Preparation of Battery-Grade FePO4·2H2O Using the Stripping Solution Generated from Resource Recycling of Bauxite Residue.

A novel process for the high-value-use of iron from bauxite residue was proposed in this work. The process was trying to use the iron-containing stripping solution generated during resource recycling of bauxite residue to produce battery-grade FePO4·2H2O product. Thermodynamics calculation indicates that Fe and P in the stripping solution mainly existed in the form of FeHPO4+, and the theoretical pH for the conversion reaction from FePO4·2H2O to Fe(OH)3 was 1.72. The optimal condition for the synthesis of FePO4·2H2O using the stripping solution was determined as: reaction pH of 0.8, reaction temperature of 90°C, Fe/P ratio of 1, and reaction time of 24 h. XRD result showed that the synthesized FePO4·2H2O was well-crystallized and perfectly matched with the characteristic peaks of FePO4·2H2O. Moreover, all the parameters of the synthesized iron phosphate meet the quality requirements of battery precursor.

Spectroscopic Study of the Behavior of Mo(VI) and W(VI) Polyanions in Sulfuric-Phosphoric Acid Mixtures.

The solution chemistry of Mo(VI) and W(VI) in mixtures of sulfuric and phosphoric acids is relevant to the development of practicable hydrometallurgical processes for the recovery and separation of these two elements from low-grade scheelite ores. The behavior of Mo(VI) and W(VI) in such mixtures has been studied using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), nuclear magnetic resonance (NMR), and small-angle X-ray scattering (SAXS) spectroscopies, along with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Where applicable, these techniques have produced a self-consistent picture of the similarities and differences between the chemical speciation of Mo(VI) and W(VI) as functions of solution composition, mostly at a constant phosphorous/metal (P/M; M = Mo(VI) or W(VI)) ratio of ∼1. In dilute acidic media (0.02 mol·kg-1 H+, without H2SO4), Mo(VI) exists mostly (∼60%) as P2Mo5O236- with the remaining ∼40% as ß-Mo8O264-. Under the same conditions, W(VI) is largely present as NaPW11O396- (∼80%) and P2W5O236- (∼10%), with the remainder probably occurring as isopolytungstates such as W12O4212- and some tungstophosphate dimers such as P2W18O626-. At higher acid concentrations (≲5 mol·kg-1 H2SO4), polymeric Mo(VI) anions are broken down to form the oxocations MoO22+ and Mo2O52+ and their protonated forms, with the dimers becoming increasingly dominant at higher acidities (∼80% in 5 mol·kg-1 H2SO4). In stark contrast, W(VI) polyanions do not decompose at higher acidities but instead form (∼70% in 0.6 mol·kg-1 H2SO4) a Keggin ion, PW12O403-. Further acidification with H2SO4 results in the agglomeration of this Keggin ion, forming clusters of about 50 and 100 Å in diameter that ultimately produce crystalline precipitates, which could be identified in part by their X-ray diffraction patterns. Possible application of these findings to the hydrometallurgical separation of Mo and W using acidic solutions is briefly discussed, based on a limited number of batch solvent extractions.

Computational and solubility equilibrium experimental insight into Ca2+-fluoride complexation and their dissociation behaviors in aqueous solutions: implication for the association constant measured using fluoride ion selective electrodes.

Although the Ca2+-F- association is of great importance for aqueous environments and industrial systems containing F-, as well as for defluorination processes, many details of the association solvation structures and behavior remain unclear. Herein, a combination of classical/ab initio molecular dynamics simulations and density functional theory calculations was used to investigate the structure and hydration of CaFx2-x (x = 1, 2) and the association/dissociation behavior of Ca2+-F- in aqueous CaF2 solutions. The primary shell of Ca2+ is found to be very flexible in the association of Ca2+-F-, with coordination numbers dynamically oscillating in the range of 6-9, with 6 and 7 being the most favorable. The calculations show that for CaF(H2O)14+, the contact ion pair (CIP) is more favorable and occurs with no energy barrier, whereas the formation of CaF2(aq.) must overcome a ∼3.6 kJ mol-1 energy barrier; moreover, the CIP and solvent shared ion pair (SSIP) dynamically coexist for CaF2(H2O)14 in aqueous CaF2 solutions. Calculations for the dissociation process of CaF(H2O)6+ show a dramatic energy increase going from SSIP to free Ca2+ and F-, ascribed to the surprisingly long-range electrostatic attraction between Ca2+ and F- rather than to special F⋯H interactions. The energy increase results in the estimated association constant of CaF+ being larger than that previously measured using fluoride ion selective electrodes. This is attributed to the fact that the latter value might correspond to the ligand reaction of free Ca2+ and F- to form the Ca2+-F- SSIP. The combination of these results with CaF2(s) solubility measurements suggests that the higher-order Ca2+-F- complexes are absent in aqueous CaF2 solutions.

