Initial Sulfuric Acid Concentration Research Articles

Extraction of vanadium from vanadium slag by high pressure oxidative acid leaching

To extract vanadium in an environment friendly manner, this study focuses on the process of leaching vanadium from vanadium slag by high pressure oxidative acid leaching. Characterizations of the raw slag, mineralogy transformation, and the form of leach residues were made by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The result shows that the vanadium slag is composed of major phases of fayalite, titanomagnetite, and spinel. During the high pressure oxidative acid leaching process, the fayalite and spinel phases are gradually decomposed by sulfuric acid, causing the release of vanadium and iron in the solution. Meanwhile, unreacted silicon and titanium are enriched in the leach residues. With the initial concentration of sulfuric acid at 250 g·L−1, a leaching temperature of 140°C, a leaching time of 50 min, a liquid-solid ratio of 10:1 mL·g−1, and oxygen pressure at 0.2 MPa, the leaching rate of vanadium reaches 97.69%.

Pretreatment of cyanided tailings by catalytic ozonation with Mn2 +/O3

The increasing amount of cyanided tailings produced as a by-product has gained significant attention in recent years because of the rapid development of the gold industry and extensive exploitation of gold mineral resources. The effective use of these secondary resources is becoming an important and urgent problem for all environmental protection staff. Manganese-catalyzed ozonation for the pre-oxidation of cyanided tailings was studied and the effects of Mn2+ dosage, initial sulfuric acid concentration, ozone volume flow, temperature and agitation speed on pretreatment were examined. The optimum reaction conditions were observed to be: ore pulp density 2.5%, agitation speed 700r/min, temperature 60°C, Mn2+ dosage 40g/L, ozone volume flow 80L/hr, initial sulfuric acid concentration 1mol/L, and reaction time 6hr. Under these conditions, the leaching rate of Fe and weight loss could reach 94.85% and 48.89% respectively. The leaching process of cyanided tailings by Mn2+/O3 was analyzed, and it was found that the leaching of pyrite depends on synergetic oxidation by high-valent manganese and O3, in which the former played an important part.

Effect of current density and sulfuric acid concentration on persulfuric acid generation by boron-doped diamond film anodes

This research investigated the effects of current density and sulfuric acid concentration on the rates of persulfate generation by boron-doped diamond film anodes. Also investigated was the maximum conversion of sulfate to persulfate that could be achieved from electrol- ysis of sulfuric acid. Experiments were performed in batch systems using a rotating disk electrode (RDE) and a flow- through reactor with parallel plate electrodes. Both the RDE and flow-through experiments showed that there was a linear relationship between persulfate generation rates and current density. Persulfate generation rates became current limited at sulfuric acid concentrations of 2.25 M and above; however, Faradaic efficiencies under current- limited conditions were only *60 %, and were only weakly dependent on the current density. Persulfate gen- eration rates in the flow-through reactor showed similar dependencies on current density and sulfuric acid concen- tration as those in the RDE reactor, but were 20-50 % lower. Acid catalyzed and thermal decomposition of per- sulfate limited the maximum conversion of sulfate to per- sulfate. A maximum fractional conversion of 78 % was achieved using an initial sulfuric acid concentration of 0.77 M. Surprisingly, this value was independent of the current density over the range of 100-300 mA cm -2 .

Effect of Oxidant on the Leaching Rate of Indium from Water Quenching Slag

Extracting indium from water quenching slag, which contains poor indium, by two process of leaching, the effect of different oxidants and dosages on the leaching rate of indium in water quenching slag were studied. The leaching conditions: temperature 80 °C, leaching time 2 h, the liquid to solid ratio of neutral leaching 8︰1, the liquid to solid ratio of acid leaching 2︰1, initial concentration of sulfuric acid 500 g·L-1, adding different oxidants, the concentration was detected by crystal violet spectrophotometry. Test results showed that the leaching rate of indium was significantly improved by adding hydrogen peroxide and potassium permanganate. Compared with the effect of different oxidants, the effect of potassium permanganate was significantly higher than that of hydrogen peroxide on the leaching rate of indium.

