Solution pH and Jarosite Management during Ferrous Iron Biooxidation in a Novel Packed-Column Bioreactor

2015 ◽  
Vol 1130 ◽  
pp. 291-295 ◽  
Author(s):  
Mwema Wanjiya ◽  
Faysol Chowdhury ◽  
Tunde Victor Ojumu
Keyword(s):  
Packed Column ◽  
Base Case ◽  
Airflow Rate ◽  
Solution Ph ◽  
Ph Values ◽  
Column Bioreactor ◽  
Duration Of Operation ◽  
Mineral Sulfides ◽  
Kinetics Of ◽  
Ferrous Oxidation

Jarosite formation is undesirable in bioleaching processes as it depletes the needed ferric reagent for the oxidation of most sulfide minerals. Although it creates kinetic barriers thereby retarding the leach rates of most minerals, jarosite serves as support for the attachment of bioleaching microbes, facilitating biooxidation rate. Microbial ferrous-oxidation by mesophilic microbe was studied in a recently reported novel packed-column bioreactor with a view to investigate the potential of using solution pH to manage jarosite accumulation in the bioreactor in addition to establishing a base case data for the bioreactor. Experiments were conducted in the bioreactor packed with glass balls (15mm diameter) at constant temperature of 38.6 °C, residence time of 18 hours, airflow rate of 20 mLs-1and pH values of 1.3, 1.5 and 1.7. The results showed that the amount of jarosite accumulation is proportional to the solution pH, and to the duration of operation of the bioreactor. Jarosite precipitation concentrations of 4.95, 5.89 and 7.08 gL-1were obtained after 10 days of continuous operation at solution pH values of 1.3, 1.5 and 1.7 respectively, while after 15 days the precipitations concentrations increased to 5.50, 7.90, 9.98 gL-1respectively. The results also showed that 33% and 52% precipitate reduction could be achieved by gradual decrease in the bioreactor solution pH to 1.5 and 1.3 after being continuously operated for 10 days at pH 1.7 respectively after an addition of 5 days. A maximum ferrous oxidation rate (), 6.85 mmol.L-1.h-1and the affinity kinetic constants (,), of 0.001 and 0.006 for Hansford and Monod models respectively. Although a directly relationship exist between jarosite formation and pH, the results of this study may be relevant in bioleach heaps or at least in column bioreactors to manage/control jarosite accumulation thereby improving the leach kinetics of mineral sulfides.

Heterogeneous oxidation of diclofenac in the presence of α-MnO2 nanorods: influence of operating factors and mechanism

2015 ◽  
Vol 71 (9) ◽  
pp. 1340-1346 ◽  
Author(s):  
Jian Li ◽  
Tuqiao Zhang ◽  
Miaomiao Ye
Keyword(s):  
Ph Value ◽  
Reaction Pathway ◽  
Complete Removal ◽  
Solution Ph ◽  
Heterogeneous Oxidation ◽  
Oxidation Activity ◽  
Ph Values ◽  
Anions And Cations ◽  
Oxidation Efficiency ◽  
Kinetics Of

Diclofenac (DCF), one of the pharmaceutical and personal care products that has been widely detected in water, was selected as a model pollutant to evaluate the oxidation activity of α-MnO2 nanorods. The results showed that the heterogeneous oxidation process is highly pH dependent, with higher degradation efficiency at lower pH values. The complete removal of DCF was obtained within 80 min at the solution pH value of 2.5. The oxidation kinetics of DCF can be modeled by Langmuir–Hinshelwood equation (R2 > 0.999). The effects of various operating parameters, including initial solution pH, α-MnO2 dosage, anions, and cations, on the oxidation efficiency were investigated in detail. A possible reaction pathway for DCF was proposed. In addition, it was demonstrated that the α-MnO2 nanorods can be recycled without decreasing their oxidation activity after 10 cycles.

Kinetic of oxidation of methyl orange by vanadium(V) under conditions VO2+ and decavanadates coexist: Catalysis by Triton X-100 micellar medium

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Methyl Orange ◽  
Solution Ph ◽  
Vanadium Concentration ◽  
Limiting Behavior ◽  
First Order ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetic Pattern ◽  
Triton X ◽  
Kinetics Of

The kinetics of oxidation of methyl orange by vanadium(V) {V(V)} has been investigated in the pH range 2.3-3.79. In this pH range V(V) exists both in the form of decavanadates and VO2+. The kinetic results are distinctly different from the results obtained for the same reaction in highly acidic solution (pH < 1) where V(V) exists only in the form of VO2+. The reaction obeys first order kinetics with respect to methyl orange but the rate has very little dependence on total vanadium concentration. The reaction is accelerated by H+ ion but the dependence of rate on [H+] is less than that corresponding to first order dependence. The equilibrium between decavanadates and VO2+ explains the different kinetic pattern observed in this pH range. The reaction is markedly accelerated by Triton X-100 micelles. The rate-[surfactant] profile shows a limiting behavior indicative of a unimolecular pathway in the micellar pseudophase.

