Pressure Acid Leaching Research Articles

Effective separation and recovery of iron and chromium from laterite residue in the presence of calcium chloride

In nitric acid pressure leaching (NAPL) for the treatment of limonitic laterite ores, the comprehensive utilization of leach residue is significant for resource recovery and environmental protection. In this work, the recovery and separation of iron and chromium from NAPL residue by metallization reduction roasting−magnetic separation with calcium chloride as additive was studied. The following optimum parameters were obtained: 1100 °C roasting temperature, 25 % reductant dosage, 40 min roasting time, 7 % calcium chloride dosage, 200 mT magnetic field intensity, and 40 s rod mill time (D50 = 7.20 µm). Under these optimum conditions, 81 wt% iron content in the concentrate and 7.4 wt% chromium in the tailings were obtained. The corresponding recovery rates of iron and chromium were 95 % and 64 %, respectively. The microstructure and composition of leach residue and process products were investigated by SEM, EDS, and XRD to study the phase transition and polymerization of substances during roasting. The results showed that iron was mainly enriched in the magnetic concentrate, and chromite and silicate minerals dominated the tailings. Analysis of the action of calcium chloride in the reduction roasting revealed that calcium chloride was beneficial for the liberation of Fe from fayalite and the migration and polymerization of iron.

Oxygen Pressure Acid Leaching of Laterite Ore Tailing: Recycling Alkali and Preparing Heat Storage Material

Oxygen Pressure Acid Leaching of Laterite Ore Tailing: Recycling Alkali and Preparing Heat Storage Material

Sustainable process for valuable-metal recovery from circulating fluidized bed fly ash through nitric acid pressure leaching

Circulating fluidized bed fly ash ( CFBFA ) is receiving widespread attention due to its threat to the environment and its high content of alumina (30–50%), gallium (30–100 g/t), etc. In this research, nitric acid pressure leaching technology was proposed to selectively extract aluminum and gallium from CFBFA. The E-pH diagram of the Al–Fe–H 2 O system and experiments proved that the leachate ranged within pH −0.5 to 1, which was not favorable for the generation of Al(OH) 3 colloids. Moreover, Al entered the leachate as Al 3+ , and the divalent iron was initially oxidized by NO 3 − and then hydrolyzed to form hematite . The lg c Fe3+ at equilibrium of Fe 3+ hydrolysis had a certain relationship with pH. Thus, at high acidity with increased temperature, more Al entered the solution and more Fe entered the residue. Based on experiments, the optimum conditions were found to be as follows: leaching temperature of 220 °C, liquid-to-solid ratio of 4:1 mL/g, HNO 3 concentration of 340 g/L, and leaching duration of 2 h. The leaching rate of Al, Fe, and Ga were approximately 80%, 6%, and 78% respectively. The basic separation of aluminum and iron could be realized during leaching. In the evaporation, concentration and crystallization process of the leachate, aluminum nitrate precipitated out at room temperature when leachate density exceeded 1.38 g/cm 3 . A greater density of the leachate was concentrated, and crystallization benefited the formation of aluminum nitrate crystals with less crystal water. • A feasible process for recovering aluminum from solid waste (CFBFA) was developed. • The E-pH diagram of Al–Fe–H 2 O system at high temperature was analyzed. • Aluminum and iron were basically separated during the leaching process. • The leaching agent could be regenerated and the process was sustainable.

Separation and recovery of scandium from high pressure sulfuric acid leach liquor of limonitic laterite

