EQUILIBRIUM AND KINETIC STUDIES OF THE ADSORPTION OF 2,4-D AND PICLORAM ON HUMIC ACID

1973 ◽  
Vol 53 (4) ◽  
pp. 429-434 ◽  
Author(s):  
S. U. KHAN
Keyword(s):  
Humic Acid ◽  
Adsorption Process ◽  
Initial Period ◽  
Kinetic Studies ◽  
Time Intervals ◽  
Rate Limiting Step ◽  
Equilibrium Data ◽  
Dichlorophenoxy Acetic Acid ◽  
Rate Limiting ◽  
Physical Type

Equilibrium and kinetic studies of the adsorption of 2,4-D (2,4-dichlorophenoxy acetic acid) and picloram (4-amino-3,5,6-trichloropicolinic acid) on a humic acid have been made. The equilibrium data followed the Freundlich-type isotherm. Rate constants, activation energies, heats of activation, and entropies of activation were calculated for the adsorption of the two herbicides on humic acid. The rate data indicated a physical type of adsorption. In the overall adsorption process the rate-limiting step for the initial period was shown to be the diffusion of the herbicide molecules to the surface of humic acid. However, the rate-limiting process at longer time intervals was interpreted to be intraparticle diffusion of the herbicide molecules into the interior of the humic acid particles.

Removal of Mg from spring water using natural clinoptilolite

Clay Minerals ◽  
2012 ◽  
Vol 47 (1) ◽  
pp. 81-92 ◽  
Author(s):  
S. Tomić ◽  
N. Rajić ◽  
J. Hrenović ◽  
D. Povrenović
Keyword(s):  
Ion Exchange ◽  
Kinetic Studies ◽  
Spring Water ◽  
Zeolite A ◽  
Zeolitic Tuff ◽  
Rate Limiting Step ◽  
Intra Particle Diffusion ◽  
Pseudo Second Order ◽  
Natural Clinoptilolite ◽  
Rate Limiting

AbstractNatural zeolitic tuff from Brus (Serbia) consisting mostly of clinoptilolite (about 90%) has been investigated for the reduction of the Mg concentration in spring water. The sorption capacity of the zeolite is relatively low (about 2.5 mg Mg g-1for the initial concentration of 100 mg Mg dm-3). The zeolitic tuff removes Mg from water solutions by ion exchange, which has been demonstrated by energy dispersive X-ray analysis (EDS). The extent of ion exchange was influenced by the pH and the initial Mg concentration. Kinetic studies revealed that Lagergen's pseudo-second order model was followed. Intra-particle diffusion of Mg2+influenced the ion exchange, but it is not the rate-limiting step. Rather than having to dispose of the Mg-loaded (waste) zeolite, a possible application was tested. Addition to a wastewater with a low concentration of Mg showed that it could successfully make up for the lack of Mg micronutrient and, accordingly, enabled the growth of phosphate-accumulating bacteriaA. Junii, increasing the amount of phosphate removed from the wastewater.

scholarly journals Synchronized Infection of Cell Cultures by Magnetically Controlled Virus

2005 ◽  
Vol 79 (1) ◽  
pp. 622-625 ◽  
Author(s):  
Hillel Haim ◽  
Israel Steiner ◽  
Amos Panet
Keyword(s):  
Adsorption Process ◽  
Diffusion Rate ◽  
Cell Attachment ◽  
Diffusion Limited ◽  
Rate Limiting Step ◽  
Immunodeficiency Virus ◽  
Rate Limiting ◽  
And Diffusion ◽  
Entry Mechanism

ABSTRACT To override the diffusion-limited adsorption step of viral infection, we magnetically synchronized cell attachment. Human immunodeficiency virus type 1-based lentivirus preparations were rendered magnetically reactive by association with magnetite nanoparticles, 50 nm in diameter. Application of a magnetic field resulted in immediate redistribution of the viral inoculum to the cell-associated state and completion of the productive adsorption process within 1 min. Independent of adsorption time, viral concentration, and diffusion rate, infection subsequently progressed by the receptor-mediated entry mechanism. Synchronization of this rate-limiting step of infection may now be applied to analyze isolated events in the viral replication sequence.

scholarly journals Study on the Adsorption Kinetics of Acid Red 3B on Expanded Graphite

2008 ◽  
Vol 5 (4) ◽  
pp. 802-809 ◽  
Author(s):  
Xiu-yan Pang ◽  
Fei Gong
Keyword(s):  
Activation Energy ◽  
Adsorption Kinetics ◽  
Adsorption Process ◽  
Expanded Graphite ◽  
Chemical Oxidation ◽  
Adsorption Rate ◽  
Order Kinetic ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Expanded graphite (EG) is a kind of important adsorbent for organic compound such as oil and dyes. We have investigated the adsorption kinetics characteristics of this adsorbent for dye. EG was prepared with 50 mesh crude graphite through chemical oxidation intercalation of potassium permanganate and vitriol, and dye of acid red 3B was used as model sorbate. We have studied the adsorption kinetic models and rate-limiting step of the process. Adsorption rate and activation energy of the adsorption process were calculated. Kinetic studies show that the kinetic data are well described by the pseudo second-order kinetic model. The equilibrium adsorbance increases with the increase of the initial acid red 3B concentration. Initial adsorption rate increases with the increase of the initial dye concentration and temperature. Adsorption process of acid red 3B on EG has small activation energy. Internal diffusion appears to be the rate-limiting step for the adsorption process.

