Acid Leaching Process Research Articles

Kinetics of iron(III)-catalyzed oxidation of arsenic(III) in acidic solutions with SO2/O2 gas mixture using different iron sources

Oxidation of arsenic(III) to arsenic(V) is very important in arsenic removal and immobilization operations. Limited studies on arsenic(III) oxidation at pH below 1.5 as is the case of acid plant and leaching process effluents have been reported. In this work, the kinetics of As(III) oxidation with SO2/O2 gas mixture at low pH (0.3–1.0) sulfuric acid solutions was investigated in the presence of different iron sources as catalyst: (i) Fe(III); (ii) Fe(II); and (iii) FeOOH residue. In the absence of Fe(III) the initial rate of As(III) oxidation at 90 °C is 0.6 mmol/L·min increasing to 1.1 mmol/L·min with Fe(III)/As(III) molar ratio = 0.1. Higher additions of Fe(III) bring only modest increase in rate. In the presence of Fe(II) the oxidation of As(III) is delayed initially due to competing oxidation of Fe(II) subsequently accelerating with the build-up of Fe(III), which acts as catalyst. Use of FeOOH (industrial goethite residue) provides a cost-effective source of Fe(III) catalytic species while simultaneously acts as neutralizing agent. A complex kinetic behavior is followed. Oxidation is reaction-controlled over the temperature range 25–50 °C shifting to mixed regime control from 70 to 80 °C becoming finally fully mass-transfer controlled at 90 °C. The catalytic role of Fe(III) is rationalized on the basis of a radical chain mechanism.

Insight into effect of CaCO3 on reduction roasting of fine-grained silicate type iron oxide ore and its application on Fe separation and recovery

To solve the problem of processing of refractory iron oxide ore resulted from its fine-grained disseminated structure, in this paper, an improved technology was innovatively proposed, which consisted of three stages of reduction roasting-acid leaching followed by magnetic separation, and CaCO3 was introduced during roasting process. Mechanism analyses indicated that kaolinite, a major gangue in ore, can be thermally dehydrated to amorphous metakaolin during roasting process, and CaCO3 can in part react with metakaolin——converting the stable kaolinite gangue mineral into acid-soluble Ca3Al2(SiO4)3, and subsequently Ca3Al2(SiO4)3 was selectively removed by acid leaching process. Moreover, the presence of CaCO3 can also improve the gathering state of Fe-rich particles, which is beneficial for magnetic separation. Iron concentrate obtained via the proposed technology contained 53.73% Fe, 9.02% Mn, 7.51% Al, and 2.46% Si, with a Fe recovery ratio of 88.20%, which surely meet the iron ore quality requirement of steel and iron industry.

Processing of Mica for Extraction of Alumina and Potash Values

Mica sample containing 34% alumina and 9% potash has been investigated as a potential dual source of alumina and potash. It was found that planetary milling had a strong effect on structure breakdown as well as on the release of alumina and potash values. Both alumina and potash were extracted from mica using mechanical milling followed by hydrochloric acid leaching and precipitation process. The optimal conditions derived from statistical design yielded 72% alumina and 75% potash values in the form of γ-alumina and sylvinite. The analysis of the final precipitate was carried out by different characterization techniques such as XRD, SEM–EDS, XRF, BET surface area analysis.

Efficient separation of chromium and vanadium by calcification roasting–sodium carbonate leaching from high chromium vanadium slag and V2O5 preparation

Calcification roasting–sodium carbonate (Na2CO3) leaching process was carried out to separate chromium and vanadium efficiently from high chromium vanadium slag (HCVS). Then vanadium existed in the form of ammonium metavanadate (NH4VO3) after precipitation from the purified leaching liquid, and highly pure V2O5 was prepared, while chromium remained in the vanadium tailings in the form of (Fe0.6Cr0.4)2O3. The effects of separation behaviors of chromium and vanadium under different roasting and leaching conditions were studied systematically. In order to elucidate the phase evolution, XRD and SEM were used during the whole process. After calcification roasting and Na2CO3 leaching, 93.19% of vanadium and 0.04% of chromium was extracted when CaO was added to HCVS in a mole rate n(CaO)/n(V2O5) of 0.5, roasted at 900 °C and maintained for 60 min. The roasted samples were added to 160 g/L Na2CO3 solution with the mass ratio of liquid to solid (L/S) of 10, then heating at 80 °C for 60 min. CaO tended to combine with vanadium and form alkali soluble calcium vanadate, while almost all of chromium was more likely to react with iron and form (Fe0.6Cr0.4)2O3. 94.00% of vanadium was then precipitated as NH4VO3 from the vanadium–containing supernatant after CO32– removing, when NH4Cl was added with the mole rate of n(NH4+)/n(V) of 6 and precipitated for 120 min at 5 °C. The purity of V2O5 was 99.68%, which was prepared by roasting NH4VO3. This process achieved the high efficiency separation of chromium and vanadium from HCVS compared with the traditional calcification roasting–acid leaching process. And the chromium-containing vanadium tailings can be used as the raw material to extract chromium and prepare Fe-Cr alloy.

