The leaching kinetics of brannerite ore in sulfate solutions with iron(III)

A kinetic study of the leaching of powdered brannerite ore by sulfuric acid has been investigated. The effects of stirring speed ranging from 100 to 1,000?min^?1, particle size ranging from 20 to 120???m, concentration of Fe(III) ranging from 0.0025 to 0.20?M, acid concentration ranging from 0.1 to 2.0?M and temperature ranging from 15 to 90?°C on uranium dissolution are reported. The dissolution rate was founded to be significantly influenced by the temperature and concentration of the acid in solution. The experimental data for the dissolution rates of uranium have been analyzed with the shrinking-core model for reaction control. The apparent activation energy for the dissolution of uranium has been evaluated using the Arrhenius expression.     

Kinetics of aluminum extraction from aluminum ash by leaching with sulfuric acid

Abstract

To explore the high value of aluminum ash development and utilization, factors (granularity of aluminum ash, leaching temperature, leaching time, sulfuric acid concentration, and liquid solid ratio) affecting the leaching rate of aluminum were evaluated. The kinetics of the leaching process was also investigated. The results indicate that the leaching rate of aluminum in aluminum ash can reach 88.9% under the following conditions: leaching temperature, 100?°C; leaching time, 120?min; sulfuric acid concentration, 2.5?mol/L; and liquid–solid ratio (mass ratio), 1.3:1. Studies on the leaching dynamics of aluminum in aluminum ash showed that leaching was divided into two stages. At the initial stage (i.e. at the leaching rate x?≤?0.3), the external diffusion resistance and the diffusion resistance of the solid product layer are negligible, and leaching is controlled by chemical reaction at the interface. The apparent activation energy was 5733.25?J/mol. At the leaching rate x?=?0.3–0.9, the leaching rate was controlled by the non-steady diffusion of the liquid film in the porous solid by the fluid reactant H₂SO₄. The apparent activation energy was 25390.87?J/mol.     

Beneficiation of zinc from electric arc furnace dust using hydrometallurgical approach

Zinc bearing wastes such as electric arc furnace dust (EAFD) obtained from steel making constitute an important resource for zinc extraction. Inclusion of heavy metals such as Pb, Cd, Cu, Cr, Ni, etc., in these wastes makes them hazardous to use and/or dispose. In the present research work, leaching kinetics of EAFD with sulfuric acid has been investigated and various experimental parameters such as concentration of lixiviant, stirring rate, sample particle size, liquid/solid proportion, and temperature of the reaction have been optimized. It has been found that the dissolution rate of EAFD increases with rise in temperature, acidic strength, rate of stirring, liquid to solid proportion and with reduction in EAFD particle size. From the analysis of leaching kinetic data by means of graphical and statistical methods, it has been evaluated that the leaching kinetics of EAFD is dictated by surface diffusion reaction. Apparent energy of activation for the leaching reaction of EAFD with sulfuric acid is found to be 13.1 kJ mol^–1 within the temperature range of 308 to 358 K.     

А kinеtiс аnаlysis fоr prоduсtiоn of саlсium bоrоgluсоnаtе frоm colemanite

In this paper, the kinetic model of colemanite dissolution in gluconic acid solutions was carried out in a batch reactor. The effects of the particle size, reaction temperature, stirring speed, gluconic acid concentration, and solid/liquid ratio on colemanite dissolution were experimentally studied. The empirical parameters were the gluconic acid concentration (0.05-0.2 M), the temperature (20-50°C), the solid/liquid ratio (0.05/500-1.5/500 g⋅L⁻¹), particle size (193.5-1000 μm), and stirring speed (400-700 rpm). The kinetic models for heterogeneous solid-liquid reactions were used with the dissolution data in evaluating the kinetic. The dissolution of colemanite in gluconic acid solutions was controlled by diffusion through the product layer. The activation energy was found to be 8.39 kJ⋅mol⁻¹. The rate expression associated with the dissolution rate of colemanite depending on the parameters chosen may be summarized as follows:      

Dissolution kinetics of cerussite in an alternative leaching reagent for lead

The dissolution kinetics of cerussite was investigated using methanesulphonic acid (MSA) as an alternative leaching reagent. The effects of particle size, stirring speed, acid concentration, and reaction temperature on the lead dissolution rate were determined. The dissolution process followed the kinetic law of the shrinking-core model, and a corresponding mixed control model was found suitable for representing the rate-controlling step. The mixed kinetic model comprised two stages: surface chemical reaction (283 K to 303 K) and diffusion through the product layer (303 K to 323 K). The activation energies of these sequential stages were 43.20 kJ mol^?1 and 17.20 kJ mol^?1, respectively. The corresponding dissolution kinetic equations are also presented to describe the dissolution reaction. The results indicated that methanesulphonic acid could be used as an effective leaching reagent for extracting lead from cerussite minerals.     

