scholarly journals Active Carbon as an Adsorbent for Lead Ions

1997 ◽  
Vol 15 (10) ◽  
pp. 815-824 ◽  
Author(s):  
Sohail Akhtar ◽  
Riaz Qadeer
Keyword(s):  
Active Carbon ◽  
Physical Adsorption ◽  
Order Rate Constant ◽  
Ion Concentration ◽  
Lead Ions ◽  
Lead Ion ◽  
First Order ◽  
First Order Kinetics ◽  
Isotherm Equations ◽  
Time Lead

A commercial active carbon has been tested as an adsorbent for the removal of lead ions from aqueous solutions. Optimum conditions for maximum adsorption in terms of shaking time, lead ion concentration, temperature and concentration of different acids were established. The results obtained reveal that the adsorption of lead ions on active carbon is athermic (ΔH = 0) in nature and follows first-order kinetics. The first-order rate constant was evaluated as 0.049 min−1 and the intraparticle diffusion rate as 3.07 × 10−4 (g/g min1/2). The data also obey the Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherm equations over the concentration range studied. The magnitude of the adsorption energy, 7.61 kJ/mol, calculated from the β-constant of the D-R equation lies in the energy range for physical adsorption which is attributed to weak bonding between the lead ions and the active carbon.

scholarly journals Biosorption of Lead Ions from Aqueous Solution UsingFicus benghalensisL.

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Venkateswara Rao Surisetty ◽  
Janusz Kozinski ◽  
L. Rao Nageswara
Keyword(s):  
Aqueous Solution ◽  
Process Parameters ◽  
Contact Time ◽  
Batch Process ◽  
Ion Concentration ◽  
Lead Ions ◽  
Lead Ion ◽  
Maximum Adsorption Capacity ◽  
Ficus Benghalensis ◽  
Leaf Powder

Ficus benghalensisL., a plant-based material leaf powder, is used as an adsorbent for the removal of lead ions from aqueous solution using the biosorption technique. The effects of process parameters such as contact time, adsorbent size and dosage, initial lead ion concentration, and pH of the aqueous solution on bio-sorption of lead byFicus benghalensisL. were studied using batch process. The Langmuir isotherm was more suitable for biosorption followed by Freundlich and Temkin isotherms with a maximum adsorption capacity of 28.63 mg/g of lead ion on the biomass ofFicus benghalensisL. leaves.

Dissipation of Alachlor in Four Soils as Influenced by Degradation and Sorption Processes

Weed Science ◽  
1994 ◽  
Vol 42 (2) ◽  
pp. 233-240 ◽  
Author(s):  
Pau Y. Yen ◽  
William C. Koskinen ◽  
Edward E. Schweizer
Keyword(s):  
Surface Soil ◽  
Sandy Loam ◽  
Soil Depth ◽  
Order Rate Constant ◽  
Silty Clay ◽  
Clay Loam ◽  
Corn Production ◽  
First Order ◽  
Degradation Data ◽  
First Order Kinetics

Laboratory studies were conducted to determine the influence of degradation and sorption processes on the dissipation of alachlor in one Colorado soil (Kim clay loam) and three Minnesota soils (Port Byron silt loam, Webster silty clay loam, and Estherville sandy loam) as a function of soil depth. Persistence and movement of alachlor in an irrigated corn production system also were determined on the Kim soil. Laboratory degradation data fit first-order kinetics, and rate constants ranged from 0.0094 to 0.0251 d-1and varied with soil type and depth. For instance, in 60- to 75-cm-depth Kim soil, alachlor degraded at a slower rate (k = 0.011 d-1) than in surface soil samples (k = 0.022 d-1). Alachlor sorption to the four soils was moderate (Kf= 0.7 to 7.4; Kf,oc= 71 to 470) and concentration dependent (1/n < 1.0). Significant hysteretic desorption of alachlor from soils also was observed (1/n desorption < 1/n sorption). The combined effect of degradation and sorption processes has been used to classify a chemical's potential to leach to groundwater. Based on Kf,ocand dissipation half-life, alachlor would be classified as a “leacher” in Kim, Port Byron, and Estherville soils and classified as transitional between “leacher” and “nonleacher” in the Webster soil. The dissipation first-order rate constant (k) of alachlor in Kim soil in the field was 0.036 α 0.012 d-1. Dissipation was apparently not due to leaching since bromide applied at the same time remained in the top 15 cm during the first 28 d. It appears that laboratory-derived leaching indices may overestimate actual leaching and should be used with caution for predictive or regulatory purposes.

