given. Electron exchanges from electrons and small charged radicals to electrodes induce complete current.

Potassium alum crystal derived from aluminum salt in water treatment sludge by nanofiltration

The major method used for the recovery of aluminum from water purification sludge is through acidification or alkalization, however, the cost of the acid and alkali limits the amount available for use, and thus results in the low concentration of dissolved aluminum salt; moreover, the metal ions and organic matter dissolved simultaneously in the process will also increase the difficulty in reuse. Therefore, this study used sulfuric acid to dissolve aluminum in the sludge from the water treatment plant, followed by the low price nanofiltration membranes to increase the concentration of aluminum ions, and then adding potassium sulfate to produce the potassium alum crystal, which has less impurity. The influences of the molar ratio of potassium to aluminum and the temperature on the recovery of crystals are investigated. The result showed that there was good crystal recovery when the molar ratio of potassium to aluminum is above 1.6, but the recovery rate decreased as the temperature increased.

2D modeling of the regeneration surface growth on crystals

A physical model is proposed to describe the growth of regeneration surfaces (flat crystal surfaces that are not parallel to any possible faces). According to this model, the change in the growth rate of a regeneration surface during its evolution and the decrease in the number of subindividuals forming the growth front can be explained by the implementation of two types of geometric selection: within each subindividual (the absorption of rapidly growing faces by slowly growing ones) and between subindividuals (when subindividuals absorb each other). A numerical modeling of the growth of the regeneration surface (30.30.19) of potassium alum crystals showed quantitative agreement between the model proposed and the experimental data.

On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion

Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (β2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.

Growth-Sector Boundaries and Growth-Rate Dispersion in Potassium Alum Crystals

Crystals of potassium alum, pure and slightly doped with Cr 3+ , were grown from aqueous solution by slow temperature lowering. In addition, short re-dissolution periods were introduced in order to provoke growth defects and changes of growth rates. Crystal slices of about 1 mm thickness were studied by conventional LANG X-ray diffraction topography using MoKa radiation. For Cr-doped crystals, boundaries between {100}, {100} and {111} growth sectors appear by pronounced dynamical X-ray topographic contrast similar to that of stacking faults. Re-dissolution experiments provoke the formation of inclusions on {100} faces, followed by an increase of the { 100} growth rate by the factor of about six, relative to the neighboured {111} faces. X-ray topographs show that this-increase is correlated with the formation of dislocations, which interestingly have pure-edge character. During further growth these dislocations penetrate the {100}-{111} growth sector boundary and vanish from the {100} face, which slows down and finally adopts its former growth rate before re-dissolution.

The influence of internal crystal perfection on growth rate dispersion in a continuous suspension crystallizer

The objective of the work presented here is to demonstrate the influence of induced lattice strain on growth behaviour of potassium alum crystals in a continuously operated mixed suspension mixed product removal (MSMPR) crystallizer. Therefore crystal size distributions in the crystallizer and individual growth velocities, especially of small particles (initial size 20–60 μm) in a flow-through cell, were simultaneously determined. Moreover Laue diffraction patterns of crystals withdrawn from the MSMPR crystallizer were carried out indicating lattice deformation and strain. Most crystals exhibit constant crystal growth (CCG) behaviour with significant growth rate dispersion. The mean growth rate of small particles in the sub-sieve size range is considerably smaller than the mean rate of product sized crystals at constant supersaturation. Small potash alum crystals show a clear tendency of increased lattice strain with increasing supersaturation which can be explained by the refaceting process of attrition nuclei in the crystallizer. The average amount of induced strain in crystals having the same growth history is obviously related to crystal size. Only slightly strained particles with sufficiently high growth rates will reach the product size range in the MSMPR crystallizer.

Effects of Bismarck Brown dye on the crystallization kinetics of potassium alum in a CMSMPR crystallizer.

This study examined the effects of an additive, Bismarck Brown dye, on the crystallization kinetics of potassium alum crystals in a well-mixed continuous crystallizer. In the data analysis, size-dependent growth kinetics was assumed. The addition of Bismarck Brown dye depressed crystal growth and nucleation rates. The supersaturation of solution at steady state in the crystallizer increased as the Bismarck Brown concentration increased under the constraint of constant retention time and magma density. In this case the growth rate was enhanced but the nucleation rate was reduced. The predicted kinetic behaviors influenced by the addition of Bismarck Brown dye were in good agreement with the experimental results.

Crystal growth mechanism of size-dependent systems in a fluidized bed.