A spectroscopic study of solvent effects on the formation of Cu(ii)-chloride complexes in aqueous solution.

A combination of electronic (UV-vis) and X-ray absorption (EXAFS, XANES) spectroscopies has been used to investigate the formation of copper(ii)/chloride complexes in concentrated aqueous solutions. It is established that lowering the water activity by the addition of Mg(ClO4)2 at a constant Cl-/Cu(ii) ratio results in the replacement of water molecules by Cl- ions in the primary coordination shell of Cu(ii). This behavior closely parallels the effect of increasing the Cl-/Cu(ii) ratio and demonstrates that full understanding of the stoichiometry and structures of the complexes formed in concentrated metal-ion chloride solutions requires explicit consideration of the role of the solvent.

Prediction of pulmonary pressure after Glenn shunts by computed tomography-based machine learning models.

OBJECTIVES: This study aimed to develop non-invasive machine learning classifiers for predicting post-Glenn shunt patients with low and high risks of a mean pulmonary arterial pressure (mPAP) > 15 mmHg based on preoperative cardiac computed tomography (CT). METHODS: This retrospective study included 96 patients with functional single ventricle who underwent a bidirectional Glenn procedure between November 1, 2009, and July, 31, 2017. All patients underwent post-procedure CT, followed by cardiac catheterization. Overall, 23 morphologic parameters were manually extracted from cardiac CT images for each patient. The Mann-Whitney U or chi-square test was applied to select the most significant predictors. Six machine learning algorithms including logistic regression, Naive Bayes, random forest (RF), linear discriminant analysis, support vector machine, and K-nearest neighbor were used for modeling. These algorithms were independently trained on 100 train-validation random splits with a 3:1 ratio. Their average performance was evaluated by area under the curve (AUC), accuracy, sensitivity, and specificity. RESULTS: Seven CT morphologic parameters were selected for modeling. RF obtained the best performance, with mean AUC of 0.840 (confidence interval [CI] 0.832-0.850) and 0.787 (95% CI 0.780-0.794); sensitivity of 0.815 (95% CI 0.797-0.833) and 0.778 (95% CI 0.767-0.788), specificity of 0.766 (95% CI 0.748-0.785) and 0.746 (95% CI 0.735-0.757); and accuracy of 0.782 (95% CI 0.771-0.793) and 0.756 (95% CI 0.748-0.764) in the training and validation cohorts, respectively. CONCLUSIONS: The CT-based RF model demonstrates a good performance in the prediction of mPAP, which may reduce the need for right heart catheterization in post-Glenn shunt patients with suspected mPAP > 15 mmHg. KEY POINTS: • Twenty-three candidate descriptors were manually extracted from cardiac computed tomography images, and seven of them were selected for subsequent modeling. • The random forest model presents the best predictive performance for pulmonary pressure among all methods. • The computed tomography-based machine learning model could predict post-Glenn shunt pulmonary pressure non-invasively.

Phase Chemistry for Hydration Sensitive (De)intercalation of Lithium Aluminum Layered Double Hydroxide Chlorides.

