In this study, the crystallization of scandium from ammonium fluoride strip liquor, obtained by solvent extraction, was investigated using an anti-solvent crystallization technique. Acetone, ethanol, ...methanol and isopropanol were added individually to the strip liquor as the anti-solvent and scandium was precipitated and obtained in the form of (NH4)3ScF6 crystals. The results show that scandium can be effectively crystallized from the strip liquor to obtain an intermediate, marketable scandium product. Yields greater than 98% were obtained using an anti-solvent to strip liquor volumetric ratio of 0.8. Acetone had the least performance at lower anti-solvent to strip liquor volumetric ratios, possibly due to its limited H bonding capability with water molecules when compared to alcohols.
The recovery of scandium from waste streams of mining and metallurgical operations presents an opportunity to balance supply and demand of this commodity. This study expands on the research focusing ...on the recovery of scandium as (NH
4
)
3
ScF
6
from strip liquors by antisolvent crystallization using ethanol as the antisolvent. The effect of process conditions including reducing the rate of supersaturation generation, agitation mechanism, feeding point location with respect to local supersaturation, and seeding are assessed with emphasis on the final crystal size distributions (CSD) and morphology. Reducing the rate of supersaturation generation by reducing the ethanol concentration and by controlling the rate of antisolvent addition had the greatest effect on increasing the crystal sizes, although broader CSDs were obtained. Morphological modifications, without polymorphic transformations, were also observed when one-pot addition of 60 or 70% v/v ethanol was conducted, but not observed when the dilute antisolvents were fed at a controlled low addition rate.
Impact of process conditions on product quality is investigated in the recovery of high purity (NH
4
)
3
ScF
6
by antisolvent crystallization.
The recovery of scandium from waste streams of other mining and metallurgical processing industries is gaining research interest due to the scarcity of scandium-containing ores. Hydrometallurgical ...techniques such as leaching, solvent extraction and crystallization amongst others have been successfully applied to recover scandium salts from such waste streams. Scandium can be recovered as (NH
4
)
3
ScF
6
by antisolvent crystallization from NH
4
F strip liquors obtained after solvent extraction. The coextraction of metal impurities such as Fe, Al, Zr and Ti causes contamination of the final solid product. The extent of coprecipitation of ammonium metal fluorides depends on their initial concentration in the strip liquor and their solubility in the NH
4
F-antisolvent mixtures. Here, the solubility of ammonium metal fluorides of Sc, Zr, Fe, Al and Ti is reported separately in 3 mol L
−1
NH
4
F-ethanol mixtures at 25 °C as well as in a system containing all five solid phases. The solubility of (NH
4
)
3
ZrF
7
is slightly higher than that of (NH
4
)
3
ScF
6
, while the solubilities of (NH
4
)
3
FeF
6
and (NH
4
)
3
AlF
6
are significantly lower in comparison to (NH
4
)
3
ScF
6
. The solubility of (NH
4
)
2
TiF
6
is 1-2 orders of magnitude higher than those of other ammonium metal fluorides. When a mixture of ammonium metal fluoride salts is dissolved in the same 3 mol L
−1
NH
4
F-ethanol mixture as for the individual salts, the resultant solubility of the ammonium metal fluorides of Sc, Zr and Fe decreases significantly, while the resultant solubility of ammonium aluminum hexafluoride increases. This is likely due to changes in solution speciation with increased NH
4
F concentration and ionic strength.
The solubility of ammonium metal fluorides is evaluated in NH
4
F-ethanol mixtures and the implications for antisolvent crystallization of (NH
4
)
3
ScF
6
are discussed.
•(NH4)3ScF6 solubility decreases with increased NH4F concentration.•(NH4)3ScF6 solubility decreases with increased alcohol concentration.•(NH4)3ScF6 solubility relates to system dielectric constant ...for different alcohols.•(NH4)3ScF6 transforms into NH4ScF4 in water and other phases in low fluoride media.•(NH4)5Sc3F14 is a possible transformation product of (NH4)3ScF6 in 0.5 mol/L NH4F.
