A consideration of the correct calculation of thermodynamic parameters of adsorption

The Langmuir and Freundlich isotherm equations have been widely used for interpreting various adsorption processes. There are, however, many serious mistakes in the literature in determination or calculation of thermodynamic parameters, especially in the determination of the change in the free energy of adsorption using Langmuir, Freundlich and Henry constants. Many authors used these constants for the determination of Delta G expressed instead of dimensionless in some concentration units (for example: 1 mol(-1), 1 g(-1), ml mg(-1), etc.)

Sorption processes at the interface of colloidal silicon dioxide

Colloidal silica, the production of which has been patented all over the world, has a remarkable application in over a hundred different industrial branches. Laboratory process, which can serve as a basis for an industrial production of this important material, has been developed in this work, solely on the basis of available literature data and personal contacts. A complete characterization of initial, intermediate and final product has been made. Experimental data unambiguously suggest that the quality of the colloidal silica obtained, fully corresponds to the quality of the products commercially available from the leading world companies. This work is devoted to a better understanding of the sorption properties of colloidal silica and solids obtained from it. Accordingly, we intended to fulfill the following goals: to examine the sorption of alkali metals from aqueous solutions, sorption of a numerous organic compounds on the solid materials obtained by coagulation from the colloidal silica, to study the stability of the colloidal silica in the presence of alkali metal ions and, finally, to determine the heat of immersion of powders obtained from colloidal silica. The sorption of alkali metal ions from aqueous solutions on colloidal silica, has been studied at 298 K using the potentiometric titration method. Due to the considerable solubility of the colloidal silica, at the elevated pH values, the limit of the method used had to be determined. The application of the potentiometric titration method has been critically reconsidered with special regard to the literature data concerning the region in which dissolution process is a dominant one. The obtained hysteresis on the sorption-desorption curves, is explained in view of significant solubility of the colloidal silica at the particular pH region. Alkali metal ion selectivity sequence corresponds to the Hofmeister series, i.e. for the cations of the same charge the sorption affinity decreases with the increased hydrated radii, and this is valid for the lower electrolyte concentrations and low pH values. A change in alkali metal ion sorption sequence has been found at the given pH values as a consequence of both ion concentration and pH values of the solution. Such a behaviour was successfully explained taking into account activities of the cations studied. On the basis of these date, it is possible to predict the sorption sequence of alkali metal ions on the colloidal silica surface, and to our opinion on other Si02 forms as well, taking into consideration the electrolyte concentration and pH of the solution. We do think that the solution composition is of great importance for the sorption properties of other inorganic oxides and should be accepted as a suggestion for further investigations..

Determination of the point of zero charge of alumina by batch equilibration method

In this work we present the points of zero charge, pHpzc, of five commercial alumina samples, of an alumina/solution ratio of 0.100g/25 ml, obtained by batch equilibration method. As an inert electrolyte, KNO3 of 0.001 - 0.1 moldm-3 concentration was used. The obtained points of zero charge values are about 7 and they are independent of KNO3 concentration, except the sample labeled as ICN (Alumina B). In this case, the increase in electrolyte concentration (from 0.001 to 0.1 moldm-3) leads to a decrease in pHpzc (from 7.5 to 6.7) indicating specific sorption of K+ ions on the sample.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Adsorption isotherms of chloroform on macroporous copolymers determined by inverse gas chromatography

The inverse gas chromatography (IGC) under finite surface coverage conditions was used for the determination of adsorption isotherms of chloroform on macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), PGME and copolymer modified with ethylene diamine, EDA, PGME-en. The specific surface areas of initial and modified copolymer samples calculated from IGC data are in fair agreement with those determined by the BET method from the low-temperature nitrogen adsorption isotherms.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Коментари на рад под насловом Адсорпција стронцијума на различитим натријумом измењеним бентонитима, Аутори: Сања Мариновић, Марија Ајдуковић, Наташа Јовић-Јовичић, Предраг Бранковић, Тихана Мудринић, Бојана Недић-Васиљевић и Александра Милутиновић-Николић, објављеног у Journal of the Serbian Chemical Society, volume 82, issue 4, 2017, стр. 449–463

Recently, Marinovic et al. have presented a study on the adsorption of strontium on different sodium-enriched bentonites. However, some experimental procedures and methods used, as well as presentation and interpretation of some data, are questionable, i.e., erroneous.Недавно је у Journal of the Serbian Chemical Society објављен рад (JSCS 82(2017)449–463) под насловом “Адсорпција стронцијума на различитим натријумом измењеним бентонитима”, чији су аутори Сања Мариновић, Марија Ајдуковић, Наташа Јовић-Јовичић, Предраг Банковић, Тихана Мудринић, Бојана Недић-Васиљевић и Александра Милутиновић-Николић. Циљ ових добронамерних коментара је био да се укаже на: погрешно израчунавање појединих величина, грешке у и нтерпретацији добијених/израчунатих резултата као и грешке изнете у закључцима рада. Аутор ових коментара верује да ће изнети коментари бити од користи не само ауторима предметног рада већ и осталим ауторима и рецензентима који раде у области адсорпције/сорпције из раствора