Lithium aluminum layered double hydroxide chlorides (LADH-Cl) have been widely used for lithium extraction from brine. Elevation of the performances of LADH-Cl sorbents urgently requires knowledge of the composition-structure-property relationship of LADH-Cl in lithium extraction applications, but these are still unclear. Herein, combining the phase equilibrium experiments, advanced solid characterization methods, and theoretical calculations, we constructed a cyclic work diagram of LADH-Cl for lithium capture from aqueous solution, where the reversible (de)hydration and (de)intercalation induced phase evolution of LADH-Cl dominates the apparent lithium "adsorption-desorption" behavior. It is found that the real active ingredient in LADH-Cl type lithium sorbents is a dihydrated LADH-Cl with an Al:Li molar ratio varying from 2 to 3. This reversible process indicates an ultimate reversible lithium (de)intercalation capacity of ∼10 mg of Li per g of LADH-Cl. Excessive lithium deintercalation results in the phase structure collapse of dihydrated LADH-Cl to form gibbsite. When interacting with a concentrated LiCl aqueous solution, gibbsite is easily converted into lithium saturated intercalated LADH-Cl phases. By further hydration with a diluted LiCl aqueous solution, this phase again converts to the active dihydrated LADH-Cl. In the whole cyclic progress, lithium ions thermodynamically favor staying in the Al-OH octahedral cavities, but the (de)intercalation of lithium has kinetic factors deriving from the variation of the Al-OH hydroxyl orientation. The present results provide fundamental knowledge for the rational design and application of LADH-Cl type lithium sorbents.

Direct contact versus solvent-shared ion pairs in saturated NiCl2 aqueous solution: a DFT, CPMD, and EXAFS investigation.

In this work, a systematic investigation of the competition coordination of H2O and Cl(-) with Ni(2+) in saturated NiCl2 aqueous solution at room temperature was conducted using density functional theory (DFT), Car-Parrinello molecular dynamics (CPMD) simulations, and extended X-ray absorption fine structure (EXAFS) spectra. The calculated results reveal that the six-coordinated structure is favorable for [NiCl(x)(H2O)(n)](2-x) (x = 0-2; n = 1-12) clusters in the aqueous phase. The hydration energy calculation shows that the six-coordinated solvent-shared ion pair (SSIP) ([Ni(H2O)6(H2O)(n-6)Cl](+)) is more stable than its contact ion pair (CIP) ([NiCl(H2O)5(H2O)(n-5)](+)) isomer as n ≥ 9 in the aqueous phase, and the six-coordinated solvent-shared ion pair with a dissociated double Cl(-) (SSIP/d) ([Ni(H2O)6(H2O)(n-6)Cl2](0)) is more preferable than its CIP ([NiCl2(H2O)4(H2O)(n-4)](0)) and solvent-shared ion pair with single dissociated Cl(-) (SSIP/s) ([NiCl(H2O)5(H2O)(n-5)Cl](0)) isomers as n ≥ 11. The six-coordinated SSIP/d ([Ni(H2O)6(H2O)(n-6)Cl2](0)) conformers are the dominant structures in a saturated NiCl2(aq) solution (NiCl2 concentration: ~5.05 mol·kg(-1), corresponding to n ≈ 11). The CPMD simulations exhibited that there are six water molecules with Ni-O distance at ~205.0 pm on average around each Ni(2+) in the first hydration sphere, even in the saturated NiCl2 aqueous solution (~5.05 mol·kg(-1)) at room temperature, and no obvious Ni-Cl interaction was found. The EXAFS spectra revealed that the first solvation shell of Ni(2+) is an octahedral structure with six water molecules tightly bound in the NiCl2(aq) solution with a concentration ranging from 1.00 to 5.05 mol·kg(-1), and there is no obvious evidence of Ni-Cl contact ion pairs. A comprehensive conclusion from the DFT, CPMD, and EXAFS studies is that there is no obvious direct contact between Ni(2+) and Cl(-), even in saturated NiCl2 aqueous solution at room temperature.

A novel risk stratification model for STEMI after primary PCI: global longitudinal strain and deep neural network assisted myocardial contrast echocardiography quantitative analysis.

