Acid Leaching Technique Research Articles

Extraction of gamma iron oxide (γ-Fe2O3) nanoparticles from waste can: Structure, morphology and magnetic properties

In this work, the transformation of waste iron cans to gamma iron oxide (γ-Fe2O3) nanoparticles following acid leaching precipitation method along with their structural, surface chemistry, and magnetic properties was studied. Highly magnetic iron-based nanomaterials, maghemite with high saturation magnetization have been synthesized through an acid leaching technique by carefully tuning of pH and calcination temperature. The phase composition and crystal structure, surface morphology, surface chemistry, and surface composition of the synthesized γ-Fe2O3 nanoparticles were explored by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDS). The XRD results confirm the cubic spinel structure having crystallite size 26.90–52.15 nm. The XPS study reveals the presence of Fe, O element and the binding energy of Fe (710.31 and 724.48 eV) confirms the formation of γ-Fe2O3 as well. By dynamic light scattering (DLS) method and zeta potential analyzer, the particle size distribution and stability of the systems were investigated. The magnetic behavior of the synthesized γ-Fe2O3 nanoparticles were studied using a vibrating sample magnetometer (VSM) which confirmed the ferrimagnetic particles with saturation magnetization of 54.94 emu/g. The resultant maghemite nanoparticles will be used in photocatalysts and humidity sensing. The net impact of the work stated here is based on the principle of converting waste into useful nanomaterials. Finally, it was concluded that our results can give insights into the design of the synthesis procedure from the precursor to the high-quality gamma iron oxide nanoparticles with high saturation magnetization for different potential applications which are inexpensive and very simple.

Migration of transition metals and potential for carbon mineralization during acid leaching of processed kimberlite from Venetia diamond mine, South Africa

Carbonation of mafic and ultramafic rocks and mineral wastes provides a permanent way to sequester excess atmospheric CO2. Recent research has shown that this method also offers the potential for enhanced recovery of critical metals from mine tailings. In this study, processed kimberlite from the Venetia diamond mine (South Africa) was used in column acid leaching experiments to assess both its carbonation potential and whether critical metals such as nickel could be recovered during mineral carbonation. Processed kimberlite was treated daily with one pore volume of either deionized water or dilute hydrochloric acid (0.04 M, 0.08 M, 0.12 M and 0.16 M) for 28 days. Iron-rich yellow precipitates consistent with yellow ground formed during the experiments both at the top of the residue columns (corresponding to the inlets of the columns) and within the leachates collected from the bases of columns. The carbonation potential and mobility of transition metals were investigated using a combination of quantitative X-ray diffraction (XRD) using Rietveld refinements, inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM) coupled with EDXS, and synchrotron-based X-ray fluorescence microscopy (XFM). Our results show that the high proportion of clay minerals (e.g., lizardite, smectite, talc, chlorite) in the processed kimberlite act as the primary source for Mg and transition metals such as Ni; however, calcite dissolution is the main source for Ca. The amount of Mg and Ca extracted from processed kimberlite increases with HCl concentration. If acid leaching of processed kimberlite were used at Venetia, the amount of Mg leached from clay minerals would provide an estimated CO2 offset potential ranging from 2.1 to 15.8 % of the mine's total annual emissions. The leached Ca from silicate dissolution could also provide an estimated CO2 offset potential ranging from 2.1 to 8.1 % of the mine's total annual emissions. However, the amount of CO2 released by calcite dissolution during this process is equivalent to 2.1–14.3 % of total annual CO2 emissions at Venetia., thus resulting in a net estimated CO2 offset potential of 2.1–9.6 % if the Ca released from calcite could not be recarbonated. If all of the Ca could be reprecipitated as calcite, the acid leaching techniques employed in this study could offset 4.2–23.9 % of the Venetia mine's CO2 emissions. Ultimately, greater concentrations and/or amounts of acid may be used to access more of the offset potential of Mg phyllosilicates in kimberlite, but the CO2 released by calcite dissolution must also be won back by recarbonation.

