The Development of Innovated Complex Process for Treatment of Old Flotation Tailings of Copper-Zinc Sulfide Ore

The possibility of selective Cu and Zn leaching from the sample of old pyrite tailings, which is one of the most widespread types of solid waste forming during non-ferrous metal production, using sulfuric acid solutions and water was studied. It was shown that water leaching provided selective extraction of Cu and Zn and comparatively low iron ion extraction. At the same time, acid leaching provided the obtainment of pregnant solutions with high ferric ion concentration, which can be used for oxidative leaching of substandard copper concentrates. Water and acid leaching also provided increased Au recovery by cyanidation. The results suggest that acid leaching can be an effective approach for processing old flotation tailings, which allows the extraction of base metals from these wastes and treating flotation tailings for subsequent cyanidation. Effective flotation treatment methods should also provide environmental load reduction, which is caused by the long-term storage of metal-bearing wastes.

Kinetics and Optimization of Metal Leaching from Heat-Resistant Nickel Alloy Solid Wastes

Recycling waste from the production and consumption of heat-resistant alloys to return them to production is an urgent task due to the high cost of the components contained in these alloys. The kinetics and conditions of the acid leaching process of the grinding waste of a heat-resistant nickel alloy are studied depending on the composition of the acid solution (H₂SO₄, HCl, HNO₃, and their mixtures) at room temperature to boiling point temperature and various acid concentrations (1.5 to 3.0 mol/L), ratios of waste to solution (1:10 to 3:10), fraction sizes (0.04-1 mm), and contact duration (1 to 120 h). The linearization of experimental data by the Gray-Weddington, Gistling-Brownstein, and Kazeev-Erofeev equations showed that the rate of the leaching process was influenced by both the chemical reactions between sulfuric acid and metals included in the grinding waste and the diffusion of reagents through the film of reaction products and undissolved impurities. Optimal conditions for acid dissolution of the grinding waste have been established to obtain the maximum degree of extraction of the main component of the alloy, nickel. The processing of powder particles with a size of less than 0.1 mm should be carried out in a solution of sulfuric acid with a concentration of 3.0 mol/L at a temperature of 100 °C for 6 h with a ratio of solid to liquid phases of 1:10. The reported results are very important for industry personnel to recover metals and for environmentalists to treat the alloy waste.

Carbonate Coprecipitation for Cd and Zn Treatment and Evaluation of Heavy Metal Stability Under Acidic Conditions

Mining wastes or combustion ash are materials of high carbon sequestration potential but are also known for their toxicity in terms of heavy metal content. To utilize such waste materials for engineered carbon mineralization purposes, there is a need to investigate the fate and mobility of toxic metals. This is a study of the coprecipitation of metals with calcium carbonate for environmental heavy metal mitigation. The study also examines the stability of precipitated phases under environmentally relevant acid conditions. For a wide range of cadmium (Cd) and zinc (Zn) concentrations (10 to 5000 mg/L), induced coprecipitation led to greater than 99% uptake from water. The calcium carbonate phases were found to contain amounts as high as 9.9 wt % (Cd) and 17 wt % (Zn), as determined by novel synchrotron techniques, including X-ray fluorescence element mapping and three-dimensional (3D) nanotransmission X-ray microscopy (TXM). TXM imaging revealed first-of-a-kind observations of chemical gradients and internal nanoporosity within particles. These observations provided new insights into the mechanisms leading to the retention of coprecipitated heavy metals during the dissolution of calcite in acidic (pH 4) solutions. These observations highlight the feasibility of utilizing carbonate coprecipitation as an engineered approach to the durable sequestration of toxic metals.