scholarly journals Mechanism-based inactivation of gastric peroxidase by mercaptomethylimidazole

1993 ◽  
Vol 296 (1) ◽  
pp. 79-84 ◽  
Author(s):  
U Bandyopadhyay ◽  
D K Bhattacharyya ◽  
R K Banerjee
Keyword(s):  
Ph Dependence ◽  
Order Rate Constant ◽  
Order Kinetic ◽  
First Order ◽  
First Order Kinetics ◽  
Mechanism Of Inhibition ◽  
Catalytically Active ◽  
Pseudo First Order ◽  
Inactivation Process ◽  
Gastric Peroxidase

The mechanism of inhibition of gastric peroxidase (GPO) activity by mercaptomethylimidazole (MMI), an inducer of gastric acid secretion, has been investigated. Incubation of purified GPO with MMI in the presence of H2O2 results in irreversible inactivation of the enzyme. No significant inactivation occurs in the absence of H2O2 or MMI, suggesting the involvement of peroxidase-catalysed oxidized MMI (MMIOX.) in the inactivation process. The inactivation follows pseudo-first-order kinetics consistent with a mechanism-based (suicide) mode. The pseudo-first-order kinetic constants at pH 8 are ki = 111 microM, k(inact.) = 0.55 min-1 and t1/2 = 1.25 min, and the second-order rate constant is 0.53 x 10(4) M-1 x min-1. Propylthiouracil also inactivates GPO activity in the same manner but its efficiency (k(inact./ki = 0.46 mM-1 x min-1) is about 10 times lower than that of MMI (k(inact./ki = 5 mM-1 x min-1). The rate of inactivation with MMI shows pH-dependence with an inflection point at 7.3, indicating the involvement in the inactivation process of an ionizable group on the enzyme with a pKa of 7.3. The enzyme is remarkably protected against inactivation by micromolar concentrations of electron donors such as iodide and bromide but not by chloride. Although GPO oxidizes MMI slowly, iodide stimulates it through enzymic generation of I+ which is reduced back to I- by MMI. Although MMIOX. is formed at a much higher rate in the presence of I-, a constant concentration of I- maintained via the reduction of I+ by MMI, protects the active site of the enzyme against inactivation. We suggest that MMI inactivates catalytically active GPO by acting as a suicidal substrate.

Kinetics and mechanism of the osmium-tetroxide-catalysed oxidation of mandelate ion by hexacyanoferrate(III) ion

1968 ◽  
Vol 21 (12) ◽  
pp. 2913 ◽  
Author(s):  
NP Singh ◽  
VN Singh ◽  
MP Singh
Keyword(s):  
Benzoic Acid ◽  
Oxidation Product ◽  
Osmium Tetroxide ◽  
Reaction Rate ◽  
Zero Order ◽  
Ion Concentration ◽  
First Order ◽  
First Order Kinetics ◽  
Catalysed Oxidation ◽  
Hydroxyl Ion

The osmium-tetroxide-catalysed oxidation of mandelate ion by hexacyanoferrate(111) ion has been studied kinetically. The reaction rate has been found to be independent of hexacyanoferrate(111) ion while the order with respect to both osmium tetroxide and mandelate ion comes out to be unity. The reaction rate follows first-order kinetics at low hydroxyl ion concentration and becomes zero order at higher concentrations. The course of the reaction has been considered to proceed through the formation of an activated mandelate-OsO4, complex which decomposes in alkaline medium giving reduced osmium(V1) followed by a fast oxidation by hexacyanoferrate(111) ion. The probable course of the reactions is also described with the help of its oxidation product, benzoic acid.

scholarly journals Removal Of Lead (Pb2+) From Aqueous Solutions By Natural Bentonite

2015 ◽  
Vol 4 (1) ◽  
Author(s):  
Wahyu Wilopo ◽  
Doni Prakasa Eka Putra ◽  
I Wayan Warmada ◽  
Tsuyoshi Hirajima
Keyword(s):  
Aqueous Solution ◽  
Grain Size ◽  
Adsorption Process ◽  
Exchange Process ◽  
Freundlich Isotherm ◽  
Exchange Capacity ◽  
Ion Concentration ◽  
Lead Ions ◽  
Lead Ion ◽  
Batch Adsorption

