Nitric Acid Leaching Research Articles

Sustainable recycling of iron concentrate obtained from the processing of iron-silicate uranium ore

In the processing of iron silicate ore by blast-furnace smelting for uranium extraction, the problem of safe reuse of iron concentrate arises. That concentrate contains up to 65% of iron and therefore can be used as raw material for ferrous metallurgy. This provides significant resource savings compared to other industrial uranium ore processing technologies. However, the increased content of radioactive elements (U, Ra, Po) in this concentrate requires the development of methods for separating these elements before smelting. In this regard, we studied the distribution of radioactive elements (U, 228Ra, 210Po, and 210Pb) in ordinary ore of the Pershotravneve deposit (Ukraine) and other products (agglomerates, slag, dust, iron concentrate). Data on nitric acid leaching of ore under various conditions showed a possibility of reducing the radioactivity of slag for up to 84% calculated for 210Po and 210Pb. Results indicate a significant release of 210Po and 210Pb into the gaseous phase during agglomeration, which requires the implementation of an additional off-gases cleaning system. Nevertheless, the results show that mixing the iron concentrate with ordinary ore (in an amount of ≤3 wt%) leads to an insignificant increase in the overall activity during agglomeration (no more than 4–10% for 210Po and 210Pb altogether). Thus, such slags can be safely used as a building material.

Extraction of Lanthanum Oxide from Different Spent Fluid Catalytic Cracking Catalysts by Nitric Acid Leaching and Cyanex 923 Solvent Extraction Methods

A laboratory-scale procedure was developed to obtain lanthanum oxide from spent fluid catalytic cracking catalyst, commonly used in the heavy crude oil cracking process. Two different solids, consisting mainly of silica, alumina, and a certain amount of rare earth elements, were leached under several conditions to recover the rare earths. Nitric acid leaching lead to the highest recovery of lanthanum, reaching a recovery percentage greater than 95% when a 1.5 M concentration was used. Subsequently, liquid phases were subjected to a liquid–liquid extraction process using Cyanex 923 diluted in Solvesso 100, and the lanthanum was quantitatively extracted. Lanthanum was also quantitatively stripped using oxalic acid to obtain the corresponding lanthanum oxalates, as revealed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared (FTIR) techniques. After thermal treatment at 1200 °C for 2 h, these solids yielded lanthanum oxide.

Nitric Acid Dissolution of Tennantite, Chalcopyrite and Sphalerite in the Presence of Fe (III) Ions and FeS2.

This paper describes the nitric acid dissolution process of natural minerals such as tennantite, chalcopyrite and sphalerite, with the addition of Fe (III) ions and FeS2. These minerals are typical for the ores of the Ural deposits. The effect of temperature, nitric acid concentration, time, additions of Fe (III) ions and FeS2 was studied. The highest dissolution degree of sulfide minerals (more than 90%) was observed at a nitric acid concentration of 6 mol/dm3, an experiment time of 60 min, a temperature of 80 °C, a concentration of Fe (III) ions of 16.5 g/dm3, and an addition of FeS2 to the total mass minerals at 1.2:1 ratio. The most significant factors in the break-down of minerals were the nitric acid concentration, the concentration of Fe (III) ions and the amount of FeS2. Simultaneous addition of Fe (III) ions and FeS2 had the greatest effect on the leaching process. It was also established that FeS2 can be an alternative catalytic surface for copper sulfide minerals during nitric acid leaching. This helps to reduce the influence of the passivation layer of elemental sulfur due to the galvanic linkage formed between the minerals, which was confirmed by SEM-EDX.

Development of Kinetic Parameters for Nitric Acid Leaching of Phlogopite and the Characterization of Solid Products