Acid Leaching Extraction Mechanism of Aluminum and Iron Ions from Coal Gangue Based on CaF2 Assistance and Process Optimization

To reveal how CaF₂ improves the dissolution ratios of aluminum and iron ions in coal gangue, CaF₂ and hydrochloric acid are used to extract Al³⁺ and Fe³⁺ from the coal gangue calcined powder. The leaching ratios of Al³⁺ and Fe³⁺ are measured, and the filter residues are analyzed by BET, XRD, and SEM. The results show that adding 3% CaF₂ could increase the extraction ratio of Al³⁺ from 62.96% to 92.10% under optimized conditions, and that of Fe³⁺ is increased from 85.12% to 95.73%. The mechanism of CaF₂ as an auxiliary to improve the leaching ratio of Fe³⁺ is that HF reacts with the thin layers of gangue calcined powder containing silica to form soluble SiF₄, thus forming pores that promote the diffusion of H⁺ and inner ions, improving the leaching ratios of Al³⁺ and Fe³⁺. Finally, the CaF_2-assisted acid leaching process is optimized. The results showed that it is efficient and feasible to extract Al³⁺ and Fe³⁺ with the assistance of CaF₂ and that HF has a catalytic effect in the reaction system. This work provides a reference for the next step of actual production.

Rare-Earth Elements Extraction from Low-Alkali Desilicated Coal Fly Ash by (NH4)2SO4 + H2SO4

Coal fly ash (CFA) obtained from pulverized coal furnaces is a highly refractory waste that can be used for alumina and rare-earth elements (REEs) extraction. The REEs in this type of CFA are associated with a mullite and amorphous glassy mass that forms a core-shell structure. In this research, it was shown that complete dissolution of amorphous aluminosilicates from the mullite surface with the formation of the low-alkali mullite concentrate prior to sulfuric acid leaching with the addition of (NH₄)₂SO₄ helps to accelerate the extraction of REEs. The extraction degree of Sc and other REEs reaches 70-80% after 5 h of leaching at 110 °C and acid concentration of 5 M versus less than 20% for the raw CFA at the same conditions. To study the leaching kinetics of the process, the effects of temperature (90-110 °C), liquid-to-solid ratio (5-10), and leaching time (15-120 min) on the degrees of Al and rare-earth elements (REEs) extraction were evaluated. After 120 min of leaching at 110 °C and L/S ratio = 10, the extraction of Al was found to be lower than 30%. At the same time, total REEs (TREE) and Fe extraction were greater than 60%, which indicates that a part of the TREE was transferred into the acid soluble phase. After leaching, the residues were studied by laser diffraction (LD), X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM-EDS) to evaluate the leaching mechanism and the solubility of Al- and Fe-containing minerals, such as mullite, hematite, and amorphous aluminosilicate.

A Novel Technique for the Preparation of Iron Carbide and Carbon Concentrate from Blast Furnace Dust

Blast furnace (BF) dust is a typical refractory iron resource. A novel technology-based utilization of BF dust as iron carbide and carbon concentrate by applying carburization roasting followed by magnetic separation and acid leaching is proposed. Under optimized conditions, an electric arc furnace (EAF) burden assaying 80.79% Fe and 7.63% C with a corresponding iron recovery rate of 87.26% and a carbon concentrate assaying 67.06% C with a corresponding carbon recovery rate of 81.23% were prepared. Furthermore, the carburization behavior and separation mechanism were revealed using X-ray powder diffraction, scanning electron microscopy, and optical microscopy. The results show that the separation efficiency of iron carbide, gangue, and carbon is very low. Na₂SO₄ is a highly effective additive to strengthen the separation efficiency as it can enhance the carburization index, enlarge the iron carbide particle size, improve the embed embedded relationship of iron carbide and gangue, and promote the gangue leaching efficiency. The study demonstrates that preparation of iron carbide and carbon concentrate from BF dust using the proposed technology is a feasible method.

Using One-Step Acid Leaching for the Recovering of Coal Gasification Fine Slag as Functional Adsorbents: Preparation and Performance

Coal gasification fine slag (FS), a kind of by-product of coal chemical industry, was recovered for the preparation of functional adsorbents by acid leaching process, which was orthogonally optimized by HCl, HNO₃, HF, HAc, and H₂SO₄. Methylene blue (MB) was used to evaluate the performance of functional adsorbents. The results demonstrated that 57.6% of the leaching efficiency (R_LE) and 162.94 mg/g of adsorption capacity (C_AC) of MB were achieved under the optimal conditions of HNO₃ of 2.0 mol/L, acid leaching time of 2.0 h, and acid leaching temperature of 293K. The detections on X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and BET surface area (SBET) indicated that the synthesized functional adsorbents were characterized by mesoporous materials. The good fitting of adsorption process using pseudo-second-order and Langmuir models demonstrated that the chemisorption contributed to MB removal. The results of thermodynamics further revealed that the adsorption process of MB occurred spontaneously due to the exothermic properties. The work is expected to develop a novel and cost-effective strategy for the safe disposal of FS, and potentially offer an alternative pathway to increase the additional value for the coal chemical industry.