Synthesis and Characterization of Silica and Silica Cellulose from Natural Materials as Matrix for Various Sensor Applications: A Mini Review

Sensors play a crucial role in various fields by enabling the detection and analysis of a wide range of substances, including hazardous substance detection, environmental and food safety monitoring, pharmaceutical industry, gas analysis, and others. Research continues to identify and develop sensor matrix materials that can increase the sensitivity, selectivity and responsiveness of sensors. Silica, an oxide mineral is a potential matrix material for sensor applications because of its unique characteristics. It has a large pore structure and modifiable pore size distribution. Silica’s stable chemical properties, high-temperature resistance and corrosion resistance make it an ideal matrix material for a wide range of sensor applications. In recent years, silica cellulose also become a potential material for sensor applications. Silica cellulose is produced by combining silica with cellulose components from natural materials, such as rice husk ash, bamboo leaf ash, rice straw ash, and other plant fibers. This article provides a comprehensive exploration of various methods of synthesis and characterization of silica and silica cellulose materials. The methods include sol-gel, acid leaching, alkaline extraction, and other techniques for extracting cellulose from natural sources. In addition, sensor applications that have been tested using this material are also discussed, including its use in detecting molecular compounds, food and environmental applications. The development of silica and silica cellulose materials based on natural materials is considered because of their sustainability. By continuing to explore the potential of these materials, it is hoped that it can make a significant contribution in the development of sensor technology that is more innovative, environmentally friendly and sustainable.

The Use of Acid Leaching to Recover Metals from Tailings: A Review

Mine tailings deposits are often overlooked by the industry, posing significant environmental challenges due to chemical hazards and inadequate maintenance. Nevertheless, such mineral deposits hold considerable economic potential for processing, and the adoption of innovative technologies may also address critical chemical and physical stability issues. Existing research has demonstrated the feasibility of recovering target metals—i.e., copper, iron, manganese, cobalt, zinc, and others—through the application of acid leaching techniques with consistently high yields and metal recovery rates. Therefore, a compilation was carried out from 2008 onwards, on working conditions such as leaching agent, acid concentration, oxidizing-reducing reagent, particle size, O2 pressure, stirring speed, solid–liquid ratio, temperature, and leaching time. At present, there are no reviews on the recovery of metals via acid leaching in tailings, so this study can serve as support for future researchers who want to project themselves in this area, ordering the procedures and the results obtained by the research carried out. Regarding the evaluation, it can be commented that research has shown that acid leaching of tailings has achieved recoveries of over 90% in different metals, such as Zn, Cu, and Fe, which indicates that the treatment is efficient and recommended for different types of tailings.

The Recovery of Vanadium Pentoxide (V2O5) from Spent Catalyst Utilized in a Sulfuric Acid Production Plant in Jordan.

Vanadium is a significant metal, and its derivatives are widely employed in industry. One of the essential vanadium compounds is vanadium pentoxide (V2O5), which is mostly recovered from titanomagnetite, uranium-vanadium deposits, phosphate rocks, and spent catalysts. A smart method for the characterization and recovery of vanadium pentoxide (V2O5) was investigated and implemented as a small-scale benchtop model. Several nondestructive analytical techniques, such as particle size analysis, X-ray fluorescence (XRF), inductively coupled plasma (ICP), and X-ray diffraction (XRD) were used to determine the physical and chemical properties, such as the particle size and composition, of the samples before and after the recovery process of vanadium pentoxide (V2O5). After sample preparation, several acid and alkali leaching techniques were investigated. A noncorrosive, environmentally friendly extraction method based on the use of less harmful acids was applied in batch and column experiments for the extraction of V2O5 as vanadium ions from a spent vanadium catalyst. In batching experiments, different acids and bases were examined as leaching solution agents; oxalic acid showed the best percent recovery for vanadium ions compared with the other acids used. The effects of the contact time, acid concentration, solid-to-liquid ratio, stirring rate, and temperature were studied to optimize the leaching conditions. Oxalic acid with a 6% (w/w) to a 1/10 solid-to-liquid ratio at 300 rpm and 50 °C was the optimal condition for extraction (67.43% recovery). On the other hand, the column experiment with a 150 cm long and 5 cm i.d. and 144 h contact time using the same leaching reagent, 6% oxalic acid, showed a 94.42% recovery. The results of the present work indicate the possibility of the recovery of vanadium pentoxide from the spent vanadium catalyst used in the sulfuric acid industry in Jordan.