Background: In ST-segment elevation myocardial infarction (STEMI) with the restoration of TIMI 3 flow by percutaneous coronary intervention (PCI), visually defined microvascular obstruction (MVO) was shown to be the predictor of poor prognosis, but not an ideal risk stratification method. We intend to introduce deep neural network (DNN) assisted myocardial contrast echocardiography (MCE) quantitative analysis and propose a better risk stratification model. Methods: 194 STEMI patients with successful primary PCI with at least 6 months follow-up were included. MCE was performed within 48 h after PCI. The major adverse cardiovascular events (MACE) were defined as cardiac death, congestive heart failure, reinfarction, stroke, and recurrent angina. The perfusion parameters were derived from a DNN-based myocardial segmentation framework. Three patterns of visual microvascular perfusion (MVP) qualitative analysis: normal, delay, and MVO. Clinical markers and imaging features, including global longitudinal strain (GLS) were analyzed. A calculator for risk was constructed and validated with bootstrap resampling. Results: The time-cost for processing 7,403 MCE frames is 773 s. The correlation coefficients of microvascular blood flow (MBF) were 0.99 to 0.97 for intra-observer and inter-observer variability. 38 patients met MACE in 6-month follow-up. We proposed A risk prediction model based on MBF [HR: 0.93 (0.91-0.95)] in culprit lesion areas and GLS [HR: 0.80 (0.73-0.88)]. At the best risk threshold of 40%, the AUC was 0.95 (sensitivity: 0.84, specificity: 0.94), better than visual MVP method (AUC: 0.70, Sensitivity: 0.89, Specificity: 0.40, IDI: -0.49). The Kaplan-Meier curves showed that the proposed risk prediction model allowed for better risk stratification. Conclusion: The MBF + GLS model allowed more accurate risk stratification of STEMI after PCI than visual qualitative analysis. The DNN-assisted MCE quantitative analysis is an objective, efficient and reproducible method to evaluate microvascular perfusion.

Automatic Myocardial Contrast Echocardiography Image Quality Assessment Using Deep Learning: Impact on Myocardial Perfusion Evaluation.

OBJECTIVE: The image quality of myocardial contrast echocardiography (MCE) is critical for precise myocardial perfusion evaluation but challenging for echocardiographers. Differences in quality may lead to diagnostic heterogeneity. This study was aimed at achieving automatic MCE image quality assessment using a deep neural network (DNN) and investigating its impact on myocardial perfusion evaluation. METHODS: The Resnet-18 model was used for training and testing on internal and external data sets. Quality assessment involved three aspects: left ventricular opacification (LVO), shadowing, and flash adequacy; the quality score was calculated based on image quality. This study explored the impact of the DNN-based quality score on perfusion evaluation (normal, delay or obstruction) by echocardiographers (two seniors, one junior and one novice). Additionally, the effect of the score difference between re-scans on perfusion evaluation was investigated. RESULTS: The time cost for DNN prediction was 0.045 s/frame. In internal validation and external testing, the DNN achieved F1 and macro F1 scores >90% for quality assessment and had high intraclass correlation coefficients (0.954 and 0.892, respectively) in sequence quality scores. The proportion of segments deemed uninterpretable increased as the DNN-based quality score decreased. The agreement of perfusion assessment between one senior and others decreased as the quality score decreased. And the greater the score difference between the re-scans, the lower was the agreement on perfusion assessment by the same echocardiographer. CONCLUSION: This study determined the effectiveness of DNN for real-time automatic MCE quality assessment. It has the potential to reduce the variability in perfusion evaluation among echocardiographers.

Thermodynamic and Kinetic Studies on the Conversion of Solvent-Shared to Contact Ion Pairs in Sparingly Soluble MF2 (M = Mg2+ and Ca2+) Aqueous Solutions: Implications for Understanding Supersaturated Behavior and Association Constant Determination.

The thermodynamic and kinetic behaviors of Mg2+-F- ion pairing in aqueous solution are investigated theoretically and experimentally and are contrasted to those of Ca2+-F-. Thermodynamically, similar to CaFx(H2O)142-x (x = 1 and 2), MgF(H2O)y+ (y = 14-20) contact ion pairs (CIPs) are more stable than their solvent-shared ion pairs (SSIPs), whereas the CIPs and SSIPs of MF2(H2O)y are almost isoenergetic. However, in kinetics, the conversion of SSIPs to CIPs for M2+-F- (M = Mg2+ and Ca2+) ion pairing must overcome a high energy barrier due to the strong hydration of Mg2+ and F-. The kinetics dominate after the thermodynamics and kinetics are balanced, which hinders the formation of M2+-F- CIPs in practical MF2 aqueous solutions (less than or equal to saturated concentrations). This result is also supported by the 19F nuclear magnetic resonance spectra of saturated MF2 solutions. Although the interaction between Mg2+ and F- is slightly stronger than that between Ca2+ and F- due to the smaller radius of Mg2+, the formation of Mg2+-F- CIPs needs to go through two rate-limiting steps, the dehydration and entrance of F- (i.e., via exchange mode) with a higher energy barrier, due to the ability of strongly bound water molecules and rigorous octahedral coordinated configuration of Mg2+, while the formation of Ca2+-F- CIPs only goes through a single rate-limiting step, the entrance of F- (i.e., via swinging mode) with a lower energy barrier, due to the flexible coordination configuration of Ca2+. This is responsible for precipitation in MgF2 aqueous solution requiring a larger supersaturation degree and a lower precipitation rate than in CaF2. These kinetic factors lead to the association constants previously reported for MF+ determined by a fluoride ion-selective electrode (ISE) combined with the titration method, where the MF2 solutions were always unsaturated at the titration end point, which actually corresponds to those of the ligand process going from completely free M2+ and F- to their SSIPs. A possible strategy to accurately determine the association constants of MF+ and MF2(aq) CIPs by fluoride ISEs is proposed. The present results suggest that judging the formation of M2+-F- CIPs in practical solutions from a theoretical calculation perspective requires significant consideration of the kinetic factors, except for the thermodynamic factors.