Influence and hydrolysis kinetics in titanyl sulfate solution from the sodium hydroxide molten salt method

Hydrated titanium dioxide (HTD) was precipitated by thermal hydrolysis in purified titanyl sulfate solution (TSS) obtained through the sodium hydroxide molten salt clean method. Various factors including the stirring speed and initial concentrations of TiOSO4, sulfuric acid, and sodium ion were studied. The main influence factors in the hydrolysis process were the initial concentrations of TiOSO4 and sulfuric acid. Contrary to the ferrous ion, the sodium ion improved the ionic activity of Ti4+, but did not decrease the crystal size. The Boltzman growth model (x=A2+(A1−A2)/{1+exp[(t−t0)/dt)]}, which focuses on two main parameters (CTiOSO4andCH2SO4), fits the hydrolysis process well with R2>0.97. An increase in sulfuric acid concentration negatively affected the hydrolysis rates and the value of A2, while t0 increased. An increase in titanyl sulfate concentration directly reduced the hydrolysis rates and particle size of HTD, contrary to the trend for the value of t0. A simulation software called 1stopt was used to observe the relationship between Z (A1, A2, t0, dt) and a, b (CTiO2andCH2SO4).

Chlorine Dioxide–Iodine–Sodium Thiosulfate Oscillating Reaction Investigated by the UV–Vis Spectrophotometric Method

A new chlorine dioxide–iodine–sodium thiosulfate chemical oscillatory reaction was studied by the UV–Vis spectrophotometric method. The initial concentrations of sodium thiosulfate, chlorine dioxide, iodine, sulfuric acid, and pH have great influences on the oscillations observed at wavelength 238 nm. The oscillations occur as long as the reactants are mixed. The amplitude and the number of oscillations are associated with the initial concentrations of reactants. The equations for the triiodide ion reaction rate changes with reaction time and the initial concentrations in the oscillation stage are an attenuation sine function. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.

Pressure leaching technique for manganese smelter dust

Pressure leaching of manganese smelter dust with air as pressurized gas in a sulfuric acid medium was investigated. Optimum operating parameters were established as follows: liquid-to-solid ratio (mL/g), 5:1; initial sulfuric acid concentration, 120g/L; leaching temperature, 120°C; air pressure, 0.8MPa; ore ratio (manganese smelter dust amount/pyrite amount), 1:0.5; leaching time, 2h; and agitation speed, 500r/min. Extraction rates of manganese and iron were obtained at 96.1% and 7%, respectively, under these conditions; and residual percentage of final acid was about 34.9%. Manganese can be effectively separated from impurities, such as iron, through leaching process. Leaching efficiency of manganese increased from 72.9% to 96.1%, whereas that of iron and the residual percentage of final acid both decreased with increase in leaching time from 40min to 120min. Pyrite was coated by elemental sulfur when temperature was higher than 119°C, resulting in its inability to act as a reductant and to react with manganese dioxide. Therefore, leaching temperature must be lower than 120°C. Pressure leaching technique for manganese smelter dust was proven to be effective and reliable.

Effect of Initial Substrate Concentrations and Temperature on the Oscillatory Behavior of Phloroglucinol-Based Belousov–Zhabotinsky Reaction

Abstract The present study introduces the use of phloroglucinol (1,3,5-trihydroxybenzene) as organic substrate in BZ reaction for the first time. This work has been carried out to assess the influence of initial reagent concentrations on the behavior of phloroglucinol–bromate–ferroin-based BZ reaction in a stirred batch reactor. The oscillations are followed by observing the change in redox potential. Different oscillatory parameters like induction time (tin), time period (tp), amplitude (A), frequency (v), and number of oscillations (N) show different changes with respect to changes in the initial concentrations of organic substrate, bromate and sulfuric acid, and these observations have been explained on the basis of FKN mechanism. The behavior of the aforesaid system in different aqueous acid media has been reported and it is found that sulfuric acid is the best medium for studying the system as it shows a wide oscillatory window compared to that of nitric acid. In phosphoric and perchloric acids the system does not show any oscillatory behavior. Activation parameters of the reaction have been derived by studying the reaction over a temperature range of 15 to 40 ± 0.1 °C. The effect of different catalysts on the oscillatory behavior has been studied and it is found that the system gives good oscillatory behavior with ferroin and Ce(III) whereas a poor response is seen when Mn(II) and Ce(IV) are used as catalysts.