Evaluation of the acid leaching technique for recovery of U3O8 and ThO2 in niobium/tantalum slag

This study presented the recovery of uranium oxide and thorium oxide from aluminothermic slag from the metallurgical processing of columbite – a niobium/tantalum mineral with the presence of U3O8 and ThO2 – from a mining-industrial facility. The methodology consisted of sampling, comminution, and leaching using sulfuric acid. The head sample showed contents of (1.78 + 0.14) % for U3O8 and (3.66 + 0.04) % for ThO2. The metallurgical recovery reached values above 80% for the uranium oxide and above 70% for the thorium oxide for pH < 1.5 and process time greater than eight hours.

Recycling of waste carbon residue from spent lithium-ion batteries via constant-pressure acid leaching

Waste carbon residue (WCR) was efficiently detoxicated and regenerated to high-purity graphite (PGC) used in lithium-ion batteries through the constant-pressure acid leaching technique. The leaching conditions were optimized by the combination of orthogonal and single-factor experiments. Results show that PGC with 99.5% purity is regenerated at temperature of 60 °C, initial acid concentration of 12%, leaching time of 180 min, and liquid-to-solid ratio of 25:1, satisfying the requirements of commercial graphite. Meanwhile, the sodium hydroxide precipitation process was designed to recover valuable components from leachate efficiently. Ni, Co, Mn, and Al recoveries reach 96.92%, 87.5%, 97.83%, and 92.17%, respectively, at pH=11. Moreover, the co-product NaF can be recovered with purity over 99% via evaporative crystallization. The loss rate of fluorine is less than 0.5%, thereby eliminating the pollution risk of fluorine to the environment. The proposed process shows considerable environmental and economic benefits.

Red Mud as a Secondary Resource of Low-Grade Iron: A Global Perspective

Managing red mud (RM), a solid waste byproduct of the alumina recovery process, is a serious ecological and environmental issue. With ~150 million tons/year of RM being generated globally, nearly 4.6 billion tons of RM are presently stored in vast waste reserves. RM can be a valuable resource of metals, minor elements, and rare earth elements. The suitability of RM as a low-grade iron resource was assessed in this study. The utilization of RM as a material resource in several commercial, industrial operations was briefly reviewed. Key features of iron recovery techniques, such as magnetic separation, carbothermal reduction, smelting reduction, acid leaching, and hydrothermal techniques were presented. RMs from different parts of the globe including India, China, Greece, Italy, France, and Russia were examined for their iron recovery potential. Data on RM composition, iron recovery, techniques, and yields was presented. The composition range of RMs examined were: Fe2O3: 28.3–63.2 wt.%; Al2O3: 6.9–26.53 wt.%; SiO2: 2.3–22.0 wt.%; Na2O: 0.27–13.44 wt.%; CaO: 0.26–23.8 wt.%; Al2O3/SiO2: 0.3–4.6. Even with a high alumina content and high Al2O3/SiO2 ratios, it was possible to recover iron in all cases, showing the significant potential of RM as a secondary resource of low-grade iron.

Comparison on the physicochemical properties of alumina extracted from various aluminum wastes

