Increase In Sulphuric Acid Concentration Research Articles

Extraction of Zinc in Presence of Cobalt through Hollow Fibre Supported Liquid Membrane from Simulated Industrial Wastewater

Many industrial wastewaters contain toxic metals such as zinc, chromium, cobalt in the form of fluorides and nitrates as anions. Transport of Zn 2+ from simulated industrial wastewater was studied using di-2-ethylhexyl phosphoric acid (D2EHPA) diluted in kerosene as the organic phase. The hollow fibre supported liquid membrane was operated in continuous recycle mode. Effect of feed phase pH, carrier concentration, sulphuric acid concentration in the strip phase, and flow rate on Zn 2+ transport was examined. The feed phase pH was varied in the range of 1.5–2.5. The organic phase concentration was varied in the range of 10-30 %. At the feed phase pH of 2, the extraction rates were found to be high. About 12% rise in mass transfer flux of Zn 2+ ions was observed with an increase in D2EHPA concentration from 10% to 20%. The mass transfer flux of Zn 2+ ions was found to be increased by 28% with an increase in sulphuric acid concentration from 0.5 M to 1 M. The flow rate variation study suggests that mass transfer resistance is mainly contributed by diffusion mechanism through the membrane.

Electrochemical evaluation of cr-mn austenitic stainless steel in aqueous sulphuric acid and influence of thiocyanate ions

PurposeLow nickel austenitic stainless steel (ASS) has attracted much attention worldwide because of its economical price. This study aims to investigate the effect of different corrosive environments on the corrosion behavior of chrome-manganese (Cr-Mn) ASS. The tests were carried out as a function of H2SO4 concentrations, temperature and addition of ammonium thiocyanate (NH4SCN) (0.01 M). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of Cr-Mn ASS. It was observed that with increasing H2SO4 concentration, temperature and with the addition of NH4SCN solution, icorr, icrit and ipassive values increased. EIS data show decreasing charge transfer resistance value with increasing concentration and temperature. Higher corrosion rate with increasing temperature and concentration of H2SO4 is related to the anions (SO42−), which is responsible for reducing the stability of passive films. With the presence of 0.01 M NH4SCN thiocyanate (SCN− anion), there is a higher dilution of the passive film resulting in a higher corrosion rate. Energy-dispersive spectroscopy (EDS) analysis reveals the adsorption of sulfur on the surface in NH4SCN containing a solution. The significant presence of counter ions and the adsorbed sulfur species on the steel surface play a vital role in corrosion behavior.Design/methodology/approachAll the experiments were performed on a 3 mm thick sheet of Cr-Mn ASS (202 ASS) in hot rolled condition. The samples were then annealed at 1,050°C for 1 h, followed by water quenching. For microstructural examination, they were electrochemically etched in 10 Wt.% oxalic acid solution at 1 amp for 90 s. A computer-controlled Potentiostat (Biologic VMP-300) was used. After the cell was set up, the working electrode (WE) was electrostatically cleaned at −1 V vs saturated calomel electrode (SCE) for 30 s to remove the air-formed film. Then, WE were allowed to attain stable open circuit potential (OCP) for 1 h, following by the EIS test and potentiodynamic polarization test. The polarization test was started from a cathodic potential (−1.2 V vs SCE) and continued up to an anodic potential (1.6 V vs SCE) a scan rate of 0.1667 mV/s. EIS experiment was conducted on the same instrument by using a sinusoidal AC signal of 10 mV in a frequency range of 1,000,000 to 0.01 Hz at OCP.FindingsPotentiodynamic polarization graph shows that with the increase in sulphuric acid concentration. Increasing temperature from 20°C to 80°C in 0.5 M H2SO4 solution increases the corrosion rate (icorr) of Cr-Mn ASS. On the addition of 0.01 M NH4SCN to the sulfuric acid solution (0.1, 0.5 and 1 M) the corrosion rate increases drastically almost four to five times. EDS and XRD analysis shows the presence of sulfur over the oxide film and preferential site for dissolution of Cr and Mn at the steel surface when NH4SCN is added to the sulfuric acid solution.Originality/valueA study on the corrosion behavior of Cr-Mn ASS is scanty according to the author’s knowledge. Therefore, the present study will investigate the corrosion behavior of Cr-Mn ASS on SO4−2 anions, temperature and the addition of SCN− ion in sulfuric acid.

