Modeling of Equilibria for the Solvent Extraction of Ammonia with LIX84I

Abstract

Solvent extraction of valuable metals such as copper and nickel is often carried out from ammoniacal alkaline solutions with chelating extractants, during which coextraction of ammonia is inevitable. In the present study, as a basis of modeling of the whole ammoniacal extraction process, the equilibrium distribution ratios of ammonia between a 3 mol L -1 ammonium nitrate solution and LIX84I (the active component of which is 2-hydroxy-5-nonylacetophenone oxime, HR) dissolved in a nonpolar diluent were measured as a function of pH and LIX84I concentration at 298 K. We successfully modeled the measurement results by assuming the formation of two associated species, (HR) n ･(NH 3 ) and (HR･NH 3 ) n , the aggregation of HR, and the dissociation of NH 4 + . Fourier transform infrared spectroscopy results suggested that ammonia was extracted via hydrogen bonding with HR, and these results were in accord with the proposed equilibrium model. IntroductionSolvent extraction is a commonly used method for hydrometallurgical recovery of metal ions because of its high separation efficiency and relatively low cost. Acidic solutions are the usual media for solvent extraction, but ammoniacal alkaline solutions are sometimes employed for the processing of copper and nickel, owing to the ability of these metal ions to form complexes with ammonia.This process consists of the following steps: (i) Extraction of both copper and nickel from the ammoniacal alkaline solutions with a chelating reagent such as a β-hydroxyoxime or a β-diketone; metal extraction is accompanied by ammonia extraction. (ii)Scrubbing of coextracted ammonia with dilute acid to avoid the accumulation of ammonium salts in the electrolyte in the subsequent step; these salts tend to precipitate, owing to theirSelective stripping of nickel from the organic phase with an acid at a relatively low concentration. (iv)Stripping of copper with an acid at a higher concentration and simultaneous regeneration of the extractant. Although this process has been extensively studied [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], quantitative studies of the equilibria are scarce. Flett and Melling [19] are the only investigators to have analyzed ammonia extraction; they showed good agreement between experimental results obtained with a -hydroxyoxime (LIX65N, 10 vol%) in an aliphatic diluent and the results obtained with a model that assumed the formation of a monomeric 1:1 extractant/ammonia adduct. As for metal extraction, Rice et al. [20] studied nickel extraction with SME-529 (the former brand name of LIX84I). Tanaka and Alam [21] conducted a detailed study of the equilibrium for nickel extraction with LIX84I and obtained satisfactory agreement between experimental and calculated results; however, these investigators did not consider ammonia extraction during the analysis.Our ultimate goal is to establish a quantitative equilibrium model for the ammoniacal process, including extraction of copper, nickel, and ammonia with LIX84I and their stripping or scrubbing, t...

Equilibrium Modeling of the Extraction of Copper and Ammonia from Alkaline Media with the Extractant LIX84I

“…In our previous paper 19) , we examined the equilibria established during the extraction of ammonia with LIX84I (active component, 2-hydroxy-5-nonylacetophenone oxime, HR) from a 3 kmol m −3 solution of ammonium nitrate in the absence of metal ions, and found that the distribution ratios obtained experimentally were in good agreement with those calculated by an equilibrium model which assumed the formation of adducts between ammonia and the extractant.…”

Equilibrium Modeling for Solvent Extraction of Nickel and Ammonia from Alkaline Media with the Extractant LIX84-I

“…19) The concentration of ammonia in the loaded organic phase was determined in the same way after complete stripping with 0.1 kmol m ¹3 HCl. 17) Distribution ratios of the metals ion M 2+ (where M = Ni or Cu) (D(M)) and of NH 3 (D(NH 3 )) were calculated as…”

“…Here i denotes the order of aggregation and a positive integer ranging to infinity, and K m is assumed to be independent of i. 17) nickel, and copper 18) Extraction equilibrium of ammonia with HR (K 1 ) is expressed as…”

“…The dependencies of log D(NH 3 ) on pH eq and I were consistent with those we reported proviously. 17,18) Log D was calculated at a given pH eq and I (Fig. 5, curves).…”

“…We have previously examined extraction of nickel, 16) ammonia, 17) and copper and ammonia 18) from alkaline media with the commercial extractant LIX84-I (active component, 2-hydroxy-5-nonylacetophenone oxime; HR). The equilibrium model we proposed can reproduce the experimental values with satisfactory accuracy at a given equilibrium pH (pH eq ).…”