Extraction of Sc from Sc-rich limonitic laterite without interfering with the main nickel-cobalt production circuit will significantly enhance the economic value of laterite. A process for separation and recovery of Sc from high pressure acid leach (HPAL) liquor of limonitic laterite was proposed in this paper. Based on the chemical composition of the leach liquor, precipitation thermodynamic analysis and experiments were conducted. The results indicated that after a first step to precipitate Fe3+ at pH = 2.5 and 90 °C, Sc could be enriched through a second step precipitate at pH = 4.8 and 60 °C to 267 g/t in Sc-containing precipitate. Then, Sc was re-leached from the Sc-containing precipitate via 1 mol/L sulfuric acid at L:S ratio of 5 mL/g, 80 °C, and 40 min. Meanwhile, gypsum in the Sc-containing precipitate transformed into calcium sulfate hemihydrate during leaching. After that, Sc was synergistically extracted from the leach solution via 5% P204 and 2.5% TBP. Moreover, impurities extracted into the organic phase during the extraction of Sc were scrubbed by HCl. Finally, Sc was stripped by NaOH. By using this process, Sc could be efficiently recovered from limonitic laterite in a facile way.

Simultaneous adsorption of V(V) in both anionic and cationic forms from acid leaching solution using iminodiacetic acid chelating resin

An efficient separation and extraction method for the recovery of V(V) in both anionic and cationic species from pressure acid leaching solution of vanadium shale was developed using the iminodiacetic acid chelating resin CH-90. The optimum process parameters were explored. The mechanism of V(V) adsorption and selective separation between V(V) and impurities were revealed by FTIR, XPS, SEM-EDS, and DFT theory. Experiments showed that under the conditions of pH= 1.6, adsorption temperature of 40 ℃, bed volume of 20 mL, and feed liquid flow rate of 2 BV/h, the resin had the best effect on V(V) with an adsorption rate of 91.3% and impurity ions adsorption rate less than 20%; The desorption rate of V(V) can reach 100% when 2 mol/L HCl as the desorption agent; 4 mol/L HCl could restore the performance of resin. The reaction between the resin and V(V) included the electrostatic interaction between H2V10O284- and -N, and the coordination reaction in which VO2+ chelated with N and O atoms. DFT calculation results showed that resin preferentially adsorbed H2V10O284- during the adsorption process. CH-90 resin contributed to simultaneously separating V(V) in the form of H2V10O284- and VO2+ from a complex sulfuric acid leaching system at low pH.

Dissolution behavior and porous kinetics of limonitic laterite during nitric acid atmospheric leaching

In our previous study, the mineral evolution and porous kinetics during nitric acid pressure leaching of limonitic laterite has been investigated. In order to optimize the nitric acid leaching technology, this paper investigated the dissolution behavior and porous kinetics of limonitic laterite during nitric acid atmospheric leaching. The experimental results showed that Ni and Fe had consistent leaching behavior, whereas Co was only consistent with Mn in the early stages of leaching. The DFT (Density functional theory) simulations of goethite dissolution revealed that H+ attacked the bridging O first with adsorption energy of −1.37 eV, while NO3– attacked the Fe with adsorption energy of −3.07 eV, hence promoting the dissolution of Fe from the goethite crystals. Based on meticulous modeling analysis, the leaching of Ni could be described by grain model-cylindrical particle. In the early stage of leaching, the Ni extraction is regulated by chemical reactions with an activation energy of 88.4 kJ/mol. In the latter stage, the leaching is regulated by pore diffusion with an effective diffusivity of 1.37 × 10-11 m2/min at 90 °C. This study clarified the dissolution behavior of limonitic laterite, and described nickel leaching using a porous kinetic model.

Leaching Behavior of Scandium from Limonitic Laterite Ores Under Sulfation Roasting–Water Leaching

In the present study, the leaching behavior of scandium from limonitic laterites under sulfation roasting–water leaching (SAL) was explored. The mineralogical analysis of limonitic laterites showed that scandium was associated with the iron phase. The roasting temperature played an important role in the iron phase conversion during the sulfation roasting process. With an increase in the roasting temperature from 100 to 800 °C, the iron phase (goethite, magnetite, and hematite) gradually converted to monoclinic Fe2(SO4)3 (400 °C), then to rhombohedral Fe2(SO4)3 (600 °C), and finally to hematite (800 °C). Due to the iron phase conversion mechanism, the leaching efficiency of scandium gradually increased first and then decreased with the increase of roasting temperature from 100 to 800 °C. When limonitic laterites roasted at temperature of 600 °C for 2 h with sulfuric acid/laterite ratio of 1/4 (mL/g), a total of 81.15% of scandium and only 0.37% of iron were extracted into leaching solution at 30 °C with the liquid-to-solid ratio of 4:1 (mL/g) for 1 h with agitation. The SAL process enables the selective and efficient enrichment of scandium from low-grade limonitic laterites with lower costs for equipment and operation compared to high-pressure acid leaching (HPAL), lower acid consumption, and lower dissolution of iron compared to atmospheric pressure acid leaching (AL).