AbstractSouth Africa is a net importer of fertilizer products, importing all of its potassium, as well as 60–70% of its nitrogen requirements. Thus, domestic prices are impacted significantly by international prices, shipping costs, and exchange rates. Producing these fertilizers locally would be far more economical. Phlogopite, a rich source of potassium, is discarded in large quantities during mining operations; the objective of the present study, therefore, was to determine the acid-leaching characteristics and behavior of phlogopite as a means of releasing potassium. Phlogopite samples were leached with nitric acid (source of nitrogen for fertilizers) at various concentrations, temperatures, and reaction times. The feed phlogopite and leached residue samples corresponding to conversions of 14% (LP1), 44% (LP2), and 100% (LP3) were collected and analyzed using X-ray fluorescence spectroscopy (XRF), X-ray diffractometry (XRD), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Brunauer–Emmett–Teller surface area and porosity analysis (BET), thermogravimetric analysis (TGA), and field emission gun-scanning electron microscopy (FEG-SEM). The feed phlogopite was highly crystalline. The absence of defects in the lattice meant that the motion of H+ atoms penetrating into the lattice was restricted, suggesting internal diffusion-controlled leaching. Furthermore, results obtained from the various analytical techniques corroborated each other in terms of the release of cations during leaching. All leaching experiments were conducted batchwise, in a closed system. The gravimetric data from the experiments were used to identify a suitable model which predicts accurately the leaching behavior. The reaction was found to be internal diffusion-controlled, and the D1 model, which represents one-dimensional diffusion through a flat plate, predicts the leaching behavior most accurately. The observed activation energies (Ea) and pre-exponential constants (k0) varied with initial nitric acid concentration ([H+]0).

A Study on Optimization of Nitric Acid Leaching and Roasting Process for Selective Lithium Leaching of Spent Batreries Cell Powder

A Study on Optimization of Nitric Acid Leaching and Roasting Process for Selective Lithium Leaching of Spent Batreries Cell Powder

Recovery of tungsten trioxide from waste diamond core drilling crowns by nitric acid leaching

A cost-effective and simple hydrometallurgy procedure for recycling the diamond core drilling crowns by nitric acid leaching, followed by the sodium hydroxide leaching, has been developed. The effect of temperature, nitric acid/sodium hydroxide concentration, leaching time and stirring rate were studied. For the acid leaching process the optimal values for parameters were 60 °C, 1.0 M HNO3, 2.5 h, and 800 rpm. It has been noted that the key factors in the alkaline leaching process were temperature and NaOH concentration. For the alkaline leaching, the optimal parameters were 100 °C, 40% concentration of NaOH solution, and leaching time of 4 h. Identification and characterisation of products in all technological processes were performed by X-Ray Diffraction (XRD), scanning electron microscope using energy-dispersive X-ray spectroscopy (SEM-EDS), and laser desorption ionisation mass spectrometry (LDI-MS). The analysis of solutions in all phases was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The use of LDI-MS as a new approach to identify the products after phases in the recycling process was an important part of the study, and the results were consistent with the XRD analysis. The total tungsten recovery was over 95.6%, with a high purity of the obtained tungsten trioxide.

Intensification of tellurium separation through the multistage bulk liquid membrane technique from nitric acid leaching liquor of Copper anode slime

Intensification of tellurium separation through the multistage bulk liquid membrane technique from nitric acid leaching liquor of Copper anode slime

Intensification and optimisation of nickel recovery from spent hydrogenation catalysts via ultrasound-augmented hydrometallurgy

Spent catalysts generated from various processing industries such as those involved in the hydrogenation of fats and oils pose severe environmental issues if not treated and disposed of aptly. In this present work, process intensification was provided by the means of ultrasonic irradiation via an ultrasonic bath to ascertain the positive effects it imparts on the nitric acid and sulphuric acid leaching of spent silica-supported nickel hydrogenation catalysts. The extent of nickel recovered from ultrasound-assisted leaching was compared to that of the conventional mechanical stirring technique, whereby the actual ultrasonic densities of the ultrasound source were determined. Ultrasonic irradiation appreciably enhanced the extraction of nickel from the spent catalyst in all instances due to the physical and chemical effects of acoustic cavitation. In particular, sonication resulted in the expedited extraction of Ni, allowing a time reduction of 2 h in recovering ca. 70% Ni. Furthermore, it was also discovered that nitric acid was a more efficient leaching agent than sulphuric acid, achieving an improvement of ca. 20% in recovering Ni at 70 °C under ultrasonic conditions. Additionally, process optimisation was executed by adopting the response surface methodology, in which the modelled optimal conditions were ultrasonic bath amplitude = 67%, leaching temperature = 60 °C, nitric acid concentration 12.5 vol% and pulp density = 7.5%. Ultimately, the Ni recovery recorded under the optimal conditions was 99.37% in 2 h. Finally, an approximate economic analysis was performed to ascertain the recovery costs of nickel using the ultrasonic method. This study demonstrated the beneficial usage of ultrasound technology in the process intensification of hydrometallurgy, which could be employed on an industrial scale for higher recovery efficiencies and improved sustainability.

