Ion Exchange in Concentrated Solutions. III. Magnesium Chloride- Hydrochloric Acid and Aluminum Chloride- Hydrochloric Acid Systems*

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1 May, 1958] Ion Exchange in Concentrated Solutions. III. 445 Ion Exchange in Concentrated Solutions. III. Magnesium Chloride- Hydrochloric Acid Aluminum Chloride- Hydrochloric Acid Systems* By Hitoshi OHTAKI Kazuo YAMASAKI (Received January 6, 1958) The ion-exchange equilibria in sodium chloride-hydrochloric acid1), lithium chloride-hydrochloric acid1) beryllium chloride-hydrochloric acid2) systems were studied in previous reports. In * Read before 10th Annual Meeting of Chemical Society of Japan held at Tokyo in April, ) H. Kakihana, N. Maruichi K. Yamasaki, J. Phys. Chem., 60, 36 (1956). 2) H. Ohtaki K. Yamasaki, This Bulletin, 31, 6 (1958). present report, equilibria in magnesium chloride-hydrochloric acid aluminum chloride-hydrochloric acid systems. are investigated. Experimental The Resin.-The resin used was Dowex 50-X8 (hydrogen form) of mesh size obtained by wet screening. It was dried at 40. The water content of resin used was determined from

2 446 r Hitoshi weight decrease on drying at OHTAKI 110. It was about %, i. e., ml. per gram -resin used for magnesium chloride-hydrochloric acid system 9.82%, i. e., 0.11ml. for that used for aluminum chloride-hydrochloric acid system. The amount of resin used in one batch experiment was 3.6g. The exchange capacity of resin used was determined in each series of experiments. Reagents.Magnesium chloride of reagent grade was used without purification. Aluminum chloride was dissolved in water to prepare a concentrated solution. After adding hydrochloric acid, concentrated solution was cooled by freezing mixture stream of dried hydrogen chloride was passed through it. White crystals of aluminum chloride precipitated. After filtration crystals were washed with cold concentrated hydrochloric acid n dissolved in water containing a small amount of hydrochloric acid to prevent hydrolysis. This solution was mixed with hydrochloric acid to prepare sample solutions. Procedure.-All procedures used for determination of adsorbed water are similar to those used in previous studies1.2). Mixtures of N magnesium chloride 0.11 N hydrochloric acid those of N aluminum chloride N hydrochloric acid were used. In concentration range lower than 0.5 N of hydrochloric acid hydrolysis of aluminum chloride occurred, while too much presence of hydrochloric acid caused to crystallize some part of aluminum chloride. Therefore concentration of hydrochloric acid was maintained lower than 3 N when that of aluminum chloride was 0.9 N. The concentration of magnesium ion was determined by titration with m ethylenediaminetetraacetate solution using Eriochrome Black T as indicator3). The concentration of aluminum ion was titrated by 0.03M ethylenediaminetetraacetate solution with Chrome Azurol S as indicator4). Hydrogen ion concentrations of se solutions were determined by titration with 0.1 N barium hydroxide. Brom Cresol Purple (ph of color change: ) was used as indicator for magnesium chloride-hydrochloric acid system, while Methyl Yellow (ph of color change: ) was used for aluminum chloride-hydrochloric acid system, because aluminum chloride was hydrolyzed in higher ph range. Results Discussion 1) Water in Resin.-The amount of water adsorbed by resin which was in contact with external solution was estimated indirectly by measuring amounts of hydrogen ion before 3) G. Schwarzenbach, tion", F. Enke Stuttgart, - 4) M. Theis, Z. anal. "Die komplexometrische 2nd Ed. p. 54 (1956). Chem., 114,106 (1955). Titra- Kazuo after using YAMASAKI ion-exchange following [Vol. equilibrium equation1.2): 31, No. 4 (1) In equation (1), A' denotes adsorbed water in resin at equilibrium round square brackets denote concentration amount of ions, respectively. V represents volume of original solution taken up in one batch experiment (30ml.); subscripts S, Q, R 0 denote external solution at equilibrium, quasi-exchange phase*, resin phase at equilibrium original solution, respectively1,2); E represents total exchange capacity of resin used. When original water content of resin used is represented by A", total amount of water in resin is (2) Amounts of water per gram of dried resin thus determined are given in Tables I II toger with or data. As clearly shown in se tables values of water in resin for aluminum chloride-hydrochloric acid system are generally smaller than those for beryllium chloride-hydrochloric acid2) magnesium chloride-hydrochloric acid systems. It is known that larger charge of ion exchanged in resin phase is, more resin shrinks. The experimental data shown in Tables I II are consistent with this fact. 2) Ionic Species in External Solution Resin.-As shown in Tables I II, sum of amounts of hydrogen ion, [H+]R metal ion [Mg2+]R or [Al3+],Z in resin phase is larger than total exchange capacity of resin used. These discrepancies are supposed to have been caused by formation of complexes* such as MgCl+, AICl2+ or AlCl2+ which exchange with hydrogen ions. The existence of such complexes containing chlorine in resin phase is verified by detection of a minute amount of chloride ion in solution eluted from resin by sodium nitrate even after washing resin thoroughly with water. * This phase consists of two kinds of solution: one is solution which adheres to surface of resin particles or is solution which penetrates into resin without being exchanged at time of exchange equilibrium. See References 1 2.