Thermodynamic analysis and application for preparing FePO4 from nitric acid pressure leach laterite residue by selective leaching in phosphoric acid and induced precipitation

Currently, with the increasing demand of nickel and cobalt, more and more attention has been placed on hydrometallurgical processing to treat laterite ore. The nitric acid pressure leaching (NAPL) has several advantages. In order to solve the problems of environmental pollution and resource wastage caused by the NAPL residue, this work proposes a novel and green process for treating laterite residue to prepare high-purity iron phosphate. The laterite residue was subjected to selective leaching by 6.0 mol L−1 phosphoric acid. The pregnant leach solution (PLS) was used to prepare iron phosphate by induced precipitation. The selective leaching was conducted using 6.0 mol L−1 H3PO4 of to obtain high extraction of iron. After leaching and clarification of PLS iron phosphate was precipitated in two steps by controlling temperature and pH, to yield more than 94% iron phosphate. The reaction mechanism of the induced precipitation was analyzed, which illustrated that intermediate products were first formed from the leach liquor and then transformed to FePO4(s). Characterization of the iron phosphate showed that the product displayed flowerlike morphology with high purity and dispersion. This process not only solves the serious environmental damage by accumulation and landfill of laterite residue, but also improve the efficiency of resource utilization for the hydrometallurgical nickel laterite industry.

Investigation of the thermal behavior of Mg(NO3)2·6H2O and its application for the regeneration of HNO3 and MgO

The nitric acid pressure leaching (the NAPL) process has caught people’s attention owing to the increasing demand for nickel and cobalt, and the gradual depletion of nickel sulfide. In this process, iron, aluminum, nickel, and cobalt are separated successively by MgO. Therefore, a large amount of Mg(NO3)2·6H2O is generated, which is an important carrier to achieving the cycling of HNO3 and MgO via pyrolysis. However, the thermal behavior data of Mg(NO3)2·6H2O are insufficient. Hence, related experiments were carried out, which indicated four stages in this process with the absorption energy of 212.85 kJ/mol. Moreover, the hypotheses 3(Mg(NO3)2·nH2O) → Mg3(OH)4(NO3)2 + 4HNO3 (n = 4/3, the coexistence of Mg(NO3)2·2H2O and Mg(NO3)2) determining the most possible route to form Mg3(OH)4(NO3)2 was confirmed. The four–step model (A → B → C → D → E) showed a strong correlation with TG curves and can be described appropriately with the Fn, Fn, An, and An models, respectively. The molecular dynamic simulation revealed that dehydration and decomposition process include melting, dehydration, formation of anhydrous magnesium nitrate, and pyrolysis. Finally, a novel technical route for HNO3 and MgO regeneration was proposed with the natural gas consuming about 8.52 × 10-3 Nm3 per mole of Mg(NO3)2·6H2O.

Enrichment of scandium and aluminum from limonitic laterite during the nitric acid pressure leaching process