Deposition of Arsenic from Nitric Acid Leaching Solutions of Gold–Arsenic Sulphide Concentrates

At present, the processing of refractory gold–arsenic sulphide concentrates is becoming more relevant due to the depletion of rich crude ore reserves. In the process of the nitric acid leaching of arsenic sulphide minerals, solutions are formed containing 20–30 g/L of arsenic (III). Since market demand for arsenic compounds is limited, such solutions are traditionally converted into poorly soluble compounds. This paper describes the investigation of precipitating arsenic sulphide from nitric acid leaching solutions of refractory sulphide raw materials of nonferrous metals containing iron (III) ions using sodium hydrosulphide with a molar ratio of NaHS/As = 2.4–2.6, which is typical for pure model solutions without oxidants. The work studied the effect of temperature, the pH of the solution and the consumption of NaHS and seed crystal on this process. The highest degree of precipitation of arsenic (III) sulphide (95–99%) from nitric acid leaching solutions containing iron (III) ions without seed occurs with a pH from 1.8 to 2.0 and a NaHS/As molar ratio of 2.8. The introduction of seed crystal significantly improves the precipitation of arsenic (III) sulphide. An increase in seed crystal consumption from 0 to 34 g/L in solution promotes an increase in the degree of transition of arsenic to sediment from 36.2 to 98.1% at pH = 1. According to SEM/EDS and XRF sediment data, from the results of experiments on the effect of As2S3 seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulphide and the Fetotal/Fe2+ ratio in the final solution, it can be concluded that the addition of a seed accelerates the crystallisation of arsenic (III) sulphide by increasing the number of crystallisation centres; as a result, the deposition rate of As2S3 becomes higher. Since the oxidation rate of sulphide ions to elemental sulphur by iron (III) ions does not change significantly, the molar ratio of NaHS/As can be reduced to 2.25 to obtain a precipitate having a lower amount of elemental sulphur and a high arsenic content similar to that precipitated from pure model solutions.

Behaviour of lead and selenium during sequential sodium carbonate and nitric acid leaching of slime generated by the sulphuric acid plant of the Balkhash copper smelter

This paper examines the process of selenium precipitation from the slime generated by the sulphuric acid plant of the Balkhash Copper Smelter. Contrary to similar tailings generated by non-ferrous metals industry, such slime has a high concentration of selenium (12.5–4.6 wt. %). By utilizing it in the production process, one can raise the output of selenium by more than 30% compared with the amount of selenium recovered by the smelter from copper anode slimes. The slime that was used in the experiments had been separated from the slurry produced as a result of scrubbing of metallurgical gases generated by copper smelting and matte converting processes. The slime was rinsed with water to remove sulphuric acid from it and then dried at 105 oC. With the help of new-generation analytical equipment, the slime was analyzed for qualitative, quantitative and material compositions. 15 elements with significantly varying concentrations were detected. The main components include lead (51.17 wt. %) and selenium (12.49 wt. %), which are present in the form of lead sulphates and elemental selenium. Other lead and mercury compounds are also present as disseminations – i.e. different salts of selenium acids. Considering the forms in which lead and selenium are mainly found in the slime, lead was initially converted into carbonates by sodium carbonate leaching, and then nitric acid was used to make lead transfer from the cake into the solution. The authors looked at the effect produced by the sodium carbonate concentration (50–200 g/dm3), solid-to-liquid ratio (1:(2–6)), process duration (20–120 min) and temperature (20–70 oC) at constant slime feed and stirrer RPM on the behaviour of lead and selenium. Optimum conditions were identified in which both elements almost completely remain in the carbonate cake, and only 0.019% Pb and 0.17% Se get extracted into the solution. Different quantities of three carbonate-containing compounds of lead and seven selenium compounds were found in the cake. When the carbonate cake is leached with nitric acid, almost all of the lead transfer to the solution, while selenium remains in the cake as an elementary substance and mercury selenides. As compared with the slime, the concentration of selenium in the cake increased by 5.6 times. This research was funded by the Science Board of the Ministry of Science and Education of the Republic of Kazakhstan under the following programme: Development and Implementation of Innovative Technology Ensuring a Higher Recovery of Non-Ferrous, Noble, Rare and Rare Earth Metals, as well as Fulfillment of Production Targets by Industrial Companies of the Republic of Kazakhstan Set for 2018–2020.

