Pressure Acid Leaching Research Articles

Preparation of High-Purity Quartz Sand by Vein Quartz Purification and Characteristics: A Case Study of Pakistan Vein Quartz

This study focuses on the purification and evaluation of the high-purity quartz (HPQ) potential of vein quartz ore from Pakistan. Vein quartz is grayish-white and translucent, with its mineral composition mainly comprising quartz crystal. Processed quartz sand is obtained from quartz raw ore through purifying technologies, including crushing, ultrasonic desliming, flotation, high-temperature calcination, water quenching, hot pressure acid leaching, and chlorination roasting. The microscopic characteristics show that the vein quartz raw ore has a medium-coarse granular metacrystalline structure, high quartz content, with only a small quantity of fine-grained K-feldspar. The inclusions primarily consist of large-sized primary inclusions and secondary fluid inclusions developed along the micro-fractures, and the content of inclusions in most areas of the crystal is very low or even nonexistent. The quartz ore with such inclusion characteristics is considered a relatively good raw material for quartz. Component analysis shows that the main impurity elements in the quartz ore are Al, K, Ca, Na, Ti, Fe, and Li, with a total impurity element content of 128.86 µg·g−1. After purification, only lattice impurity elements Al, Ti, and Li remain in the processed quartz sand, resulting in a total impurity element content of 24.23 µg·g−1, an impurity removal rate of 81.20%, and the purity of SiO2 reaching 99.998 wt.%. It is suggested that when the quartz raw ore contains high content of lattice impurity elements, such as Al, Li, and Ti, it is difficult to remove them by the current purification method. In industrial production, considering the economic cost, if quartz sand still contains high content of lattice impurity elements Al, Ti, and Li after flotation, it cannot be used as a raw material for high-end HPQ.

Erosion wear characteristics of metal seal floating ball valve in gas–solid–liquid three-phase flow

During high-pressure acid leaching, sulfuric acid slurry acts as the transportation medium in the withdrawal drum for acid pressure leaching. Over time, the metal-sealed float valve at the pipeline outlet may experience internal leakage. To address this issue, the Euler–Lagrange method for fluid dynamics is used to evaluate the corrosion wear characteristics of the valve in a three-phase flow. Specifically, we investigate the erosion and wear properties of the ball valve core as it opened and closed. To further understand how different ball valve openings impact erosion characteristics, we establish a correlation between the corrosion rate and the drag coefficient. Our research findings indicate that as the valve’s relative opening decreases from 80% to 20%, the corrosion wear rate gradually increases. In addition, the number of particles within the valve cavity also follows a similar trend. These erosion results highlight the significant influence that particle quantity has on erosion. Moreover, with an increase in particle size, both the erosion gradient range and maximum erosion rate decrease.

Study on the treatment of pyrolysis products from the nitric acid pressure leach liquor of laterite

As the demand for nickel increases sharply, it is of great significance to extract valuable metals such as nickel and cobalt from lateritic nickel ore with huge reserves. Based on the nitric acid pressure leaching process (NAPL) of laterite nickel ore, a clean process of laterite nickel ore treatment is proposed. The process includes concentration and crystallization of pressure leaching solution of nitric acid, pyrolysis of mixed nitrate crystal, alkaline leaching of mixed oxides and acid leaching of alkaline leaching residue. Based on previous work, the high-pressure alkaline leaching process of pyrolysis products (mixed oxides) and atmospheric pressure sulfuric acid leaching process of alkaline leaching residue were studied in this paper. First, the Eh-pH diagrams of metal-water system of common elements in laterite nickel ore was summarized according to the reaction equations of different substances in aqueous solution, and the subsequent wet leaching process was guided. The following alkaline leaching experiments showed that under the conditions of 300 g/L NaOH concentration, 3.5 mL/g liquid–solid ratio, 160 °C leaching temperature and 1 h leaching temperature, 85.0 % of aluminum in mixed oxides can be leached and scandium can be enriched by 13 times. Finally, under the conditions of initial sulfuric acid concentration of 4 M, temperature of 100 °C, leaching time of 30 min and liquid–solid ratio of 4 mL/g, the leaching rates of Al, Ni, Mg, Co, Mn, Fe and Sc in alkaline leaching residue were 92.0 %, 97.5 %, 98.4 %, 92.3 %, 62.7 % and 68, respectively. A new procedure for treating lateritic nickel ore is proposed, allowing for thorough recovery and usage of important components. The technique is green and environmentally benign, resulting in closed-loop production of laterite-nickel ore treatment with numerous application possibilities.