Based on the two-step model, surface-integration coefficients of potassium alum crystals below 5 × 10–4 m grown in a well-suspended fluidized bed were found to decrease sharply with decreasing crystal size so that the growth process is controlled by surface integration for small crystals. The mass-transfer coefficient is independent of crystal size and solution velocity. The mass-transfer resistance becomes significant when crystal size increases, and finally the growth rates become constant since both mass-transfer and surface-integration coefficients are constant. For larger crystals, there is no dominating step in the growth process, both resistances being important.The crystal growth behavior of various systems other than potassium alum was also examined. Finally, an experimental method for estimating the order of surface-integration rate is suggested.

Growth kinetics of potassium alum crystal in a well-agitated vessel

Growth rates of potassium alum crystal in a well-agitated vessel were determined from the de-supersaturation curve of the solution. The mass transfer and surface integration coefficients were then estimated using the two-step model. Both coefficients were found to increase with increasing crystal size. Judging from the Damköhler number for crystal growth and the over-all order of the growth rate equation, it is concluded that both mass transfer resistance and surface integration resistance are significant in the growth process.

CRYSTAL DISSOLUTION AND GROWTH IN A LEAN FLUIDIZED-BED CRYSTALLIZER

Dissolution and growth rates of potassium alum crystal were measured in a lean fluidized-bed crystallizer in which the flow rate of solution was set near the settling velocity of seed crystals. The...

Crystal growth kinetics of the two-step model

The single crystal technique was used to measure the growth rate of the potassium alum (111) face and the magnesium sulfate (110) face. The two-step model was found appropriate to describe the growth kinetics with the surface integration order of two for potassium alum crystal and of one for magnesium sulfate crystal. The individual rate constants, K d and K r, were determined accordingly.

Size‐dependent crystal growth—A manifestation of growth rate dispersion in the potassium alum‐water system

AbstractGrowth of potassium alum crystals was characterized by the advance rates of crystals on the leading edge of population distributions and by the advance rates of the modes of these distributions. Growth rates of crystals on the leading edge appeared to follow size‐dependent kinetics, but the observed spread of the distribution about the average size was much greater than would be expected from size‐dependent growth alone. The spread of the distribution was correlated with the extent of growth determined from the net advance of the average crystal size. These quantitative and qualitative results show that what has often been referred to as size‐dependent growth is in fact a manifestation of growth rate dispersion.

Kinetics of dissolution of potassium alum crystals in a flow cell in the presence of Fe++ cations

AbstractDissolution rates of the {111} face of potassium alum crystals have been measured in situ in a flow cell. Dependence of the mass dissolution fluxes on the subsaturation and on the presence of Fe++ cations has been studied. No influence of these cations over the concentration range 0–165 ppm on the dissolution kinetics has been observed. In addition, the dissolution process has been found to be of a purely diffusive character.

Effects of bismarck brown R on the growth rates of large and small potassium alum crystals

Experimental data show that Bismarck Brown R, at a concentration of 10 ppm, substantially inhibited growth rates of potassium alum. All faces of the crystal were affected similarly, although there was some evidence that inhibition of the (111) faces was slightly greater. Growth rates of small crystals were inhibited more than larger crystals; this is explained using observations of growth rate dispersion believed due to variations in screw dislocation activities. Data showing time-dependent inhibition of growth was used to support the hypothesis that Bismarck Brown R forms complexes or chelates that completely inhibited growth.

Morphology and size distribution of fragments from potassium alum crystals caused by different treatments, of importance to secondary nucleation

Abstract The morphology and size distribution of potassium alum particles potentially causing secondary nucleation were investigated by scanning electron microscopy.

The effect of surface treatments on initial breeding of potassium alum

Abstract Using potassium alum crystals shaken for different durations as seeds, the number N of nuclei produced was correlated with the number of seeds N s and the seed diameter d s. This result was coupled with the density of alum particles adhering to the surface of the seed crystals. It was found that the secondary nucleation was principally due to alum particles broken off from the original crystals by the shaking operation.

Oscillating crystal growth rates

AbstractA number of papers in the literature have reported that under certain conditions the growth rate of a crystal may not assume a unique value at a given supersaturation. These papers implied either that identical crystals growing in a supersaturated solution under identical conditions did not all grow at the same growth rate or that a given growing crystal was alternating between two values of growth rate.In this work the existence of such a phenomenon was clearly demonstrated by experiments with sodium chloride crystal whiskers in which the growth was monitored semi‐continuously. It was observed that instead of being a continuous process, crystal growth was intermittent in nature. Growth was characterized by two alternating periods, a growth period during which rapid growth occurred and a period of small or non‐existent growth.This work also showed that this type of intermittent growth could account for another phenomenon previously reported in an investigation with potassium alum crystals; that in certain supersaturation regions the growth rates appeared to be insensitive to changes in supersaturation.It is also pointed out that the existence of periodic rates will complicate the expressions for the kinetics of growth used in the analysis of crystallizers and that the insensitivity of growth rates to supersaturation may affect the stability of continuous crystallizers.