IMPROVEMENT OF THE TECHNO¬LOGY FOR OBTAINING MANGANESE(IV) OXIDE FROM SECONDARY RAW MATERIALS

Today's level of integrated use of minerals and beneficiation wastes in Ukraine, in particular, at the Kryvbas GOK, is unsatisfactory, as it is generally allowing the production of additional types of construction products. The volume of mining is growing, but only a small percentage of the extracted volume is transferred to the finished product. The residue in the form of waste is returned to the environment, polluting it. The reason for this is the lack of technology for integrated mineral processing and waste disposal.
 The article presents the results of industrial tests of off-balance manganese ore processing technology of Ordzhonikidze GOK with a manganese content of 15–30%. It is shown that nitric acid leaching of manganese with subsequent precipitation of impurities with soda or alkali allows you to consistently purify manganese from transition and alkaline earth metals. The obtained manganese oxide has a high degree of purity, which allows obtaining pure compounds Mn (NO3)2∙6H2O, MnO2 and metallic manganese for chemical current sources. The use of columnar clarifiers with a fluidized bed with the application of pulsations allowed to eliminate time-consuming filtration processes. Concomitantly formed sodium nitrate serves as a raw material for mineral fertilizers. Experimental studies on the beneficiation of off-balance manganese ores allowed us to determine the main technological parameters of the extraction of components and to develop a technological scheme of beneficiation.
 According to the proposed technological scheme, it is possible to obtain high-quality concentrates of manganese (IV) oxide. The use of optimal technological parameters of enrichment allows up to 95% of Mn to be extracted from off-balance manganese raw materials. In the long run, this will reduce dependence on imports of manganese raw materials and significantly reduce the cost of domestic manganese products.

Thermodynamics of Copper Arsenious Raw Materials Dissolution in Nitric Acid

This article describes thermodynamic study of hydrometallurgical method for processing of copper arsenious gold-containing raw material. Chemical and phase composition of the material were researched. Calculations of the Gibbs energy change were conducted for possible reactions of the main minerals, present in the raw material, with nitric acid. Eh-pH diagrams and solid/liquid equilibrium distribution diagrams, which were constructed in order to confirm the possibility of obtaining the required reaction products through nitric acid leaching of the studied raw material.

Recovery of niobium during comprehensive processing of pyrochlore-monazite-goethite ores

This paper looks at the pyrochlore-monazite-goethite ores of the Chuktukonsk deposit (0.98wt.% Nb2O5) and their processing with the help of acidbased (HNO3, H2SO4) and sulphatization techniques. Nitric-acid pressure leaching was found to be an efficient processing technique for this type of ore: ore size –0.074 mm; CHNO3 = 25%; CH2O2 = 5%; τ = 2 h; solid-to-liquid = 1:9; heat treatment mode: 1 h at 160 oC followed by 1 h at 230 oC. As a result, rare earth metals and manganese are leached to the solution while all of the contained niobium remains in the cake. Two different techniques were tested to recover niobium from the cake. One is based on the use of alkali (NaOH sintering), the other is an extractive leaching technique that combines acid leaching with liquid-liquid extraction of tributyl phosphate in one stage. It was established that niobium mi nerals can be efficiently decomposed when using a mixture of hydro fluoric and sulphuric acids with the concentrations of 4.08 and 8.46 mol/L, correspon dingly, as a leaching agent. At the weight ratio of 1:2:1 of the solid to aqueous to organic phase and after the slurry has been stirred intensively for 5 minutes, niobium fluorides, which form as a result of interaction between hydrofluoric acid and the cake components, can be recovered with a 50% solution of tributyl phosphate in octane. After that they transfer to an organic phase while impurities get accumulated in the solid residue. As niobium-containing cake has a high concentration of silicon, it is recommended to first remove silicon from the cake using a strong alkaline solution.

Recovery of valuable materials from phosphorus slag using nitric acid leaching followed by precipitation method

PS, the principal waste of phosphorus production, comprises some elements such as Si, Ca, Fe, Al, rare earth metals (REMs), etc. Due to the high annual production volumes of PS, it is discarded in disposal areas, leading to severe environmental pollution and ecosystem damage. Therefore, the most important objective of this work was to present a recovery process for valuable materials including ∑REMs2O3, SiO2, and Ca(NO3)2. These materials have a critical role in various industries. In the present study, they were recovered by the leaching process with 8 M nitric acid, the S-to-L phase ratio of 1:3, the contact time of 120 min, and the temperature of 75 °C. Afterward, precipitation with oxalic acid and pH adjustment by ammonia were performed. The elemental analysis as well as the structural, morphological, and molecular properties of PS and the extracted products were characterized using ICP-MS, XRD, FESEM, EDS, FT-IR, SAXS, and nitrogen adsorption-desorption measurement. The results indicated that the recovery efficiencies of ∑REMs2O3, SiO2, and Ca(NO3)2 from PS were 88.14%, 97.64%, and 92.37%, respectively. Moreover, the purities of ∑REMs2O3, SiO2, and Ca(NO3)2 were 99.04%, 99.16%, and 99.03%, respectively.