Behavior of calcium lignosulfonate under oxygen pressure acid leaching condition

The behavior of calcium lignosulfonate (CLS) in the oxygen pressure acid leaching process of ZnS concentrate was investigated using total organic carbon assessment (TOC), UV–visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR), and gas chromatography-coupled mass spectrometry (GC–MS) as characterization methods. The effect of the CLS degradation products on zinc electrowinning was also discussed. The results showed that the temperature was positively correlated with the degradation of CLS, while the initial acidity had only significant effects in the range of 0–50 g/L and oxygen partial pressure range of 0–0.1 MPa. At an oxygen partial pressure of 0.2 MPa, an acidity of 160 g/L, and a reaction temperature of 150 °C, about 82.4% of CLS was degraded. In the oxygen pressure acid leaching process, CLS underwent polymerization and decomposition reactions, and its aromatic rings and side chain groups were damaged to varying degrees. At 120 °C, CLS was partially converted into sulfonic acids, phenols, and esters of higher molecular weights. At 150 °C, CLS further degraded into lower-molecular-weight aromatic ethers and sulfonic acids with shorter carbon chains. These organics were relatively stable and were the main sources of organic compounds during the oxygen pressure leaching process of zinc concentrates. The addition of CLS had a significant negative impact on zinc electrowinning, which was related to the adsorption of CLS on the cathode surface, enhancing cathodic polarization and inhibiting zinc reduction kinetics.

Efficient nickel extraction from nickel matte by combined atmospheric-oxygen pressure acid leaching: Thermodynamic analysis and sulfur conversion mechanism

Atmospheric acid leaching was prevalently employed in extraction nickel from nickel matte owing to its gentle effect, but the leaching efficiency of nickel still remains limited. In this paper, the efficient nickel leaching from nickel matte and sulfur conversion mechanism through the combined atmospheric-oxygen pressure acid leaching process were investigated. Factors affecting nickel leaching and sulfur conversion from nickel matte were systematically investigated on the basis of thermodynamic calculations. The results showed that the nickel leaching rate after atmospheric acid leaching could reach 79.91 % under the optimized conditions of H2SO4 concentration of 300 g/L, H2O2 dosage of 7 %, 80 °C, liquid–solid ratio of 8 mL/g, and 3 h. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDS) analyses indicated that the S8-coating produced during atmospheric acid leaching and the small amount of NiO passivation film on the surface of the nickel matte impeded the further leaching of nickel. The S8-coating and NiO passivation film were converted to H2SO4 and water-soluble NiSO4, respectively, after the oxygen pressure leaching process. The Ni3S2 and NiS in the nickel matte were released to continue leaching, and the nickel extraction rate reached 99.11 %. The specific optimized process parameters were H2SO4 concentration of 90 g/L, operating pressure of 1.5 MPa, 180 °C, L/S of 10 mL/g and 3 h. This provided a green economical and efficient method for the extraction of nickel from nickel matte.

Selective and efficient extraction of lithium from spodumene via nitric acid pressure leaching

The thriving electric vehicle market has fueled a remarkable surge in the demand for lithium. Consequently, a heightened emphasis has emerged on the extraction of lithium from spodumene deposits. However, the sustainable growth of the lithium industry encounters challenges. The traditional process has the disadvantages of high acid consumption, high extraction rate of impurities and difficult purification of leach liquor. To address these challenges, this study proposes a process for the selective and efficient extraction of lithium from spodumene via nitric acid pressure leaching. In an autoclave at 200 °C, initial nitric acid concentration of 1 mol/L, liquid-to-solid ratio of 2.5 mL/g, and holding time of 30 min, 95 % Li was extracted, with low extraction rate of impurity elements. During pressure leaching, the aluminum–silicate cage structure of β-spodumene remains intact, while H+ freely exchanges with Li+ within the structure, resulting in the formation of HAlSi2O6. Subsequently, the leach liquor underwent thermal decomposition at 250 °C to achieve lithium-aluminum separation. It's noteworthy that nitric acid can be recycled in the process, resulting in low acid consumption. The proposed process has the potential to contribute significantly to the lithium industry by facilitating the adoption of environmentally friendly and sustainable practices.

