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%.
MODELLING OF NITRIC ACID AND WATER EXTRACTION FROMAQUEOUS SOLUTIONS CONTAINING A SALTING-OUT AGENT BY TRI-N-BUTYLPHOSPHATE
ABSTRACT A thermodynamic model is presented for nitric acid and water extraction equilibria by tri-n-butylphosphate (10, 30, 50 and 100 vol%) in dodecane from aqueous solutions containing nitric acid (0-14M) and in presence or not of a salting-out agent (lithium nitrate, ammonium nitrate). The activity coefficient of nitric acid was calculated from experimental data using MIKULIN's equation, and those of the components in the organic phase were calculated by SERGIEV SKI I-D ANNUS’ equation. A satisfactory description of the distribution of nitric acid and water is obtained in a wide range of acidity of the aqueous phase by taking into account the formation of the following complexes: TBP, TBPH2O, HNO3H2O,TBP HNO3,(TBP)2HNO3H2O,TBP.(HNO3)2
Activities and interaction in the Tri-n-butyl phosphate-water system
Abstract The solubility of water in TBP at 25°C and various water activities was measured by the isopiestic vapour balancing technique. The solubility follows Henry's law, XH2O = (0·478 ± 0·002)aH2O up to XH2O = 0·36 (CH2O = 1·2 M) at aH2O = 0·75, then deviates gradually at higher concentrations up to XH2O = 0·511 (CH2O = 3·58 ± 0·02 M) at saturation. The corresponding activities of TBP were calculated via the Gibbs-Duhem relation, and from these, the partial molal free energies of mixing. The activity coefficients of TBP are close to unity throughout, the greatest deviation being at water saturation: fTBP = 1·054 (mole fraction scale). Densities and thence partial molal volumes, as a function of the molality of water in TBP, were determined at both 25°C, V H 2 O = (17·08 ± 0·05) + (0·422 ± 0·04)m 1 2 and V TBP = 273·8 and 2°C, V H 2 O = (16·69 ± 0·03) + (0·526 ± 0·03)m 1 2 and V TBP = 268·3 n 1/ mole . The densities and excess partial free energies and also dielectric constants of the TBP·H2O mixtures were examined for evidence of compound formation. The former did not show any such evidence. Dielectric constants at 2°C showed a slight interaction at mole ratio 1:1, indicating that a TBP·H2O complex does exist but is only weakly bonded.