Stability of zirconia sol in the presence of various inorganic electrolytes

Zirconia sol was prepared from zirconium oxychloride solutions by forced hydrolysis at 102ºC. The prepared sol consisted of almost spherical, monoclinic, hydrated zirconia particles 61 nm in diameter. The stability of zirconia sol in the presence of various inorganic electrolytes (LiCl, NaCl, KCl, CsCl, KBr, KI, KNO3, and K2SO4) was studied by potentiometric titration method. Dependence of the critical concentration of coagulation (CCC) on the dispersion pH was determined for all studied electrolytes. The critical coagulation concentration values, for all investigated electrolytes, are lower at higher pH. These values for all 1:1 electrolytes are equal in the range of experimental error. For a given pH value, CCCs of K2SO4 are 3-4 orders of magnitude lower than the corresponding values for 1:1 electrolytes. [Projekat Ministarstva nauke republike Srbije, br. III 45012

Determination of intrinsic equilibrium constants at an alumina/electrolyte interface

Intrinsic ionization and complexation constants at an alumina/electrolyte interface were studied by the site binding model, while the sorption of alkali cations from aqueous solutions was interpreted by the triple-layer model. The surface properties of alumina were investigated by the potentiometric acid-base titration method. The point of zero charge (pH(pzc)) of alumina obtained by this method was found to be 7.2. The obtained mean values of the intrinsic protonation and ionization constants of the surface hydroxyl groups and the intrinsic surface complexation constant, in different electrolytes, are pK(a1)(int) = 4.4, pK(a2)(int) = 9.6 and pK(M+)(int) = 9.5, respectively

Preparation of concentrated rhenium solutions

The conditions of the desorption of rhenium from the anion exchange resin Dowex 1×8 by nitric acid were determined. The solution (5×10-3 mol/dm3 Re in 0.15 mol/dm3 NaCl) was passed through the column containing 0.1 g of the resin. The total sorbed amount of rhenium was 200 mg/g of the resin. It was then eluted by nitric acid in the concentration range of 0.16-7.2 mol/dm3 . The most favourable elution profile was found with 3.0 mol/dm3 HNO3. Over 77% of the total rhenium was desorbed with 5 ml of this eluence. Over 95% of the sorbed rhenium was recovered by using 20 ml of nitric acid in the concentration range of 0.9-7.2 mol/dm3 .Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

A comparative analysis of scientific outputs of countries formed from former Yugoslav republics and some other countries for the period 2008-2012

Scientific outputs of six countries (republics of the former Yugoslavia - the Socialist Federal Republic of Yugoslavia): Serbia, Croatia, Slovenia, Bosnia and Herzegovina, Former Yugoslav Republic of Macedonia and Montenegro were discussed in this paper. For the purpose of comparison, the data for seven neighbouring countries of the former Yugoslavia (Albania, Greece, Bulgaria, Romania, Hungary, Austria and Italy) were given as well. Also, the data for the Group of Eight (G8) countries (the United States, Canada, the United Kingdom, France, Italy, Germany, Japan and the Russian Federation) and some European countries similar in population to ex-Yugoslav republics were included. To gain a more complete picture on the outputs in scientific production (e.g., publications and patents), data on several developed European countries, as well as the countries from other continents were given. The analysis, which included 33 countries, was made based on different bibliometric indicators for the period of five years (2008-2012). The data were collected from international databases

The influence of chemical and thermal treatment on the point of zero charge of hydrous zirconium oxide

Two zirconia samples were prepared by precipitation from aqueous zirconium oxychloride and zirconyl sulfate solutions with potassium hydroxide. The prepared zirconia samples were amorphous. The pH(pzc) values of the zirconia samples, determined in NaCl and NaNO3 solutions, were 6.6 +/- 0.1 and 6.9 +/- 0.1, respectively. After prolonged hydration of zirconia in doubly distilled water, the pH(pzc) decreased to 4.7 +/- 0.3. Crystallization into tetragonal (metastable) + monoclinic zirconia appeared at 691 K. Above 873 K, the tetragonal metastable phase changes to a monoclinic phase. It was shown that crystallite sizes of zirconia treated at 673-1273 K increased from 9.5 to 40.5 nm, respectively. The increase in temperature from 385 to 1070 K increased the pH(pzc) of zirconia samples from 6.6 to 9.0, respectively