Bioleaching of a lateritic ore (Piauí, Brazil) in percolators

Heap leaching of laterites for extraction of nickel and cobalt is an attractive alternative to capital and energy intensive high pressure acid leaching, the dominant hydrometallurgical processing technology for limonitic laterites. Conventional approach for heap leaching of laterites is leaching with sulfuric acid. Consumption of sulfuric acid during heap leaching is substantial and industrial-scale operations require construction of a sulfuric acid production plant on site. In this study, heap bioleaching of laterites was simulated in laboratory scale column percolators and bioleaching of nickel and cobalt from lateritic material was successfully demonstrated for the first time. The process is based on biooxidation of the bacterially modified “wet sulfur” inside column percolators by sulfur-oxidizing acidophilic bacteria Acidithiobacillus thiooxidans. The “wet sulfur“ was generated in a bioreactor with the bacterial culture, harvested, and mixed with lateritic ore before forming agglomerates to be filled in the percolator columns. Liquid was circulated with a flow rate of 8 mL/min. Maximum metal extraction was 66% nickel, 95% cobalt, 10% iron, 55% magnesium and 89% manganese from the Piauí lateritic ore after one month bioleaching. For comparison, chemical leaching with 1 M sulfuric acid with or without addition of 10 g/L of ferrous sulfate heptahydrate as reductant resulted in extraction of approximately 80% nickel, 86% cobalt, 33% iron, 50% magnesium and 81% manganese. With bioleaching a higher cobalt but lower nickel and iron extraction was achieved, i.e. a better selectivity of nickel over iron extraction, as well as a relatively higher pH of the pregnant leach solution requiring less limestone and, consequently, lower CO2 emission and generation of iron cake waste in case of laterite bioleaching. Overall, the results are promising and show potential of laterite heap bioleaching to be further developed to application on industrial scale.

Medium-temperature calcination and acid pressure leaching extract the Al2O3 from coal gangue: activation mechanism and kinetic analysis.

Bauxite is an important strategic resource, and it is facing with the problem of balance between high demand of bauxite ore and low resource of bauxite reserves in China. This research takes the Fuxin coal gangue as the object and extracts Al2O3 by medium-temperature calcination and acid pressure leaching process. The results show that at a calcination temperature of 650 °C, calcination time of 2 h, acid pressure leaching temperature of 160 °C and acid pressure leaching time of 6 h, the extraction ratio of Al2O3 reaches 80.19%. Furthermore, the research finding that the complete activation temperatures of kaolinite and muscovite are 650 °C and 850 °C, respectively, and the decomposition reactions of active Si, active Al, and metakaolinite occur above 800 °C, which leads to a low extraction ratio of Al2O3. The acid pressure leaching process can directly destroy the muscovite structure at a calcination temperature of 650 °C. The acid pressure leaching kinetic equations are studied by three kinetic models, and the apparent activation energies of the reactions are calculated by the Arrhenius formula. The results show that acid pressure leaching is subject to solid residue in-layer diffusion control, and the kinetic equation is "". The apparent activation energy is 13.48 kJ mol-1.

Cathode Active Material Synthesis and Battery Performance Tests for Li-Ion Batteries Obtained from Domestic Raw Materials: A Special Case Study from Ore to Battery

The energy requirement brought by technological developments from the past to the present evolves depending on the society's desire to be mobile, which is increasing day by day. Many technological devices such as electrical vehicles, smart phones, computers, drones, cameras meet the required energy from rechargeable lithium-ion batteries. However, the increasing world population and the increasing specifications of the technological devices developed in parallel with the per capita energy consumption by making the raw material resources needed for the production of these technological devices even more important. Nickel, cobalt and manganese compounds, which are the main raw materials used in the cathode production of NMC type lithium-ion batteries, are among these elements of strategic and critical importance, and the production of these chemicals in appropriate quality is of great importance for the industrial development of lithium-ion-based domestic battery technologies in each country. Meta Nikel Kobalt A.Ş., is the first and the only industrially scaled nickel-cobalt plant using HPAL technology in northern hemisphere at . In Gördes plant, nickel-cobalt-manganese hydroxide intermediate product concentrate (MHP) is produced from low grade Gördes lateritic ore following the unit operations of ore preparation, mineral processing, high pressure acid leaching, neutralization and precipitation and is currently completely exported to overseas. However, due to the responsibility of transforming domestic resources to high value-added technological products and obtaining value-added products, research in this field has been regarded and the necessary technological infrastructure and specific knowledge have been created. Within the scope of this project, precious metals in the MHP intermediate product obtained from Gördes lateritic ore were leached and valuable elements are taken to the liquid phase and crystallized after further purification processes such as solvent extraction and ion exchange. As a result, metal salts with purity up to 99.99% were obtained. The obtained nickel, cobalt and manganese sulphate salts were precipitated together with the developed co-precipitation process to obtain precursor in the form of NMC 622. After that, the precursor is treated with lithium and the cathode active material (CAM) is obtained by going through various heat treatments by systematically designed test campaign. The coin cell made with the CAM obtained from domestic raw materials showed a capacity of 184.55 mAh/g at 0.1C. It showed a capacity of 170.58 mAh/g in the first cycle and 157.45 mAh/g in the 50th cycle at 0.5 C, and the capacity conservation was calculated as 92.3% after 50 cycles at 0.5 C. The CAM obtained in the pilot-scale studies carried out according to the lab-scale developed process and sent to for making pouch type battery. In the 10 Ah capacity cells of the produced pouch type, 82% capacity conversation has been achieved as a result of 1000 cycles at a charge/discharge rate of 0.5 C at 100% CoC(Dept of Discharge) in the voltage range of 3-4.15V. Figure 1

