Recovery of nitric acid from waste etching solution using solvent extraction.
A process was developed to recover nitric acid from the waste stream of wafer industry using solvent extraction technique. Tributyl phosphate (TBP) was selected among several extractants because of its better selectivity towards HNO(3), overall superiority in operation, favorable physical properties and economics. The waste solution containing 260 g/L CH(3)COOH, 460 g/L HNO(3), 113 g/L HF and 19.6g/L Si was used as feed solution for process optimization. In the pre-treatment stage >99% silicon and hydrofluoric acid was precipitated out as Na(2)SiF(6). Equilibrium conditions for HNO(3) recovery were optimized from the batch test results as: four stages of extraction at an organic:aqueous (O:A) ratio of 3, four stages of scrubbing at O:A ratio of 5 and five stages of stripping at an O:A ratio of 1.5. The extraction of HNO(3) was suppressed by the presence of acetic acid (HAc) in the feed solution. To examine the feasibility of the extraction system a continuous operation was carried out for 200 h using a multistage mixer-settler. The concentration of pure HNO(3) recovered was 235 g/L with a purity of 99.8%.
Science and technology of tributyl phosphate
Volume 3 is primarily devoted to the PUREX process, with special emphasis on its chemistry. Chapter 1 describes the general process layout and special flowsheets applied in various plants, together with the chemistry of both the product elements and the process reagents. Two more chapters deal with the details of fission product and neptunium behavior in the process. Another nuclear application of tributyl phosphate (TBP) solvent extraction is the recovery of plutonium values from fuel fabrication scrap and similar wastes, which is treated in Chapter 4. Computer modeling of extraction processes is an exciting and most useful area where great progress has been made in recent years, and this is dealt with in Chapter 5. Finally, there are extraction procedures where TBP does not primarily act as an extractant by itself, but instead is used as a phase modifier to improve the compatibility of reactants in a different extractant-diluent system.
Heats of dilution of trialkyl phosphates in iso-octane and carbon tetrachloride: Interpretation in terms of self-association
The heats of solution and dilution of triethyl phosphate (TEP), tripropyl phosphate (TPP), and tributyl phosphate (TBP) in iso-octane have been measured at 25°C. The enthalpy of dilution was found to decrease with hydrocarbon chain length. The resulting apparent molal heat content, φL, values are interpreted in terms of the degree and nature of the associated species present assuming that the heat of dilution is essentially due to the breakdown of the various associated species. The results are consistent with a monomer-to-dimer model. Equilibrium constants and enthalpy change values are calculated for the dimerization reaction. The heat of dilution of TBP in carbon tetrachloride was exothermic rather than endothermic, indicating significant solute-solvent interaction.