scholarly journals Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-Linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

2020 ◽  
Vol 17 (3) ◽  
pp. 788 ◽  
Author(s):  
Daixi Zhou ◽  
Guangyu Xie ◽  
Xinjiang Hu ◽  
Xiaoxi Cai ◽  
Yunlin Zhao ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Adsorption Process ◽  
Reaction System ◽  
Freundlich Isotherm ◽  
Fractional Factorial ◽  
Separation Performance ◽  
Initial Concentration ◽  
Rate Limiting Step ◽  
Rate Limiting ◽  
Competing Ions

Cr(VI) contamination has posed great threat to both the ecosystem and human health for its carcinogenic and mutagenic nature. A highly effective adsorbent for the removal of Cr(VI) was prepared and its adsorption mechanism was thoroughly discussed in this study. In detail, magnetic BiFeO3 and kenaf biochar were loaded on cross-linked chitosan to obtain chitosan-kenaf biochar@BiFeO3 (CKB) for improving adsorption capacity towards Cr(VI). The adsorption process of Cr(VI) onto CKB was evaluated as a function of the pH, the existence of competing ions, the initial concentration of Cr(VI) and contact time. The results show that CKB exhibits the highest adsorption capacity under the optimal pH 2.0. The presence of competing ions such as Ca2+, NO3−, SO42−, and Cl− decreases the adsorption capacity; among them, Ca2+ and NO3− show the greatest hindrance. By studying the effect of initial Cr(VI) concentration on the adsorption capacity, it was found that CKB in the solution was enough to remove Cr(VI) for all treatments (10–200 mg/L). The adsorption experimental data were well fitted with pseudo-first-order model, suggesting that chemisorption is not the dominant rate-limiting step. Freundlich isotherm model can better explain the adsorption process, indicating a non-ideal adsorption towards Cr(VI) on a heterogeneous surface of CKB. A 25-1 Fractional Factorial Design (FFD) showed that pH and initial concentration of Cr(VI) have significant influence on Cr(VI) adsorption in our reaction system. In general, excellent adsorption efficiency of CKB indicates that it may be a good candidate for the remediation of Cr(VI)-contaminating wastewater.

scholarly journals Kinetic studies of formate dehydrogenase

1970 ◽  
Vol 120 (4) ◽  
pp. 763-769 ◽  
Author(s):  
D. Peacock ◽  
D. Boulter
Keyword(s):  
Carbon Dioxide ◽  
Formate Dehydrogenase ◽  
Kinetic Studies ◽  
Kinetic Mechanism ◽  
Product Inhibition ◽  
Reverse Reaction ◽  
Enzyme Form ◽  
Rate Limiting Step ◽  
Measurable Rate ◽  
Rate Limiting

1. The kinetic mechanism of formate dehydrogenase is a sequential pathway. 2. The binding of the substrates proceeds in an obligatory order, NAD+ binding first, followed by formate. 3. It seems most likely that the interconversion of the central ternary complex is extremely rapid, and that the rate-limiting step is the formation or possible isomerization of the enzyme–coenzyme complexes. 4. The secondary plots of the inhibitions with HCO3− and NO3− are non-linear, which suggests that more than one molecule of each species is able to bind to the same enzyme form. 5. The rate of the reverse reaction with carbon dioxide at pH6.0 is 20 times that with bicarbonate at pH8.0, although no product inhibition could be detected with carbon dioxide. The low rate of the reverse reaction precluded any steady-state analysis as the enzyme concentrations needed to obtain a measurable rate are of the same order as the Km values for NAD+ and NADH.

Photoenhancement of Gas-Solid Reactions by Surface Excitation

1983 ◽  
Vol 29 ◽  
Author(s):  
Carol I. H. Ashby
Keyword(s):  
Thermal Effects ◽  
Kinetic Studies ◽  
Wavelength Dependence ◽  
Reaction Rates ◽  
Thermal Reaction ◽  
Subsequent Formation ◽  
Rate Limiting Step ◽  
Surface Excitation ◽  
Rate Limiting ◽  
Reactive Excited State

ABSTRACTUltraviolet irradiation of the surface of graphite leads to the enhancement of the reaction of graphite with hydrogen to form methane under conditions where photo-induced thermal effects are negligible. Wavelength dependence of the photoenhancement correlates with excitation of the π-valence to π-conduction transition of graphite centered at 260 nm. Subsequent formation of some reactive excited state species leads to enhanced reaction rates. Likely candidates for such reactive species have been identified by comparative kinetic studies of the thermal and the photoenhanced reactions. For example, at low temperatures (< 500 K), the rate-limiting step of the thermal reaction is addition of H to surface CH3 groups, and the observed photoenhancement can be explained by activation of these CH3 groups.