A study of dissolution kinetics of a Nigerian galena ore in hydrochloric acid

The results of experimental investigation on the study of dissolution kinetics of a Nigerian galena ore in hydrochloric acid solution were discussed. The influence of acid concentration, temperature, particle size, stirring speed and solid/liquid ratio on the extent of dissolution was examined. The elemental analysis by XRF showed that the galena ore is composed mainly of PbS with metals such as Sn, Fe and Zn occurring as minor elements and Mn, Rb, Sr and Nb as traces. The XRD analysis indicated galena as the dominant mineral phase, with the presence of associated minerals, such as α-quartz (SiO₂), sphalerite (ZnS), cassiterite (SnO₂), pyrite (FeS₂) and manganese oxide (MnO₂).Results of leaching studies showed that galena dissolution in HCl solution increases with increasing acid concentration and temperature; while it decreases with particle diameter and solid/liquid ratio at a fixed stirring rate of 450 rpm. The study showed that 94.8% of galena was dissolved by 8.06 M HCl at 80 °C within 120 min with initial solid/liquid ratio of 10 g/L. The corresponding activation energy, E_a was calculated to be 38.74 kJ/mol. Other parameters such as reaction order, Arrhenius constants, reaction and dissociation constants were calculated to be 0.28, 73.69 s^?1, 1.73 ± 0.13 × 10³ and 1.37 ± 0.024 × 10⁴ mol L^?1 s^?1, respectively. The mechanism of dissolution of galena was established to follow the shrinking core model for the diffusion controlled mechanism with surface chemical reaction as the rate controlling step for the dissolution process. Finally, the XRD analysis of the post-leaching residue showed the presence of elemental sulphur, lead chloride and α-quartz.     

Kinetic studies on the extraction of uranium(VI) from phosphoric acid medium by bulk liquid membrane containing di-2-ethylhexyl phosphoric acid

To go through the first stage of industrial solvent extraction process in order to recover uranium from phosphate rocks by liquid membrane techniques, as a simple model, the kinetics of facilitated transport of uranium(VI) from a dilute phosphoric acid medium into more concentrated phosphoric acid media as a receiving phase through a bulk liquid membrane containing di-2-ethylhexyl phosphoric acid as a carrier was studied. The influence of phosphoric acid concentration in the source and receiving phases, carrier concentration, type of solvent, stirring speed and temperature were investigated. The kinetic parameters (k _e, k _s, t _max, J _max) were calculated for the interface reactions assuming two consecutive, irreversible first-order reactions. The activation energy values were calculated as 29.40 and 19.51 kJ mol^?1 for extraction and stripping, respectively. The values of calculated activation energy indicated that both the extraction and stripping processes were controlled by mixed regime (both kinetic and diffusion). In addition, the influence of adding trioctyl-phosphine oxide into the membrane phase as a synergic agent on the transport kinetics was determined.     

Leaching characteristics and kinetics of radioactive element uranium and thorium from Ta/Nb tailing

The tantalum (Ta)/niobium (Nb) tailing is the tailing after smelting Ta/Nb ore. The tailing contains a certain amount of radioactive element uranium (U) and thorium (Th). U and Th from Ta/Nb tailing were leached by nitric acid and sulfuric acid. Leaching effect and kinetics were investigated under the conditions of different acid concentration, temperature, liquid–solid ratio and time. The results showed that the leaching effects of sulfuric acid on U and Th were much better than that of nitric acid. Kinetic analysis shows that the leaching of U and Th by nitric acid and sulfuric acid are surface chemical reaction.

     

Enhanced uranium bioleaching high-fluorine and low-sulfur uranium ore by a mesophilic acidophilic bacterial consortium with pyrite

The high level of fluorine and low sulfur in the ore could significantly undermine the bioleaching effectiveness. Here, a strategy to improve the bioleaching efficiency by introducing fluoride-resistant mesophilic eosinophils coupled with pyrite supplement was investigated in a bioleaching system with such ore. The results of column and heap bioleaching showed that 89.25% and 90.40% of uranium were recovered with the consortium and pyrite addition, which increased the uranium leaching rates by 13.22% and 8.96% as compared with the sulfuric acid leaching. Hence, it provides a method to improve uranium bioleaching efficiency of the high-fluorine and low-sulfur uranium ore by the consortium adding pyrite.

