Search Results (8)

Experiments were conducted to evaluate domestic low-grade laterites and serpentinite waste as potential secondary sources of nickel and magnesium and to assess leaching residues for carbon dioxide adsorption. Solids were leached chemically using sulfuric acid, while bioreductive dissolution under anoxic conditions employed a consortium of microorganisms dominated by Sulfobacillus. The efficiency of laterite bioreduction was 26.81% for Ni and 63.92% for Mg. In the case of serpentinite, 20.54% Ni and 92.88% Mg were extracted. The chemical dissolution yielded 26.73% Ni and 61.37% Mg in the case of laterites and 16.20% Ni and 77.49% Mg for serpentinite waste. Specific surface area was analyzed during the processes, showing a systematic increase over time. Based on the changes in this parameter, a mathematical description of the process was proposed using a shrinking particle model (SPM). Except for laterite bioreduction, leaching was shown to be a two-stage process controlled by a chemical reaction. The serpentinite solid processed in the presence of microorganisms exhibited the highest surface area (267 m²/g) and a CO₂ adsorption capacity of 19.9 cm³/g. Full article

An alternative laterite nickel ore processing using sulfuric acid as a leaching agent to produce class 1 nickel as a raw material for electric vehicle batteries produces natrojarosite residue as a by-product during the precipitation of iron and aluminum step. The natrojarosite residue contained iron and high sulfur, which is challenging to utilize as an iron source for steel manufacturing since sulfur can contaminate the steel product. This study focuses on sulfur elimination and iron extraction from natrojarosite. The natrojarosite was roasted for sulfur removal isothermally at different temperatures ranging from 500 until 1100 °C for 4 h. Roasting at 1100 °C resulted a decrease in sulfur content from 12.18% to 3.81% and an increase in iron content from 16.23% to 28.54%. The sulfur released during roasting can, in principle, be recirculated to a sulfuric acid plant and reused as a leaching agent in the nickel ore processing plant. The unroasted and roasted natrojarosite residues were then reduced by coconut shell charcoal in the temperature range of 1000–1400 °C. The results showed that the metallic iron could be obtained from both unroasted and roasted natrojarosite residue at a temperature of 1200 °C and higher. The sulfur content in the oxide phase of unroasted natrojarosite residue was significantly higher than roasted natrojarosite residue. However, the roasting did not significantly influence the sulfur content in the metal phase. The sulfur content in the metal phase from unroasted and roasted natrojarosite residue was less than 1.2%. This result indicated that the removal of sulfur and metal oxide reduction in the natrojarosite residue could be carried out simultaneously in one stage where the natrojarosite residue is reduced by carbonaceous material at a temperature of 1200 °C or higher. Full article

In this study, the valorization potential of Polish laterite leaching residues through alkali activation with the use of NaOH and Na₂SiO₃ solutions as activators was investigated. The effect of the main factors, namely the H₂O/Na₂O molar ratio in the activating solution, the curing temperature, and the ageing period on the main properties of the produced alkali activated materials (AAMs) was assessed. The experimental results showed that AAMs with sufficient compressive strength were only produced when the laterite leaching residues were mixed with significant quantities of metakaolin; thus, when the mass ratio of laterite leaching residues and metakaolin was 0.50, after curing at 40 °C for 24 h and ageing for 7 days, the produced AAMs acquired compressive strength that slightly exceeded 25 MPa. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy (SEM–EDS) analysis were used for the characterization of the raw materials and selected AAMs. Furthermore, the structural integrity of the specimens was investigated after immersion in distilled water and acidic solution (1 mol L⁻¹ HCl), or after firing at higher temperatures. Finally, the toxicity of the produced AAMs was assessed with the use of standard leaching tests. Full article

In this experimental study, the alkali activation of acid leaching residues using a mixture of sodium hydroxide (NaOH) and alkaline sodium silicate solution (Na₂SiO₃) as activators is investigated. The residues were also calcined at 800 and 1000 °C for 2 h or mixed with metakaolin (MK) in order to increase their reactivity. The effect of several parameters, namely the H₂O/Na₂O and SiO₂/Na₂O ratios present in the activating solution, the pre–curing time (4–24 h), the curing temperature (40–80 °C), the curing time (24 or 48 h), and the ageing period (7–28 days) on the properties of the produced alkali activated materials (AAMs), including compressive strength, porosity, water absorption, and density, was explored. Analytical techniques, namely X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and elemental mapping analysis were used for the identification of the morphology and structure of the final products. The experimental results show that the laterite acid leaching residues cannot be alkali activated in an unaltered state, and the compressive strength of the produced AAMs barely reaches 1.4 MPa, while the mixing of the residues with 10 wt% metakaolin results in noticeably higher compressive strength (41 MPa). Moreover, the calcination of residues at 800 and 1000 °C has practically no beneficial effect on alkali activation. Alkali activated materials produced under the optimum synthesis conditions were subjected to high temperature firing for 2 h and immersed in distilled water or acidic solution (1 mol L⁻¹ HCl) for 7 and 30 days in order to assess their structural integrity under different environmental conditions. This study explores the potential of alkali activation of laterite leaching residues amended with the addition of metakaolin for the production of AAMS that can be used as binders or in several construction applications in order to enable their valorization and also improve the environmental sustainability of the metallurgical sector. Full article