Mathematical modeling of the extraction of uranium(VI) into a polymer inclusion membrane composed of PVC and di-(2-ethylhexyl) phosphoric acid

A mathematical model describing the extraction of uranium(VI) from sulfuric acid solutions into polymer inclusion membranes composed of di(2-ethylhexyl) phosphoric acid (D2EHPA) and poly(vinyl chloride) (PVC) has been developed and numerically solved. It assumes ideal mixing in the solution and Fickian diffusion of the uranium(VI)–D2EHPA complex within the membrane. The model has been fitted to transient extraction data obtained for different membrane compositions and thicknesses and different initial solution concentrations of uranium(VI) and sulfuric acid. This has allowed a reliable determination of the membrane extraction constant (Kex=4.72×103) and diffusion coefficient (Dm=4.13×10−14, 6.46×10−14 and 7.39×10−14m2s−1 for membranes containing 35%, 40% and 45% (m/m) D2EHPA, respectively). The very good agreement between the model and the experimental extraction data confirms the model's validity. This model provides an in-depth understanding of the physicochemical processes involved in the extraction of uranium(VI) into D2EHPA/PVC PIMs and can be used for the optimization of this process using numerical simulation.

Sodium chlorite–iodine–methyl acetoacetate oscillatory reaction investigated by UV–vis spectrophotometric method

A new sodium chlorite–iodine–methyl acetoacetate chemical oscillatory reaction was studied using UV–vis spectrophotometric method. The initial concentrations of methyl acetoacetate, sodium chlorite, iodine, sulfuric acid, and the pH value have great influence on the oscillation observed at wavelength of 585 nm. There is a pre-oscillatory or induction period; the amplitude and the number of oscillations are associated with the initial concentration of reactants. The equations for the I3−–starch complex reaction rate changing with reaction time and the initial concentrations in the oscillation stage were obtained. The time of induction period decreases with the initial concentration of methyl acetoacetate or sulfuric acid, and increases with the initial concentration of sodium chlorite. A good linear relationship exists. Oscillatory reaction can be accelerated by increasing temperature. The apparent activation energies in terms of the induction period and the oscillation period were 114.28 and 64.92 kJ/mol, respectively. It may indicate that the two stages have different reaction mechanisms. The reaction of producing enol isomer by keto-enol tautomerism is an important step to constrain the time of induction period.

Chlorine Dioxide-Iodide-Methyl Acetoacetate Oscillation Reaction Investigated by UV-Vis and Online FTIR Spectrophotometric Method

In order to study the chemical oscillatory behavior and mechanism of a new chlorine dioxide-iodide ion-methyl acetoacetate reaction system, a series of experiments were done by using UV-Vis and online FTIR spectrophotometric method. The initial concentrations of methyl acetoacetate, chlorine dioxide, potassium iodide, and sulfuric acid and the pH value have great influence on the oscillation observed at wavelength of 289 nm. There is a preoscillatory or induction period, and the amplitude and the number of oscillations are associated with the initial concentration of reactants. The equations for the triiodide ion reaction rate changing with reaction time and the initial concentrations in the oscillation stage were obtained. Oscillation reaction can be accelerated by increasing temperature. The apparent activation energies in terms of the induction period and the oscillation period were 26.02 KJ/mol and 17.65 KJ/mol, respectively. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.

Oxygen Pressure Acid Leaching of Vanadium Slag

Oxygen pressure acid leaching process was used to extract vanadium from vanadium slag (Panzhihua steelmaking plant of China). The single factor experiment was finished and the effects of temperature, leaching time, liquid to solid ratio, stirring speed, initial concentration of sulfuric acid, and were investigated on the leaching rate of vanadium, titanium and iron. The leachate and residue were characterized by ICP, XRF, XRD, SEM and EDX. The experiment results indicate when temperature is 140 °C, leaching time is 120 min, liquid to solid ratio is 20:1(ml:g), stirring speed is 500 rpm, initial acid concentration is 200 g/L, oxygen partial pressure is 0.5 MPa, and particle size is -0.075~+0.055 mm, leaching rate of vanadium is 97.89% and the content of vanadium in the residue is 0.586%. Leaching rate of titanium and iron is 12.78% and 94.45% respectively. Vanadium could be extracted effectively through the oxygen pressure acid leaching process.

Homogenous nucleation of sulfuric acid and water at close to atmospherically relevant conditions

Abstract. In this study the homogeneous nucleation rates in the system of sulfuric acid and water were measured by using a flow tube technique. The goal was to directly compare particle formation rates obtained from atmospheric measurements with nucleation rates of freshly nucleated particles measured with particle size magnifier (PSM) which has detection efficiency of unity for particles having mobility diameter of 1.5 nm. The gas phase sulfuric acid concentration in this study was measured with the chemical ionization mass spectrometer (CIMS), commonly used in field measurements. The wall losses of sulfuric acid were estimated from measured concentration profiles along the flow tube. The initial concentrations of sulfuric acid estimated from loss measurements ranged from 108 to 3 × 109 molecules cm−3. The nucleation rates obtained in this study cover about three orders of magnitude from 10−1 to 102 cm−3 s−1 for commercial ultrafine condensation particle counter (UCPC) TSI model 3025A and from 101 to 104 cm−3 s−1 for PSM. The nucleation rates and the slopes (dlnJ/dln [H2SO4]) show satisfactory agreement when compared to empirical kinetic and activation models and the latest atmospheric nucleation data. To the best of our knowledge, this is the first experimental work providing temperature dependent nucleation rate measurements using a high efficiency particle counter with a cut-off-size of 1.5 nm together with direct measurements of gas phase sulfuric acid concentration.

