Abstract: This study aims at extending the general methodology for the study of predominance and reactivity of ionic homogeneous solutions to precipitation reactions. This extension was satisfactorily formulated by the definition of the fraction of species concept in heterogeneous systems for the first time. An easy form to fully integrate the ion product concept with other descriptions of homogeneous ionic reactions, to obtain predominance zone diagrams (PDZ), to enrich the use logarithmic relative diagrams, to generate continuous equations from titration curves, and to generalize side-reaction coefficients to heterogeneous systems using easy-to-compute algorithms of calculation is shown.

The new representation was applied in a study case exemplified by the hydrolysis of copper (II) in the absence and the presence of complexing ligands considering soluble and insoluble species of the metal ion. The results perfectly compare to those obtained by established numerical and graphical methods of analysis of solution equilibria showing the equivalence among the different descriptions.

Pre-nucleation clusters (PNCs) theory of precipitation reactions was used as a mean to interpret the theoretical implication that this view engendered.

Keywords: Distribution fraction diagram, predominance zone diagram, precipitation reactions, side-reaction coefficients, modeling precipitation reactions.

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A Thermodynamic Model on a Linear Rule between the Molal Concentration Exponential and the Osmotic Coefficients on Mole Fraction Base in Electrolyte Solutions and its Application
Pages 194-212
Zheng Fang

DOI: http://dx.doi.org/10.6000/1929-5030.2015.04.04.5

Published: 17 December 2015

Abstract: A linear rule is discovered. That is the osmotic coefficients on mole fraction base (ω) are linearly related to the molal concentration exponential (m^k₂) in single electrolyte solutions. Based on this rule, a thermodynamic model is developed and successfully used to the single electrolytes with various valent types, such as uniunivalent, biunivalent, triunivalent, tetraunivalent,bibivalent, andtribivalent to predict their conventional osmotic coefficients on molal base (Φ), and also other properties, such as the relative molal vapor pressure lowering, the equivalent conductivity. Besides m^k₂, the x^k₂ (the concentration exponential of mole fraction of solute) m^k₂ln(m^k₂), and x^k₂ln(x^k₂) are also linearly related to ω, respectively. They are all capable to be used to reproduce some properties of single electrolyte solutions. The examples with satisfied results have been given.

A Preliminary Study on the Removal of Methylene Blue from Aqueous Solution using Moringa Pods as Bioadsorbent under Column Operation

Pages 84-90

Mirla Rodríguez, Saúl Flores and Alexandra Argotte

DOI: https://doi.org/10.6000/1929-5030.2017.06.02.4

Published: 19 June 2017

Abstract: Moringa pods (MP) was used as bioadsorbent to remove methylene blue (MB) from aqueous solutions under fixed-bed column operation. The bioadsorbent was analyzed by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Surface area (Brunauer-Emmet-Teller) and point of zero charge (pH_PZC) were determined. In this study, pH influence (2.0 to 10.0) was evaluated, keeping constant conditions of bed height (11.0 cm), bioadsorbent dose (2.0 g), dye concentration (20 mg L^-1), volume (25 mL), contact time (24 h) and room temperature. The MB concentration was determined using UV-spectrophotometry at 662 nm. The results showed that the adsorption was pH dependent. The highest dye removal occurs at pH 7.0 (_˜100%). Infrared spectrum and morphological changes observed by SEM indicate the existence of bioadsorption phenomenon. An adsorption mechanism possible by intermolecular interactions was proposed. The study revealed the applicability of MP for removal of MB at low cost, efficient, eco-friendly and relatively neutral pH.

Keyword: Agricultural waste, cationic dye, adsorption, aqueous system, fixed-bed<.

A Thermodynamic Model on a Linear Rule between the Molal Concentration Exponential and the Osmotic Coefficients on Mole Fraction Base in Electrolyte Solutions and its Application
Pages 194-212
Zheng Fang

DOI: http://dx.doi.org/10.6000/1929-5030.2015.04.04.5

Published: 17 December 2015

Abstract: A linear rule is discovered. That is the osmotic coefficients on mole fraction base (ω) are linearly related to the molal concentration exponential (m^k₂) in single electrolyte solutions. Based on this rule, a thermodynamic model is developed and successfully used to the single electrolytes with various valent types, such as uniunivalent, biunivalent, triunivalent, tetraunivalent,bibivalent, andtribivalent to predict their conventional osmotic coefficients on molal base (Φ), and also other properties, such as the relative molal vapor pressure lowering, the equivalent conductivity. Besides m^k₂, the x^k₂ (the concentration exponential of mole fraction of solute) m^k₂ln(m^k₂), and x^k₂ln(x^k₂) are also linearly related to ω, respectively. They are all capable to be used to reproduce some properties of single electrolyte solutions. The examples with satisfied results have been given.