The presence of 50–100 (g/t) scandium in limonitic laterite makes it an important source for the extraction of Sc together with nickel and cobalt. This study aims to separate and enrich Sc and Al from limonitic laterite during the nitric acid pressure leaching (NAPL) process for treating limonitic laterite without interfering with the main nickel‑cobalt production circuit. Extractions of 86.2% Sc and 71.0% Al were obtained under the most suitable conditions for leaching limonitic laterite. The Sc and Al were selectively, homogeneously precipitated with MgCO3 suspension after adjusting the pH to 4.5 at 60 °C. The precipitate contains about 27% Al and 0.037% Sc. Moreover, 0.68% of Ni and 3.62% of Mg were also found in the Sc-containing Al precipitate and their precipitation behaviour and mechanism were examined. Specifically, a small amount of Mg and Al co-precipitate to produce the layered double hydroxides (MgAl LDHs). The Sc-containing Al precipitate was leached by NaOH with initial concentration of 20% and liquid-to-solid ratio of 3.5 mL/g at 80 °C for 1 h allowing 94.6% of Al to be dissolved. The resultant sodium aluminate solution contains 65.4 g/L of Al, which could be directly applied to the recovery of Al. Scandium enrichment in the leach residue achieved a content of 0.245%. The proposed method demonstrates the potential to enhance the economic value of limonitic laterite through the recovery of Sc and Al.

Extraction of Scandium from Red Mud of Alumina Refining by High Pressure Acid Leaching in Sulfuric Acid Solution

Extraction of Scandium from Red Mud of Alumina Refining by High Pressure Acid Leaching in Sulfuric Acid Solution

Selective Extraction of Nickel and Cobalt From Sintered Nickel Alloy by Oxygen Pressure Acid Leaching Process

Selective Extraction of Nickel and Cobalt From Sintered Nickel Alloy by Oxygen Pressure Acid Leaching Process

Microwave pretreatment for enhanced selective nitric acid pressure leaching of limonitic laterite

Microwave pretreatment for enhanced selective nitric acid pressure leaching of limonitic laterite

A study into the behaviour of nickel, cobalt and metal impurities during partial neutralisation of synthetic nickel laterite pressure leach solutions and pulps

The behaviour of nickel (Ni), cobalt (Co) and major impurities such as aluminium (Al), trivalent chromium [Cr(III)] and ferric iron [Fe(III)] during the partial neutralisation of synthetic pressure acid leach (PAL) liquors and pulps was investigated. Ferric iron precipitation took place between pH85°C 2 to 3, and up to 54% of Cr(III) and 42% of Al were co-precipitated with Fe(III). Haematite appeared to act as a seed and promote the removal of Fe(III) from solution at a pH85°C as low as 2. Precipitation of the remaining Al and Cr(III) from solution did not commence until at or above pH85°C 3.5, and virtually went to completion at pH85°C 4 (96% precipitation extent). There was a linear correlation between the %Cr(III) precipitation and %Al precipitation from solution, which suggests that the behaviour of the two species is related and that Cr(III) is unlikely to behave independently in solution. Nickel and cobalt losses were strongly dependent on pulp pH, and valuable metal losses rapidly climbed above pH85°C 3 and further increased after 1 h of ageing; this behaviour appears to be consistent with adsorption processes. Cobalt losses were found to increase significantly in the presence of haematite whilst Ni losses were unchanged, suggesting that there is partitioning of Ni and Co during partial neutralisation of PAL pulps with Co preferentially adsorbing onto haematite. Final Ni losses were on average 1.95% and were unaffected by the presence of haematite; final Co losses were 0.38% in the absence of haematite and increased to 3.30% in the presence of haematite.

An investigation into potential pathways for nickel and cobalt loss during impurity removal from synthetic nickel laterite pressure acid leach solutions via partial neutralisation