The aim of the present work is to investigate the ability of natural bentonite (untreated) from Pacitan, East Java to remove lead ions from aqueous solution. The bentonite has specific surface area and cation exchange capacity of 27.52 m2 g−1 and 65.20 meq/100 gr of bentonite, respectively. Towards this aim, batch adsorption experiments were carried out and the effect of various parameters on this removal process has been investigated. The effects of pH, grain size of bentonite, adsorption time and lead ion concentration on the adsorption process were examined. The optimum pH for adsorption was found to be 9, with the finer grain size of bentonite is more effective. In adsorption studies, residual lead ions concentration reached equilibrium in a duration of 24 hours. Adsorption of lead on bentonite appeared to follow Freundlich isotherm. Our results demonstrate that the adsorption process was mostly dominated by ion exchange process. Keywords: Removal, lead, aqueous solution, natural bentonite, adsorption.

Kinetics and mechanism of the reaction of dimethyl acetylphosphonate with water. Expulsion of a phosphonate ester from a carbonyl hydrate

1978 ◽  
Vol 56 (13) ◽  
pp. 1792-1795 ◽  
Author(s):  
Ronald Kluger ◽  
David C. Pire ◽  
Jik Chin
Keyword(s):  
Rate Constant ◽  
Electronic Effect ◽  
Order Rate Constant ◽  
Ion Concentration ◽  
First Order ◽  
Cleavage Reactions ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Hydrolysis Of ◽  
Mechanism Of The Reaction

Dimethyl acetylphosphonate (DAP) is rapidly cleaved in water to acetate and dimethylphosphonic acid. The half time for reaction at pH 7, 25 °C is estimated to be 3 s. The reaction is first order in hydroxide ion concentration and first order in DAP concentration. Rates of reaction were measured over the pH range 3.8 to 6.5 at 25 °C, 6.5 and 7.0 at 5 °C, 4.5 to 6.5 at 35 °C, and 4.5 to 6.0 at 45 °C. The average observed second-order rate constant at 25 °C is 2.4 × 106M−1 s−1. DAP is converted rapidly to a hydrated carbonyl adduct. The mechanism for the formation of the observed products is proposed to be analogous to cleavage reactions of other carbonyl hydrates, proceeding from a monoanion conjugate in this case. The estimated rate constant for the unimolecular cleavage of the carbonyl hydrate anion is 2 × 103 s−1. The rapid hydrolysis of DAP results from energetically favourable formation of a hydrate due to the electronic effect of the phosphonate diester. This effect also promoles ionization of the hydrate. The ionized hydrate readily expels the phosphonate diester to achieve the overall rapid hydrolysis.

Kinetics of glycoluril template-directed Claisen condensations and mechanistic implications

2002 ◽  
Vol 80 (5) ◽  
pp. 517-527 ◽  
Author(s):  
Mohammad Rahimizadeh ◽  
Karen Kam ◽  
Stephen I Jenkins ◽  
Robert S McDonald ◽  
Paul HM Harrison
Keyword(s):  
Uv Spectroscopy ◽  
Condensation Reaction ◽  
Order Rate Constant ◽  
Nucleophilic Attack ◽  
First Order ◽  
Order Rate ◽  
First Order Kinetics ◽  
Benzoyl Group ◽  
Excess Base ◽  
Kinetics Of

Eight N-acetyl-N-aroyl-glycolurils were prepared and found to undergo efficient tert-butoxide-promoted Claisen-like condensation between the two acyl moieties. The kinetics for formation of each of the N-(aroylacetyl)gly coluril products were monitored by UV spectroscopy. The reaction exhibited pseudo-first-order kinetics in substrate in the presence of excess base. For the parent benzoyl compound the observed first-order rate constant (kobs) was linearly dependent on the concentration of the base, tert-butoxide. A Hammett plot of the resulting apparent second-order rate constants (kapp) vs. σ for each of the eight aroyl derivatives was linear and had a positive ρ value 1.04 ± 0.04), demonstrating that the substituent on the aromatic ring exerts a significant effect upon the condensation reaction. The corresponding plot for three [D3]acetyl analogues was also linear, but the slope was reduced by 20% relative to the protonated compounds. The isotope effect (kHapp/kDapp) thus increased from 1.4 (benzoyl) to 2.6 (p-nitrobenzoyl). The results are consistent with a three-step mechanism in which both deprotonation of the acetyl entity and the ensuing nucleophilic attack of the resulting enolate on the benzoyl group are partially rate-determining steps. The tetrahedral intermediate thus produced rapidly collapses to the product. For the [D3]acetyl benzoyl derivative, exchange of substrate deuterium with solvent hydrogen due to reprotonation of the enolate intermediate occurs at a rate that is similar to that of condensation, but the enolate partitions towards the product when electron withdrawing groups are present in the aroyl ring. Thus, despite the presence of a large excess of co-solvent tert-butanol, the efficiency with which the enolate undergoes condensation remains high. The clean kinetics observed allows further exploration of the details of this intramolecular Claisen-like condensation process.Key words: Claisen condensation, glycoluril, kinetics, Hammett, mechanism.

