The influence of the solvent in nucleation of tolbutamide, a medium‐sized, flexible and polymorphic organic molecule, has been explored by measuring nucleation induction times, estimating ...solvent–solute interaction enthalpies using molecular modelling and calorimetric data, probing interactions and clustering with spectroscopy, and modelling solvent‐dependence of molecular conformation in solution. The nucleation driving force required to reach the same induction time is strongly solvent‐dependent, increasing in the order: acetonitrile<ethyl acetate<n‐propanol<toluene. The combined DFT and MD modelling results show that in acetonitrile, ethyl acetate and n‐propanol the nucleation difficulty is a function of the strength of solvent–solute interaction, with emphasis on the interaction with specific H‐bonding polar sites of importance in the crystal structure. A clear exception from this rule is the most difficult nucleation in toluene despite the weakest solvent–solute interactions. However molecular dynamics modelling predicts that tolbutamide assumes an intramolecularly H‐bonded conformation in toluene, substantially different from and more stable than the conformation in the crystal structure, and thus presenting an additional barrier to nucleation. This explains why nucleation in toluene is the most difficult and why the relatively higher propensity for aggregation of tolbutamide molecules in toluene solution, as observed with FTIR spectroscopy, does not translate into easier nucleation. Thus, our combined experimental and molecular modelling study suggests that the solvent can influence on the nucleation not only via differences in the desolvation but also through the influence on molecular conformation.
The crystal nucleation of tolbutamide in propanol, ethyl acetate and acetonitrile is governed by solvent–solute interaction strength. In toluene, however, the deciding factor is not the solvent–solute interaction strength, which is the weakest, but the propensity for the existence of intra‐molecularly H‐bonded (“wrong”) conformers. The results overall suggest that in case of tolbutamide the previously observed influence of desolvation on the nucleation process needs to be complemented by a second mechanism, namely the formation of crystal‐incompatible conformers in solution.
•Optimum conditions for separation of rare earth elements by anti-solvent crystallization was determined.•High purity and high recovery percentages were reached.
Rare earth elements (REE) have been ...selectively recovered from NiMH battery leach liquors by antisolvent precipitation. The active anode material was leached using sulfuric acid. The REE were then separated from the other elements by precipitation as sulfates after addition of either ethanol or 2-propanol (antisolvent). In a second step, Ni and Co are separated as sulfates by the same technique. The concentration of elements in different acid alcohol mixtures at 25 °C and −10 °C respectively are presented as a function of time after addition of the alcohol, and the optimum conditions for separation of the REE in pure form are presented. Under optimum conditions, 5.6 mol/L (Organic/Aqueous (O/A) volumetric ratio = 0.7) of 2-propanol at 25 °C, 82% of the REE have precipitated 3 h after addition of the antisolvent and the purity is 99.9%.
Over 2100 induction time experiments were carried out for the medium-sized, antipsychotic drug molecule, risperidone in seven different organic solvents. To reach the same induction time the required ...driving force increases in the order: cumene, toluene, acetone, ethyl acetate, methanol, propanol, and butanol, which reasonably well correlates to the interfacial energies as determined within classical nucleation theory. FTIR spectroscopy has been used to investigate any shifts in the spectra and to estimate the interaction of solute and solvent at the corresponding site. The solution condition has also been investigated by Density Functional Theory (DFT) calculations over (1 : 1) solvent-solute binding interactions at 8 different sites on the risperidone molecule. The DFT computational results agree with the spectroscopic data suggesting that these methods do capture the binding strength of solvent molecules to the risperidone molecule. The difficulty of nucleation correlates reasonably to the DFT computations and the spectroscopic measurements. The results of the different measurements suggest that the stronger the solvent binds to the risperidone molecule in solution, the slower the nucleation becomes.
In the present study, the recovery of rare earth elements (REEs) from an apatite concentrate in the nitrophosphate process of fertilizer production has been studied. The apatite concentrate has been ...recovered from iron ore tailings in Sweden by flotation. In the first step, the apatite is digested in concentrated nitric acid, after which Ca(NO3)2.4H2O is separated by cooling crystallization. The solution is then neutralized using ammonia whereby the REEs precipitate mainly as phosphates (REEPO4.nH2O) and together with calcium as REEn Cam (PO4)(3n+2m)/3. In this work, the degree of rare earth coprecipitation during seeded cooling crystallization of Ca(NO3)2.4H2O has been studied. The solubility of calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) in acidic nitrophosphoric acid solutions in the temperature range of −2°C to 20°C has been determined. For the neutralization step, it is shown that the calcium concentration and the final pH play an important role in determining the concentration of REEs in the precipitate. It is found that reaching maximum recovery of REE with minimum simultaneous precipitation of calcium requires careful control of the final pH to about 1.8. It is further observed that the precipitation yield of REEs and iron is favored by a longer residence time and higher temperature. Finally, the effect of seeding with synthesized REE phosphate crystals as well as a mixture of REE and Ca phosphates on the precipitation rate and the composition of the precipitate was studied.