3 May, 1958] Ion Exchange in Concentrated TABLE Solutions. III I A PART OF THE DATA FOR THE MgCl2-HCl SYSTEM. 447

4 448 Hitoshi A PART * The in all amount cases. of A13+ ion Therefore OHTAKI OF THE in values DATA Kazuo TABLE II FOR THE YAMASAKI AICl3-HCl quasi-exchange of [A13+]Q are phase not given [Vol. SYSTEM.* is too in this small table. to be determined 31, No. 4

5 May, 1958] Ion Fig. 1. Relation between MgCl+ to Mg2+ in apparent fraction resin. Exchange in Concentrated ratio of resin of Mg ion in Solutions. Hydrogen Fig. 3. -HCl III 449 ion concentration in external solution at equilibrium Selectivity coefficients of AIC12 system plotted against (H+)s. formed. In Fig. 1 values of ratio of MCl+ to Me2+ ion in resin mmgcl/mm g are plotted against apparent fraction ion in resin, XMg*. The ratio increases as XMg decreases. Thus, in range of lower concentration chloride at same time of higher concentration of hydrochloric acid, magnesium in resin phase consists almost entirely of MgCl+, it is possible that a large part present in external solution also forms chloro-complex MgCl+. In Fig. 2 values of selectivity coefficient calculated after formula (3) Hydrogen Fig. 2. ion concentration in external solution at equilibrium Selectivity coefficients of MgC12 Amounts of Mg2+ MgCl+ ions in resin phase can be readily calculated from values of E, [H+]R [Mg2+]R provided that no or complexes are are plotted against (H+)s, hydrogen ion concentration of external solution. In range of higher values of (H+)s, as already described, ionic species predominant is considered to be MgCl+. Consequently selectivity coefficient thus calculated represents that of exchange * Hydroxo-complexes are formed with difficulty in such a strong acidic system as resin phase concerned. Actually water may be coordinated to se ions in forming [Mg(OH2)5Cl]2+,IAl(OH2)5Cl]2+, [Al(OH2)4Cl2]+.

6 450 [Vol. 31, No. 4 system of MgCl+-H+ rar than that of Mgt+-H+ system. The selectivity coefficient of aluminum chloride-hydrochloric acid system was calculated by similar formula as (3): These data are plotted against (H +)s in Fig. 3. In this system it is difficult to estimate amount of individual species of aluminum like All+, AlCl2+ or AlCl2+ in similar way as in magnesium chloride-hydrochloric acid system. Summary (4) Ion-exchange equilibria in concentrated solutions chloridehydrochloric acid aluminum chloridehydrochloric acid system were studied. Amounts of water present in resin at equilibrium were estimated for se systems. In magnesium chloridehydrochloric acid system a large part of magnesium in resin exists as MgCl+ at equilibrium when concentration of hydrochloric acid is high. Selectivity coefficients chloride-hydrochloric acid of aluminum cholridehydrochloric acid systems were calculated. A part of of expenses of present study was defrayed by Grant-in-Aid for Fundamental Scientific Research from Ministry of Education. Chemical Institute, Faculty of Science, Nagoya University Chikusa-ku, Nagoya