scholarly journals Acid Hydrolysis of Bis(2,2'; 6',2''–Terpyridyl) Iron(II) Complex in the Water Pools of CTAB/Hexane/Chloroform Reverse Micelles-A Kinetic Study in Confined Medium

2020 ◽  
Vol 15 (3) ◽  
pp. 853-860
Author(s):  
K. V. Nagalakshmi ◽  
P. Shyamala
Keyword(s):  
Ionic Strength ◽  
Acid Hydrolysis ◽  
Reverse Micelles ◽  
Order Rate Constant ◽  
Micellar Medium ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Of Reaction ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of acid hydrolysis of bis(2,2';6',2''–terpyridyl) iron(II) complex has been studied in CTAB/Hexane/Chloroform reverse micelles. The reaction obeys first order kinetics with respect to each of the reactants at all values of W, {W= [H2O]/[CTAB]}. In the reverse micellar medium, the reaction is much slower compared to aqueous medium due to low micropolarity of the water pools which does not facilitate a reaction between reactants of same charge. The effect of variation of W {W=[H2O]/[CTAB]} at constant [CTAB] and variation of [CTAB] at fixed W has been studied. The second order rate constant (k2) of the reaction increases as the value of W increases up to W = 8.88 and remains constant thereafter and it is independent of concentration of [CTAB] at constant W. The variation of rate of reaction with W has been explained by considering variation of micropolarity and ionic strength of water pools of reverse micelles with W. Copyright © 2020 BCREC Group. All rights reserved 

Oxidation of the mercurous ion by peroxidase

1986 ◽  
Vol 64 (5) ◽  
pp. 969-972 ◽  
Author(s):  
Donald C. Wigfield ◽  
Season Tse
Keyword(s):  
Elemental Mercury ◽  
Order Rate Constant ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Order Rate ◽  
First Order Kinetics ◽  
Cold Vapour ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Mercurous Ion

The kinetics of oxidation of the mercurous ion by peroxidase have been measured by following the disappearance of mercurous ion using cold-vapour atomic absorption spectroscopy. Pseudo-first-order kinetics are observed with respect to mercurous ion, and the pseudo-first-order rate constants are linearly related to peroxidase concentration, showing first-order dependence on peroxidase. This behaviour is identical to oxidation of elemental mercury, and the second-order rate constant, 1.44 × 104 M−1 s−1 at 23 °C, is also, within experimental error, the same as that for elemental mercury oxidation. The data are interpreted in terms of peroxidase-induced disproportionation of the mercurous dimer, followed by two-electron oxidation of zero-valent mercury.

A Study on Lead Adsorption by the Hen Egg Shells from Enshi, Hubei Province, China

2019 ◽  
Vol 294 ◽  
pp. 11-16
Author(s):  
Heng Heng Gong ◽  
Tao Li ◽  
Wen Ya Zhang ◽  
Zhao Jiang Liao
Keyword(s):  
Aqueous Solution ◽  
Hubei Province ◽  
Lead Ions ◽  
Lead Ion ◽  
Water Quality Standards ◽  
Order Model ◽  
Lead Adsorption ◽  
First Order ◽  
Egg Shells ◽  
Hen Egg

The hen egg shells (HES) from EnShi, HuBei Province, China, which contain selenium, are used as adsorbent for the adsorption of lead ion from its aqueous solutions. The selenium in the HES could help to remove lead from its aqueous solution. The HES had been found to be the more efficient in the experiment and removed about 95% of lead from its aqueous solution. The final concentration of lead ion was found lower than the waste water quality standards from the initial concentration of lead ion 100.0 mg/L through these two steps of adsorptions. One gram of the HES can adsorb nearly 31.71±0.040 mg of lead ions. The adsorption kinetics was fitted by first-order model throughout the period. The present adsorption process is spontaneous, indicating HES can be availably used for the removal of lead ions from its aqueous solution.

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