Selective leaching of nickel and cobalt from sintered nickel alloy by oxygen pressure acid leaching process

Selective leaching of nickel and cobalt from sintered nickel alloy by oxygen pressure acid leaching process

Investigation of the thermal behavior of Ca(NO3)2·4H2O and its application for the regeneration of HNO3 and CaO

Nitric acid pressure leaching has great potential in treating limonitic laterite. A new method is designed to improve the downstream process. The resulting calcium nitrate solution is concentrated/crystallized/pyrolyzed to achieve the regeneration of nitric acid and calcium oxide. Calcium nitrate pyrolysis is the core process to realize the new method, but the dynamic analysis of this process is relatively lacking and the pyrolysis mechanism is controversial. In this paper, TG-DSC, TG-MS and XRD were applied to systematically study the thermodynamics and phase evolution of calcium nitrate tetrahydrate. It is found that pyrolysis of calcium nitrate tetrahydrate can be divided into four stages: removing free water and part of crystal water, removing residual crystal water, stable existence of anhydrous calcium nitrate, and its decomposition after melting. Calcium nitrite and nitrogen are absent in the process of calcium nitrate pyrolysis. Three iso-conversion methods, including Flynn-Wall-Ozawa method, Kissinger-Akahira-Sunose method and Starink method, were applied to determine activation energies of calcium nitrate pyrolysis as 224.4 kJ/mol, 221.8 kJ/mol and 222.2 kJ/mol. The kinetic mechanism model of calcium nitrate pyrolysis determined by Melak method is closer to An model, which is the random nucleation and growth reaction. Calcium nitrate pyrolysis process further expands the industrial application of nitric acid pressure leaching.

Preparation of a High-Silicon ZSM-5 Molecular Sieve Using Only Coal Gangue as the Silicon and Aluminum Sources.

The traditional preparation of ZSM-5 molecular sieves relies on chemical reagents to provide silicon and aluminum sources, which are limited as raw materials and cannot be commonly used in production practice. Using coal gangue as the raw material and using medium-temperature chlorination roasting and the pressure acid leaching process to control the silicon-aluminum ratio [n(Si/Al)] of coal gangue, a ZSM-5 molecular sieve was prepared using the alkali melting hydrothermal method. The pressure acid leaching process solved the limitation that kaolinite and mica cannot simultaneously be activated. Under optimal conditions, the n(Si/Al) of the coal gangue increased from 6.23 to 26.14 and complied with the requirements for the synthesis n(Si/Al) of a ZSM-5 molecular sieve. The effect of n(Si/Al) on the preparation of the ZSM-5 molecular sieve was studied. Finally, spherical granular ZSM-5 molecular sieve material with a microporous specific surface area of 169.6329 m2/g, an average pore diameter of 0.6285 nm, and a pore volume of 0.0988 cm3/g was prepared. Providing ideas for the high-value utilization of coal gangue, it is significant for solving the problem of coal gangue solid waste, as well as the problem of ZSM-5 molecular sieve feed stock.