Treatment of high-concentration phosphorus wastewater based on foamed concrete

Phosphorus is a nonrenewable resource, and the recovery of phosphorus from wastewater containing high concentrations of phosphorus is of great importance. In this work, a novel method for highly efficient treatment of high-concentration phosphorus-containing wastewater (50 mg/L, 100 mg/L and 150 mg/L) with low energy consumption was developed by using the block waste foam concrete (FC) as a potential phosphorus recovery material. The results showed that acid leaching significantly improved the accumulation efficiency of phosphorus in calcium hydroxyphosphate (HAP) via accelerating the release of calcium in wastewater. The recovery rate of phosphorus could reach 99.0% under the pH value of 9.0 at 25 °C, using 2.0 g FC. It was also found that the microporous structure of the surface of FC provided the adsorption sites for phosphorus, resulting in the adsorption rate in different concentrations of phosphorus-containing wastewater up to 14.5%. It indicated that FC achieved the recovery of phosphorus from high-concentration phosphorus-containing wastewater by coupling HAP crystallization and physical adsorption to polyphosphorus.

An Eco-Friendly Acid Leaching Strategy for Dealkalization of Red Mud by Controlling Phase Transformation

The alkaline components in red mud represent one of the crucial factors restricting its application, especially for the construction and building industry. The phase state of alkaline components has a significant influence on the dealkalization of red mud. In this work, an environmentally friendly acid leaching strategy is proposed by controlling the phase transformation of red mud during active roasting pretreatment. With a moderate roasting temperature, the alkaline component is prevented from converting into insoluble phases. After acid leaching with a low concentration of 0.1 M, a high dealkalization rate of 92.8% is obtained. Besides, the leachate is neutral (pH = 7) and the valuable metals in red mud are well preserved, manifesting a high selectivity and efficiency of diluted acid leaching. The calcination experiment further confirms the practicability of the strategy in the construction field, where the cementitious minerals can be formed in large quantities. Compared with the traditional acid leaching routes, the diluted acid leaching strategy in this work is acid saving with low valuable element consumption. Meanwhile, the secondary pollution issue can be alleviated. Hence, the findings in this work provide a feasible approach for the separation and recovery of alkali and resource utilization of red mud.

Selective Scandium (Sc) Extraction from Bauxite Residue (Red Mud) Obtained by Alkali Fusion-Leaching Method

Bauxite residue, known as “red mud,” is a potential raw material for extracting rare-earth elements (REEs). The main REEs (Sc, Y, La, Ce, Nd, Nb, and Sm) from the raw bauxite are concentrated in RM after the Bayer leaching process. The earlier worldwide studies were focused on the scandium (Sc) extraction from RM by concentrated acids to enhance the extraction degree. This leads to the dissolution of major oxides (Fe₂O₃ and Al₂O₃) from RM. This article studies the possibility of selective Sc extraction from alkali fusion red mud (RMF) by diluted nitric acid (HNO₃) leaching at pH ≥ 2 to prevent co-dissolution of Fe₂O₃. RMF samples were analyzed by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and inductively coupled plasma mass spectrometry (ICP-MS). It was revealed that Sc concentration in RMF can reach up to 140–150 mg kg⁻¹. Sc extraction was 71.2% at RMF leaching by HNO₃ at pH 2 and 80 °C during 90 min. The leaching solution contained 8 mg L⁻¹ Sc and a high amount of other REEs in the presence of relatively low concentrations of impurity elements such as Fe, Al, Ti, Ca, etc. The kinetic analysis of experimental data by the shrinking core model showed that Sc leaching process is limited by the interfacial diffusion and the diffusion through the product layer. The apparent activation energy (E_a) was 19.5 kJ/mol. The linear dependence of Sc extraction on magnesium (Mg) extraction was revealed. According to EPMA of RMF, Sc is associated with iron minerals rather than Mg. This allows us to conclude that Mg acts as a leaching agent for the extraction of Sc presented in the RMF in an ion-exchangeable phase.

