Kinetics of extraction of nitric acid into binary mixture of tri-n-butyl phosphate and normal paraffin hydrocarbon

Selective Separation of HNO3 and HCl by Extraction: The Investigation on the Noncovalent Interaction between Extractants and Acids by Density Functional Theory

There is a huge demand for the highly selective separation of HNO₃ and HCl in many industries, and solvent extraction is considered a feasible method. In this article, DFT calculations were performed to investigate the interactions between acids and extractants including alcohols, ketones, phosphorus, and amines. One of the significant findings to emerge from this study is that amines bind to acids through ion association. Nevertheless, the interaction between acids and alcohols, ketones, and phosphorus with a (RO)₃P═O structure is mainly dominated by hydrogen bonds. The change of Gibbs free energy in the extraction process shows that the phosphorus ((RO)₃P═O) is superior to other types of extractants in the selective separation of HNO₃ and HCl. Furthermore, after the alkoxyl group (RO-) in phosphorus ((RO)₃P═O) is replaced by RN- or R- with less electronegativity, the interaction between HCl and the substituted extractants transitions from a hydrogen bond to ion association, but there are still strong hydrogen bonds between them and HNO₃. That will lead to a decrease in the selectivity of phosphorus due to the change in interaction types. This new understanding should help the design and screening of efficient extractants for the separation of mineral acids.

Online Monitoring of Solutions Within Microfluidic Chips: Simultaneous Raman and UV-Vis Absorption Spectroscopies

Microfluidics is an appealing analytical tool in the global effort to close the nuclear fuel cycle. Using a microfluidic chip permits the analysis of greatly reduced sample volumes compared to what is necessary for traditional analytical methods. There is a commensurate reduction in disposal volume and cost. The development of novel sensors is necessary to take full advantage of the microchip configuration, where optical-spectroscopy-based approaches offer a powerful route to characterize chemical composition. This study uses simultaneously applied UV-vis and micro-Raman spectroscopies adapted to function on the microscale to analyze in situ both the Nd³⁺ (UV-vis-active) and HNO₃ (Raman-active) concentrations in the same sample. An adjustable translation platform was designed to hold the micro-Raman probe above and perpendicular to the chip face and the UV-vis probe in the plane of the chip. These complimentary spectral techniques when processed through multivariate partial least-squares (PLS) models gave an accurate picture of the widely varying solution concentrations as a function of time for each solution component. Solution matrix effects can drastically alter analyte signatures as measured by both UV-vis absorbance and Raman spectroscopy. PLS methods successfully modeled these spectral changes and accurately measured concentrations of components of interest within the microfluidic chip.