Aluminum production, which is primarily derived from bauxite mines, increased dramatically worldwide throughout the year. This phenomena results in an increase in aluminum waste in landfills, which creates an environmental hazard. Furthermore, it reduces the groundwater quality due to the toxicity of metal ions and flammable gases released from the process. Therefore, a recycling strategy is needed to reduce the negative environmental impacts of aluminum waste. Aluminum oxide (Al2O3), or commercially known as alumina, can be extracted with a low-cost method. From literature, it was found that the extraction of Al2O3 from aluminum waste only requires 5% of the total energy needed, making it a cost-effective recycling method. Al2O3 is commonly extracted from Bayer process, but the technology used to produce Al2O3 leads to high electricity and fuel consumption. Alternative extraction methods for Al2O3 have been extensively investigated, including sol–gel, hydrothermal, and leaching-precipitation procedures. Although the extraction of Al2O3 has been widely studied, the comparison on physicochemical properties of Al2O3 from various aluminum waste (i.e. aluminum dross (AD), aluminum foil (AF) and aluminum can (AC)) has not been explored. Therefore, this paper evaluates the physicochemical properties of Al2O3 extracted from AD, AF and AC. All the extracted Al2O3 was prepared using acid leaching technique and from the analyses conducted, Al2O3 extracted from AD having the highest percentage of Al2O3 than AC and AF. The experiment was then extended by investigating the effect of calcination temperature source (i.e. 700, 800, 900, 1000 and 1100 °C), utilizing the best alumina source. The results showed that the phase of Al2O3 transformed from γ → θ → κ → α with the increased in calcination temperature. This indicates that the extraction technique and calcination temperature play important role in the extraction and transformation of Al2O3 phases.

Geochemical exploration for buried sandstone-hosted uranium mineralization using mobile U and Pb isotopes: case study of the REB deposit, Great Divide Basin, Wyoming

Mobile radiogenic lead isotopes ( 206 Pb, 207 Pb, 208 Pb and 210 Pb) represent products of radioactive decay of their parental uranium and thorium isotopes ( 238 U, 235 U, 232 Th), and are considered potential geochemical pathfinders of buried sandstone-type uranium deposits. Soil samples collected along a geochemical traverse intersecting buried uranium roll front mineralization at the REB deposit in the Great Divide Basin, Wyoming, USA were studied. Mineralization of this deposit is hosted in weakly lithified arkosic sands, at a depth of 120–200 m, without a strong surficial expression of its presence at depth, which makes discovery of this deposit type difficult, slow and expensive. All soil samples have been analysed for ratios of the mobile long-lived Pb isotopes and their parental U and Th isotopes, determined from partial leach products obtained using a weak acid leaching technique. The samples were also analysed for trace elements, assayed both in the partial leach products and using conventional whole-soil sample assays. Ratios of the mobile radiogenic Pb isotopes to their parental U and Th isotopes ( 206 Pb/ 238 U, 207 Pb/ 235 U and 208 Pb/ 232 Th) determined in the partial leach products exhibit anomalous contents in the soil samples collected above the uranium rolls. The anomalous values are several times greater than background values, to lateral distances of 350–400 m outside of the roll fronts. Notably, conventional whole-soil assays have failed to detect the anomalies that were detected using mobile Pb isotopes. Supplementary material : Minor and trace elements assays of the geochemical samples are available at https://doi.org/10.6084/m9.figshare.c.5610980

A comparison of geochronological methods commonly applied to kimberlites and related rocks: Three case studies from Finland