Derivatives of isatin in aqueous solution. I. Kinetics of ring opening of Isatin-5-sulfonate

1981 ◽  
Vol 34 (2) ◽  
pp. 365 ◽  
Author(s):  
H Stunzi
Keyword(s):  
Ring Opening ◽  
Rate Of Change ◽  
Spectroscopic Methods ◽  
Ph Values ◽  
Buffer Region ◽  
Pka Value ◽  
Back Titration ◽  
Kinetics Of ◽  
Derivatives Of ◽  
Sulfonate Anion

The reactions of isatin-5-sulfonate anion (si-) which cause a hysteresis in pH titrations were studied by pH-metric and n.m.r, spectroscopic methods. Rapid alkalimetric titrations [I 0.15 M (KNO3),37�] gave the pKa value corresponding to the addition of OH- to si- [pKa(ring) 9.55]. The slow ring opening to the sulfonatoisatate dianion (sia2-) led to a drift of the pH values towards an equilibrium buffer region. Its pKa, value [pKa(eq) 3.44] corresponds to the reaction si-+H2O ↔ sia 2-+H+ Rapid back-titration gave the pKa value of the ring-opened species Hsia- [pKa(open) c. 1.3]. The rate law for the ring opening d[sia]/dt=k2 [siOH](OH)+k1*[si] was obtained from the rate of change of pH. N-Methylisatin-5-sulfonate behaves analogously.

scholarly journals Kinetics of thiamin cleavage by sulphite

1969 ◽  
Vol 113 (4) ◽  
pp. 611-615 ◽  
Author(s):  
J. Leichter ◽  
M. A. Joslyn
Keyword(s):  
Aqueous Solutions ◽  
Rate Constant ◽  
Sulphur Dioxide ◽  
First Order ◽  
Ph Values ◽  
Rate Of Reaction ◽  
Kinetics Of

Results are presented on the rate of thiamin cleavage by sulphite in aqueous solutions as affected by temperature (20–70°), pH(2·5–7·0), and variation of the concentration of either thiamin (1–20μm) or sulphite (10–5000μm as sulphur dioxide). Plots of the logarithm of percentage of residual thiamin against time were found to be linear and cleavage thus was first-order with respect to thiamin. At pH5 the rate was also found to be proportional to the sulphite concentration. In the pH region 2·5–7·0 at 25° the rate constant was 50m−1hr.−1 at pH5·5–6·0, and decreased at higher or lower pH values. The rate of reaction increased between 20° and 70°, indicating a heat of activation of 13·6kcal./mole.

Statistical Modeling, Optimization and Kinetics of Mn2+ Adsorption in Aqueous Solution Using a Biosorbent

2019 ◽  
Vol 233 (8) ◽  
pp. 1201-1214 ◽  
Author(s):  
Elaheh Tajari ◽  
Narges Samadani Langeroodi ◽  
Mahnaz Khalafi
Keyword(s):  
Wheat Bran ◽  
Low Cost ◽  
Weight Ratio ◽  
P Value ◽  
Core Shell ◽  
Optimal Conditions ◽  
Solution Ph ◽  
Shell Weight ◽  
Removal Ratio ◽  
Kinetics Of

Abstract This paper describes the adsorption of Mn2+ ions from water with a mixture of wheat bran and Japanese medlar core shell (weight ratio of 30–70 wheat bran to Japanese medlar core shell) as low-cost adsorbent. Scanning Electron Microscope was used to characterize the adsorbent. The response surface methodology (RSM) that is usually approximated by a second-order regression model was employed to evaluate the effects of solution pH, initial Mn2+ concentration, adsorbent weight and contact time on the removal ratio of the Mn2+ ions. In this regard, the significant variables initial Mn2+ ions concentration, pH, adsorbent weight and square pH were found based on the small P-value for the model coefficients. The predicted optimal conditions were also performed. In the process optimization, maximal value of the removal ratio of Mn2+ was achieved as 96.91%. Additionally, this paper discusses the kinetic of adsorption in optimal conditions.

scholarly journals Inhibition of staphylococcal α-toxin. A kinetic evaluation of aromatic polysulphonic acids as inhibitors of haemolysis

1968 ◽  
Vol 108 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Margaret Robson Wright ◽  
J. P. Arbuthnott ◽  
I. R. W. Lominski
Keyword(s):  
Inhibitory Activity ◽  
Maximum Rate ◽  
Lag Time ◽  
Test Compound ◽  
Rabbit Erythrocyte ◽  
Compound I ◽  
Kinetic Evaluation ◽  
Ph Values ◽  
Inhibitory Compounds ◽  
Kinetics Of