Trapping nitrous gases during nitric acid leaching of sulfide concentrates

Gas-air mixtures that form in nitric acid leaching of sulfide raw materials possess the following peculiarities making a negative impact on trapping of nitrogen oxides: elevated temperature, different oxidation level of nitrogen oxides, slow oxidation of NO in region of low concentrations, and instability of the resulting gas-air mixture flow. Therefore, well-known methods of trapping nitrous gases shall be adapted to specific sulfide raw material. We propose a process flow diagram for trapping nitrous gases formed during nitric acid leaching of sulfide concentrates at atmospheric pressure on the example of Zhezkazgan concentrate. The paper addresses theoretical aspects of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases, and typical reactions of interaction of the proposed absorbents with nitrogen oxides. The choice of water-ore pulp as an absorber was made because of similarity between the mechanism of absorption of nitrogen oxides for neutral and alkali ore suspensions and the one for alkali solutions: nitrogen dioxide and nitrous anhydride are absorbed with formation of a solution of nitrates and nitrites. Due to availability in a liquid phase of ferrous iron along with NO2 and N2O3, acidic suspensions are also capable to absorb nitric oxide, to some extent, with formation of Fe(NO)SО4 complex. Process water absorbs only nitrogen dioxide, with formation of nitric and nitrous acids. Nitrous acid is an unstable compound in acidic environments and decomposes with formation of water and nitrogen oxide. At the stages of trapping nitrogen oxides with water-ore pulp and process water (circulating solution), it is recommended conditioning of gas-air mixtures by choosing the volume of additionally introduced air, in an amount to provide the highest rate of nitrogen oxide oxidation. At the stages of sulfuric acid and alkaline trapping of nitrogen oxides, it is recommended conditioning of gas-air mixtures by selecting the volume of additionally introduced air and the oxidation time of nitrogen oxide that provide an equimolecular mixture of NO and NO2. A distinctive feature of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases is possibility to use the products of absorption at the stage of sulfide concentrate leaching. The extended tests of trapping nitrous gases have been conducted. The plant capacity by the gas-air mixture ranged 17–21 m3/h, and by leached concentrate — 12–15 kg/h. In this case, the degree of capturing nitrous gases reached 96.8%. Return of the products of absorption of nitrous gases in the form of condensate, water-ore pulp, nitrosyl sulfuric acid, nitric acid solution, nitritenitrate lye allows to reduce the nitric acid consumption by 7–10 times relative the values obtained without using the trapping system. In this case, the degree of copper extraction into the leaching solution was 97.7%. The extraction degree of silver, rhenium, zinc was respectively 98.0%, 99.0%; 98.5%.

Extraction of Metals from Scrap Marble Cutting Segments in Nitric Acid Solutions

Extraction of cobalt, copper, and silver from scrap saw-blade segments using nitric acid solutions (0.1–0.4 M, 20–60°C) were investigated using response surface methodology. Extraction of cobalt and iron was more extensive than copper and silver, i.e., 35.7–96.2% Co and 72.6–100% Fe versus 8.50–35.4% Cu and 8.11–22.5% Ag. Statistical analysis of the experimental data has shown that increasing the acid concentration or temperature enhances the rate and extent of leaching of metals. Under suitable conditions, almost complete leaching of cobalt (99.9%), as well as high extractions of copper (95.9%) and silver (94.9%), were achieved. The activation energy, calculated to be 40.3 kJ/mol, indicates that nitric acid leaching of these metals occurs as a chemically controlled reaction. These findings have demonstrated that nitric acid as an effective oxidant/leaching agent could be suitably used for the extraction of cobalt, copper, and silver from scrap segments.