Despite their economic and scientific significance, the tectonic drivers that lead to the genesis of kimberlites and related rocks remain enigmatic. The presence of any spatio-temporal relationship(s) between the rift, drift and collision history of continents and the emplacement of kimberlites can only be elucidated with accurate geochronological constraints. In this study, we evaluated the three most common radiogenic dating methods used to determine the emplacement ages of kimberlites and related rocks - Rb-Sr phlogopite, U-Pb perovskite and 40Ar/39Ar phlogopite. We selected minimally altered samples from the Kaavi-Kuopio kimberlites, ultramafic lamprophyres and kimberlites from Kuusamo, and olivine lamproites from the Lentiira-Kuhmo-Kostomuksha cluster, all located in Finland. Our 33 new age determinations indicate that the olivine lamproites and ultramafic lamprophyres were emplaced on the Karelian craton during the interval between ~1180–1210 Ma, the Kuusamo kimberlites between ~730–750 Ma, and the Kaavi-Kuopio kimberlites between ~585–620 Ma.Our results show that the Rb-Sr method regularly yields reproducible eruption ages from either magmatic or macrocrystic (xenocrystic) mica. In addition, the method can be employed on a single population of mineral separates using a sequential acid-leaching technique, without the need for an estimate of 87Sr/86Sr(i). The U-Pb perovskite technique typically requires significant correction for ‘common-Pb’ i.e. Pb incorporated at the time of mineral formation and unrelated to subsequent radiogenic ingrowth. Here, we utilised isotope dilution analyses of co-existing spinel to extend the ‘spread’ in U-Pb isochron space obtained by in situ LA-ICP-MS analyses of perovskite and enhance the accuracy and precision of intrusion ages. Our tests also show that two-point U-Pb isochrons based on solution analyses of perovskite and spinel generally provide anomalously older ages. Relative to Rb-Sr and U-Pb results from the same kimberlite, we show that apparently precise 40Ar/39Ar plateau-ages, determined from step-heating experiments, are often anomalously ‘old’, which is attributable to 39Ar recoil effects. In cases where the 40Ar/39Ar step-heating spectra are even marginally ‘disturbed’, 40Ar/39Ar total-gas ages compare favourably with ages from other geochronometers and appear to provide accurate estimates for the emplacement age of kimberlites and related rocks.Overall, there is good agreement between the three geochronometers using the above approaches, which indicates that Rb-Sr phlogopite, U-Pb perovskite and 40Ar/39Ar phlogopite dating can provide robust age constraints for the emplacement of kimberlites and related rocks. The geochronometer of choice will rely on the freshness, abundance and size of datable material. Wherever possible, the application of multiple geochronometers is recommended.

Statistical optimization of titanium recovery from drinking water treatment residue using response surface methodology

Water treatment plants generate vast amounts of sludge and its disposal is one of the most expensive and environmentally problematic challenges worldwide. As sludge from water treatment plants contains a considerable amount of titanium, both can create serious environmental concerns. In this study, the potential to recover titanium from drinking water treatment residue was explored through acid leaching technique. Statistical design for the optimization of titanium recovery was proposed using response surface methodology (RSM) based on a five-level central composite design (CCD). Three independent variables were investigated, namely the acid concentration (3 M–7 M), temperature (40 °C – 80 °C) and solid/liquid ratio (0.005–0.02 g/mL). According to the analysis of variance (ANOVA), the p-value (<0.0001) indicated the designed model was highly significant. Optimization using RSM gave the best fit between validated and predicted data as elucidated by the coefficient of determination with R2 values of 0.9965. However, acid concentration and solid/liquid ratio showed an initial increase in titanium recovery followed by recovery reduction with increasing concentration and ratio. Quadratic RSM predicted the maximum recovery of titanium to be 67.73% at optimal conditions of 5.5 M acid concentration, at a temperature of 62 °C with a solid/liquid ratio of 0.01 g/mL. The verification experiments gave an average of 66.23% recovery of titanium, thus indicating that the successfully developed model to predict the response. This process development has significant importance to reduce the cost of waste disposal, environmental protection, and recovery of economically valuable products.

Optimization of microwave roasting-acid leaching process for vanadium extraction from shale via response surface methodology

In this work, Microwave roasting (MR) was used in vanadium (V) extraction from shale for its cleanness and high efficiency. Response surface methodology (RSM) was used to optimize conditions for MR-acid leaching, the enhancement mechanism of MR for V oxidization and structural distortion of muscovite were investigated using density functional theory (DFT) and a variety of micro-Characterization methods. A Box-Behnken experimental design has been used to monitor the V extraction characteristics, as affected by MR temperature, MR time, H2SO4 concentration and leaching time. In the optimized conditions, a V leaching efficiency of 93.4% was reached. Compared with conventional roasting (CR)-acid leaching technique, MR technique had absolute advantages, its roasting temperature was reduced by 115 °C, roasting time was reduced by 32 min, H2SO4 concentration was reduced by 10%v/v and leaching time was reduced by 4 h. Selective thermal effect of MR enhanced activations of coal and pyrite and results in cracking of particles, promoting the oxidation of low-valent V. MR had an absolute advantage in dehydroxylation of muscovite, resulting the spacing expansion of Al–O(OH) octahedral structure layer as about 1.3 times as that of CR and significantly enhancing the release of V.

