Kurt A. Kraus

Ion exchange procedures : I. Cation exchange in concentration HCl and HClO4 solutions☆

A broad survey of the cation exchange behavior of the elements in HCL and HClO4 solutions is presented and adsorption functions are given. The results are also summarized in the form of two “Periodic Tables” which give the distribution coefficients of the elements as a function of M HCl and MHClO4. Many elements are strongly adsorbed from concentrated HClO4 solutions. There are large differences in adsorbability between HCl and HClO4 solutions, particularly at high ionic strength. Application of these data to high ionic strength cation exchange separation is illustrated.

Anion exchange studies : XXVI. A column method for measurement of ion exchange equilibria at high temperature. Temperature coefficient of the Br−-Cl− exchange reaction

Abstract A packed column method for the precision measurement of temperature coefficients of ion exchange equilibria has been developed and equipment suitable for operation up to 200° is described. Use of the equipment is illustrated with the bromide (tracer)-chloride anion exchange system in the range 0° to 150° for which the enthalpy change was found to be a linear function of temperature.

Hyperfiltration studies x. Hyperfiltration with dynamically-formed membranes

Abstract The usual configuration projected for the hyperfiltration (reverse osmosis) desalination process utilizes specially cast cellulose acetate membranes placed on suitable supports. We have found that salt-rejecting interfacial layers or membranes with frequently remarkably high permeation rates can be formed dynamically on porous bodies when certain additives are present in the pressurized feed solutions. Materials with nominal pore diameters near one micron may be used; rejecting layers have been formed dynamically on substrates with pore diameters as high as 5 microns. After initial formation of the membranes, very low concentrations of additives, of the order of 1 ppm are frequently sufficient to maintain their properties. The additives which so far have given the most interesting results would be expected to form ion-exchange membranes. Examples are: organic polyelectrolytes, colloidal dispersions of hydrous oxides, solutions of hydrolyzable ions, ground-up low-cross-linked ion-exchange beads, and certain natural products such as clays and humic acid. For these, dependence of rejection on feed concentration and on the charge type of the salt is generally consistent with an ion-exchange mechanism for rejection. Membranes have also been formed from neutral (uncharged) additives. The chemical nature of the porous body on which the membranes are dynamically deposited does not seem of primary importance. Membranes have been formed on porous silver and other porous metals, porcelain, porous carbons, sintered glass, and “Millipore” filters. The principal potential advantages of this class of membranes are their high production rates, frequently several hundred gallons ft -2 day -1 , the simplicity of their formation, and the possibility of making them “self-healing”. In addition, some solutes which are to be removed from feeds are capable of forming dynamic membranes, which in a sense are then “self-rejecting”. With the dynamic membranes so far developed, salt rejection is less than with cellulose acetate and, for most, rejection decreases with increasing salt concentration. In addition, performance is often deleteriously affected by presence of polyvalent counter-ions in the feed solutions. At the present stage of development these dynamic membranes thus seem likely to be more applicable to the treatment of low concentration saline feeds, wastes and polluted waters, than to high concentration feeds.

ADSORPTION ON INORGANIC MATERIALS. VI. REACTION OF INSOLUBLE SULFIDES WITH METAL IONS IN AQUEOUS MEDIA.

Abstract Sulfides of Ag(I), FE(II), Cu(II), Zn(II), Pb(II), Cd(II), and As(III), “adsorb” a number of transition metal ions from solution. The process proceeds primarily through metathetical reactions in which the metal of the sulfide is displaced by appropriate ions in solution. The reactions are usually fast and can be carried out in small columns at flow rates of several cm/min. With Ag(I) and 1- to 2-cm columns of various sulfides, flow rates as high as 50 cm/min were feasible without breakthrough. The percent conversion of the sulfides at 50% breakthrough varied from 5% for the reaction of Hg(II) with CuS at 25° to about 128° for the reaction of Hg(II) with Ag2S. With ZnS uptakes as high as 20 moles of Ag(I) per liter of bed were obtained at 50% breakthrough and a flow rate of 7 cm/min. While possibility of conversion must depend on relative stability of the sulfides, neither the rate of reaction nor the completeness of conversion seems related to the relative solubilities. The nature of the solid and the ease with which diffusion takes place are presumably important factors.

Interaction of Vortex Streets

Vortex street eddies shed from multiple cylinders located one behind the other in the plane of flow were observed to interact in a very complex fashion. Contraction, expansion, cancellation, and coalescence of vortices occurred for different values of cylinder separation and Reynolds number. The results appear to have important implications both for turbulence promotion during heat or mass transfer and for theoretical interpretation of vortex street phenomena.

Salt Rejection by a Porous Glass

Porous glass partly filters dissolved salt from aqueous solutions passed through it under pressure. Rejection of salt can be increased by increase in the pH of the solution or by addition of Th(IV). The filtration seems to accord with a mechanism of salt exclusion characteristic of ion exchangers.

Hyperfiltration studies V. Salt rejection of membranes by a concentration polarization method

Abstract A method was developed for rapid measurement of the salt rejecting characteristics of hyperfiltration membranes based on the theory of concentration polarization in an unstirred system. A piston forces solution through a cylinder (an adapted one cc tuberculin syringe) sealed at one end by a membrane. The transmission rate of the membrane and the concentration of the effluent are measured and the concentration-flux curves compared with those computed theoretically through solution of the time-dependent diffusion equation. Results have been obtained that agree well with theory and also with other experimental observations.

Anion exchange studies—XXX a number of elements in ethylenediaminetetraacetic acid solutions

Adsorbabilities of a number of metals (Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Co, Ni and Zn) in EDTA solutions were studied as a function of EDTA concentration, supporting electrolyte concentration (NH4Cl) and pH. Applicability of the results to separations is discussed and illustrations of several separations are given. Adsorbability of EDTA by the chloride form of the exchanger was determined as a function of loading. The selectivity of the exchanger for EDTA is sufficiently low to permit separations in EDTA solutions with the resin remaining substantially in the chloride form. From measurement of distribution coefficients of metals as a function of EDTA and chloride concentration, the charges of a number of EDTA complexes was verified. Adsorbabilities as a function of pH at constant EDTA and supporting electrolyte concentrations were consistent with published constants for metal-EDTA equilibria. The stability constant for the EDTA complex of Ra(II) was estimated from the anion exchange data to be 107·4.

Adsorption on inorganic materials : VII. Hydrous tin oxide and SnO2-filled carbon☆

Abstract An adsorbent based on “filling” the macropores of activated carbon with tin oxide was prepared and characterized. This material, as well as hydrous tin oxide, has an unsually high selectivity for lithium permitting its separation from the other alkali metals. This selectivity is not shown by a number of other hydrous oxides, such as those of Al(III), Fe(III), Zr(IV), and Nb(V).

Hyperfiltration studies VI. Salt rejection by dynamically-formed polyelectrolyte membranes

Abstract Salt-filtering layers can be formed on porous bodies by circulating by them pressurized solutions containing small concentrations of organic polyelectrolytes. These films reject substantial fractions of solute from dilute solutions, frequently with high transmission rates through the membranes (e.g. 100 to 200 gpd/ft 2 under 35 atm. pressure). Possibilities of applications in hyperfiltration (reverse osmosis) processes are discussed briefly.