Distributed contrastive learning for medical image segmentation.

Supervised deep learning needs a large amount of labeled data to achieve high performance. However, in medical imaging analysis, each site may only have a limited amount of data and labels, which makes learning ineffective. Federated learning (FL) can learn a shared model from decentralized data. But traditional FL requires fully-labeled data for training, which is very expensive to obtain. Self-supervised contrastive learning (CL) can learn from unlabeled data for pre-training, followed by fine-tuning with limited annotations. However, when adopting CL in FL, the limited data diversity on each site makes federated contrastive learning (FCL) ineffective. In this work, we propose two federated self-supervised learning frameworks for volumetric medical image segmentation with limited annotations. The first one features high accuracy and fits high-performance servers with high-speed connections. The second one features lower communication costs, suitable for mobile devices. In the first framework, features are exchanged during FCL to provide diverse contrastive data to each site for effective local CL while keeping raw data private. Global structural matching aligns local and remote features for a unified feature space among different sites. In the second framework, to reduce the communication cost for feature exchanging, we propose an optimized method FCLOpt that does not rely on negative samples. To reduce the communications of model download, we propose the predictive target network update (PTNU) that predicts the parameters of the target network. Based on PTNU, we propose the distance prediction (DP) to remove most of the uploads of the target network. Experiments on a cardiac MRI dataset show the proposed two frameworks substantially improve the segmentation and generalization performance compared with state-of-the-art techniques.

Myocardial Segmentation of Cardiac MRI Sequences With Temporal Consistency for Coronary Artery Disease Diagnosis.

Coronary artery disease (CAD) is the most common cause of death globally, and its diagnosis is usually based on manual myocardial (MYO) segmentation of MRI sequences. As manual segmentation is tedious, time-consuming, and with low replicability, automatic MYO segmentation using machine learning techniques has been widely explored recently. However, almost all the existing methods treat the input MRI sequences independently, which fails to capture the temporal information between sequences, e.g., the shape and location information of the myocardium in sequences along time. In this article, we propose a MYO segmentation framework for sequence of cardiac MRI (CMR) scanning images of the left ventricular (LV) cavity, right ventricular (RV) cavity, and myocardium. Specifically, we propose to combine conventional neural networks and recurrent neural networks to incorporate temporal information between sequences to ensure temporal consistency. We evaluated our framework on the automated cardiac diagnosis challenge (ACDC) dataset. The experiment results demonstrate that our framework can improve the segmentation accuracy by up to 2% in the Dice coefficient.

[CuCl3]- and [CuCl4]2- hydrates in concentrated aqueous solution: a density functional theory and ab initio study.