Incorporation of Fe3C and Pyridinic N Active Sites with a Moderate N/C Ratio in Fe–N Mesoporous Carbon Materials for Enhanced Oxygen Reduction Reaction Activity

A facile and effective route was reported to synthesize iron–nitrogen codoped mesoporous carbon nanomaterials (Fe–N–C) as a high-performance oxygen reduction reaction (ORR) catalyst by pyrolyzing glycine, polyvinylpyrrolidone (PVP), citric acid, and FeCl3 through a heat-treatment (700–900 °C) process accompanied by an acid leaching technique. Among the as-prepared catalysts, the Fe–N codoped carbon-800 after treatment with acid (Fe–N–C-800–acid) and the Fe–N–C-900 catalyst possessed excellent activity with onset potentials of 0.93 and 0.92 V, respectively, and basically identical half-wave potentials of 0.75 V as well as a higher current density of 4.3 and 2.7 mA cm–2 at −0.56 V (vs RHE) through selective four-electron transfer kinetics (n = 3.5 and 3.7, respectively). Moreover, they exhibit comparable Tafel slope values of 100 and 108 mV dec–1, respectively, compared to 20% Pt–C (99 mV dec–1) as well as excellent durability and resistance to methanol. The relevant abundance of Fe3C and pyridine N in the ...

Microstructural stability of supported metal catalysts: A phase field approach

The long-term stability of supported metal catalysts designed for solid-oxide fuel cell (SOFC) anodes is evaluated using a phase field simulation approach. Porous support structures are numerically sintered and then infiltrated with a nanoscale catalyst phase to mimic scaffolds fabricated via both pyrolysis and acid leaching techniques. Simulations capture the dewetting, particle agglomeration, and coarsening processes that occur during extended operation at elevated temperatures. We systematically explore the microstructural evolution of the active phase for a range of infiltration loadings from 2 to 21% and report on common performance metrics, such as triple phase boundary (TPB) density and contiguity. Ostwald ripening and particle migration and coalescence events are identified as dominant mechanisms contributing to severe reductions in the TPB density and catalyst deactivation. Despite marked differences between the simulated pyrolyzed and leached scaffold structures, the resulting TPB densities are comparable in value. Additionally, we show that tuning the metal catalyst/scaffold contact angle between 60∘ and 120∘ does not significantly affect TPB density. More broadly, this work elucidates the challenges associated with stabilizing nanoscale dispersions prepared by infiltration and similar techniques.

Novel process of alumina extraction from coal fly ash by pre-desilicating—Na2CO3 activation—Acid leaching technique

Alumina extraction from coal fly ash (CFA) by Na2CO3 activation-acid leaching method could make Al2O3 and SiO2 in CFA achieve high value utilization simultaneously, which shows wide application prospects. The large consumption of Na2CO3, however, limits its industrial application. A novel process of alumina extraction from coal fly ash by “Pre-desilicating—Na2CO3 activation—acid leaching” has been proposed in this work. By this process, the consumption of Na2CO3 decreased significantly thanks to the adjustment of Al/Si molar ratio in the raw materials. The effects of pre-desilication conditions on the dissolution of SiO2 in coal fly ash, the effect of the novel process on the consumption of Na2CO3 and the phase transformations and the alumina dissolutions at various consumption of Na2CO3 were investigated. The results showed that the dissolution of SiO2 reached 37.3% at 20% (by weight) of NaOH concentration, 1mL/g of liquid to solid ratio, 100°C and 2.0h, when the Al/Si molar ratio in coal fly ash could be raised to 1.21 from 0.81. The mixed coal fly ash with an Al/Si molar ratio of 1 could be obtained by mixing desilicated and the as-received coal fly ash. The dissolution of Al2O3 of the mixed coal fly ash reached ~87% at the Na/Al molar ratio of 1. The consumption of Na2CO3 decreased obviously and the reduction percentage reached 53.1% at Na/Al molar ratio of 1.0 after undergoing the pre-desilication process compared with the Na2CO3 direct activation process. This work could provide a novel thought for the utilization of coal fly ash with high value and high efficiency.