A spectroscopic investigation of kinetics and mechanism of ruthenium(III)-catalyzed oxidation of N-(2-hydroxyethyl)phthalimide by cerium(IV) in aqueous sulphuric acid and sulphate media

AbstractThe oxidation of N-(2-hydroxyethyl)phthalimide with cerium(IV) with a small amount of ruthenium(III) present as a catalyst has been studied by spectrophotometric means. The spectroscopic study has been carried out in aqueous H2SO4 and SO42- media at constant ionic strength of I = 1.60 mol dm−3. Stoichiometric analysis shows that one mole of NHEP reacts with two moles of cerium(IV). The oxidation products were identified by IR and GC–MS. Orders with respect to substrate, oxidant, ruthenium(III) and acid concentrations were determined. Increase in sulphuric acid concentration increases the rate. Effect of ionic strength and solvent polarity of the medium on the rate of the reaction was studied. The added product, cerium(III), has no significant effect on the rate of reaction. The active species of oxidant in sulphate medium and catalyst are CeSO42+ and [Ru(H2O)6]3+. Based on the experimental results a suitable mechanism is proposed. The activation parameters and the thermodynamic quantities are also...

Xanthan from sulphuric acid treated tapioca pulp: Influence of acid concentration on xanthan fermentation

Xanthan gum was produced by fermentation of sulphuric acid pre-treated tapioca pulp. Effect of sulphuric acid concentration (0.5%, 2.5% and 5.0%) on xanthan fermentation was investigated. Maximum xanthan yield (7.1g/l) was obtained with 0.5% sulphuric acid pre-treatment. Further, increase in sulphuric acid concentration caused formation of inhibitory substance and lowered xanthan yield. The product was confirmed as xanthan using FTIR, 1H NMR analyses. Viscosity was measured by Brookfield viscometer and the molecular weight was determined from the intrinsic viscosity. The results confirmed that the yield and quality of xanthan produced were strongly influenced by the acid concentration.

Effect of operating variables on performance of membrane electrolysis cell for carrying out Bunsen reaction of I–S cycle

Membrane electrolysis is coming up as one of the alternatives to direct contact mode of carrying out Bunsen reaction of I–S cycle. It has potential to reduce the use of excess iodine and water. A two-compartment membrane electrolysis cell with graphite electrodes and Nafion 117 membrane was used for Bunsen reaction. Effect of six independent variables on cell voltage was determined for current density values of up to 80 A/dm2. The variables were anolyte pressure, catholyte pressure, temperature, sulphuric acid concentration, HI concentration, and I2/HI molar ratio in catholyte. Flow rate of anolyte and catholyte were identified where mass transfer resistance was not significant before performing experiments with different independent variables. Cell voltage was analysed by identifying three different regimes based on its variation with current density and current density ranges where electrode resistance or ohmic resistance dominated are identified. Current efficiency was measured for 1 A/dm2 and was found to be close to 100% irrespective of values of the independent variable. Minimum amount of heat equivalent of electric energy required for membrane electrolysis was calculated and increase in its value with increase in sulphuric acid concentration was compared with estimate of reduction in heat required for concentration of sulphuric acid.

Ruthenium(III) mediated oxidation of succinic acid by cerium(IV) in aqueous sulphuric acid medium - A kinetic and mechanistic approach

The oxidation of succinic acid by ceriuim(IV) has been studied spectrophotometrically in aqueous sulphuric acid medium at 298 K at constant ionic strength of 1.6 mol dm ―3 . A minute amount of ruthenium(m) (10- 6 mol dm ―3 ) is sufficient to enhance the slow reaction between succinic acid and cerium(IV). The main reaction products are cerium(III) and oxaloacetic acid. The stoichiometry is 1: 4, that is [suc. acid]: [Ce IV ] = 1: 4. The reaction is first order in both cerium(IV) and ruthnium(III) concentrations. The order with respect to suc. acid concentration varies from first order to zero order, as the succinic acid concentration increases. Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulpahte decreases the rate of reaction. The added product cerium(III) retards the reaction rate. The active species of oxidant and catalyst are Ce(SO 4 ) 2 and [Ru(H 2 O) 6 ] 3+ respectively. Possible mechanism is proposed. The activation parameters were determined with respect to slow step and reaction constants involved have been determined.

Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm−3. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO4)2 and [Mn(H2O)4]2+. A mechanism is proposed, and the reaction constants and activation parameters have been determined.

Mechanistic study of cerium(IV) oxidation of antimony(III) in aqueous sulphuric acid in the presence of micro amounts of manganese(II) by stopped flow technique

The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric acid medium. A minute amount of manganese(II) (10−5 mol dm−3) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations. The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst are Ce(SO4)2, [Sb(OH)(HSO4)]+ and [Mn(H2O)4]2+, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed and reaction constants involved have been determined.