This paper investigates the phase equilibria of ammonium scandium fluoride phases in pure water, aqueous NH4F solutions and in mixtures of NH4F and alcohols. The solubility of the solid phases was determined at 25 °C. It was observed that (NH4)3ScF6 transforms into NH4ScF4 when contacted with pure water for 24 h. Solid phase transformation was also noted in NH4F solutions of concentration ≤ 0.5 mol/L. At NH4F concentrations ≥ 0.8 mol/L, no phase change has been observed, and the solubility of (NH4)3ScF6 decreases with increasing NH4F concentration due to the common ion effect. In NH4F-alcohol mixtures, the solubility of (NH4)3ScF6 decreases in the order: methanol > ethanol > 1,3-propane-diol > 2-propanol. This aligns with the decrease in the effective dielectric constant of the resulting solvent mixture, which is very similar for NH4F-alcohol mixtures formed by ethanol and 1,3-propane-diol.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Scandium (Sc), declared a critical raw material in the European Union (EU), could face further supply issues as the EU depends almost entirely on imports from China, Russia, and Ukraine. In this ...study, a tandem nanofiltration-solvent extraction procedure for Sc recovery from titania (TiO2) acid waste was piloted and then augmented by antisolvent crystallization. The new process, comprising advanced filtration (hydroxide precipitation, micro-, ultra-, and nanofiltration), solvent extraction, and antisolvent crystallization, was assessed in relation to material and energy inputs and benchmarked on ScF3 production. From ∼1 m3 of European acid waste containing traces of Sc (81 mg L–1), ∼13 g of Sc (43% yield, nine stages) was recovered as (NH4)3ScF6 with a purity of approximately 95%, demonstrating the technical feasibility of the approach. The production costs per kilogram of ScF3 were lower than reported market prices, which underscores a competitive process at scale. Although a few technical bottlenecks (e.g., S/L separation and electricity consumption) need to be overcome, combining advanced filtration with solvent extraction and antisolvent crystallization promises a future supply of this critical raw material from European secondary sources.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Scandium (Sc), declared a critical raw material in the European Union (EU), could face further supply issues as the EU depends almost entirely on imports from China, Russia, and Ukraine. In this ...study, a tandem nanofiltration-solvent extraction procedure for Sc recovery from titania (TiO
) acid waste was piloted and then augmented by antisolvent crystallization. The new process, comprising advanced filtration (hydroxide precipitation, micro-, ultra-, and nanofiltration), solvent extraction, and antisolvent crystallization, was assessed in relation to material and energy inputs and benchmarked on ScF
production. From ∼1 m
of European acid waste containing traces of Sc (81 mg L
), ∼13 g of Sc (43% yield, nine stages) was recovered as (NH
)
ScF
with a purity of approximately 95%, demonstrating the technical feasibility of the approach. The production costs per kilogram of ScF
were lower than reported market prices, which underscores a competitive process at scale. Although a few technical bottlenecks (e.g., S/L separation and electricity consumption) need to be overcome, combining advanced filtration with solvent extraction and antisolvent crystallization promises a future supply of this critical raw material from European secondary sources.