The primary pathways by which nickel (Ni) and cobalt (Co) loss could occur from acidic sulfate solution during partial neutralisation of synthetic nickel laterite pressure acid leach solutions (to pH 4 at 85 °C) was investigated. Knowledge of the avenues by which Ni and Co loss occurs will enable minimisation of valuable metal losses through optimisation of the partial neutralisation process. Precipitation of Ni and Co as their hydroxides did not appear to be a pathway by which metal loss occurred during partial neutralisation. Additionally, co-precipitation of Ni and Co with either Fe(III) or Al was not found to be a significant route for valuable metal loss. Adsorption onto freshly precipitated hydrous oxides of Al and Fe(III), as well as haematite, a major component of nickel laterite pressure leach discharge solids, appeared to be the primary route by which Ni and Co loss occurs during partial neutralisation. There was a preference for Co to adsorb onto haematite and ferric iron precipitates whilst Ni preferentially adsorbed onto Al precipitates. The molar ratio of Al to Fe(III) in the synthetic feed liquor was found to be a key variable controlling Ni and Co loss during partial neutralisation. Final Ni losses initially increased with increasing Al/Fe molar ratio in the feed, being at their highest in the absence of Fe(III) (10.7% Ni loss), and when the Al/Fe molar ratio in solution was unity (11.9% Ni loss), then decreased significantly when the Al/Fe ratio in the feed liquor was greater than or equal to 2 (2% Ni loss). Cobalt losses generally decreased with increasing Al/Fe ratio in solution except for in the presence of haematite where Co losses were 3.30%, confirming that Co adsorption onto haematite is a significant route by which loss of this valuable metal occurs during partial neutralisation.

Vanadium extraction from roasted vanadium-bearing steel slag via pressure acid leaching

In this study, pressure acid leaching technology was used to extract vanadium from vanadium-bearing steel slag, and the optimum parameters and mechanism for vanadium extraction were investigated. Pressure acid leaching significantly enhanced vanadium leaching from roasted vanadium-bearing steel slag. The suitable leaching conditions were liquid/solid ratio of 5:1, sulfuric acid concentration of 20%, oxygen pressure of 1.0 MPa, and leaching temperature of 160 °C. The maximum leaching rate was 87.8%, which was obviously higher than that under atmospheric acid leaching at 60 °C. Regardless of pressure acid leaching or roasting pretreatment, the increase in the oxidation degree facilitated efficient vanadium extraction from vanadium-bearing steel slag. As pressure acid leaching was employed for vanadium extraction, both the interfacial transfer and diffusion across the product layer could affect the leaching rate. The variant of the shrinking core model was more suitable for describing the leaching kinetics of vanadium, and the activation energy calculated from the apparent rate constant was 20.87 mol−1.

Recovery of Indium from Hard Zinc Slag by Pressure Leaching and Solvent Extraction

In this study, hydrometallurgical processes involving pressure acid leaching and solvent extraction were developed to aid recovery of indium from zinc slag, which is produced in the imperial smelting process. Four different acid leaching methods were studied, namely atmospheric leaching, atmospheric leaching with KMnO4, roasting-atmospheric leaching, and oxygen pressure leaching in a sulfuric acid medium. Oxygen pressure acid leaching is the most effective method for indium extraction, and 94.1% of indium was leached under the optimum conditions, i.e., 300 g/L H2SO4,oxygen pressure 0.4 MPa, liquid/solid ratio 10 mL/g, and temperature 100°C for 5 h. X-ray diffraction and scanning electron microscopy examination of the raw material and leaching residue samples indicated that the intermetallic compounds Cu5Zn8and Cu2Zn, metallic zinc, and iron in the raw material dissolved, leaving the insoluble components PbSO4 and Pb as the major compounds in the leaching residue. A 98.5% proportion of the indium in the leaching solution was selectively extracted with 30% bis(2-ethylhexyl) phosphate and 70% kerosene by three-stage counter-current extraction, and 99.5% of the indium in the loaded organic phase was stripped by 6 mol/L HCl through four-stage counter-current stripping. The overall recovery yield of indium through all processes was approximately 92%.

Radiological assessment of bauxite residue processing to enable zero-waste valorisation and regulatory compliance