Chloride and iodide mediated oxidation of antimony(III) by cerium(IV) in aqueous sulphuric acid medium

The micro amounts of iodide (10−7) (mol dm−3) and chloride (10−2) (mol dm−3) mediated oxidation of antimony(III) by cerium(IV) in an aqueous sulphuric acid medium have been studied spectrophotometrically at 25 °C and μ = 3.10 mol dm−3. The stoichiometry is 1:2 in chloride and iodide mediated reactions. i.e. one mole of antimony(III) requires two moles of cerium(IV). In the case of chloride mediated reaction, the reaction was first order in cerium(IV) and halide concentrations, whereas in the case of iodide mediated reaction the order with respect to [cerium(IV)] was unity and with respect to iodide concentrations was more than unity (ca. 1.4). In both chloride and iodide mediated reactions the order with respect to antimony(III) concentrations was less than unity. Increase in sulphuric acid concentration increased the rate. The order with respect to H+ ion concentration was less than unity. Added products, cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant was understood to be $$\hbox{H}_{3}\hbox{Ce}(\hbox{SO}_{4})_{4}^{-}$$ , whereas that of reductant as SbCl3 in the case of chloride and SbI2+ in case of iodide mediated reactions. The possible reaction mechanisms were proposed and the activation parameters were determined and discussed.

Ruthenium(III) Mediated Cerium(IV) Oxidation of Thallium(I) in Aqueous Sulphuric Acid--A Kinetic and Mechanistic Study

The cerium(IV) oxidation of thallium(I) has been studied in an aqueous sulphuric acid medium. A minute amount (10 6 mol dm 3 ) of ruthenium(III) is sufficient to catalyse the reaction. The reaction is first order in [cerium(IV)] in the presence of ruthenium(III) catalyst. The order in [thallium(I)] varies from zero to unity, whereas that in [ruthenium(III)] is unity. Increase in sulphuric acid concentration accelerates the reaction rate. The added products cerium(III) and thallium(III) do not significantly effect the reaction rate. The active catalyst, substrate and oxidant species are [Ru(H 2 O) 6 ] 3+ , Tl(SO 4 ) and H 3 Ce( SO 4 ) 4 , respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.

Acid leaching of chromite

The kinetics of the chemically controlled reaction between chromite and sulphuric acid, to form chromium(III) sulphate has been studied in the temperature range 140° – 210°C. The effect of temperature, sulphuric acid concentration and perchloric acid addition on the rate of dissolution of chromium has been studied. Perchloric acid is found to increase the rate of reaction. Increase in sulphuric acid concentration favours the formation of acid insoluble sulphates. The activation energy for the reaction is 77 kJ/mol in the temperature range 140° – 210°C and 82% by weight sulphuric acid concentration. A response — surface model in four predictor variables has been described for the dissolution of chromium.

Kinetics and Mechanism of the Oxidation of Some Aldoses by Cerium(IV)

Abstract The kinetics of oxidation of some aldoses by cerium(IV) have been studied spectrophotometrically in sulphuric acid medium. The reactions are second order; first order with respect to both cerium(IV) and aldose concentration. The reaction rate decreases with increase in sulphuric acid concentration. The mechanisms for the reactions are discussed.

ビス-2-エチルヘキシルアセトアミドによるNb, Taの抽出

Extraction of Nb and Ta from acid solutions with bis-2-ethylhexyl acetamide and stripping of these metals with sulphuric acid solutions were investigated. The organic phase was a binary solution of bis-2-ethylhexyl acetamide and xylene, while the aqueous phase was composed of hydrofluoric acid solution or hydrofluoric-sulphuric acid solution containing 3.5-13 kg/m3Nb and 5-10 kg/m3Ta. Sulphuric acid, hydrochloric acid and nitric acid were used as salting out agents to understand the effect on the extraction.Both metals were not sufficiently extracted from hydrofluoric acid solutions, whereas the extraction of both metals remarkably increased with an addition of sulphuric acid to the aqueous phase. The separation factor decreased with an increase in the concentration of hydrofluoric acid at the constant sulphuric acid concentration of 5.8N, and both metals were completely coextracted in the aqueous condition of 6N hydrofluoric acid and 8N sulphuric acid.The stripping occurred for both metals with a high efficiency, when water or dilute sulphuric acid solution was used as a stripping agent. The increase in sulphuric acid concentration caused less stripping of Ta, while the stripping of Nb was maintained at 80% up to 7N sulphuric acid. The separation factor reached the maximum with the value of 116 in the use of 6.5N sulphurtc acid.The extraction behavior of Fe(II), Fe(III), Sn(IV) and Mn(II) was also examined with the results that these metals were not extracted even to the extent of the lowest limit of atomic absorption spectrophotometer. Moreover, the comparison of this extractant with MIBK and TBP, which were in common use, was carried out.