Solvent Extraction of Iron from Aluminium Nitrate Solutions
Total Page：16
File Type：pdf, Size：1020Kb
SOLVENT EXTRACTION OF IRON FROM ALUMINIUM NITRATE SOLUTIONS by MICHAIL IOANNOU STEFANAKIS Mill, and Met. Engineer National Technical University of Athens A thesis submitted for the Degree of Doctor of Philosophy of the University of London Department of Metallurgy and January 1982 Materials Science, Royal School of Mines, Imperial College of Science and Technology. F I I Dedicated to my parents and my brother I '$ucris KpU7TTea0a\ 4> i X e i ... ! (HpaKAeiT os The real constitution of things, is accustomed to hide itself Heraclitus [G.K. Kirk, "Heraclitus: The Cosmic Fragments", Cambridge 1954, p.227] ABSTRACT A study has been carried out on the solvent extraction of iron(lll) from aluminium nitrate solutions using Versatic 10 extractant in Escaid 110 diluent. Factorial experiments were performed for the evalu- ation of the effect of variables such as, temperature, extractant and aqueous iron(IIl) concentration, pH and aqueous aluminium concentration. Extraction isotherms of iron(III) were derived using the AKUFVE 110 apparatus coupled with a pH-stat deVice. Equilibrium data were evaluated by classical slope analysis and by the use of statistical techniques. Statistical determination of the most probable complexes in the organic phase was carried out by a computer program. Infrared analysis of the extracts was also performed and the results were found to be in good agreement with the aforementioned methods. Equilibrium constant values derived by the statistical analysis of equilibrium data were used for the formulation of a chemically-based model for the prediction of equilibrium composition profile of a countercurrent cascade. A computer program was written to perform the stagewise calculations and the agreement between experi- mental and predicted values was found to be It seems that iron purification of aluminium leach liquors arising from acid treatment of non-bauxite aluminium-bearing materials for the production of aluminium is technically feasible by solvent extraction with Versatic 10 acid. V CONTENTS Abstract 1V Contents v List of symbols x Chapter 1 INTRODUCTION 1 Chapter 2 ACIDIC METHODS FOR PRODUCING ALUMINA FROM NON-BAUXITIC ALUMINIUM BEARING MATERIALS 4 • Chapter 3 CARBOXYLIC ACIDS AS METAL EXTRACTANTS 13 3.1 Applications 13 3.2 Distribution of carboxylic acids between the aqueous and organic phases l4 3.3 Equilibrium data treatment 18 3.4 Mechanism of iron extraction 24 3.5 Mechanism of Aluminium extraction 33 3.6 Modelling of equilibrium data 34 Chapter 4 EXPERIMENTAL PROCEDURE AND MATERIALS 39 4.1 Materials and their specifications 39 4.2 Analytical methods 4l 4.2.1 Iron 41 4.2.2 Aluminium 45 4.2.3 pH 45 4.3 Experimental procedure 48 Chapter 5 PRELIMINARY EXPERIMENTS 55 5.1 Initial observations 55 5.2 Loading of Versatic 10 with Fe(lll) and AI(III) 57 5.2.1 Experimental 57 » vi Page 5.2.2 Results 57 5.2.3 Discussion 60 5.3 Phase separation studies 6l Chapter 6 2k_1 FACTORIAL EXPERIMENTS 63 6.1 Introduction 63 6.2.1 Experimental 6.2.2 Results 6.2.3 Discussion 76 6.3 Coextraction of Al(IIl) 79 6.4 Conclusions 79 Chapter 7 EQUILIBRIUM EXTRACTION ISOTHERMS OF Fe(lll) 81 7-1 Introduction 8l 7.2.1 Experimental 82 7-2.2 Results and Discussion 82 7.3 Characteristics of Al(lll) extraction - Coextraction of Al(lll) with Fe(IIl) 108 7.4 Conclusions 109 Chapter 8 HYDRATION IN THE ORGANIC PHASE m 8.1 Introduction 111 8.2 Experimental procedure Hi 8.2.1 Standardization of Karl Fischer reagent with water-methanol solution 112 8.2.2 Standardization of Karl Fischer reagent with water 112 8.2.3 Determination of water in the organic phase 112 8.3 Results 113 8.4 Discussion H3 8.5 Conclusions H5 vii Page Chapter 9 STATISTICAL EVALUATION OF EQUILIBRIUM DATA FOR THE DETERMINATION OF Fe(lll) COMPLEXES IN THE ORGANIC PHASE 117 9.1 Introduction 117 9.2 Derivation of extraction equation and limitations 117 9.3 Results and Discussion 121 9.3-1 Computational method and discussion 121 9.3-2 Equilibrium data analysis 124 9.4 Conclusions 153 Chapter 10 INFRARED ANALYSIS OF Fe(IIl)-HV COMPLEXES 155 10.1 Introduction 155 10.2 Experimental procedure 162 10.3 Results atd Discussion 163 10.4 Conclusions 176 Chapter 11 CHEMICAL MODELLING OF COUNTER- CURRENT EQUILIBRIUM DATA 177 11.1 Introduction 177 11.2 Computer-aided solution of solvent-extraction cascade 180 11.3 Experimental 184 11.4 Results and Discussion 186 11.4.1 Relationship between Fe(IIl) extracted into the organic phase and pH change of the aqueous phase 186 11.4.2 Batch simulation of countercurrent extraction and modelling of the equilibrium data of the cascade 190 11.5 Conclusions 196 viii Page Chapter 12 FURTHER DISCUSSION AND CONCLUSIONS 197 Appendices 6.1 Calculation of Standard error of effects and analysis of variance 205 6.2 Calculation of Standard error of effects using high order interactions 207 6.3 Factorial experimentation