In this work, structures and thermodynamic properties of [CuCl(3)](-) and [CuCl(4)](2-) hydrates in aqueous solution were investigated using density functional theory and ab initio methods. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) structures were both taken into account. Our calculations suggest that [CuCl(3)(H(2)O)(n)](-) clusters might favor a four-coordinated CIP structure with a water molecule coordinating with the copper atom in the equatorial position for n = 3 and 4 in aqueous solution, whereas the four-coordinated SSIP structure with one chloride atom dissociated becomes more stable as n increases to 5. For the [CuCl(4)](2-) cluster, the four-coordinated tetrahedron structure is more stable than the square-planar one, whereas for [CuCl(4)(H(2)O)(n)](2-) (n ≥ 1) clusters, it seems that four-coordinated SSIP structures are slightly more favorable than CIP structures. Our calculations suggest that Cu(2+) perhaps prefers a coordination number of 4 in CuCl(2) aqueous solution with high Cl(-) concentrations. In addition, natural bond orbital (NBO) calculations suggest that there is obvious charge transfer (CT) between copper and chloride atoms in [CuCl(x)](2-x) (x = 1-4) clusters. However, compared with that in the [CuCl(2)](0) cluster, the CT between the copper and chloride atoms in [CuCl(3)](-) and [CuCl(4)](2-) clusters becomes negligible as the number of attached redundant Cl(-) ions increases. This implies that the coordination ability of Cl(-) is greatly weakened for [CuCl(3)](-) and [CuCl(4)](2-) clusters. Electronic absorption spectra of these different hydrates were obtained using long-range-corrected time-dependent density functional theory. The calculated electronic transition bands of the four-coordinated CIP conformer of [CuCl(3)(H(2)O)(n)](-) for n = 3 and 4 are coincident with the absorption of [CuCl(3)](-)(aq) species (∼284 and 384 nm) resolved from UV spectra obtained in CuCl(2) (ca. 10(-4) mol·kg(-1)) + LiCl (>10 mol·kg(-1)) solutions, whereas the calculated bands of [CuCl(3)(H(2)O)(n)](-) in their most stable configurations are not when n = 0 - 2 or n > 4, which means that the species [CuCl(3)](-)(aq) exists in those CuCl(2) aqueous solutions in which the water activity is neither too low nor too high. The calculated bands of [CuCl(4)(H(2)O)(n)](2-) clusters correspond to the absorption spectra (∼270 and 370 nm) derived from UV measurements only when n = 0, which suggests that [CuCl(4)](2-)(aq) species probably exist in environments in which the water activity is quite low.

A deep learning approach with temporal consistency for automatic myocardial segmentation of quantitative myocardial contrast echocardiography.

Quantitative myocardial contrast echocardiography (MCE) has been proved to be valuable in detecting myocardial ischemia. During quantitative MCE analysis, myocardial segmentation is a critical step in determining accurate region of interests (ROIs). However, traditional myocardial segmentation mainly relies on manual tracing of myocardial contours, which is time-consuming and laborious. To solve this problem, we propose a fully automatic myocardial segmentation framework that can segment myocardial regions in MCE accurately without human intervention. A total of 100 patients' MCE sequences were divided into a training set and a test set according to a 7: 3 proportion for analysis. We proposed a bi-directional training schema, which incorporated temporal information of forward and backward direction among frames in MCE sequences to ensure temporal consistency by combining convolutional neural network with recurrent neural network. Experiment results demonstrated that compared with a traditional segmentation model (U-net) and the model considering only forward temporal information (U-net + forward), our framework achieved the highest segmentation precision in Dice coefficient (U-net vs U-net + forward vs our framework: 0.78 ± 0.07 vs 0.79 ± 0.07 vs 0.81 ± 0.07, p < 0.01), Intersection over Union (0.65 ± 0.09 vs 0.66 ± 0.09 vs 0.68 ± 0.09, p < 0.01), and lowest Hausdorff Distance (32.68 ± 14.6 vs 28.69 ± 13.18 vs 27.59 ± 12.82 pixel point, p < 0.01). In the visual grading study, the performance of our framework was the best among these three models (52.47 ± 4.29 vs 54.53 ± 5.10 vs 57.30 ± 4.73, p < 0.01). A case report on a randomly selected subject for perfusion analysis showed that the perfusion parameters generated by using myocardial segmentation of our proposed framework were similar to that of the expert annotation. The proposed framework could generate more precise myocardial segmentation when compared with traditional methods. The perfusion parameters generated by these myocardial segmentations have a good similarity to that of manual annotation, suggesting that it has the potential to be utilized in routine clinical practice.

Hydrates of Cu2+ and CuCl+ in dilute aqueous solution: a density functional theory and polarized continuum model investigation.