scholarly journals Sorption of Bivalent Ions by Cymbopogon citratus: Characterisation and Investigation of Biosorptive Capacity and Mechanism

2018 ◽  
Vol 4 (3) ◽  
pp. 297-302
Author(s):  
S. Jayashree ◽  
Jeyavathana Samuel ◽  
R. Vashantha
Keyword(s):  
Aqueous Solution ◽  
Metal Ion ◽  
Adsorption Process ◽  
Low Cost ◽  
Kinetic Studies ◽  
Solution Temperature ◽  
Isotherm Models ◽  
Physical Parameters ◽  
Cymbopogon Citratus ◽  
Equilibrium Data

The main objective of this study was to investigate the removal of cadmium(II) ions from aqueous solution using raw Cymbopogon citratus as an adsorbent. It was characterized by FT-IR, XRD, SEM-EDAX and its physical parameters were analyzed. Different factors such as pH, contact time, initial concentration and temperature were studied. Maximum adsorption was taken place at the optimum pH of 6 and the equilibrium data were analyzed by Langmuir, Freundlich and Temkin Isotherm models. Among those isotherm models Langmuir and Temkin were fitted well with good correlation coefficient (R2). The negative values of ΔG⁰ for all temperature shows the adsorption process for cadmium(II) ion was spontaneous in nature and feasible. The negative value of enthalpy change ΔH⁰ shows the adsorption process is exothermic and the positive value of ΔS⁰ indicates the disorderness or randomness process of adsorption. The positive value of Ea indicates the higher solution temperature favors the adsorption of metal ion onto RCC. The experimental data were analyzed by kinetic studies such as pseudo-first order, pseudo-second order and intra-particle diffusion models. Desorption was also studied and the recovery of the adsorbent was found to be 10%. Thus on the basis of these investigations the present study concludes that the raw Cymbopogon citratus (RCC) was found to be highly effective, nontoxic, environmental friendly and low cost adsorbent for the removal of toxic Cd(II) ions from aqueous solution.

scholarly journals Investigation of Adsorption of Cobalt-phthalocyanine from Aqueous Waste Stream Using UVM-7/Ag

2018 ◽  
Vol 1 (01) ◽  
pp. 29-38
Author(s):  
Amir Vahid ◽  
Majid Abdous ◽  
Shahnaz Nayyeri
Keyword(s):  
Contact Time ◽  
Mesoporous Material ◽  
Adsorption Process ◽  
Kinetic Studies ◽  
Cobalt Phthalocyanine ◽  
X Ray Diffraction ◽  
X Ray ◽  
Equilibrium Data ◽  
Thermodynamic Constant ◽  
Pseudosecond Order

The effect adsorption of cobalt-phthalocyanine-3,4’,4”,4”’- tetrasulfonicacid tetrasodium salt [Co(tsPc)-4•4Na＋] onto UVM-7/Ag mesoporous material was investigated. In addition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorptiondesorption measurement were used to examine the morphology and the microstructure of the obtained composite. Various parameters including solution adsorbent dosage, contact time, initial dye concentration and temperature were systematically studied. Equilibrium data fitted well the Langmuir models; moreover, the fitness suggests that the adsorption be monolayer and physical in nature. Kinetic studies showed that the adsorption process could be better described by the Lagergren pseudosecond- order models. Thermodynamic constant values (ΔG < 0, ΔH< 0 and ΔS< 0) demonstrated that the adsorption reactions of Co(tspc)-4 onto UVM-7/Ag were feasible, spontaneous, and exothermic under the examined conditions.

scholarly journals Equilibrium, Kinetics and Thermodynamics of the Bleaching of Palm Oil Using Activated Nando Clay

2018 ◽  
pp. 1-13
Author(s):  
Nwabanne, Joseph T. ◽  
Onu, Chijioke E. ◽  
Nwankwoukwu, Okwudili C.
Keyword(s):  
Palm Oil ◽  
Order Kinetic ◽  
Adsorbent Dosage ◽  
Bleaching Efficiency ◽  
Rate Limiting Step ◽  
Equilibrium Data ◽  
Intra Particle Diffusion ◽  
Different Temperatures ◽  
Pseudo Second Order ◽  
Rate Limiting

The effectiveness of Nando clay in the bleaching of palm oil was studied in this work. The clay was prepared by activating it with hydrochloric acid. The bleaching was carried out at different temperatures, adsorbent dosage and particle sizes. The result suggests that increase in temperature and adsorbent dosage increases the bleaching efficiency while the increase in particle size decreases the bleaching efficiency. Both the pseudo-first-order and the pseudo-second-order kinetic models describe efficiently the experimental data of the bleaching process. Intra-particle diffusion though involved in the adsorptive bleaching mechanism, is not the sole rate-limiting step in the bleaching of palm oil with activated Nando clay. The equilibrium data were described better by Langmuir and Freundlich models. The enthalpy, entropy and activation energy were determined to be 6.127 KJ/mol, 3.982 KJ/mol and 15.281 KJ respectively. The free energy was found to vary between- 3.999 to- 3.760 KJ/mol. The result indicates that bleaching efficiency of up to 96% can be obtained with the activated clay as an adsorbent.

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