     

Bioleaching of low grade uranium ore containing pyrite using A. ferrooxidans and A. thiooxidans

A process of uranium extraction from ore containing 3.1 % pyrite by bacterial leaching was investigated in shaken flasks during 90 days. The highest uranium recovery amounting to 85.1 % was obtained using binary mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans that was exceeding results obtained by traditional acid leaching technique up to 27 %. High uranium recovery was founded to be due to the high degree of pyrite dissolution that can be readily achieved by bacterial leaching (up to 98.0 %).     

Determination of uranium in plutonium by differential linear sweep oscillographic polarography

The polarographic behavior of uranium in hydroxylamine hydrochloride was investigated by differential oscillographic polarography. A procedure is presented for the determination of uranium in plutonium for concentrations of uranium greater than 10 p.p.m. Analyses of solutions containing 22 common impurities found in plutonium metal revealed that antimony, copper, and titanium cause significant interference. A reversible peak corresponding to a one-electron reduction was obtained with a peak potential of -0.167 V vs. Hg pool electrode. The diffusion coefficient is 0.51·10^-5 cm²/sec and the diffusion current constant is 1.59 with an average relative standard deviation of 2.28%. The peak current of uranium can be affected by hydrochloric, nitric, perchloric, and sulfuric acids, depending on the acid concentration.     

Kinetics of sulfuric acid breakdown of beryllium raw material activated by fusion with sodium carbonate

The kinetics of sulfuric acid breakdown of a mixture of beryl and bertrandite–phenakite–fluorite concentrates, activated by fusion with sodium carbonate, was studied. The apparent activation energy of the reaction of the granulated fusion cake with sulfuric acid was determined (E _app = 9.1 kJ mol^–1). This value of E _app is typical of diffusion-controlled processes and suggests that the process is controlled by the rate of diffusion of acid molecules to the reaction surface through the layer of the forming reaction products.     

Leaching behavior of uranium and vanadium using strong sulfuric acid from Korean black shale ore

The present scientific study focused on leaching behavior of uranium and vanadium from Korean domestic ore. The leaching process experimental conditions optimized for uranium and vanadium metals recovery from Korean domestic ore and developed the basic experimental procedures such as time, particle size, acid influence, temperature effect and pulp density (PD) behavior. Acid influence on leaching process was tested and noted that 2.0 M sulfuric acid concentration is the optimized conditions for present study. The time influence on leaching process was observed and its optimized 2 h for complete leaching process. The temperature influence tested and optimized the 80 °C for complete leaching process and PD is 50 % (wt%). The bench scale experiments developed in a laboratory and tested in pilot level each batch 100 kg of ore sample.     

The special features of the kinetics of oxidation of divalent iron during sulfuric acid leaching of pyrrhotine with the participation of nitrous acid

The kinetics of oxidation of divalent iron ions with molecular oxygen during pyrrhotine leaching in sulfuric acid solutions with the participation of nitrous acid as an activator was studied. The oxidation of Fe²⁺ to Fe³⁺ only occurred at the second slow stage of the process, when the degree of solid phase stripping reached almost 80% of the value maximum under given conditions. The order of the reaction with respect to sulfuric acid was negative (?1.1 ± 0.1), as is characteristic of sulfate media. A substantial change in effective activation energies from 7 ± 5 kJ/mol at \(c_{H_2 SO_4 }^O\) = 0.25 mol/l to 31 ± 5 kJ/mol at \(c_{H_2 SO_4 }^O\) = 1.02 mol/l could be caused by different contents of the pyrrhotine solid phase in the system at the beginning of the second leaching stage. It was assumed that the oxidation of Fe²⁺ to Fe³⁺ occurred with much lower energy expenditures in the presence of a sulfide solid phase.     

Voltammetric Behavior of Uranium(VI) in Sulfuric Acid Solutions Containing Pyridine

It was shown that 8.8 × 10^–5 to 4.4 × 10^–3 M uranium(VI) in sulfuric acid solutions containing pyridine give a clearly defined cathodic peak with a height proportional to uranium(VI) concentration. Under the specified conditions, the electroreduction of uranium(VI) is irreversible and involves one electron, the limiting current of uranium(VI) is diffusion- and kinetically controlled. The kinetic parameters of the process under study were determined, and the effect of concomitant elements on the voltammetric behavior of uranium(VI) in pyridine-containing sulfuric acid supporting electrolytes was estimated.     