Following the growing demand for Ni and Co and the dwindling supplies of sulfide nickel ore, attention has turned toward the more efficient exploitation and utilization of laterite ore. Using ammonium chloride acid solution to leach is an effective method. Our research concerned investigations on the leaching mechanism and leaching kinetics of laterite. XRD was used to demonstrate the leaching mechanism through analysis of the pattern of the leaching residue and raw ore, showing that acid concentration affects the leaching process more significantly than other factors, and that valuable metals are mainly released from goethite and serpentine. The leaching order of these materials are as follows: Goethite > serpentine > magnetite and hematite. The leaching kinetics were analyzed and this leaching process followed a shrinking core model controlled by a combination of interfacial transfer and diffusion across the solid film. Leaching data fitted to the kinetic equation perfectly, and the apparent activation energies for the leaching of nickel, cobalt, and iron were calculated to be 4.01 kJ/mol, 3.43 kJ/mol, and 1.87 kJ/mol, respectively. The Arrhenius constants for Ni, Co, and Fe were 204.38, 16.65, and 7.12 × 10⁻³, respectively, with reaction orders of Ni (a 1.32, b 0.85, c 1.53), Co (a 1.74, b 1.12, c 1.22), and Fe (a 2.52, b −0.11, c 0.94). Full article

A hydrochloric acid hydrometallurgical process was evaluated for Ni and Co extraction from a low-grade saprolitic laterite. The main characteristics of the process were (i) the application of a counter-current mode of operation as the main leaching step (CCL), and (ii) the treatment of pregnant leach solution (PLS) with a series of simple precipitation steps. It was found that, during CCL, co-dissolution of Fe was maintained at very low levels, i.e., about 0.6%, which improved the effectiveness of the subsequent PLS purification step. The treatment of PLS involved an initial precipitation step for the removal of trivalent metals, Fe, Al, and Cr, using Mg(OH)₂. The process steps that followed aimed at separating Ni and Co from Mn and the alkaline earths Mg and Ca, by a combination of repetitive oxidative precipitation and dissolution steps. Magnesium and calcium remained in the aqueous phase, Mn was removed as a solid residue of Mn(III)–Mn(IV) oxides, while Ni and Co were recovered as a separate aqueous stream. It was found that the overall Ni and Co recoveries were 40% and 38%, respectively. About 45% of Ni and 37% of Co remained in the leach residue, while 15% Ni and 20% Co were lost in the Mn oxides. Full article

In this study, column leaching experiments were carried out to investigate the extraction of Ni and Co from low-grade limonitic laterites from Agios Ioannis mines in central Greece. Tests were carried out in laboratory Plexiglas columns using H₂SO₄ as leaching solution. Parameters determining the efficiency of the process, i.e., acid concentration (0.5 M or 1.5 M) and addition of 20 or 30 g/L of sodium sulfite (Na₂SO₃) in the leaching solution, were also studied. Upflow transport of the leaching solution with the use of peristaltic pumps was carried out, while the pregnant leach solution (PLS) was recycled several times over the entire test duration. The concentration of Ni, Co, Fe, Ca, Al, Mg, and Mn in the PLS was determined by Atomic Absorption Spectroscopy (AAS). The ore and the leaching residues were characterized by different techniques, i.e., X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry and thermogravimetry (DSC/TG). The experimental results showed that (i) Ni and Co extractions increased with the increase of H₂SO₄ concentration—60.2% Ni and 59.0% Co extractions were obtained after 33 days of leaching with 1.5 M H₂SO₄; (ii) addition of 20 g/L Na₂SO₃ in the leaching solution resulted in higher extraction percentages for both metals (73.5% for Ni and 84.1% for Co, respectively), whereas further increase of Na₂SO₃ concentration to 30 g/L only marginally affected Ni and Co extractions; and (iii) when leaching was carried out with 1.5 M H₂SO₄ and 20 g/L Na₂SO₃, its selectivity was improved, as deduced from the ratios Ni/Mg, Ni/Ca and Ni/Al in the PLS; on the other hand, the ratio Ni/Fe dropped as a result of the higher Fe extraction compared with that of Ni. Full article

The presence of a considerable amount of scandium in lateritic nickel-cobalt ores necessitates the investigation of possible processing alternatives to recover scandium as a byproduct during nickel and cobalt production. Therefore, in this study, rather than interfering with the main nickel-cobalt production circuit, the precipitation-separation behavior of scandium during a pH-controlled precipitation process from a synthetically prepared solution was investigated to adopt the Sc recovery circuit into an already existing hydrometallurgical nickel-cobalt hydroxide processing plant. The composition of the synthetic solution was determined according to the hydrometallurgical nickel laterite ore processing streams obtained from a HPAL (high-pressure sulphuric acid leaching) process. In order to selectively precipitate and concentrate scandium with minimum nickel and cobalt co-precipitation, the pH of the solution was adjusted by CaCO₃, MgO, Na₂CO_3, and NaOH. It was found that precipitation with MgO or Na₂CO₃ is more advantageous to obtain a precipitate containing higher amounts of scandium with minimum mass when compared to the CaCO₃ route, which makes further processing more viable. As a result of this study, it is proposed that by a simple pH-controlled precipitation process, scandium can be separated from the nickel and cobalt containing process solutions as a byproduct without affecting the conventional nickel-cobalt hydroxide production. By further processing this scandium-enriched residue by means of leaching, SX (solvent extraction), and precipitation, an intermediate (NH₄)₂NaScF₆ product can be obtained. Full article