Suchergebnisse

The perspectives of using ion-exchange soils for growing plants in zero-gravity field are described. Standard methods for obtaining ion-exchange soils are not suitable for weakly dissociating ion-exchangers. Methods for obtaining ion-exchange soil based on weakly dissociating fibrous ion exchangers are proposed. The method using concentrated solutions made it possible to obtain ion-exchange soils with a larger content of deficient ions (K+ , NO3 – ). The suitability of the obtained ion-exchange soils was confirmed by a biological experiment.

By the method of potentiometric titration of a fibrous aminocarboxylic polyampholyte with a predominant content of carboxyl groups, the equilibrium of the cation exchange of calcium, magnesium, and potassium ions for a hydrogen ion was studied. Due to the low solubility of calcium and magnesium hydroxides in these cases, titration was carried out by Ca(OH)2 and Mg(OH)2, which are formed in solution upon contact with the H-form of the ion exchanger оf increasing portions of solid CaO and MgO. This made it possible to obtain titration curves in a wide range of pH and calcium and magnesium chlorides concentration (0–0.1 eq./L). The dependences of the swelling of ion exchangers on the neutralization degree with the bases of the studied cations are obtained. The coefficients of ion-exchange equilibria are calculated. It was found that the swelling of the ion exchanger is relatively little dependent on its ionic form. The ion exchanger has a higher affinity for calcium than magnesium ion.

On the base of fibrous ion exchangers, indicator materials were obtained for sorbates of an alkaline and acidic nature, intended to visualize the working time of the filter layer during ion exchange air purification. The optimal conditions for their production and operation were determined. The practical applicability for the manufacture of indicator cartridges for filters of deep air purification and personal protective equipment for human respiratory organs and skin with the aim of timely visualizing of the sorption resource depletion, due to the contrast and sensitivity of the color change, was demonstrated.

Titration curves of H-forms of the fibrous chelating sorbent with iminodiacetic groups based on industrial polyacrylonitrile fiber Nitron with potassium hydroxide in 1M KCl solution in the presence of Ni2+, Co2+, Cu2+ and Ca2+ chlorides were obtained. The method used made it possible to simultaneously measure the pH of the solution and the concentration of the divalent cation at each point of the titration curve. From these data, the dependences of their sorption values on the pH of the equilibrium solution were calculated. The curves of direct and back titration practically coincided in all cases. As the pH changed during titration, precipitation was observed at pH values of precipitation of the corresponding hydroxides. In this case, the increase in pH was suspended or greatly slowed down by adding alkali to the titration cell. The formation of a precipitate occurred mainly in a solution for Co2+ and Ni2+ (pH 8), when the ion exchanger was saturated with a metal ion. In the case of Cu2+ (precipitate formation pH 4), Cu2+ sorption occurs at both lower and higher pH due to ionization of carboxyl groups and partial dissolution of the precipitate. In all cases, the maximum sorption of Ni2+, Co2+, Cu2+, Ca2+ corresponded to the formation of sorption complexes of the R–N(CH2COO-)2Me2+ type.

Curves of potentiometric titration of fully protonized fibrous ion exchangers with potassium hydroxide against the background of 1 M KCl in the presence of chlorides of Ni2+, Со2+, Сu2+ and Ca2+ were obtained. The ion exchangers were synthesized by modifying of industrial polyacrylonitrile fiber with diethylenetriamine and triethylenetetraamine and predominantly contained functional groups R-CO-NH- (CH2CH2NH)nH (n = 2 or 3) and a small amount of carboxyl groups. The sorption of Ni2+, Со2+, Сu2+ и Ca2+by ion exchangers was calculated from the data obtained depending on the pH of the medium. It was found that the investigated ion exchangers with high selectivity sorb heavy metal ions in a wide range of acidity of solutions (pH 2–9) due to the formation of metal-polymer complexes with polyamine functional groups. The maximum sorption capacity is 1.5–2.7 and 4–5 meq/g for ion exchangers with n = 2 and 3, respectively.

A mathematical model for description of the sorption capacity of ion exchangers on alkaline compounds protonizable in aqueous solutions (exemplified by ammonia, mono-, diand triethylamine) was proposed. The Henry's constants for these substances were experimentally determined. The model accounts for the concentration and acid-base properties of the sorbate, relative air humidity, acid-base properties and exchange capacity of the ion exchanger, as well as spatial availability of functional groups for interaction under conditions of limited permeability of polymeric ion exchanger. The applicability of the model is illustrated by processing the experimental results on the sorption of ammonia and ethylamines by fibrous carboxylic and sulfonic cation exchangers. Good agreement between the calculated and experimental data is observed.

A set of studies necessary to determine the suitability of a fibrous anion exchanger with ternary amino groups based on industrial polyacrylonitrile fiber Nitron C as a component of ion substrates was carried out. A laboratory-prepared ion exchanger sample had a working exchange capacity equal to 0.9 meq/g for the nitrate anion, which limits the biological productivity of the substrate for growing plants, in the physiological pH range = 5.5–7.5 and the concentration of the equilibrium nutrient solution is 0.02 eq/l. This capacity is at the level of the best granular ion exchangers and significantly exceeds the capacity of the previously used fibrous ion exchangers for growing plants in zero gravity conditions on space stations in 1970–1994 (Mir, Soyuz TM-10 – TM-17). The synthesized ion exchanger is a polyampholyte and contains three types of ion exchange groups, has high hydrophilicity and mechanical properties that allow it to be processed into textiles and used for any purpose, in which fibrous ion exchangers can be used (air and water purification, human protection means, etc.).