In this work, structures, and properties of Cu(2+) and CuCl(+) hydrates in the gas and aqueous phases have been investigated using the B3LYP method. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) were both taken into account for CuCl(+) hydrates. Our calculations show that [Cu(H(2)O)(n)](2+) clusters favor a very open four-coordinated structure for n = 5-12 in the gas phase, while a five-coordinated conformer is favored for n > or = 8 in the aqueous phase. An approximate complete solvation shell of Cu(2+) in the aqueous phase needs more than 12 water molecules, while that of CuCl(+) in the aqueous phase needs only about eight water molecules. For [CuCl(H(2)O)(n)](+) clusters, the most stable structure is a four-coordinated CIP conformer for n = 4-7 in the gas phase and a five-coordinated CIP conformer for n = 8-10 in the aqueous phase. However, the five-coordinated CIP/h conformer (CIP conformer that the axial chloride atom tends to dissociate) of [CuCl(H(2)O)(n)](+) clusters becomes more favorable as n increases to 11. As the hydration process proceeds, the charges on the copper atom of [Cu(H(2)O)(n)](2+) clusters decrease, while those of [CuCl(H(2)O)(n)](+) clusters increase (probably due to the dissociation of Cl(-)). The d-d electron transition and partial charge transition band around 160 nm of the five-coordinated conformer of [Cu(H(2)O)(n)](2+) clusters and those bands (approximately 170 and approximately 160 nm) of SSIP or five-coordinated CIP/h conformers of [CuCl(H(2)O)(n)](+) clusters are coincident with the absorption of [Cu](2+)(aq) species (approximately 180 nm) resolved from the spectra obtained in trace CuCl(2) (ca. 10(-5) mol x kg(-1)) + LiCl (0-18 mol x kg(-1)) aqueous solution, while those of five-coordinated CIP conformers of [CuCl(H(2)O)(n)](+) clusters (n = 8 and 9) around 261 and 247 nm correspond to the absorption of [CuCl](+)(aq) species (approximately 250 nm). Our calculated electronic spectra indicate that the typical peak of copper(II)-chloride complexes changes from 180 to 250 nm, and 275 nm, as the process of Cl(-) coordination. For [Cu](2+)(aq), [CuCl](+)(aq), and [CuCl(2)](0)(aq) species, the central Cu(II) atom prefers five-coordination.

Hydrates of copper dichloride in aqueous solution: a density functional theory and polarized continuum model investigation.

In this work, the hydrates of copper dichloride in gas and aqueous phase have been investigated using the B3LYP method. Low-lying conformers of CuCl(2)(H(2)O)(n) clusters for n = 1-10 were obtained by an extensive conformation search. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) with one dissociated chloride atom (SSIP/s) and SSIP with two dissociated chloride atoms (SSIP/d) all were considered. Our calculations present such a trend that a four-fold CIP conformer is more favorable for CuCl(2)(H(2)O)(n) cluster (n < or = 7) and four-fold SSIP/s for n = 8-10 in the gas phase, while in aqueous solution, more stable structures are five-fold SSIP/s conformer for n = 7-9 and four-fold CIP conformer for n = 2-6. Hydrogen bond (HB) plays an important role in the CuCl(2) solvation, especially HBs formed between the first and second solvation shell water molecules. Electronic absorption spectra of CuCl(2)(H(2)O)(n) clusters were obtained using long-range-corrected time-dependent density functional theory. The calculated electronic absorption peak around 270 nm of CIP conformers is coincident with the absorption of [CuCl(2)](0)(aq) species resolved from the spectra obtained in solutions of trace CuCl(2) (ca. 10(-5) mol/kg) + LiCl (0-18 m), while those of SSIP/s (approximately 250 nm) and SSIP/d (approximately 180 nm) conformers probably correspond to the absorption spectra of [CuCl](+)(aq) and [Cu](2+)(aq) species, respectively. Natural bond orbital charge population analyses show that charge transfer (CT) between a central copper(II) atom and ligands (Cl and H(2)O) increases as the hydrated cluster expands, especially CT from Cu(2+) to the first solvation shell, which enhances the strength of HBs. Such CT becomes more apparent for SSIP structure with the dissociation of chloride ion. OH stretching vibration frequencies of proton donor type water in CuCl(2)(H(2)O)(n) clusters are obviously red-shifted in comparison to those of water clusters, due to CT between the central atom Cu and ligands. SSIP conformers have apparent IR absorption peaks of OH stretching vibration at approximately 3000 cm(-1) for the effect of half-dissociated chloride atoms.