Trace and rare earth element characteristics in Fe-Mn carbonates associated with stratiform Ag-Pb-Zn mineralization from the Lengshuikeng ore district, Jiangxi Province: Implications for their genesis and depositional environment

We performed a systematic trace and rare earth element analysis for the bedded Fe-Mn carbonate rocks related to the stratiform Ag-Pb-Zn mineralization in the Lengshuikeng ore district, Jiangxi Province, South China. Three types of Fe-Mn carbonates are distinguished, namely, the massive, breccia, and vein types. Both carbonate and silicate fractions in the samples are analyzed for their trace and rare earth element concentrations using a step acid-leaching technique. Our results show that the carbonate fractions in the massive type samples have the lowest REE concentrations but pronounced positive Eu and Y anomalies with Eu/Eu* value from 1.3 to 6.2 and Y/Ho value from 40.1 to 59.5, and similar characteristics are also shown for the silicate fractions in the massive type samples (Eu/Eu*=1.0–6.7, Y/Ho=20.7–55.1). These REE characteristics are similar to those of Sedex type massive sulfide deposits worldwide, and we suggest that the massive type Fe-Mn carbonate rocks were likely formed from an exhalative volcanic-hydrothermal fluid feeding the depression basin of a volcanic lake. The high concentrations of redox-sensitive elements and ratios such as U/Th, V/Cr and V/(V+Ni) indicate a dysoxic environment for the Fe-Mn carbonate deposition. In contrast, the breccia type and vein type Fe-Mn carbonate samples show different trace and rare earth element features from those of massive type samples, and they are more similar to the volcanic rocks and magmatic-hydrothermal fluids in the Lengshuikeng ore district and may reflect strong overprinting from volcanic and sub-volcanic magmatism related to the porphyry type mineralization in the district.

Acid leaching technique for the possible recovery of aluminium and other metal values from coal fly ashes

Acid leaching technique for the possible recovery of aluminium and other metal values from coal fly ashes

Comparison of acid leaching and fusion techniques to determine uranium in soil samples by alpha spectrometry

Dissolution of radionuclides of interest is an indispensable first step in the alpha spectrometric analysis of soil samples. In this study a uranium recovery method for the analysis of uranium isotopes in soil samples is presented. Two different soil sample dissolution techniques were used: digestion in open beaker and fusion. The results of these techniques were compared. Two proficiency test samples and one reference material prepared by the IAEA were analyzed. Better results were obtained by fusion dissolution technique but impurities were higher than with acid leaching. Results of two techniques were more or less similar within the uncertainty limits. The detection limit (a#) was evaluated as part of the quality control.

Avaliação da rota de redução do teor do elemento fósforo contido no minério de ferro através da técnica de aquecimento por energia de micro‐ondas seguida de lixiviação ácida

Iron ore when found containing high levels of phosphorus element becomes detrimental to the manufacture of steel due to the increase of its hardness making it brittle and fractures. In this sense the process of acid leaching of iron ore is seen in the literature as favorable, providing its desfosforização. However, depending on the way the element phosphorus is present in the iron ore application structure becomes additional power required for its release. Thus this work, the acid leaching process with the aim of reducing the phosphorus content in iron ore as well as the application of heating the particles of iron ore by using microwave energy. By using Termocalc® software to parse the different structures formed having different levels of phosphorus element. By scanning electron microscopy technique (SEM) was possible to observe the structure of the iron ore particles after treatment with microwave energy. Through the use of statistical design factor with central and axial points was possible to determine the optimal conditions used in the acid leaching process, the following values are found: 19.25g mass ore, leaching time 20min, leaching temperature of 65°C, agitation speed of 620rpm, average grain size of 28mm size, having a 3‐minute contact time with the microwave energy. Under these conditions the reduction of phosphorus content in iron ore sample reached a value of 52.47% was possible to demonstrate the positive effect of the sample heating process of iron ore and may therefore be regarded as increasing the acid leaching technique to reduction of the phosphorus content.