A novel strategy for harmlessness and reduction of copper smelting slags by alkali disaggregation of fayalite (Fe2SiO4) coupling with acid leaching

Copper smelting slags are difficult to achieve harmlessness and reduction because of the presence of abundant of fayalite (Fe₂SiO₄). This work proposed a novel strategy for harmlessness and reduction of copper smelting slags by alkali disaggregation of Fe₂SiO₄ coupling with acid leaching. The disaggregation changed the Fe₂SiO₄ phase by NaOH and released the embedded harmful and valuable metals. The evaluation of disaggregation effect mainly depends on further acid treatment. Especially the total leaching efficiency of As, Zn, Fe, Cu and Pb was achieved 99.7%, 62.5%, 41.5%, 99.9% and 99.1% under diluted HNO₃-H₂O₂ system, respectively. Compared with the non-disaggregated control, the efficiency was accordingly increased by 73.3%, 71.1%, 18.6%, 72.2% and 22.4%. Meanwhile, the content of As, Cu and Pb in the slags decreased from 1165.5 mg/kg, 30085.9 mg/kg and 5008.8 mg/kg to as low as 5.2 mg/kg, 21.2 mg/kg and 15.6 mg/kg, respectively. Interestingly, the strategy brought out 48.1% of the weight reduction of the copper smelting slags. The favorable effect was mainly attributed to the broken of Fe-O-Si bond thereafter improving the acid leaching activation. Therefore, the proposed strategy could potentially be a new method to realize harmlessness and reduction of copper smelting slags.

Characterization of Modified Natural Minerals and Rocks for Possible Adsorption and Catalytic Use

This study focused on natural materials such as clinoptilolite (CLI), metakaolin (MK), marlstone (MRL) and phonolite (PH). Clinoptilolite is one of the most known and common natural minerals (zeolites) with a unique porous structure, metakaolin is calcined kaolin clay, marlstone is a sedimentary rock and phonolite is an igneous rock composed of alkali feldspar and other minerals. These natural materials are mainly used in the building industry (additions for concrete mixtures, production of paving, gravels) or for water purification, but the modification of their chemical, textural and mechanical properties makes these materials potentially usable in other industries, especially in the chemical industry. The modification of these natural materials and rocks was carried out by leaching using 0.1 M HCl (D1 samples) and then using 3 M HCl (D2 samples). This treatment could be an effective tool to modify the structure and composition of these materials. Properties of modified materials were determined by N₂ physisorption, Hg porosimetry, temperature programmed desorption of ammonia (NH₃-TPD), X-ray fluorescence (XRF), X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform (DRIFT) and CO₂ adsorption using thermogravimetric analysis (TGA). The results of N₂ physisorption measurements showed that that the largest increase of specific surface area was for clinoptilolite leached using 3M HCl. There was also a significant increase of the micropore volume in the D2 samples. The only exception was marlstone, where the volume of micropores was zero even in the leached sample. Clinoptilolite had the highest acidity and sorption capacity of CO₂. TGA showed that the amount of CO₂ adsorbed was not significantly related to the increase in specific surface area and the opening of micropores. Hg porosimetry showed that acid leaching using 0.1 M HCl and 3 M HCl resulted in a significant increase in the macropore volume in phonolite, and during leaching using 3M HCl there was an increase of the mesopore volume. From the better properties, cost-efficient and environmental points of view, the use of these materials could be an interesting solution for catalytic and sorption applications.

Optimisation of sulphuric acid leaching

Copper smelter flue dust is a residue, rich in zinc, originating from the pyrometallurgical process of copper, and constitutes a potential raw material for zinc production. In order to valorise this waste by hydrometallurgical processes, its leaching with sulphuric acid at constant pH is studied. Experimental conditions (temperature, pH, and pulp density) are optimised by design of experiments in order to maximise Zn and Cu extractions while minimising the leaching of Fe. The experimental results are fitted to a full-quadratic second-order equation model by applying multiple regression analysis for extractions of Zn, Cu, and Fe. In order to determine the optimum conditions, the response surfaces are overlaid and the intersection of the plot of the three responses identifies conditions of pH and pulp density that satisfy recoveries of Zn higher than 95%, recoveries of Cu around 70%, and Fe extractions lower than 35%. Under the best conditions, that is, pH = 2, 10% of pulp density, and at 25°C, a liquor rich in zinc and copper, and a lead concentrate are obtained.