Kinetics of the disproportionation reaction of HIO2 in acidic aqueous solutions

We review and discuss kinetic studies of the disproportionation reaction of iodous acid (HIO₂) in the presence of excess of Hg²⁺‐ions. The reactions are followed at different temperatures in water solution with strongly defined acidity. The rate constants of disproportionation are determined between 285 and 303 K based on kinetic data obtained under steady‐state conditions. The calculated rate constants increase with increasing temperature and acid concentration. The corresponding values of activation energy as well as enthalpy and entropy of activation for this reaction have been calculated. The enthalpy of activation as well as entropy is higher at higher sulfuric acid concentration. Also, it was considered that the values of Gibbs energy of formation of HgI⁺ are generated during the process. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 687–691, 2010     

Decontamination of uranium-contaminated concrete

This study examined the decontamination method by washing with nitric acid for uranium contaminated concrete pieces produced from the decommissioning of a uranium conversion plant and evaluated the amount of waste sludge generated from the treatment. In addition, carbonate solution, nitric acid and sulfuric acid were used as the extraction reagents for the uranium, and their efficiencies were also compared. For concrete pieces coated with and without epoxy, the separation method of cement paste from aggregates was preferable to the leaching of uranium from concrete because of its simpler decontamination process. When concrete pieces with epoxy were heated for 2 h at 400 °C, pulverized and sequentially washed with 0.1, 2.0 and 1.0 M of nitric acid, their radioactivity reached below the limit value of uranium for self-disposal. Unlike previous results, uranium dissolved in 1 and 2 M sulfuric acid solutions was not removed by strong anion exchange resins such as IRA 910 and Ag1×8.     

Electrochemical behavior of uranium(III) in NaCl–KCl molten salt

The electro-redox behavior of uranium(III) on Mo electrode in NaCl–KCl molten salt in the temperature range 973–1073 K has been investigated using cyclic voltammetry electrochemical method and so on, such research will help to understand uranium behavior in pyro-reprocessing. The results showed that UCl₃ could be reduced into uranium metal in a quasi-reversible one-step process exchanging three electrons. The diffusion coefficients of U(III) ions were determined and the activation energy for diffusion was found to be 55.794 kJ mol⁻¹. The apparent standard potentials of U(III)/U(0) at several temperatures were calculated. The thermodynamic properties of UCl₃ have also been investigated.

     

Effect of organic and inorganic compounds on dissolution kinetics of chalcopyrite in hydrogen peroxide– Hydrochloric acid system

The addition of 2-Propanol as an organic substance and NaCl as an inorganic compound in hydrochloric acid with hydrogen peroxide as a strong leaching agent of chalcopyrite was investigated. The effects of the leaching parameters on copper extraction, such as stirring speed, H₂O₂ concentration, temperature, HCl concentration and solid/liquid ratio were studied. The maximum final copper extraction of 54.55% was obtained with 600 rpm stirring speed, 1.5 M H₂O₂, 0.5 M HCl, 600 rpm, 50 °C, 240 min of the reaction and particle size of ?106 +75 µm. Further experiments were performed when the solid-to-liquid ratio (S/L), stirring speed, temperature, HCl, H₂O₂ and leaching time were kept constant to examine the influence of NaCl and 2-Propanol concentrations in the range of 0–0.5 M and 0–3 M, respectively. The results showed that the copper extraction was increased up to 58.11% with addition of NaCl. While copper extraction yield reached 94.25% in case of addition of 2-propanol with the optimum parameters(0.5 M HCl,50 °C, 1.5 M H₂O₂, 600 rpm, particle size ?106 +75 μm, solid liquid ratio 2g/L, 3 M 2-propanol). The chalcopyrite leaching in hydrogen peroxide– hydrochloric acid system was found to be described by the interface transfer and diffusion across the product layer with activation energy of 77.14 kJ/mol. Addition of 2-propanol suggested that the reaction was under product layer diffusion control and decreased the activation energy of chalcopyrite leaching to 67.98 kJ/mol.     

Hierarchically organized silica monoliths: influence of different acids on macro- and mesoporous formation

The influence of different acids, such as hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid and acetic acid on the polymerization-induced phase separation process in the formation of hierarchically organized silica monoliths was investigated in detail. Special emphasis is given to systems synthesized from tetrakis(2-hydroxyethoxy)silane (EGMS) or tetramethoxysilane (TMOS) as the silica source in the presence of Pluronic^® P123 serving as structure-directing agent. The obtained silica monoliths exhibited a co-continuous and cellular macroporous structure comprising 2D hexagonally arranged mesopores with high specific surface areas ranging from 320–787 m² g^?1 independent of the applied silane precursor and regardless whether hydrochloric acid or sulfuric acid was used. A drastic change in macropore morphology to closed pores or particulate structures was observed for nitric, bromic as well as acetic acid. For sulfuric and nitric acid, the influence on the mesostructure was not as pronounced and 2D hexagonally arranged mesopores were obtained. With bromic and acetic acid a loss in mesopore ordering has been observed. Best developed hierarchically organized networks with respect to a co-continuous, cellular macroporous network, specific surface area and 2D hexagonally arranged mesopores were obtained for EGMS as well as for TMOS with P123 in sulfuric acid.