Nature of Monomeric Molybdenum(VI) Cations in Acid Solutions Using Theoretical Calculations and Raman Spectroscopy.

The composition and structures of the two protonated species formed from uncharged molybdic acid, MoO2(OH)2(OH2)20, in strongly acidic solutions have been investigated using a combination of density functional theory calculations, first-principles molecular dynamics simulations, and Raman spectroscopy. The calculations show that both protonated species maintain the original octahedral structure of molybdic acid. Computed p Ka values indicated that the ═O moieties are the proton acceptor sites and, therefore, that MoO(OH)3(OH2)2+ and Mo(OH)4(OH2)22+ are the probable protonated forms of Mo(VI) in strong acid solutions, rather than the previously accepted MoO2(OH)2- x(OH2)2+ x x+ ( x = 1, 2) species. This finding is shown to be broadly consistent with the observed Raman spectra. Structural details of MoO(OH)3(OH2)2+ and Mo(OH)4(OH2)22+ are reported.

Thermodynamic modeling of poorly complexing metals in concentrated electrolyte solutions: an X-ray absorption and UV-Vis spectroscopic study of Ni(II) in the NiCl2-MgCl2-H2O system.

Knowledge of the structure and speciation of aqueous Ni(II)-chloride complexes is important for understanding Ni behavior in hydrometallurgical extraction. The effect of concentration on the first-shell structure of Ni(II) in aqueous NiCl2 and NiCl2-MgCl2 solutions was investigated by Ni K edge X-ray absorption (XAS) and UV-Vis spectroscopy at ambient conditions. Both techniques show that no large structural change (e.g., transition from octahedral to tetrahedral-like configuration) occurs. Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at RNi-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range. However, XANES, EXAFS and UV-Vis data show subtle changes at high salinity (> 2 mol∙kg(-1) NiCl2), which are consistent with the formation of small amounts of the NiCl+ complex (up to 0.44(23) Cl at a Ni-Cl distance of 2.35(2) Å in 5.05 mol∙kg(-1) NiCl2) in the pure NiCl2 solutions. At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present. We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.

Pyrolysis of EVA and its application in recycling of photovoltaic modules.

The basic pyrolysis behaviour of ethylene vinyl acetate (EVA) copolymer, which is often used as a lamination agent in solar modules, was investigated in thermogravimetry, differential thermal analysis(DTA) and thermovolumetry. The TG analysis showed that the EVA pyrolysis can be accelerated under the partial oxidizing atmosphere but the end pyrolysis temperature must be higher than in nitrogen, to eliminate the coke formed. Meanwhile, a strong exothermal peak occurs at about 450 degrees C under the air condition and gets weaker obviously at the oxygen content lower than 10 vol. %. The mass balance of EVA pyrolysis was given through the thermovolumetry with the output of 10 wt. % permanent gas, 89.9 wt. % condensate and 0.1% residual coke. Besides, the composition of the permanent gas and condensate at different pyrolysis stages were analysed and interpreted on the known pyrolysis mechanism.

Solubility of rare earth metal bromides and iodides in aqueous systems.

ABSTRACT: The International Union of Pure and Applied Chemistry (IUPAC) project of collection, compilation, and critical evaluation of solubility data of bromides and iodides of the scandium group and all lanthanides in water and aqueous systems containing either halide acids, halide salts, or organic compounds is under preparation. As a result of their similarity to the chlorides, which were recently evaluated, the bromides and iodides in the lanthanide series should show some regularities in their solubility data. Unfortunately, the corresponding results show a large scatter when ordered according to the atomic number. Thus, it is complicated to select the best data for recommendation. Reasons for the inaccuracy of solubility measurements are outlined. In fact some solubility values of bromides predicted by correlation with chlorides seem to be more reliable than the experimental ones. As sufficient experimental data at various temperatures were available, the water-rich fragment of the LaBr3-H2O equilibrium phase diagram has been formed and depicted. It seems to be similar to the well-known LaCl3-H2O diagram. Several regularities, with respect to stoichiometry and solubility of compounds formed, were observed during investigations of the aqueous ternary systems. The complex iodides of various lanthanides display more regularities in their properties than the bromides do.