Self-assembled mesoporous carbon (MC) materials have been synthesized and tested for application in capacitive deionization (CDI) of saline water. MC was prepared by self-assembly of a triblock ...copolymer with hydrogen-bonded chains via a phenolic resin, such as resorcinol or phloroglucinol in acidic conditions, followed by carbonization and, in some cases, activation by KOH. Carbon synthesized in this way was ground into powder, from which activated MC sheets were produced. In a variation of this process, after the reaction of triblock copolymer with resorcinol or phloroglucinol, the gel that was formed was used to coat a graphite plate and then carbonized. The coated graphite plate in this case was not activated and was tested to serve as current collector during the CDI process. The performance of these MC materials was compared to that of carbon aerogel for salt concentrations ranging between 1000 ppm and 35,000 ppm. Resorcinol-based MC removed up to 15.2 mg salt per gram of carbon, while carbon aerogel removed 5.8 mg salt per gram of carbon. Phloroglucinol-based MC-coated graphite exhibited the highest ion removal capacity at 21 mg of salt per gram of carbon for 35,000 ppm salt concentration.
The uncertain supply of the rare-earth elements (REE) from conventional sources such as bastnaesite and monazite demands the search for alternative sources. Unconventional sources such as phosphate ...rock and mine tailings have REE contents at the level of only hundreds to a thousand parts per million, which challenges the conventional REE separation methods such as solvent extraction (SX) and ion exchange (IX). Alternatively, the potential of extraction chromatography (EXC) has been explored, as it combines the selectivity of SX and the convenience of column techniques of IX. Herein, we report a novel EXC material incorporating N,N′-dimethyl-N,N′-dioctyl-3-oxa-diglycolamide (DMDODGA) into a porous solid support because DMDODGA exhibits higher extraction efficiency for REE in SX than does conventional N,N,N′,N′-tetraoctyl-3-oxa-diglycolamide (TODGA) and as also compared with similarly made conventional TODGA-based EXC material. The extraction of mixed REE by DMDODGA and TODGA resins was evaluated in H2SO4, HCl, and HNO3 media as a function of acid concentration. The REE feed concentrations were adjusted to achieve stoichiometric REE concentration and excess REE concentration, conditions that reflect near or complete saturation of resin capacity. In general, extraction at the same acid concentration followed the order HNO3 > HCl > H2SO4. The extraction strength of the DMDODGA resin is significantly higher than that of the TODGA resin in all three examined mineral acids, especially at lower H2SO4 and HCl concentrations (0.01 and 0.1 M), making it a promising EXC material for hydrometallurgical extraction of REE.
Phosphogypsum is a byproduct created during the production of industrial wet-process phosphoric acid. This study focused on recovering rare earth elements (REEs) from a Florida phosphogypsum sample ...and investigated the effects of removing detrimental impurities such as phosphorus pentoxide (P
2
O
5
), uranium (U) and fluorine (F) during the leaching process. Experimental results indicated that REE leaching efficiency increased rapidly, reached a maximum and then began to decrease with sulfuric acid concentrations ranging from 0 to 10 percent and temperatures ranging from 20 to 70 °C. At a sulfuric acid concentration of 5 percent and leaching temperature of 50 °C, REE leaching efficiency obtained a maximum value of approximately 43 percent. Increasing the leaching time or liquid/solid ratio increased the leaching efficiency. The leaching efficiencies of P
2
O
5
, U and F consistently increased with sulfuric acid concentration, temperature, leaching time and liquid/solid ratio within the testing ranges. A fine-grain gypsum concentrate, sized smaller than 40 µm, was separated from leached phosphogypsum through elutriation, in which the P
2
O
5
, U and F content levels were reduced by 99, 70 and 83 percent, respectively, from their content levels in fresh phosphogypsum.
Six laboratory scale biogas mixed anaerobic digesters were operated to study the effect of biogas recycling rates and draft tube height on their performance. The digesters produced methane at ...0.40–0.45
L per liter of digester volume per day. A higher methane production rate was observed in unmixed digesters, while increased biogas circulation rate reduced methane production. However, different draft tube heights caused no difference in the methane production rate. Air infiltration (up to 15% oxygen in the biogas) was observed in the digesters mixed by biogas recirculation. Slight air permeability of tubing or leakage on the vacuum side of the air pump may have caused the observed air infiltration. The similar performance of the mixed and unmixed digesters might be the result of the low solids concentration (50
g dry solids per liter of slurry) in the fed animal slurry, which could be sufficiently mixed by the naturally produced biogas.