Extraction and Separation of Mn and Pb from Electrolytic Manganese Anodic Slime (EMAS) via SO2 Roasting Followed by Acid Leaching Process

Electrolytic manganese anodic slime (EMAS) with high contents of manganese and lead is a well-known refractory secondary resource because of its complex constituents and structure. Traditional stockpiling treatment of EMAS not only causes resource waste, but also leads to long-term environmental pollution. In this study, SO2 roasting followed by acid leaching process was put forward to extract and separate manganese and lead from the EMAS. Thermodynamic analysis showed that a coexistence area of MnSO4 and PbSO4 was present in both the roasting and leaching processes. During the roasting process, manganese and lead oxides were sulfated to MnSO4 and PbSO4 by SO2. Then, MnSO4 and PbSO4 could be separated in the following acid-leaching process owing to their different solubilities in acid solution. The leaching efficiencies of 92.5 wt.% for Mn and only 3.21 wt.% for Pb were obtained under optimal conditions. This study provides an alternative approach to utilize the EMAS.

Reclamation of steel shots by acid leaching for powder metallurgy applications

Acid leaching is extensively employed for extractive metallurgy, but its use on reclamation of shot blasting media has not been extensively studied. The parameters of acid leaching process such as rate of stirring, the leached material grain size, the solid (material) to liquid (acid) ratio, type of acid, concentration of acid, leaching temperature, and leaching duration govern the effectiveness of this process. The goal of this article is to investigate the effectiveness of acid leaching to recover the iron from used shot blasting media. Influence of varying leaching durations on the recovery percentage of iron from the used shot blasting media is investigated, and it is found that acid leaching can remove impurities from used shot blasting media and it can successfully recover 73.6% of iron on the particle surface level and 44.3% of iron overall. Hence, it is a feasible process for recovery of iron from used shot blasting media.

Microwave Roasting and Acid Leaching of Vanadium and Chromium from High Chromium Vanadium Slag with CaCO<sub>3</sub>

In this study, microwave irradiation technology was used for the calcification roasting followed by sulfuric acid leaching process. The effect of roasting temperature, m (CaO)/m (V2O5), and roasting time on the leaching ratio of vanadium were investigated and the roasted samples were characterized by TG-DSC, XRD, and SEM. The leaching ratio of vanadium can be significantly enhanced with the increasing in roasting temperature, m (CaO)/m (V2O5), and roasting time. The leaching ratio of chromium decreased with roasting temperature and increased with m (CaO)/m (V2O5), and roasting time. The optimal roasting parameters were roasting temperature of 850 °C, the m (CaO)/m (V2O5) of 0.85, and roasting time of 90 min. Under the optimal roasting parameters, the leaching ratio of vanadium reached 88.81%. While the leaching ratio of chromium is 3.98%. During roasting process, vanadium is oxidized to acid-soluble CaV2O5, Ca2V2O7, and CaMgV2O7. After leaching, chromium mainly exists in form of chromohercynite (FeCr2O4) and chrome-manganese spinel (Mn1.5Cr1.5O4) in leaching residues.

Iron Control in Atmospheric Acid Laterite Leaching

Iron control in the atmospheric acid leaching (AL) of nickel laterite was evaluated in this study. The aim was to decrease acid consumption and iron dissolution by iron precipitation during nickel leaching. The combined acid leaching and iron precipitation process involves direct acid leaching of the limonite type of laterite followed by a simultaneous iron precipitation and nickel leaching step. Iron precipitation as jarosite is carried out by using nickel containing silicate laterite for neutralization. Acid is generated in the jarosite precipitation reaction, and it dissolves nickel and other metals like magnesium from the silicate laterite. Leaching tests were carried out using three laterite samples from the Agios Ioannis, Evia Island, and Kastoria mines in Greece. Relatively low acid consumption was achieved during the combined precipitation and acid leaching tests. The acid consumption was approximately 0.4 kg acid per kg laterite, whereas the acid consumption in direct acid leaching of the same laterite samples was approximately 0.6–0.8 kg acid per kg laterite. Iron dissolution was only 1.5–3% during the combined precipitation and acid leaching tests, whereas in direct acid leaching it was 15–30% with the Agios Ioannis and Evia Island samples and 80% with the Kastoria sample.