Experimental study of a closed system in the sodium chlorite–iodine–ethyl acetoacetate oscillation reaction by UV–Vis and online FTIR spectrophotometric method

The sodium chlorite–iodine–ethyl acetoacetate (EAA) chemical oscillatory reaction system was studied by UV–Vis and online FTIR spectrophotometric method. The oscillation phenomenon does not occur as long as the reactants are mixed. There is a pre-oscillatory or induction period. The amplitude is small at the beginning stage and then increases with reaction time. Finally, the oscillation ceases suddenly. The amplitude and the number of oscillations are associated with the initial concentration of sodium chlorite, iodine, EAA and sulfuric acid. The equations for the triiodide ion reaction rate changing with reaction time and the initial concentrations on the oscillation stage were obtained. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.

Experimental Study of a Closed System in the Chlorine Dioxide–Iodine–Ethyl Acetoacetate–Sulfuric Acid Oscillation Reaction by UV-vis and Online FTIR Spectrophotometric Methods

The appearance of oscillations for the closed system ClO2–I2–ethyl acetoacetate depends critically on the pH in the absence of sulfuric acid, and was investigated by determining changes in the absorbance of $\mathrm{I}_{3}^{ -}$ with reaction time at the wavelength 280 nm. The pH should be 2.2–3.8 for this reaction. The initial concentrations of ethyl acetoacetate, chlorine dioxide, iodine and sulfuric acid have great influences on the oscillations observed at wavelengths of 280 nm or 350 nm. The oscillations at 280 nm occur as long as the reactants are mixed. However, at 350 nm the oscillation is preceded by a pre-oscillatory or induction period. The oscillation curve is more regular and smooth at 350 nm than that at 280 nm. The amplitude and the number of oscillations are associated with the initial concentration of each reactant. (1) The higher the initial concentration of ethyl acetoacetate, the greater is the amplitude while the number of oscillations becomes smaller. The amplitude is small at the beginning stage but increases with reaction time. An opposite influence exists for chlorine dioxide. Finally, the oscillation suddenly ceases. (2) When the initial concentration of iodine is higher, the amplitude is small at the beginning stage but then increases with reaction time. When the initial concentration of iodine is lower, the amplitude is large at the beginning stage and then decreases with reaction time. An opposite influence exists for sulfuric acid. Equations for the triiodide ion reaction rate were obtained as functions of reaction time and initial concentrations at the oscillation stage. The intermediates were detected by online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.

Experimental study of a closed system in the chlorine dioxide–iodine–ethyl acetoacetate–sulfuric acid oscillation reaction by UV–vis and online FTIR spectrophotometric methods

The appearance of oscillations for the closed system ClO2–I2–ethyl acetoacetate depends critically on the pH in the absence of sulfuric acid, and was investigated by determining changes in the absorbance of \(\mathrm{I}_{3}^{ -}\) with reaction time at the wavelength 280 nm. The pH should be 2.2–3.8 for this reaction. The initial concentrations of ethyl acetoacetate, chlorine dioxide, iodine and sulfuric acid have great influences on the oscillations observed at wavelengths of 280 nm or 350 nm. The oscillations at 280 nm occur as long as the reactants are mixed. However, at 350 nm the oscillation is preceded by a pre-oscillatory or induction period. The oscillation curve is more regular and smooth at 350 nm than that at 280 nm. The amplitude and the number of oscillations are associated with the initial concentration of each reactant. (1) The higher the initial concentration of ethyl acetoacetate, the greater is the amplitude while the number of oscillations becomes smaller. The amplitude is small at the beginning stage but increases with reaction time. An opposite influence exists for chlorine dioxide. Finally, the oscillation suddenly ceases. (2) When the initial concentration of iodine is higher, the amplitude is small at the beginning stage but then increases with reaction time. When the initial concentration of iodine is lower, the amplitude is large at the beginning stage and then decreases with reaction time. An opposite influence exists for sulfuric acid. Equations for the triiodide ion reaction rate were obtained as functions of reaction time and initial concentrations at the oscillation stage. The intermediates were detected by online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.