Chemical kinetics of dissolution of aluminum alloy 6061 was investigated for the processing of Pu-238 for deep space missions. The rate of dissolution was measured by the heat release and appeared to ...be controlled by the rate of release of Al(OH)
4
−
from the metal surface. Rates of reaction were measured from 273 to 365 K, giving an activation energy of 72 ± 13 kJ⋅(mol Al)
−1
and a pre-exponential factor of 5 ± 3 × 10
9
dm
3
mol
−1
min
−1
. Minor alloying elements did not appear to affect the reaction kinetics. The average heat of dissolution was −360 ± 70 kJ⋅(mol NaAlO
2
)
−1
. When extrapolated to an infinitely dilute solution of aluminum,
kJ⋅(mol NaAlO
2
)
−1
.
Phosphorite, or phosphate rock, is the most significant secondary rare-earth resource. It contains high amounts of phosphate-bearing minerals along with low contents of rare earth elements (REEs). In ...Florida, about 19 Mt of phosphate rock are mined annually and most are used to manufacture fertilizers using a wet process, in which sulfuric acid reacts with phosphates to produce phosphoric acid and phosphogypsum. In the wet process, REEs are also leached out into solution and eventually get lost in the leaching residue and phosphate fertilizer. Recovering REEs from Florida phosphate rock in the wet process will be beneficial to broadening rare-earth availability, improving the quality of phosphoric acid product and protecting the environment.
This study focuses on the influences of wet-process operating conditions on REE leaching efficiency. The results indicate that REE leaching efficiency increases with phosphoric acid addition in the initial pulp. At a temperature of 75 °C, a stoichiometric ratio of sulfuric acid (H
2
SO
4
) to calcium oxide (CaO) of 1.05 and a weight ratio of liquid to solid of 3.5, REE leaching efficiency reached a relatively high value of 52.82 percent. The trends of REE leaching efficiency were similar to those for phosphoric acid (P
2
O
5
). Extensive tests on the leaching residue showed that during leaching, about 90 percent of the REEs were released from the phosphate rock but only 52.82 percent ended up in the leaching solution. This phenomenon can be attributed to two factors: (1) the effect of phosphate ions (PO
4
3-
) in the solution, which caused REE ions to form REE phosphates and be precipitated into the leaching residue, and (2) the influence of large amounts of anions such as sulfate (SO
4
2-
), dihydrogen phosphate (H
2
PO
4
-
) and hydrogen phosphate (HPO
4
2-
) anions as well as the polar molecule H
3
PO
4
, which surrounded the REE cations and formed an ion atmosphere that prevented the PO
4
3-
from contacting and combining with REE cations. Interaction of these two opposite effects determined the REE distribution between leaching solution and residue.
Phosphate beneficiation in Florida generates more than one tonne of phosphatic clay, or slime, per tonne of phosphate rock produced. Since the start of the practice of large-scale washing and ...desliming for phosphate beneficiation, more than 2 Gt of slime has accumulated, containing approximately 600 Mt of phosphate rock, 600 kt of rare earth elements (REEs) and 80 million kilograms of uranium. The recovery of these valuable elements from the phosphatic clay is one of the most challenging endeavors in mineral processing, because the clay is extremely dilute, with an average solids concentration of 3 percent, and fine in size, with more than 50 percent having particle size smaller than 2 µm, and it contains nearly 50 percent clay minerals as well as large amounts of magnesium, iron and aluminum. With industry support and under funding from the Critical Materials Institute, the Florida Industrial and Phosphate Research Institute in conjunction with the Oak Ridge National Laboratory undertook the task to recover phosphorus, rare earths and uranium from Florida phosphatic clay. This paper presents the results from the preliminary testing of two approaches. The first approach involves three-stage cycloning using cyclones with diameters of 12.4 cm (5 in.), 5.08 cm (2 in.) and 2.54 cm (1 in.), respectively, to remove clay minerals followed by flotation and leaching. The second approach is a two-step leaching process. In the first step, selective leaching was conducted to remove magnesium, thus allowing the production of phosphoric acid suitable for the manufacture of diammonium phosphate (DAP) in the second leaching step. The results showed that multistage cycloning with small cyclones is necessary to remove clay minerals. Selective leaching at about pH 3.2 using sulfuric acid was found to be effective for removing more than 80 percent of magnesium from the feed with minimal loss of phosphorus.