Acid leaching process intensification for eudialyte concentrate based on energy effects

Acid leaching process intensification for eudialyte concentrate based on energy effects

Effect of erbium nanoparticles on structural and spectroscopic properties of bio-silica borotellurite glasses containing silver oxide

Er3+ NPs doped bio-silica borotellurite glasses containing silver oxide were prepared using melt quenching techniques. The silica used was extracted from rice husk by acid leaching process. Optical absorption and photoluminescence properties of the glass samples were studied. The samples were confirmed to be amorphous in nature from the XRD results. The FTIR results reveal the existing functional groups in the glass structure. XRF result shows that 98.6% silica was obtained from the rice husk. The optical absorption spectra revealed that fundamental absorption edge shifts to longer wavelength as the content of erbium NPs increases. The value of band gap had been calculated and shown to be increased with an increase content of erbium NPs. The Urbach energy was shown to be linearly decreased with an increase in content of erbium NPs oxides. The introduction of silver oxides modifies the optical properties of the glass. The emission cross-section (δe) and gain bandwidth (FWHM ×δe) for 4I13/2→4I15/2 transition were calculated from the McCumber theory. The photoluminescence spectra revealed three emission bands corresponding to 4H11/2-4I15/2 (470 nm), 4S3/2-4I15/2 (561 nm) and 4F9/2→4I15/2 (758 nm) transitions assigned to green and red emissions respectively. The results suggest that these glasses might be used as a promising candidate as well as gain media for solid state lasers.

Selectively leaching the iron-removed bauxite residues with phosphoric acid for enrichment of rare earth elements

Bauxite residue (BR) is a hazardous industrial waste and also becomes an important reserve of rare earth elements (REE). An elegant process for achieving separation of REEs against silica from an iron-removed BR was established in this paper through selective leaching of silica with simultaneous enrichment of REEs. It was found that the phosphoric acid performed better than other acids (HNO3, HCl) for multiple REEs enrichment. The ideal conditions for the leaching process was determined through response surface methodology (RSM) to be H3PO4 concentration of 1.2 mol/L, L/S ratio of 11 mL/g and leaching temperature of 40 °C. 82.3% SiO2 in iron-removed BR was leached out while the REEs (La2O3, Ce2O3, Sc2O3 and Y2O3) remained in the leached residue with recovery of more than 98%. La2O3 and Ce2O3 were proved to be in lattice replacement within the acid-resistant pervoskite and thus remained in the leached residue. Only part of Sc2O3 and Y2O3 entered into pervoskite and the remainder was trapped in the aluminosilicate minerals. The enrichment of Sc2O3 and Y2O3 in phosphoric acid leaching process was related to the low acidity of H3PO4 solution.

Pretreatment of Coal by Acid Leaching As Feedstock Preparation For Co-Gasification With Biomass

Co-gasification process of coal and biomass is believed to be one of the promising way to produce hydrogen. The mixing of coal and biomass can solve the problems that usually happened during gasification of pure coal or pure biomass. Furthermore, the presence of synergistic effect between coal and biomass may increase the hydrogen production due to Alkali and Alkaline Earth Metal (AAEM) content in the biomass. However, the synergistic effect may be hindered by the presence of silica in the coal. The present study focuses on the reduction of silica content of coal by acid leaching. Based on the result, it is found that the use of hydrofluoric acid may significantly reduce the silica content shown by the reduction of ash content in the coal. Furthermore, acid leaching process also causes the increase of surface area of the coal which may increase the possibility of AAEM attachment to the surface and thus the gas production may increase as well.

Highly efficient self-template synthesis of porous silica nanorods from natural palygorskite

A simple one-step hydrothermal acid-leaching process was employed to efficiently convert natural Pal to porous silica nanorods with a high SiO2 content and decent length of nanorods. At a lower acid concentration (2.0 mol/L), silica nanorods with the SiO2 content of 97.84% and a rod length equal to original length of Pal nanorods were obtained by this process; while only the products with lower SiO2 content of 79.92% were obtained by a normal acid-bleaching process. Although increasing acid concentration to 8.0 mol/L may enhance SiO2 content to 94.56% in normal acid-leaching process, which led to sharp reduction of length of nanorod. The synthesized porous silica nanorods have a specific surface area of 119.39 m2/g, average pore size of 7.56 nm, and better whiteness (the L*, a* and b* values are 86.130, 0.131 and 2.801, respectively). This paper provided an effective, universal approach to produce silica nanomaterials from diverse natural clay minerals.