1. The effect of a number of aromatic polysulphonic acids on the kinetics of haemolysis of rabbit erythrocyte suspensions by crude staphylococcal α-toxin was studied at pH8·6 and 6·8. 2. All of the inhibitory compounds caused an increase in the prelytic lag time (τ) of the sigmoid haemolysis curves, an increase in the time to reach 50% haemolysis (t½) and a decrease in the maximum rate of haemolysis (Rmax.). The most inhibitory compounds caused a 50% decrease in Rmax. at concentrations between 0·1 and 0·2mm. 3. The effect of pH varied considerably: compounds (I) and (II) were almost equally inhibitory at both pH values, compounds (IV) and (IX) were more inhibitory at pH6·8 than at pH8·6, and compounds (VII), (VIII), (X), (XI) and (XII) were more inhibitory at pH8·6. 4. Increased time of premixing α-toxin with compound (I) caused increased inhibition. 5. An attempt was made, where possible, to relate the inhibitory activity to the structure of the test compound.

scholarly journals Remaining phosphorus and sodium fluoride pH in soils with different clay contents and clay mineralogies

2004 ◽  
Vol 39 (3) ◽  
pp. 241-246 ◽  
Author(s):  
Marcelo Eduardo Alves ◽  
Arquimedes Lavorenti
Keyword(s):  
Buffer Capacity ◽  
Ammonium Oxalate ◽  
Clay Mineralogy ◽  
Clay Content ◽  
Response Curves ◽  
Solution Ph ◽  
Ph Values ◽  
Soil Clay ◽  
Soil Clay Content ◽  
Discriminatory Capacity

The remaining phosphorus (Prem) has been used for estimating the phosphorus buffer capacity (PBC) of soils of some Brazilian regions. Furthermore, the remaining phosphorus can also be used for estimating P, S and Zn soil critical levels determined with PBC-sensible extractants and for defining P and S levels to be used not only in P and S adsorption studies but also for the establishment of P and S response curves. The objective of this work was to evaluate the effects of soil clay content and clay mineralogy on Prem and its relationship with pH values measured in saturated NaF solution (pH NaF). Ammonium-oxalate-extractable aluminum exerts the major impacts on both Prem and pH NaF, which, in turn, are less dependent on soil clay content. Although Prem and pH NaF have consistent correlation, the former has a soil-PBC discriminatory capacity much greater than pH NaF.

New Insights into the Kinetics of the Gas-Phase Oxidation of Hexafluoropropene

2016 ◽  
Vol 41 (4) ◽  
pp. 418-427 ◽  
Author(s):  
David Lokhat ◽  
Maciej Starzak ◽  
Deresh Ramjugernath
Keyword(s):  
Gas Phase ◽  
Oxidation Process ◽  
Flow Reactor ◽  
Packed Column ◽  
Phase Reaction ◽  
Analytical Technique ◽  
Tubular Flow Reactor ◽  
Gas Phase Oxidation ◽  
Tubular Flow ◽  
Kinetics Of

The gas-phase reaction of hexafluoropropene and molecular oxygen was investigated in a tubular flow reactor at 450 kPa and within a temperature range of 463–493 K using HFP/O2 mixtures containing 20–67% HFP on a molar basis. Capillary and packed column chromatography served as the main analytical technique. The reaction yielded HFPO, COF2, CF3COF, C2F4 and c-C3F6 as gas-phase products. High molecular weight oligomers were also formed. The oligomers were found to have a polyoxadifluoromethylene structure according to elemental and 19F NMR analysis. At 493 K HFP is proposed to undergo oxygen-mediated decomposition to difluorocarbene radicals, yielding greater quantities of difluorocarbene recombination products. Kinetic parameters for a revised model of the oxidation process were identified through least squares analysis of the experimental data.

scholarly journals Study of photocatalytic activity of TiO2 fluorinated by thermal shock method for the degradation of different dyes

2015 ◽  
Vol 18 (2) ◽  
pp. 121-131
Author(s):  
Khoa Tien Le ◽  
Ngoc Chau Hoang ◽  
Tien Thuy Thai ◽  
Anh Trung Le ◽  
Thinh Nguyen Huu Pham ◽  
...  
Keyword(s):  
Methylene Blue ◽  
Photocatalytic Activity ◽  
Methyl Orange ◽  
Thermal Shock ◽  
Photocatalytic Oxidation ◽  
Organic Dyes ◽  
Cationic Dye ◽  
Solution Ph ◽  
Ph Values ◽  
Methylene Blue Cationic Dye

TiO2 P25 was fluorinated by thermal shock method in order to study the influence of thermal shock fluorination on the surface properties and the photocatalytic activity for the degradation of cationic and anionic organic dyes at different pH values. The surface charge of catalysts was characterized by the pHPZC measurement. The photocatalytic activity of catalysts was evaluated via the degradation of methylene blue (cationic dye) and methyl orange (anionic dye). The results showed that the thermal shock fluorination and the rise of solution pH can increase the surface negative charge of TiO2, which enhanced the adsorption of methylene blue and then improved the photocatalytic degradation of this cationic dye under UV and visible light. On the other hand, after the fluorination, the adsorption of methyl orange on TiO2 was strongly reduced, which limited the photocatalytic oxidation of this anion dye.

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