Sorption properties of hydrogels of transition and p-metal oxide hydroxides

Abstract

The experimental data on the sorption properties of hydrogels of Fe 1|1, Ti IV, Zr TM, Sn TM, [fl Ill, Cr llI, Sm Ill, Co 11, and Zn II oxide hydroxides are summarized. The data were obtained by the point of zero-charge method and by measuring the rates of the indicator reaction, viz., heterogeneous hydrolysis of the chloro complexes of platinum group metals. The compositions of lhe oxide hydroxides, the pH of the point of zero charge in various ionic media, and the rate constants of the indicator reactions were determined. The values obtained were analyzed in terms of their correlation with the charge, the radius, and the electronic structure of the central ion and with the composition and the preparation conditions of the oxide hydroxide. A data base that allows one to choose an appropriate oxide hydroxide sorbent for extraction of particular complex-forming metals from complexing media is presented. The data obtained confirm the model of the mechanism of heterogeneous hydrolysis and extend its predicting ability. The model was tested experimentally in relation to tin0v) oxide hydroxide.

Determination of particle size in aqueous suspensions of hydrogels of iron(III), indium(III), aluminum, chromium(III), titanium(IV), and zirconium(IV) oxohydroxides

“…7 -10 Let us try to estimate the spatial characteristics of the MOH hydrogels using the data of picnometry and sedi mentation analysis. As an example, we consider the indiogel with pH pr 11 of composition In(OH) 3 or In(OH) 3 •112Н 2 О 4 (molecular weight 2187) with a picnometric density of 1.06 g cm -3 and water as a DP.…”

“…In this case, the surface area of all particles in the fraction is 2.28•10 -4 •6.74•10 6 = 1540 m 2 . The specific surface of the hydrogel, taking into account intramicellar water, is 309 m 2 g -1 , and that, ignoring intramicellar water, is 4071 m 2 g -1 of dry In(OH) 3 . This value more than 16 fold exceeds the S sp value found 16 by us in the study of the sorption capacity of OH groups.…”

“…Sedimentation curves for the ferrogels with a suspension concentration of 0.01 (1), 0.02 (2), and 0.04 mol L -1(3)(4)(5) precipitated at рН = 7 (4), 9 (1-3), and 11(5); m is the gel weight; t is time. Water is the dispersion medium.…”

“…It remains unclear how far these conclusions can be extended to suspensions of gels ob tained by the fast alkali hydrolysis of aqueous solutions of the corresponding metal salts with continuous stirring in a vortex mode followed by washing from a mother liquor by multiple centrifuging and repulping. 3 In this work, we attempted to reveal the state of the MOH gels in suspensions using sedimentation analysis, which is widely used to determine the fractional composi tion of microheterogeneous systems. There are many vari ants of apparatus equipment and mathematical methods for processing results of sedimentation analysis, [11][12][13][14][15] which is poorly used for studying hydrogels.…”

Changes in the acid-base properties of hydrogels of metal oxide hydroxides induced by aging in solutions of electrolytes

“…Titanogels were prepared by the hydrolysis of TiCl+ followed by the neutralization of NaOH to adjust the pH to 4.5, 7, and 10; fen'o-, indio-, and chromogels were prepared by the alkaline hydrolysis of 3, In(NO3) 3. and CrCI 3, respectively, to adjust the pH to 7, 9, and 11, whereas zirconogels were hydrolyzed by Zr'O(NO3) 2 9 H20 to adjust the pH to 5.5, 7. and 10. The precipitation was performed at the permanent pH-metric controller until the desired pH of precipitation (pHi) was established in ~50 mL of the suspension, and this value was maintained unchanged for -5 min.…”