Vanadium extraction from black shale: Enhanced leaching due to fluoride addition

During the direct acid-leaching process of vanadium extraction from black shale, the participation of fluoride ions greatly improves the leaching efficiency of vanadium. Its enhanced effect is influenced by the sulfuric acid concentration, amount of added fluoride, leaching temperature, and leaching time. The migration of fluoride ions during leaching is critical for the dissolution of muscovite and the release of vanadium. In this work, we employed a central composite design of response surface methodology to design the leaching experiment. Results show that the CaF2 dosage is highly significant, and the H2SO4 concentration, CaF2 dosage, and leaching temperature all exhibit interactive effects with each other during acid-leaching. The higher concentration and reactivity of H+ and F− in solution result in a higher vanadium leaching efficiency for direct acid-leaching. The role of F− in the reaction mechanism was investigated using density functional theory simulation. After the removal of structural oxygen of tetrahedra by H+, F− closely bonds with the exposed structural aluminum atom and drags it away from the muscovite surface in the form of [AlF4]−, F− continues to coordinate with [AlF4]− to form the stable [AlF5]2− in solution. The enhanced effect of F− is mainly reflected in its smaller volume and higher electronegativity as compared to those of HSO4− and SO42−.

Leaching and concentration of P and K from P-K associated ore by using a sequential leaching process with leachate recycling

The concentrations of P and K in leaching solution are relatively low and the consumption of acid is relatively large, which are the existing problems in the leaching of P and K from P-K associated ore by using the low-temperature acid leaching process. In this work, a sequential leaching process with leachate recycling was developed, in which P and K were sequentially leached out from P-K associated ore and the obtained P- and K-containing leachates were recycled into the next leaching process. In this sequential process with leachate recycled two times the concentrations of K and P2O5 in leachate were increased from 20.18 and 15.79 g/L to 53.26 and 45.97 g/L, respectively. In comparison, in the simultaneous leaching process with leachate recycling both the leaching efficiencies of K and P and the concentrations of K and P2O5 were significantly lower than those in the sequential leaching process, which can be mainly attributed to the fact that Ca in the ore, which could react with PO43− to generate Ca-containing sediments, was precipitated first in the sequential leaching process. The sequential leaching process with leachate recycling will provide an efficient method for leaching and concentrating P and K from P-K associated ore.

Statistical Approach for Water Glass Precursor Preparation from Bamboo Leaf Silica

The bamboo leaf consists of high silica content. In this study, the bamboo silica was utilized as water glass. Water glass can also be used as eco-friendly precursors for the preparation of silica aerogel. The extraction process of silica from bamboo leaf have been carried out through acid leaching and combustion process at 750°C based on thermal gravimetry analysis. This paper is aimed to assess the effect of two types of alkali hydroxide and concentrations producing water glass of bamboo leaf silica. The result was analyzed by using a 22-factorial design with six replications. The alkali hydroxide types were sodium hydroxide and potassium hydroxide with a concentration of 4 M and 6 M, respectively. The study was executed in several steps, i.e. pre-treatment of bamboo leaf, leaching process, combustion, purification of bamboo leaf silica and synthesis of water glass. The optimum condition of water glass products was obtained at silica concentration of 41.08 ppm and density of 1.23 g/L for potassium hydroxide, while at 40.15 ppm and 1.30 g/L for sodium hydroxide. ANOVA analysis resulted in a significant effect for type of hydroxide and concentration releasing model for silica concentration response. This study also characterized the silica structure and composition by instrumentation analysis for silica solid obtained from optimum water glass condition with potassium hydroxide. It can be denoted the physical behavior of silica solid from water glass by potassium hydroxide did not differ from previous research of water glass by sodium hydroxide.