Aluminum and iron leaching from power plant coal fly ash for preparation of polymeric aluminum ferric chloride

In this work, aluminum and iron existing in coal fly ash were extracted by the method of hydrochloric acid leaching. Effects of solid-liquid ratio, reaction temperature, reaction time, acid concentration, and raw ash mesh on recovery efficiencies of Al₂O₃ and Fe₂O₃ were investigated. X-ray diffraction analysis indicated that anhydrite, hematite, mullite and quartz were the dominant minerals in the raw fly ash sample. X-ray fluorescence technique was applied to determine the mass fractions of chemical components in the raw ash and leached residues, while the concentrations of Al₂O₃ and Fe₂O₃ in leaching solutions were measured by titration method. The optimal recovery efficiencies of Al₂O₃ and Fe₂O₃, obtained under the reaction condition of 95°C, 5 h, acid concentration of 20 wt.%, a solid-liquid ratio of 1:3.5 and raw ash mesh of 400, were 42.75% and 35.10%, respectively. After removing the leached residues, the leaching solutions were employed to manufacture flocculants of polymeric aluminum ferric chloride for treating the oil recovery wastewater from polymer flooding, which possessed high contents of suspended solids (SS) and oils. Microfiltration membrane and ultraviolet spectrophotometer were utilized to determine the contents of SS and oils in water samples. Through adjusting Al/Fe molar ratio to 20:1 and basicity to 70%, the maximum removing efficiencies of SS and oils can be achieved, respectively 96.1% and 91.5%. Moreover, increasing the iron content and basicity of flocculants within certain ranges contributed to improving the settling characteristic of flocs.

Spherical Murray-Type Assembly of Co-N-C Nanoparticles as a High-Performance Trifunctional Electrocatalyst

Future renewable energy conversion requires advanced electrocatalysis technologies for hydrogen production, fuel cells, and metal-air batteries. Highly efficient trifunctional nonprecious electrocatalysts are a critical precious metal replacement for the economically viable electrocatalysis of oxygen reduction and water splitting, both of which are a triphase electrode process. Electrocatalysts with a refined porous structure and active composition beneficial for three-phase reactions are broadly pursued. Herein, a highly promising trifunctional spherical Murray assembly of Co-N-C nanoparticles was derived from low-cost Prussian blue analogues for the oxygen reduction reaction and water splitting. The Murray-type architecture with a tunable porous hierarchy for efficient mass transfer and the combination of a Co-N-C active composition are key for the improved electrocatalytic performance. Acid-leaching produced an optimized Murray-type durable and methanol-tolerant Co-N-C electrocatalyst that achieved an onset potential of 0.94 V [vs reversible hydrogen electrode (RHE)] and a half wave potential of 0.84 V (vs RHE) as well as a large diffusion-limited current density of 5.7 mA cm^-2 for the oxygen reduction reaction, which is comparable to Pt/C. In addition, it displayed low onset overpotentials of ∼150 and ∼350 mV corresponding to the hydrogen evolution reaction and oxygen evolution reaction, respectively, highlighting its great potential to be used in overall water splitting with a total splitting voltage of 1.73 V. This work highlights the importance of Murray-type electrocatalysts for multiphase energy-related reactions.

The Brittleness and Chemical Stability of Optimized Geopolymer Composites

Geopolymers are known as high strength and durable construction materials but have a brittle fracture. In practice, this results in a sudden collapse at ultimate load, without any chance of preventing the breakdown of parts or of withstanding the stress for some time. Glass fiber usage as a total anisotropic shape acting as a compact structure component should hinder the fracture mechanism. The optimized compositions in this study led to a significant reinforcement, especially in the case of flexural strength, but also in terms of the compressive strength and notch toughness. The positive and negative influence of the fibers on the complex composite properties provided chemical stability.