The distribution of polar organic compounds typical of water contaminants (organic acids, alcohols, and aromatic compounds) associated with oil and gas production was measured between water and nine ...hydrophobic, room-temperature ionic liquids. The ionic liquids used in this study were 1-butyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-hexyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-octyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-butyl-3-methylimidazolium hexafluorophosphate, trihexyltetradecylphosphonium bistrifluoromethanesulfonylimide, 1-butyl-1-methyl-pyrrolidinium bistrifluoromethanesulfonylimide, trihexyltetradecylphosphonium dodecylbenzenesulfonate, tributyltetradecylphosphonium dodecylbenzenesulfonate, and trihexyltetradecylphosphonium methanesulfonate. Sensitivity of the distribution coefficients to salinity, temperature, concentration, and pH was investigated. Partitioning into the ionic liquid varied considerably. Acetic acid did not significantly partition into the ionic liquid phase, except for the sulfonate-anion ionic liquids. The solubility of hexanoic acid in the ionic liquids was significant, where uptake of the protonated form from aqueous solution was observed for all of the ionic liquids studied. Other organics also showed high distribution coefficients, up to several hundred in the case of toluene and 1-nonanol. The distribution coefficients for toluene, 1-nonanol, cyclohexanone, and hexanoic acid were independent of ionic liquid-to-water ratio over the range from 0.02 to 1.0. The ionic liquids showed a large capacity for some organics, with solubilities measured above 100 g·L
−1
. Regeneration of the ionic liquids by rinsing and heating was studied, with mixed success. These experiments show that certain hydrophobic ionic liquids do have an affinity for organic contaminants in aqueous solution. However, practical application of the ionic liquids tested for detection or removal of selected water-soluble organics from the aqueous waste streams appears to be limited by the small, but significant, solubility of the ionic liquids in the aqueous phase and by difficulty in solvent regeneration. Further work aimed at determination of ionic liquids that dissolve target compounds and are nonhazardous and less soluble in aqueous solutions is recommended.
Selection of an aluminum alloy for target cladding affects post-irradiation target dissolution and separations. Recent tests with aluminum alloy 6061 yielded greater than expected precipitation in ...the dissolver, forming up to 10 wt.% solids of aluminum hydroxides and aluminosilicates. Aluminosilicate dissolution presents challenges in a number of different areas, including metals extraction from minerals, flyash treatment, and separations from aluminum alloys. We present experimental work that attempts to maximize dissolution of aluminum metal in caustic, along with silicon, magnesium, and copper impurities, through control of temperature, the rate of reagent addition, and incubation time. Aluminum phase transformations have been identified as a function of time and temperature, using X-ray diffraction. Solutions have been analyzed using wet chemical methods and X-ray fluorescence. These data have been compared with published calculations of aluminum phase diagrams. Approaches are given to enhance the dissolution of aluminum and aluminosilicate phases in caustic solution.
The potential of room-temperature ionic liquids for use in chemical separations was assessed, particularly for liquid-liquid extraction. The solubility, surface tension, and electrical conductivity ...of a range of imidazolium-based ionic liquids in aqueous solution were measured at room temperature and atmospheric pressure as functions of ionic-liquid, sodium chloride, and potassium-chloride concentrations. Hydrophobic ionic liquids were studied, including 1-C
n
-3-methylimidazolium cations, C
n
mim
+
, with alkyl substitutions of varying chain length, where C
n
=C
2
(ethyl), C
4
(butyl), C
6
(hexyl), and C
8
(octyl), in combination with bis(trifluoromethanesulfonyl)imide, NTf
2
−
, and bis(perfluoroethanesulfonyl)imide, BETI
−
, anions. Hydrophilic compounds were also studied, with bromide anions and C
n
mim
+
and 1-C
n
-2, 3-methylimidazolium, C
n
bmim
+
, cations, where C
n
=C
12
, C
14
and C
16
are solids at room temperature, and C
n
=C
8
, C
9
, and C
10
are liquids.
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