Change In Equilibrium Concentration Research Articles

DETERMINATION OF ADSORPTION KINETICS OF COCONUT HUSK ADSORBENT FOR HEAVY METALS REMOVAL USING LANGMUIR AND FREUNDLICH ISOTHERM EXPRESSIONS

Adsorption of heavy metal cationic ions (Cr, Pb, and Cu) onto coconut husk carbon (CHC) adsorbent has been studied using batch-adsorption method. The study was carried out to investigate the adsorption kinetic and adsorption isotherm of the coconut husk adsorbent for the removal of heavy metals in waste liquid effluent. The influence of pH, contact time, adsorbent dose, and adsorbent concentration, and temperature on the adsorption process was also studied. Results indicated an initial increase in adsorption rate, and optimal removal of heavy metal was reached within 70 minutes, further increase in contact time and temperature show significant change in equilibrium concentration. Also, further increase in adsorbent dosage revealed significant change in the sorption capacity of the CHC. The adsorption isotherms could be fitted well by both Langmuir and Freundlich models. The RI (equilibrium parameter) value in the present investigation was less than 1 (one) which indicates that the adsorption of the heavy metals ions on the CHC is favorable. The value of n for this study which indicates the degree of non-linearity between solution concentration and adsorption were 0.31–0.39, this result indicated that the adsorption of heavy metals onto the CHC is a chemical sorption. After treatment of synthetic heavy metal solution with the CHC, the adsorption isotherm model analysis revealed that the adsorption capacity (b) of CHC for the heavy metal were 89 mg/L (Cr), 125.5 mg/L (Pb), and 129.7 mg/L (Cu). Conclusively, the results indicate that the freely abundant agricultural waste-coconut husk can be treated for heavy metal adsorption but it’s not economically viable because it’s not renewable due to the chemisorption nature of the adsorption process.

English

Adsorption of Chromium on dye contaminated soil has been studied using batch adsorption technique. This study is carried out to examine adsorption capacity of Chromium on contaminated soil. The influence of contact time, pH, variation of amount of soil, initial Cr Concentration, and particle size also studied. Results revealed that adsorption rate initially increases and equilibrium reached about one hour. Further increase in contact time did not show significant change in equilibrium concentration. The Langmuir and Freundlich isotherm were used to describe the adsorption equilibrium studies. Langmuir isotherm is best fits.

Solvent Isotope-Induced Equilibrium Perturbation for Isocitrate Lyase

Isocitrate lyase (ICL) catalyzes the reversible retro-aldol cleavage of isocitrate to generate glyoxylate and succinate. ICL is the first enzyme of the glyoxylate shunt, which allows for the anaplerosis of citric acid cycle intermediates under nutrient limiting conditions. In Mycobacterium tuberculosis, the source of ICL for these studies, ICL is vital for the persistence phase of the bacterium's life cycle. Solvent kinetic isotope effects (KIEs) in the direction of isocitrate cleavage ((D₂O)V = 2.0 ± 0.1, and (D₂O)[V/K(isocitrate)] = 2.2 ± 0.3) arise from the initial deprotonation of the C2 hydroxyl group of isocitrate or the protonation of the aci-acid of the succinate product of the isocitrate aldol cleavage by a solvent-derived proton. This KIE suggested that an equilibrium mixture of all protiated isocitrate, glyoxylate, and succinate prepared in D₂O would undergo transient changes in equilibrium concentrations as a result of the solvent KIE and solvent-derived deuterium incorporation into both succinate and isocitrate. No change in the isotopic composition of glyoxylate was expected or observed. We have directly monitored the changing concentrations of all isotopic species of all reactants and products using a combination of nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. Continuous monitoring of glyoxylate by ¹H NMR spectroscopy shows a clear equilibrium perturbation in D₂O. The final equilibrium isotopic composition of reactants in D₂O revealed dideuterated succinate, protiated glyoxylate, and monodeuterated isocitrate, with the transient appearance and disappearance of monodeuterated succinate. A model for the equilibrium perturbation of substrate species and their time-dependent isotopic composition is presented.

Batch Sorption Experiments: Langmuir and Freundlich Isotherm Studies for the Adsorption of Textile Metal Ions onto Teff Straw (Eragrostis tef) Agricultural Waste

Adsorption of heavy metals (Cr, Cd, Pb, Ni, and Cu) onto Activated Teff Straw (ATS) has been studied using batch-adsorption techniques. This study was carried out to examine the adsorption capacity of the low-cost adsorbent ATS for the removal of heavy metals from textile effluents. The influence of contact time, pH, Temperature, and adsorbent dose on the adsorption process was also studied. Results revealed that adsorption rate initially increased rapidly, and the optimal removal efficiency was reached within about 1 hour. Further increase in contact time did not show significant change in equilibrium concentration; that is, the adsorption phase reached equilibrium. The adsorption isotherms could be fitted well by the Langmuir model. The value in the present investigation was less than one, indicating that the adsorption of the metal ion onto ATS is favorable. After treatment with ATS the levels of heavy metals were observed to decrease by 88% (Ni), 82.9% (Cd), 81.5% (Cu), 74.5% (Cr), and 68.9% (Pb). Results indicate that the freely abundant, locally available, low-cost adsorbent, Teff straw can be treated as economically viable for the removal of metal ions from textile effluents.

D-Glucaric Acid Esters/Lactones Used in Condensation Polymerization to Produce Hydroxylated Nylons—A Qualitative Equilibrium Study in Acidic and Basic Alcohol Solutions

Abstract Direct esterification of d-glucaric acid in acidic methanol solution produced a mixture of four esters/lactones: dimethyl d-glucarate (1), methyl d-glucarate 1,4-lactone (2), methyl d-glucarate 6,3-lactone (3), and d-glucaro-1,4:6,3-dilactone (4). The esters/lactones described in this study are activated forms of d-glucaric acid useful for condensation polymerization with diamines to produce hydroxyated nylons. Structures of the esterification products were determined using 1H NMR, 13C NMR and GC/MS techniques. Qualitative changes in equilibrium concentrations of the esters/lactones mixtures, as determined from 1H NMR spectral studies, were observed in acidic (methanol-d4/HCl) and basic (methanol-d4/triethylamine) alcohol solutions. Esterification of d-glucaric acid in ethanol produced ethyl esters/lactones mixtures which were observed to undergo changes in equilibrium composition in acidic and basic ethanol solutions comparable to those found with the methyl esters/lactones mixtures.

The Effect of Aromatic Tertiary Amines on the Copper(II) Catalyzed Decarboxylation of 3-Oxo-Glutaric Acid

The kinetics of the copper(II) catalyzed decarboxylation of 3-oxo-glutaric acid have been investigated in unbuffered solutions at 25 °C and 0.60 M ionic strength, both in the presence of aromatic tertiary amines, and with hydrated copper ions alone. The amines used were 2,2′-bipyridyl and 1,10-phenanthroline. Equilibrium constants for the formation of the various copper complexes were determined with a copper ion selective electrode, particularly for the species CuAB, where A is the 3-oxo-glutarate ion, and B is an aromatic amine. The kinetic behavior was then interpreted as arising from the simultaneous decarboxylation of all the species present containing a 3-oxo-glutarate ligand. The resulting rate constants indicated that some kinetic effect was transmitted through the copper from the base to the 3-oxo-glutarate, but the effect was relatively small, and the bulk of the catalytic effect caused by the base arose from changes in equilibrium concentrations.