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This study examines the potential use of the spent catalyst as a raw material for rechargeable batteries. The spent catalyst Ni/γ-Al2O3 still contains relatively high amounts of nickel. This indicates the potential use of the spent catalyst to be leached and purified for synthesizing nickelbased compounds so that it can be applied to rechargeable battery cathodes. In this study, the spent catalyst leaching process employed four types of organic acids: citric acid, lactic acid, oxalic acid, and acetic acid. The spent catalyst was leached under atmospheric conditions and room temperature. Organic acid concentrations were also varied at 0.1, 0.5, 1, and 2 M. The leaching process took place for 240 minutes, where sampling was conducted periodically at 30, 60, 120, 180, and 240 minutes. Experimental results showed that Ni (II) and Al (III) ions were successfully leached to the maximum when using 2M citric acids at a leaching time of 240 minutes. The conditions succeeded in leaching Ni (II) and Al (III) ions of 357.8 and 1,975.4 ppm, respectively. Organic acid, notably citric acid, has excellent potential for further development. Citric acid, as a solvent, has the ability to leach metal ions with high recovery. In addition, this acid is categorized as an eco-friendly and green solvent compared to inorganic acid. Thus, the leaching process can take place without harming the environment. [ABSTRACT FROM AUTHOR]

This work studies the leaching kinetics of nickel laterite in a citric acid solution. A new kinetics model that considers a reversible chemical reaction and internal diffusion of a product is proposed. The experiment was conducted at various temperatures (303, 333, and 358 K) and particle sizes (< 70 to 250 µm). Whereas acid concentration, pulp density, and leaching time were constant at 0.1 M, 20% w/v, and 120 min, respectively. The experimental results showed that the leaching process was dependent on temperature and particle size. In the case of Ni, Al, and Fe leachings, the formation of complex molecules might lead to a steric hindrance of product diffusion; however, this was not observable for Mg. The proposed model was found to be much better than the conventional shrinking core models (SCM). Using the proposed model, the activation energy for nickel was found to be 121.38 ± 0.0324 kJ/mol, 78.98 ± 0.4157 kJ/mol, 1,022.62 ± 9.6507 J/mol for forward reaction, backward reaction, and diffusion, respectively. [ABSTRACT FROM AUTHOR]

This work studies the leaching kinetics of nickel laterite in a citric acid solution. A new kinetics model that considers a reversible chemical reaction and internal diffusion of a product is proposed. The experiment was conducted at various temperatures (303, 333, and 358 K) and particle sizes (< 70 to 250 μm). Whereas acid concentration, pulp density, and leaching time were constant at 0.1 M, 20% w/v, and 120 min, respectively. The experimental results showed that the leaching process was dependent on temperature and particle size. In the case of Ni, Al, and Fe leachings, the formation of complex molecules might lead to a steric hindrance of product diffusion; however, this was not observable for Mg. The proposed model was found to be much better than the conventional shrinking core models (SCM). Using the proposed model, the activation energy for nickel was found to be 121.38 ± 0.0324 kJ/mol, 78.98 ± 0.4157 kJ/mol, 1,022.62 ± 9.6507 J/mol for forward reaction, backward reaction, and diffusion, respectively. [ABSTRACT FROM AUTHOR]

Saprolitic ores from Sulawesi Island (SS ore) contain serpentine and goethite as major minerals, whereas the main minerals in saprolitic ore from Halmahera Island (SH ore) are talc and goethite. Most of the nickel was incorporated in a magnesium–silica-containing mineral. The effects on nickel extraction of leaching temperature, citric acid concentration, and ore particle size were determined to investigate the leaching performances and leaching kinetics of the two saprolitic ores. Nickel leaching efficiency from SS ore is always higher than that from SH ore under the same leaching conditions. The mineral contents of the ores significantly affected the leaching performances and mineral dissolution behaviors of the samples. The results of nickel leaching efficiency and analysis of the solid residues suggest that all dissolved nickel originated from serpentine, which is more easily leached than goethite and talc. The rate of nickel extraction for SS ore was faster than that for SH ore. Nickel leaching from SS ore and SH ore followed the shrinking-core model and was controlled by diffusion of a reactant or product through the solid product layer. [ABSTRACT FROM AUTHOR]