Galvanic Leaching of Chalcopyrite in Atmospheric Pressure and Sulfate Media: Kinetic and Surface Studies

Chalcopyrite leaching rate in atmospheric pressure and in sulfate media with ferric ion is low because of passive layer formation around chalcopyrite particles. In this investigation pyrite is used as a catalyst of chalcopyrite leaching. Because of galvanic interaction between chalcopyrite and pyrite, the chalcopyrite leaching rate is increased. Effects of parameters such as stirring speed, pyrite to chalcopyrite ratio, solution potential, temperature, and initial acid concentration were investigated. Results showed that maximum copper recovery (more than 95%) is obtained in less than 24 h, stirring speed of 1150 rpm, pyrite to chalcopyrite ratio 4, solution potential 410 mV, temperature 85 °C, and initial sulfuric acid concentration 45 g/L. Also, kinetic investigation showed that chalcopyrite dissolution in the presence of pyrite followed the shrinking core model and the reaction was controlled by the surface reaction. Activation energy (Ea) was calculated at 77.79 kJ/mol. Surface studies showed that in the absence of pyrite, the surface of chalcopyrite particles was covered by passive layer.

Pressure acid leaching of zinc sulfide concentrate

Effects of particle size of the zinc sulfide concentrate, leaching temperature, solid-to-liquid ratio and additive amount on pressure acid leaching process of the zinc sulfide concentrate were studied. The results indicate that the additive can improve the reaction kinetics and the conversion rate. And sulfur can be successfully separated from the zinc sulfide concentrate as elemental sulfur. The reasonable experiment parameters are obtained as follows: the leaching temperature 150 °C, oxygen partial pressure 1 MPa, additive amount 1%, solid-to-liquid ratio 1:4, leaching time 2 h, initial sulfuric acid concentration 15%, and particle size less than 44 μm. Under the optimum conditions, the leaching rate of the zinc can reach 95% and the reduction rate of the sulfur can reach 90%.

Pressure leaching technique of smelter dust with high-copper and high-arsenic

The application of pressure leaching technology in the treatment of high-copper and high-arsenic dust was studied. The pressure leaching technique was determined as follows: the liquid to solid ratio (mL/g) of 5:1, the leaching temperature of 453 K, the retention time of 2 h, the initial sulfuric acid concentration of 0.74 mol/L, the oxygen partial pressure of 0.7 MPa, and the agitation speed of 500 r/min. Under these conditions, 95% of copper and 99% of zinc and only 6% of iron in the dust were leached, while about 20% of arsenic was also leached. The leaching technique was optimized further to restrain the leaching of arsenic by adding a small quantity of ferrous iron into the leaching system ( c(Fe 2+)=0.036 mol/L). Copper and zinc can be effectively separated from arsenic and iron in the leach. The optimal pressure leaching technique of high-copper and high-arsenic smelter dust is proved to be effective.

Experimental Study of a Closed System in the Chlorine Dioxide-Iodine-Malonic Acid-Sulfuric Acid Oscillation Reaction by UV-vis Spectrophotometric Method

The appearance of oscillations depends critically on the pH for the closed system ClO2-I2-malonic acid in the absence of sulfuric acid, and was investigated by determining the absorbance of I3− with reaction time at 280 nm. The pH should be 3.2–3.8. The initial concentrations of malonic acid, chlorine dioxide, iodine and sulfuric acid have great influence on the oscillation at 280 or 350 nm. The oscillation occurs as long as the reactants are mixed at 280 nm. However, at 350 nm the oscillation is preceded by a pre-oscillatory or induction period. The amplitude is small at the beginning stage but then increases with the reaction time. Finally, the oscillation ceases suddenly. The amplitude and the number of oscillations are associated with the initial reactant’s concentration. The higher is the initial concentration of malonic acid, iodine or sulfuric acid, the bigger is the amplitude. Also, the number of oscillations becomes small. An opposite influence exists for chlorine dioxide. The oscillation curve is more regular and smooth at 350 nm than that at 280 nm. The oscillation becomes more obvious by adding starch at 581 nm for I3−–starch complex (SI3−) than that observed without adding starch at 280 nm. The curve’s shape at 581 nm is very different from that at 280 or 350 nm. The equation for the triiodide ion reaction rate changing with reaction time and the effect of initial concentrations on the oscillation stage were obtained. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.