Enhanced extraction of nickel from limonitic laterite via improved nitric acid pressure leaching process

At a time when the world is practicing energy conservation and emission reduction in order to achieve carbon neutrality, it is particularly important to enhance the extraction of valuable metals from low-grade resources. In the current process of extracting valuable metals from limonitic laterite, the characteristic that the laterite is a highly porous mineral is often overlooked. Inspired by our previous studies on the porous kinetics of limonitic laterite during nitric acid pressure leaching, this paper investigated the enhanced recovery of nickel from limonitic laterite. Response surface methodology was first used to optimize the nitric acid pressure leaching limonitic laterite process parameters to obtain the optimum conditions (Temperature: 194 °C, Time: 75 min, Liquid/Solid: 3.4 mL/g, and the initial nitric acid concentration: 178 g/L). Based on this process condition, two enhancement options were performed, namely bleed air treatment and adding surfactant. The results showed that both bleed air treatment and the addition of surfactant promoted the leaching of limonitic laterite. The best enhancement was achieved by DTAB (dodecyl trimethyl ammonium bromide), with a 5.22% increase in nickel extraction under optimal process conditions (from 90.63% to 95.85%). Furthermore, the analysis of the reinforcement mechanism shows that the bleed air treatment mainly removes the obstruction of the leaching reaction by the air in the pore, thus accelerating the reaction. The reinforcing effect of surfactants is mainly based on improved diffusion efficiency and increased permeability.

Contribution of Obi Island Reducing the Carbon Footprint in the Transport Sector

Transportation is one of the main sectors contributing to greenhouse gas (GHG) emissions that cause global climate change. One of the decarbonization strategies from the transportation sector that can be implemented is by switching to a sustainable mode of transportation, especially battery electric vehicles (BEV). Since mid-2021, Obi Island has been producing Mixed Hydroxide Precipitate (MHP). It is an intermediate product of limonite nickel ore processed using hydrometallurgical processing techniques through the first refining plant in Indonesia using High Pressure Acid Leaching (HPAL) technology. The MHP will be processed into Nickel Sulfate (NiSO4.6H2O) and Cobalt Sulfate (CoSO4.7H2O), the primary precursor materials for electric vehicles. The potential GHG emissions reduction in the transportation sector from the processing of limonite nickel ore in Obi Island is 2.04 MtCO2 in 2022 to 21.02 MtCO2 in 2040 with a total accumulation until 2040 of 344.56 MtCO2.

Base Metals Extraction from Printed Circuit Boards by Pressure Acid Leaching

Printed circuit boards (PCBs) are a valuable source of raw materials for metal recycling considering that base metal concentration analyses have confirmed that PCB powders are multimetallic in nature and contain high concentrations of Cu, Zn, Ni, and Fe. Given that minerals are not renewable resources, these metals can be recycled through hydrometallurgical processes. In this study, we determined that 2 M sulfuric acid, 0.55 MPa oxygen pressure, and a temperature of 90 °C represent the optimal conditions for leaching of Cu, Zn, and Ni of PCBs, obtaining the highest observed values of recovery of greater than 90% for Zn and 98% for Cu and Ni. The characterization of PCBs by SEM–EDS analyses showed that plates mainly consist of Cu, Ni, and Zn. PCBs can be seen as a potential secondary resource for the recovery of copper, nickel, and zinc. The best potential and pH conditions for the extraction of Cu, Zn, and Ni were also determined on the basis of thermodynamic diagrams.

Influence of the model used for the calculation of equilibrium constants at moderate temperature for electrolytes

The formation of a solid mineral deposit can cause major problems in the conduct of industrial processes such as high pressure acid leaching. Knowledge of the chemical speciation and solubility product of the mineral can help control or inhibit its formation. This speciation is based on knowledge of the thermodynamic equilibrium constants of the dissociation/complexation reactions involved in the system and their temperature dependence. It also depends on the concentration of the different species in the system, the pressure and the activity coefficients of the chemical species present in their molecular or electrolytic form. From these thermodynamic quantities and the state of the system, it is possible to predict the direction of evolution of the reaction, i.e. whether the reactants or the products of the chemical reactions are favoured. This work presents and compares different models for the calculation of activity coefficients for ionic strengths between 0.001 – 6 molal and the calculation of thermodynamic equilibrium constants at temperatures up to 300°C (at zero ionic strength). It confirms the need for reliable thermodynamic data for modeling aqueous systems.