• Mixed oxalate precipitate (MOP) was produced from citric acid leaching of nickel laterite ores and direct oxalate precipitation. • The purity of MOP is 78%. • Leaching efficiency of nickel was around 90%; while efficiency of nickel oxalate precipitation was 100%. • This method is an alternative for recovering nickel from nickel laterite ores that is simpler and ecofriendly. In this study, an alternative method for recovering nickel and other valuable metals from nickel laterite ores is proposed and evaluated. The proposed method comprises a leaching step using citric acid to dissolve the nickel and cobalt from Indonesian nickel laterite ores, and subsequently, an oxalate precipitation step to precipitate the nickel (and cobalt) from citric acid leach filtrate. The results of the leaching experiments showed that nickel (and cobalt) can be dissolved in the leaching step using 1 M citric acid solution at 80 °C, a pulp density of 100 g/L, and leaching duration of 5 h. The results of the oxalate precipitation experiments showed that complete precipitation of nickel can be achieved at 80 °C, 500 rpm stirring speed, and precipitation duration of 3 h. This proposed method can produce Mixed Oxalate Precipitate (MOP) with a purity of 78 %. [ABSTRACT FROM AUTHOR]

Comparison effect of chemical citric acid and other leaching reagents including inorganic acid and other organic acid on nickel extraction from low-grade Indonesian saprolitic ores was evaluated. Two saprolitic ores from two different mining areas (Sulawesi Island and Halmahera Island) in Indonesia were used to investigate the leaching performance and mineral dissolution behaviors of different ore samples using different leaching reagents. Leaching was performed using citric, sulfuric, nitric, hydrochloric, lactic, and oxalic acids. The saprolitic ore from Sulawesi Island (SS) has higher serpentine and lower goethite contents than the saprolitic ore from Halmahera Island (SH). These differences significantly affect the leaching performances and metal dissolution behaviors. Citric acid and sulfuric acid were more effective than other acid solutions for nickel extraction from both samples. Citric acid was very effective for dissolving nickel from serpentine, but did not recover nickel from goethite. In contrast, inorganic acids, namely sulfuric, nitric, and hydrochloric acids, can extract nickel from lateritic ores by dissolving goethite as well as serpentine, but the nickel recoveries achieved with sulfuric acid were higher than those achieved with other inorganic acids. A comparison of the leaching performances of the two samples shows that nickel recovery from SS was higher than that from SH when citric acid leaching was used, but the samples gave similar nickel recoveries in all inorganic acid and lactic acid leaching processes. Moreover, oxalic acid is the least effective reagent for nickel extraction from both samples, because of nickel oxalate precipitation after nickel dissolution. In addition, the effect of a sulfuric acid–citric acid mixture on the nickel dissolution rate was investigated to confirm the individual influences of citric acid and sulfuric acid on the leaching behavior of each sample. The results show that an increase in the amount of sulfuric acid affected the dissolution rate of nickel in leaching of SH much more than that in leaching of SS. In general, the effect of citric acid in the mixture of sulfuric acid and citric acid is attractive. Moreover, citric acid offers not only high nickel recovery and high selectivity of leaching but also an environmentally safe process and low acid consumption. [ABSTRACT FROM AUTHOR]

The kinetics study has an essential role in the scale-up process because it illustrates the real phenomena of a process. This study aims to develop a mathematical model that can explain the mechanism of the leaching process of laterite ore using a low concentration of the citric acid solution and evaluate that model using the experimental data. As a raw material, this process used powder-shaped limonite laterite ores with a size of 125–150 µm. The leaching process is carried out using 0.1 M citric acid solution, F:S ratio of 1:20, and a leaching time of 2 h. The temperature parameter was varied at 303, 333, and 358 K. The experimental results showed that the higher the operating temperature, the higher the extracted nickel. The results of this experiment were used to evaluate the shrinking core kinetics model and the lumped model. The simulation results for both models show that the lumped model can provide better simulation results. Quantitatively, the percentage of errors from the shrinking core model is around 3.5 times greater than the percentage of errors from using the lumped model. This result shows that in this leaching process, the process mechanism that occurs involves the reactant diffusion step and the chemical reactions step; those steps run simultaneously. [ABSTRACT FROM AUTHOR]