An efficient and environmentally friendly route for PbS crystal recovery from lead ash generated in tin removal section (LATR) via high-speed leaching and recrystallization method

This paper mainly investigated the synthesis of a high purity PbS crystal directly from lead ash which was collected from Tin ash removal process (LATR). The LATR was firstly disposed by nitric acid leaching system to generate the lead nitrate solution. The PbS crystal was prepared by mixing the lead nitrate solution with the sodium sulfide at the room temperature (25?C). The effects of molar ratio of HNO3 to Pbin the LATR on Pb leaching efficiency was investigated, demonstrating that the Pb leaching efficiency could attain to 82.9 % at molar ratio of 3. The leaching ratio of As, Cu, Fe, and Al generally increased with increasing molar ratio of HNO3 to Pbin the LATR, while 99.99 wt% of Sn was still left in the residue. In the process of generating PbS crystal from the leaching solution, the yield of PbS crystal increased with increasing molar ratio of Na2S to Pbin the filtrate. The yield of PbS crystal could up to 93.1% at a molar ratio of 1.5. Overall, this method proved to be an efficient and environmental friendly route for synthesis of high quality PbS crystal directly from the common lead containing waste from the lead ore or secondary smelting factory.

Comprehensive Processing of Fine Metallurgical Dust

The processing of fine metallurgical dust by pyrometallurgical methods leads to the accumulation of impurities and deterioration in the quality of blister copper. Fine dust contains copper, zinc, lead, arsenic and iron. A hydrometallurgical method for the separation of the main components into the following products is proposed: copper-zinc residue, iron-arsenic residue, lead residue. The hydrometallurgical scheme consists of three stages of leaching: neutral and using sulfuric and nitric acids. When processing metallurgical dust according to the proposed scheme, a solution containing copper, zinc, iron and arsenic is formed, as well as a lead containing precipitate. Arsenic and iron are removed from the solution in the form of iron (III) arsenate, after which zinc and copper are precipitated. Lead in sediment is in carbonated form. The developed technology allows the extraction of: 87% copper, 88% zinc, 83% iron, 83% arsenic, 99% lead in individual products.
 Keywords: metallurgical dust, arsenic removal, nitric acid leaching

Kinetics and mechanism of arsenopyrite leaching in nitric acid solutions in the presence of pyrite and Fe(III) ions

The main sulphide minerals that serve as gold carriers in low-grade raw materials are pyrite and arsenopyrite. Traditional methods of processing such refractory raw materials rely on high-pressure or pyrometallurgical oxidisation, which destroys the crystal lattice of sulphides and releases gold particles. An alternative method of oxidation is leaching with nitric acid. The study examined the kinetics and oxidation mechanism of the natural mineral arsenopyrite in nitric acid media, along with the effect of pyrite on the kinetic characteristics of dissolution. Using the shrinking core model (SCM), it was shown that during the first 5 min of the process, the kinetic of the reaction is controlled by the chemical reaction. Further in the course of the process, the mode changes, which is confirmed by the new shrinking core model. During the period from 5 to 60 min the model was fitted according to diffusion through a product layer and interfacial transfer. The addition of Fe(III) ions and an increase in the concentration of nitric acid have a similar effect on the nitric acid leaching of arsenopyrite, which is associated with an increase in the oxidation potential of the system. The influence of pyrite on the leaching of arsenopyrite is probably associated with its catalytic action in the early stage of the process, which is due to the role of an alternative surface for the reduction of nitrate ions in electrochemical contact with arsenopyrite. The difference in the mechanisms of arsenopyrite oxidation in the presence of Fe(III) ions and pyrite was confirmed by the SEM-EDX analysis.

Optimization of Nitric Acid Leaching of Rare Earth Elements From Moroccan Natural Phosphate

Phosphate is a very important natural resource in Morocco and one of the secondary resources of rare earth elements. Our study is particularly interested in Youssoufia phosphate, which contains 228.77 ppm of rare earth elements (ΣREEs). The purpose of our work is to study the influence of different parameters (acid concentration, solid/liquid ratio and temperature) in order to determine the optimal conditions for the leaching of rare earths. An experimental design (Doehlert matrix) has been drawn up to optimize the experimental conditions of the leaching. All tests were made with nitric acid at different concentrations varying between 1.5M and 4.5M with a solid/liquid ratio of 1/12 to 1/6; reaction temperature and duration are respectively 20°C to 80 °C and 60 min. The optimal conditions are obtained when using 69 °C as temperature, 4.1 M as acid concentration and 1/9 as solid/liquid ratio.