•Optimal separation of rare earth elements in the nitrophosphate process of fertilizer production is studied.•Only 1% of REEs are co-precipitated with the Ca(NO3)2.4H2O crystals in the seeded cooling crystallization.•The calcium concentration and the final pH control the concentration of REEs in the precipitate.•Maximum recovery of REEs with minimum precipitation of calcium requires careful control of the final pH to about 1.8.•The obtained REE precipitate contains 7 to 15 mass% REEs.•The precipitation yield of REEs is favored by a longer residence time and higher temperature in presence of seeds.•The REEs precipitate in rhabdophane type: REEPO4.nH2O and in coprecipitation with calcium as REEnCam(PO4)(3n+2m)/3•The precipitation yield of REEs is favored by a longer residence time and higher temperature in presence of seeds.
In this study, different processes have been developed and applied to treat a rare earth phosphate concentrate obtained within the nitrophosphate process of fertilizer production. Methods to remove ...impurities such as Fe and Ca have been investigated as well as to separate the phosphorous and thereby facilitate dissolution of the rare earth elements (REE). These methods include thermal treatment with sodium hydroxide and sodium double sulphate precipitation with and without alkaline conversion, followed by selective dissolution in different acids. The proposed processes were compared and analyzed from the perspective of introducing an appropriate intermediate product for further individual REE separation.
The results have shown that after thermal treatment with NaOH at 400 °C, the phosphorous can be removed from the rare earth phosphate concentrate by water leaching. Investigation of different REE phosphate concentrates demonstrated that mixed Ca and REE phases, e.g. REEmCan(PO4)3m+2n/3 and CaHPO4 are less likely to dephosphorize than REE(PO4).nH2O and FePO4.H2O under these conditions. The recovery of REE to a mild acidic solution is limited by the presence of remaining phosphate ions and by the formation of REE oxide phases during the thermal treatment. The results also show that a solution containing 40 g/L REE; free of phosphorous, calcium and iron can be obtained after reprecipitation of the rare earth phosphate concentrate as sodium rare earth double sulphates followed by alkaline conversion with sodium hydroxide and dissolution in nitric acid.
•The elimination of phosphorous avoids high consumption of acids during dissolution of the REE concentrate.•Phosphorous can be mobilized from a rare earth phosphate concentrate by water leaching after thermal treatment with NaOH at 400 °C.•The REE can be separated from Ca and Fe by precipitation as NaREE(SO4)2.H2O.•By dissolving the REE hydroxide concentrate in nitric acid at a pH of 1.6, a solution containing 45g/L REE free of Ca, Fe and P can be obtained.
This is a cross-sectional, observational study to determine the frequency and associated features of HIV-associated neurocognitive disorders (HAND) in a large, diverse sample of infected individuals ...in the era of combination antiretroviral therapy (CART).
A total of 1,555 HIV-infected adults were recruited from 6 university clinics across the United States, with minimal exclusions. We used standardized neuromedical, psychiatric, and neuropsychological (NP) examinations, and recently published criteria for diagnosing HAND and classifying 3 levels of comorbidity (minimal to severe non-HIV risks for NP impairment).
Fifty-two percent of the total sample had NP impairment, with higher rates in groups with greater comorbidity burden (40%, 59%, and 83%). Prevalence estimates for specific HAND diagnoses (excluding severely confounded cases) were 33% for asymptomatic neurocognitive impairment, 12% for mild neurocognitive disorder, and only 2% for HIV-associated dementia (HAD). Among participants with minimal comorbidities (n = 843), history of low nadir CD4 was a strong predictor of impairment, and the lowest impairment rate on CART occurred in the subset with suppressed plasma viral loads and nadir CD4 ≥200 cells/mm(3) (30% vs 47% in remaining subgroups).
The most severe HAND diagnosis (HAD) was rare, but milder forms of impairment remained common, even among those receiving CART who had minimal comorbidities. Future studies should clarify whether early disease events (e.g., profound CD4 decline) may trigger chronic CNS changes, and whether early CART prevents or reverses these changes.
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