In this work, the presence of natural radionuclides in bauxite residue subjected to a neutralisation-leaching process and smelting-leaching process was investigated. The radionuclide concentrations of radium-226, radium-228 and thorium-228 were compared with the concentration of the same radionuclides in the untreated bauxite residue. It was found that neutralisation of bauxite residue at relatively high temperatures (120–150 °C) and high pressure (PCO2 = 30 bar) did not change the initial concentration of radionuclides. In fact, the concentration of radionuclides after an intensive neutralisation process remained below 500 Bq kg−1. The separation of iron from the rare-earth elements by reductive smelting permitted a significant decrease of iron concentration in the pregnant leach solution obtained after high pressure acid leaching. However, the radionuclide concentration in the slag was increased 1.5 times with respect to the initial concentration, although it did not exceed 800 Bq kg−1. Further processing of the slags by high pressure acid leaching led to the dissolution of several base metals, while a portion of the radionuclides remained unreacted in the solid fraction. Thus, a concentration of thorium-228 > 1000 Bq kg−1 was only observed after leaching a calcium oxide-based slag with hydrochloric acid. Meanwhile, in the leach liquors, the concentration of radionuclides was <100 Bq L−1. Nevertheless, based on analytical estimations using conservative assumptions, the solid residues and leach liquors produced by acid leaching in the current study are unlikely to exceed the exposure limit of 1 mSv set by the European Basic Safety Standards Directive. It should be noted that the current results are based on a specific bauxite residue studied in this work, and caution should be used in the application to other situations. The described radiological assessment of bauxite residue processing can ensure the necessary regulatory compliance and facilitate zero-waste valorisation.

Function of Interface Deposition of Calcium Sulfate in Pressure Acid Leaching of Black Shale-Hosted Vanadium

During pressure acid leaching process of black shale-hosted vanadium, increasing the reaction interface of muscovite dissolution can enhance the vanadium release. In this paper, calcium sulfate (CaSO4) deposition behavior and its effect on muscovite under K2SO4 assistance were focused on for demonstrating the function of CaSO4 on vanadium leaching from the black shale. Results showed that as K2SO4 mediated, the apparent activation energy of vanadium leaching and the apparent reaction order of sulfuric acid decreased from 24.37 kJ/mol to 16.63 kJ/mol and 2.7 to 1.9, respectively. The leaching rate and dependence on pH value were modified. The vanadium leaching acceleration owed to CaSO4 deposition on muscovite in the black shale. The ion absorption stimulations found that Ca2+ is confirmed to be easily absorbed on the six-membered ring cavity of silicon-oxygen tetrahedrons in muscovite structure prior to K+ and Na+. Meanwhile, SO42− provides two oxygen atoms to bond with Ca2+ absorbed on muscovite (001) surface. The continuous absorption and bonding create CaSO4 deposition on muscovite (001) surface which also involves the load transmitting. The stress load transmitting correlates to pore formation in muscovite particles. It was proved that massive micropores initiated and proliferated in the existing pores under K2SO4 assistance. The porosity caused by CaSO4 deposition greatly increased the reaction interface of muscovite dissolution and accelerate internal diffusion of H+ to the reaction interface, which can significantly weaken the vanadium leaching dependence on acid.

Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO3 and simultaneous synthesis of fibrous CaSO4·2H2O by-products

An innovative technology, nitric acid pressure leaching of limonitic laterite ores, was proposed by our research team. The HNO3 regeneration is considerable significance for the improvement of the proposed technology and its commercial application, but it has not been systematically investigated. Herein, regenerating HNO3 from Ca(NO3)2 solution with low-cost H2SO4, and simultaneous synthesis of fibrous CaSO4·2H2O by-products were studied. As a theoretical basis, the solubility of CaSO4·2H2O in HNO3 medium is studied. It is concluded that the solubility of CaSO4·2H2O increases with increasing temperature or increasing HNO3 concentration, which has considerable guiding significance for the subsequent experimental research and analysis. Then, the effects of various factors on the residual Ca2+ concentration of filtrate, the regenerated HNO3 concentration and the morphology of synthesized products are investigated using ICP-AES and SEM. And the effect mechanism is also analyzed. The results indicate the regenerated HNO3 concentration reaches 116 g/L with the residual Ca2+ concentration being 9.7 g/L at the optimum conditions. Moreover, fibrous CaSO4·2H2O by-products with high aspect ratios (length, 406.32 µm; diameter, 14.71 µm; aspect ratio, 27.62) can be simultaneously synthesized.