data 208 6.4 Data of combined effect of ionic strength and temperature on Fe(lll) extraction 210 7.1 Data for extraction isotherms 211 7.2 Computer regression program "REG" and output Surface data generation computer program "SURFGEN" for MATMAP three-dimensional plotting 217 7.3 Slope analysis calculations 22 5 7.4 Calculations relating alkali consumption with Fe(IIl) extraction 23 3 7.5 Data on the loading-stripping cycle of Fe(lll) 238 9.1 Computer programs "KSTAT" for the statistical evaluation of equilibrium data and "KPREDG" for prediction and correlation with the experimental data 239 9.2 Details of the subroutine G02CCF for correlation and regression analysis 244 9-3 Correlation tables of predicted and experimental data representing the most probable Fe(lIl)-HV complexes in the organic phase 247 1 X Page 10.1 Infrared evaluated data and calculation of the sum of association and solvation numbers 253 11.1 Equilibrium data obtained with the CRODA reactor 256 11.2 Computer program "MIXSETl" for the solution of a countercurrent cascade, sample output and modifications required with preset pH(N) 257 References 262 Acknowledgements 271 > X List of symbols AG free energy change HL carboxylic acid HV Versatic 10 acid K' thermodynamic equilibrium constant K apparent equilibrium constant or stage number P partition constant I_> K _ dimerization constant dm K acid dissociation constant a D distribution coefficient concentration M moles/litre Y mean activity coefficient x polymerization number s solvation number n,n-m association number m,r hydroxylation number h hydration number I ionic strength or generator in factorial designs B activity coefficient product of the equilibrium constant expression t student's t-value a significance level $ degrees of freedom x mean x value RC regression coefficient CC correlation coefficient s standard deviation cr standard deviation of the population A difference Y frequency pH pH of 30% extraction 0.5 O.D. optical density L ligand or aqueous flow rate X ligand G organic flow rate Y metal concentration in the organic phase X metal concentration in the aqueous phase xi YO metal concentration of the solvent feed XF metal concentration of the aqueous feed X(K),Y(K) aqueous and organic metal concentrations of the Kth stage of a countercurrent cascade pH(K) pH of the Kth stage A(K) coefficient of an empirical regression equation g proportionality factor between acid concentration change and metal extracted or number of replicated runs df dilution factor sum KFR Karl Fischer reagent It litre t 1 CHAPTER 1 INTRODUCTION Aluminium is the most abundant metal in the earth's crust, having an average concentration 15-6%, almost twice the value for iron in the continental areas. At present, in the western world, aluminium is produced almost exclusively from bauxite ore by a combination of the Bayer and Hall-Heroult processes. Bauxite is a rich aluminium ore containing 45-60% Al 0 . Alternative processes developed during the war for the production of alumina from aluminium bearing non-bauxitic resources, were abandoned after the war, because bauxite was cheap and abundant and could be economically treated by the Bayer process. However, the formation of the Inter- national Bauxite Association (IBA) by the major bauxite producing countries has resulted in increases in the bauxite price. This triggered interest in the economic reevaluation of alternative processes for alumina production from indigenous non-bauxite aluminium materials. Such materials include by-products of other operations, for example, fly ash from power stations and colliery spoil and coal ash, and utilization of these materials would have the advantage of producing a cleaner environment. The strategic importance of utilizing indigenous aluminium materials is also a stimulating factor in those countries which lack bauxite deposits. Of the various process routes available for recovery of alumina from non-bauxite materials, acid dissolution methods appear to be the most economically attractive. Among the most promising of these are the Pechiney H+ process, hydrochloric acid leaching followed by HC1 injection to precipitate A1C1 '6Ho0, and nitric acid 3 ^ leaching followed by solvent extraction for iron removal. None of these, however, can compete economically at the present time with the production of aluminium from bauxite ore by the Bayer process. Nevertheless, research into acid routes still continues. k 2 Acid leach routes apart from the desired dissolution 3 + of aluminium succeed in bringing Fe ions into the solution which have to be removed or bypassed in order to precipitate alumina to meet the target impurity levels of of the aluminium industry. One of the means achieving that goal is the solvent extraction technique. Past experience had shown that di-02 ethylhexyl) phosphoric acid (D2EHPA) alone or in a mixture with tri- butyl phosphate (TBP) were successful in removing the iron.