Abstract
Abstract The selective extraction of nitric and acetic acids from a simulated etching waste acid was investigated using a mixture of the extractants Alamine 336 (N235) and methyl isobutyl ketone (MIBK). The effects of dilution of the etching waste acid, N235 and MIBK concentrations, organic/aqueous (O/A) phase ratio, extraction temperature, and contact time were systematically studied. The results demonstrate that with an extractant mixture of the composition 12.5 vol% N235 and 87.5 vol% MIBK, 75% acetic acid and 85% nitric acid were extracted. However, only 3% phosphoric acid was co-extracted in a single-stage contact under the following conditions: phosphoric acid concentration of 385 g/L in the diluted acid, O/A ratio of 1.5:1, reaction temperature of 25–35 °C and reaction time of 10 min. The McCabe-Thiele analysis predicts that over 98% acetic acid and 99% nitric acid can be extracted, with co-extraction of only 5% phosphoric acid through a three-stage counter-current operation at an O/A ratio of 3:2. Further, ∼99% HNO 3 , 99% HAC, and 99% H 3 PO 4 loaded in the organic phase were stripped using 0.25 mol/L NH 3 ·H 2 O as the stripping agent at an O/A ratio of 1:2. Therefore, it is feasible to achieve almost complete separation of nitric acid and acetic acid from the waste acid to obtain purified phosphoric acid and a binary compound fertilizer containing the nutritional elements nitrogen and phosphorus. The compositions of the extraction complexes of different acids were determined to be H 3 PO 4 ·2N235, HAC·1.5N235 and HNO 3 ·N235 for the N235 extraction and HAC·2MIBK for the MIBK extraction of HAC. The results can explain the extraction tendencies of the three acids obtained above. Analyses of the FT-IR spectra of the loaded organic phases indicate that the N235 extraction of HNO 3 occurred by the ion pair association mechanism, while the acetic acid extraction using N235 or MIBK was realized through hydrogen bonding.
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