Extractive Separation of Oxalic and Nitric Acids Using Tributyl Phosphate
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NOLOGY OF ORGANIC SUBSTANCES
Extractive Separation of Oxalic and Nitric Acids Using Tributyl Phosphate G. V. Kostikovaa, * and I. E. Mal’tsevaa aFrumkin
Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, 119071 Russia *e-mail: [email protected] Received February 9, 2018; revised March 16, 2018; accepted April 24, 2018
Abstract—The extraction of nitric and oxalic acids by neutral compounds TBP, DBBP, and TBPO have been studied. The optimal conditions of their separation are determined. The simulation of separation process of nitric and oxalic acids from waste solutions after the oxalate precipitation of rare-earth elements using undiluted TBP as extractant is performed by the simple counterflow method and the counterflow method with part of flow being returned into the center of cascade. Keywords: extraction, tributyl phosphate, nitric acid, oxalic acid, separation DOI: 10.1134/S0040579519050105
INTRODUCTION The oxalate precipitation of rare-earth concentrates or individual lanthanides performed in warm solutions containing 60 g/L of rare-earth elements (REEs); 1 M of HNO3; and approximately three-fold excess of stoichiometrically required amount of oxalic acid, sodium oxalate, or ammonium oxalate is one of the final stages of extractive processes of isolation and separation of REEs [1–4]. After the separation of oxalate residue, solutions containing about 1 M of HNO3 and 0.3 M of oxalic acid, which cannot be used for the production of nitrogen fertilizers due to a high concentration of oxalate anion, are obtained. If the large-capacity production of REEs is soon launched in Russia, then these solutions will be unreclaimable waste harming the environment like before. Thus, the separation of nitric and oxalic acids from the solutions obtained after oxalate precipitation is an urgent problem. Its solution would allow regenerating valuable oxalic acid and using nitric acid for the by-product acquisition of nitrogen fertilizers. Neutral oxygen-containing compounds characterized by high extractive ability towards various acids can be used as extractants to solve this problem by the liquid extraction technique. Tributyl phosphate is one of the most available and widespread extractants used in industry. However, phosphonates and phosphine oxides attracted interest in terms of these studies. Literary sources contain rather detailed data on the extraction of different inorganic acids by neutral oxygen-containing extractants [5–11]. However, the selective extraction of oxalic acid is significantly less
studied [12–15]. In these papers the distribution of acids between aqueous and organic phases was studied and the compositions of the extracted compounds and thermodynamic characteristics of extractive systems were determined. However, the solution of every particular problem requires additional studies taking into account all the required initial conditions. EXPERIMENTAL Commercial tributyl phosphate (TBP), dibutyl butylphosphonate (DBBP), and tributylphosphine oxide (TBPO) of technica
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