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Available for:
IJS, KILJ, NUK, PNG, UL, UM
Bauxite residues, i.e., red mud, can be processed to recover various valuable end products, while reducing the environmental impact of the waste. Scandium is one of the valuable elements in bauxite ...residues. It is possible to extract and enrich scandium from red mud by leaching and solvent extraction. Scandium can then be recovered from the pregnant strip liquor by crystallization. Different crystallization techniques can be used to generate the supersaturation required for scandium to crystallize out as a salt. In the present study, the crystallization of an ammonium scandium fluoride phase by cooling and antisolvent crystallization techniques is presented. Cooling crystallization gave a low yield of ammonium scandium hexafluoride, (NH
4
)
3
ScF
6
, below 50% at the lowest temperature of 1 °C investigated. Antisolvent crystallization using ethanol gave almost complete recovery with precipitation efficiency greater than 98% for an ethanol-to-strip liquor volumetric ratio of 0.8. Solubility data of (NH
4
)
3
ScF
6
under different temperatures and in different ethanol–strip liquor mixtures is herein presented. The product obtained by antisolvent crystallization had very minute crystals (< 2 µm) due to the high supersaturation generated upon adding ethanol to the strip liquor, while it was easier to obtain larger crystals by cooling crystallization. Fe and Ti impurities were detected in the solid product, and an insight into the mechanism of impurity uptake is discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In higher eukaryotes, histone methylation is involved in maintaining cellular identity during somatic development. As most nucleosomes are replaced by protamines during spermatogenesis, it is unclear ...whether histone modifications function in paternal transmission of epigenetic information. Here we show that two modifications important for Trithorax- and Polycomb-mediated gene regulation have methylation-specific distributions at regulatory regions in human spermatozoa. Histone H3 Lys4 dimethylation (H3K4me2) marks genes that are relevant in spermatogenesis and cellular homeostasis. In contrast, histone H3 Lys27 trimethylation (H3K27me3) marks developmental regulators in sperm, as in somatic cells. However, nucleosomes are only moderately retained at regulatory regions in human sperm. Nonetheless, genes with extensive H3K27me3 coverage around transcriptional start sites in particular tend not to be expressed during male and female gametogenesis or in preimplantation embryos. Promoters of orthologous genes are similarly modified in mouse spermatozoa. These data are compatible with a role for Polycomb in repressing somatic determinants across generations, potentially in a variegating manner.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Includes bibliography.
Eutectic Freeze Crystallization (EFC) is a separation technique which involves simultaneous crystallization of water and solute under eutectic conditions. It can be applied to ...treatment of various industrial aqueous streams containing dissolved organic and inorganic contaminants, such as reverse osmosis (RO) retentate brine streams. Since antiscalants are dosed in RO feed streams, these become concentrated in the retentate brine stream and could have an undesirable effect on crystallization kinetics of both ice and salt in EFC. In this study, the impact of a phosphonate antiscalant on the kinetic processes of nucleation and growth in EFC was investigated. Firstly, the effect of an antiscalant on the thermodynamic phase equilibria of a binary Na2SO4 aqueous solution was experimentally determined. The effect of the antiscalant on the nucleation and growth rates of both ice and salt in a continuous EFC process was then established for concentrations of 200, 350 and 500 mg/L of antiscalant. Product quality parameters such as the Crystal Size Distribution (CSD), morphology and purity of crystals were also measured since they are directly affected by the kinetic rate processes investigated.
Cohesin folds mammalian interphase chromosomes by extruding the chromatin fiber into numerous loops. "Loop extrusion" can be impeded by chromatin-bound factors, such as CTCF, which generates ...characteristic and functional chromatin organization patterns. It has been proposed that transcription relocalizes or interferes with cohesin and that active promoters are cohesin loading sites. However, the effects of transcription on cohesin have not been reconciled with observations of active extrusion by cohesin. To determine how transcription modulates extrusion, we studied mouse cells in which we could alter cohesin abundance, dynamics, and localization by genetic "knockouts" of the cohesin regulators CTCF and Wapl. Through Hi-C experiments, we discovered intricate, cohesin-dependent contact patterns near active genes. Chromatin organization around active genes exhibited hallmarks of interactions between transcribing RNA polymerases (RNAPs) and extruding cohesins. These observations could be reproduced by polymer simulations in which RNAPs were moving barriers to extrusion that obstructed, slowed, and pushed cohesins. The simulations predicted that preferential loading of cohesin at promoters is inconsistent with our experimental data. Additional ChIP-seq experiments showed that the putative cohesin loader Nipbl is not predominantly enriched at promoters. Therefore, we propose that cohesin is not preferentially loaded at promoters and that the barrier function of RNAP accounts for cohesin accumulation at active promoters. Altogether, we find that RNAP is an extrusion barrier that is not stationary, but rather, translocates and relocalizes cohesin. Loop extrusion and transcription might interact to dynamically generate and maintain gene interactions with regulatory elements and shape functional genomic organization.
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