High pressure acid leaching of low germanium bearing silica residue (GRS): Characterization of leach residue and mechanistic details of germanium leaching

This study investigates the leaching behavior of germanium from low germanium bearing silica residue (GRS) with high silicon content by the acid leaching process. The results showed that high-pressure acid leaching process could effectively extract more germanium from the GRS compared with the conventional acid leaching process, and that the leaching of germanium was positively correlated with the leaching temperature. The leaching efficiency of germanium reached 73.8% at 240 °C, which is 3.5 times higher than that obtained from the conventional acid leaching process. Further studies demonstrated that the leaching of germanium was directly related to the polymerization and crystallization behavior of silicon. At leaching temperatures below120 °C, silicon could transform into amorphous and highly polymeric SiO2, which increased the germanium adsorption capacity of silicon, leading to reduced leaching of germanium. Above 120 °C, the depolymerization and polycondensation reaction of polysilicic acid was enhanced, resulting in the conversion of silicon into dense oligomeric silica with a low specific surface area. This conversion reduced the adsorption and encapsulation of germanium on silicon, which was conducive to the leaching of germanium.

Ammonia leaching process for selective extraction of nickel and cobalt from polymetallic mixed hydroxide precipitate

Nitric acid pressure leaching process (NAPL) uses nitric acid as the leaching medium to produce cobalt and nickel raw materials. Based on the benefits of nitric acid pressure leaching process for laterite ore, this paper proposes a process of "nitric acid pressure leaching-neutralization precipitation-reductive ammonia leaching separation". Firstly, thermodynamic analysis confirmed the possibilities of nickel and cobalt leaching from ammonia solution. Then the impacts of leaching agent composition, temperature, time, and liquid-solid ratio on nickel and cobalt extraction ratios were investigated. Finally, the leaching behaviors of nickel and cobalt during ammonia leaching were investigated using the shrinking core model. In addition, the phase and morphology of the leach residue were studied using X-ray diffraction (XRD) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS). The reductive ammonia leaching method for treating MHP results in high nickel and cobalt extraction ratios, good separation results, and recyclable material, all of which have significant industrial application value.

Recovery of scandium and aluminum from limonitic laterite intermediate product

The discovery of Sc-rich Ni-Co laterite highlights the potential of the extraction of Sc from Ni-Co laterite. In the nitric acid pressure leaching (NAPL) process of treating limonitic laterite, Sc precipitates with Al and concentrates in Sc-bearing Al residue. Thus, this intermediate product becomes an important resource for Sc. This paper presents a combined process to recover Sc and Al from Sc-bearing Al residue, which consists of alkaline leaching, acid leaching and solvent extraction. First, by controlling alkalinity, 94.3% Al was separated from the Sc-bearing Al residue, while 96.8% Sc was enriched in leach residue. Then, the obtained Sc-rich residue was totally leached with sulfuric acid. Moreover, Sc in leach solution was synergistically extracted by 10% Di-(2-ethylhexyl) phosphoric acid (P204) and 5% Tributyl phosphate (TBP). Finally, the co-extracted impurities in the Sc-loaded organic phase were scrubbed by HCl solution, followed by the Sc was stripped with NaOH solution. Sc-bearing Al residue is an advantageous Sc resource, and the proposed process could achieve comprehensive utilization of Sc-bearing Al residue in a facile way.

Crystallization and pyrolysis of nitric acid pressure leach liquor of limonitic laterite and separation of valuable metals

Based on the advantages of nitric acid pressure process (NAPL) for laterite nickel ores, this study innovatively proposes nitric acid pressure leach liquor crystallization pyrolysis-mixed metal oxides separation process. Firstly, the feasibility and the possible reactions of mixed nitrate pyrolysis were confirmed by thermodynamic analysis. Subsequently, the optimal pyrolysis temperature was experimentally investigated. Then, the pyrolysis process of combined nitrate was thermodynamically analyzed, and the phase composition of mixed metal oxides was determined by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS). The Pourbaix diagram shows that using NaOH as leaching agent can selectively separate aluminum from mixed metal oxides, and the variables influencing aluminum's leaching rate are investigated. The experimental results are as follows: the optimal pyrolysis temperature of mixed nitrate crystals is 600 °C; the pyrolysis products are mainly oxides with the formation of NiAl2O4 and MgAl2O4 spinel phases; the aluminum leaching rate is 81.9% under the optimal alkali leaching conditions. The presence of spinel phase is not favorable for aluminum leaching. After leaching, an enriched residue of 15.8% Ni, 1.9% Co and 0.19% Sc was obtained.