Assessment of the Ion-SAFT-VR EOS for estimation of metal sulfates solubility at high temperature acid leaching process

The SAFT-VR (statistical associating fluid theory of variable range) equation of state is coupled with MSA (mean spherical approximation) in which molecule-ion and coulombic interactions are embedded. Also, the effect of change in dielectric constant is described by Born term as result of solvation. The SAFT-VR parameters for water and metal sulfates are firstly optimized by the experimental data. After this stage, the solubility of MgSO4 and Al2(SO4)3 in ternary systems, i.e. MgSO4-H2SO4-H2O and Al2(SO4)3-H2SO4-H2O, is obtained at high temperatures. Next, the solubility of MgSO4 is presented in different concentrations of Al2(SO4)3 in the quaternary systems as H2SO4–MgSO4–Al2(SO4)3–H2O. Also, the solubility of the other metal sulfate, namely Al2(SO4)3, is calculated in the presence of MgSO4 in this system at 250 °C. Finally, the results of the Ion-SAFT-VR model for ternary systems are compared with the Pitzer and the E-NRTL models. The results show that the Ion-SAFT-VR model can more accurately predict the solubility of metal sulfates in the studied systems than other models.

Innovative technology for the production of high-purity sand silica by thermal treatment and acid leaching process

The production of high purity silica out of natural sand plays a critical role as a starting material in the industry of glass and high grade silicon. In this paper, we expose a novel processing method for the purification of sand silica. This method is a subsequent combination of thermal treatment and acid leaching. Firstly, samples of Tunisian natural sand were submitted to a rapid thermal annealing in an infra-red furnace under O2 atmosphere at fixed temperature and time 1000 °C and 1 h, respectively. Subsequently, the samples were soaked in an aqueous acid solution composed hydrofluoric acid and a hydrochloric acid concentration. This last acid leaching step was intended to remove the gettered impurities during the annealing step. Various characterization techniques such as optical absorption, energy dispersive X-ray analysis, electronic paramagnetic resonance analysis and atomic absorption spectroscopy were used aiming to evaluate the effectiveness of this impurity gettering technology. The results show substantial reduction in all metallic impurities in silica after three successive purification cycles improving the purity from 99.7 to 99.9%.

Evaluating the effect of leaching on trace element and Nd-Pb isotopic systematics in continental basalts

Leaching technique was mostly carried out on submarine rock powder to minimize or eliminate secondary effect of seawater interaction on Sr and Pb isotope magmatic signatures. However, the effect of leaching on trace element contents is comparatively poorly established. To investigate such effects, we have compared trace element and Nd-Pb isotopic data for acid leached ∼290 Ma Keping basalts in the Tarim Large Igneous Province (NW China) with unleached data on the same rocks. Rare earth elements (REE), Y, Th and U contents of leached sample grains (0.6–1.0 mm size) are 10–65% lower than those of unleached grains of the same sample, whereas other trace elements are not affected. Sm/Nd, Lu/Hf, U/Pb and Th/Pb ratios are fractionated by acid leaching between leached and unleached sample grains. Nd isotope values are unaffected by leaching, but 208Pb/204Pb and 206Pb/204Pb values of leached samples are significantly lower than those of unleached samples. X-ray diffraction results suggest that removal of secondary epidote during the acid leaching process could result in the fractionation of REE, Y, Th and U contents, and Sm/Nd, Lu/Hf, U/Pb and Th/Pb ratios, and 208Pb/204Pb and 206Pb/204Pb values. These results suggest that when the samples have been leached with strong acid (>1N HCl), their trace element cannot be used to trace the sources and petrogenesis. If leaching is applied to old (e.g., >100 Ma) continental basalts in order to eliminate contamination during sample collection, storage, sawing and crushing, Th/Pb and U/Pb ratios used to calculate the initial Pb isotope values, should be obtained on the same leached samples.

Vanadium extraction from a magnetite ore using alkaline roasting and acid leaching processes: optimization of parameters by response surface methodology

In this work, thealkaline roasting and sulfuric acid leaching processes were employed to extract vanadium from the magnetite ore of Saghand mine in central Iran. The response surface methodology based on the central composite design model was applied to optimize the parameters involved in the processes. The studied roasting parameters were temperature (900-1100 °C), sodium carbonate percentage (30-50 wt%), and time (1-3 h). In addition, the studied leaching factors included temperature (70-90 °C), liquid-to-solid ratio (L/S) (5-20 mL/g), sulfuric acid concentration (2-6 M), and time (3-6 h). Under the optimal conditions, the values for temperature, time, and sodium carbonate amounted to 1010 °C, 2.1 h, and 41 wt%, respectively, for the roasting process, while the values for temperature, L/S, sulfuric acid concentration, and time for the leaching process were estimated to be 85 °C, 12.4 mL/g, 4.25 M, and 4.7 h, respectively. Under these conditions, about 83.8 ± 0.9% of vanadium was leached from the magnetite ore.