Ehsan Vahidi

Recovery of lithium and cobalt from spent lithium-ion batteries using organic acids: Process optimization and kinetic aspects

An environmentally-friendly route based on hydrometallurgy was investigated for the recovery of cobalt and lithium from spent lithium ion batteries (LIBs) using different organic acids (citric acid, Dl-malic acid, oxalic acid and acetic acid). In this investigation, response surface methodology (RSM) was utilized to optimize leaching parameters including solid to liquid ratio (S/L), temperature, acid concentration, type of organic acid and hydrogen peroxide concentration. Based on the results obtained from optimizing procedure, temperature was recognized as the most influential parameter. In addition, while 81% of cobalt was recovered, the maximum lithium recovery of 92% was achieved at the optimum leaching condition of 60°C, S/L: 30gL-1, citric acid concentration: 2M, hydrogen peroxide concentration: 1.25Vol.% and leaching time: 2h. Furthermore, results displayed that ultrasonic agitation will enhance the recovery of lithium and cobalt. It was found that the kinetics of cobalt leaching is controlled by surface chemical reaction at temperatures lower than 45°C. However, diffusion through the product layer at temperatures higher than 45°C controls the rate of cobalt leaching. Rate of lithium reaction is controlled by diffusion through the product layer at all the temperatures studied.

Investigating the Synergistic Effect of D2EHPA and Cyanex 302 on Zinc and Manganese Separation

The synergistic effect of Cyanex 302 on the extraction of zinc and manganese with D2EHPA in sulfate media was investigated. Experiments were carried out in the pH range of 1.0–5.0, temperature of 23, 40, and 60°C with sole D2EHPA and Cyanex 302 as extractant and D2EHPA to Cyanex 302 ratios of 1:3, 1:1, and 3:1. The experimental results showed that the co-extraction of zinc and manganese increased with increasing equilibrium pH and temperature. Increasing the D2EHPA to Cyanex 302 ratio in the organic phase, caused a left shifting of the extraction isotherm of zinc and a right shifting of the extraction isotherm of manganese. Thus, a better separation of zinc over manganese was achieved. At low pHs, the separation factor is low when pure D2EHPA is used as an extractant; however, using Cyanex 302 as a synergist, the separation factor increases and results in a better separation of zinc from manganese. Stoichiometric coefficient of zinc for single D2EHPA and Cyanex 302 and their mixture was calculated to be close to 6.

Recovery of zinc from leach residues with minimum iron dissolution using oxidative leaching

Leaching was performed to recover zinc from a zinc leach residue which contained 9.87% Zn and 4.93% Fe. During sulfuric acid leaching, Fe was dissolved as well as Zn which can reduce the Zn extraction efficiency. Leaching the residue in the presence of an oxidizing reagent such as hydrogen peroxide or manganese dioxide significantly reduced the iron content of the leach liquor. Effect of pH, temperature, solid/liquid ratio, reaction time and hydrogen peroxide or manganese dioxide concentration on the recovery of zinc and iron in non-oxidative and oxidative leaching conditions were investigated. By using the optimum oxidative leaching conditions, iron recovery reduced from 70% in non-oxidative leaching to 0.4 and 5% in the presence of MnO2 and H2O2, respectively, with acceptable Zn recovery. This reduction in the iron content was due to the different iron compounds formed at different conditions.

Environmental life cycle assessment on the separation of rare earth oxides through solvent extraction

Over the past decade, Rare Earth Elements (REEs) have gained special interests due to their significance in many industrial applications, especially those related to clean energy. While REEs production is known to cause damage to the ecosystem, only a handful of Life Cycle Assessment (LCA) investigations have been conducted in recent years, mainly due to lack of data and information. This is especially true for the solvent extraction separation of REEs from aqueous solution which is a challenging step in the REEs production route. In the current investigation, an LCA is carried out on a typical REE solvent extraction process using P204/kerosene and the energy/material flows and emissions data were collected from two different solvent extraction facilities in Inner Mongolia and Fujian provinces in China. In order to develop life cycle inventories, Ecoinvent 3 and SimaPro 8 software together with energy/mass stoichiometry and balance were utilized. TRACI and ILCD were applied as impact assessment tools and LCA outcomes were employed to examine and determine ecological burdens of the REEs solvent extraction operation. Based on the results, in comparison with the production of generic organic solvent in the Ecoinvent dataset, P204 production has greater burdens on all TRACI impact categories. However, due to the small amount of consumption, the contribution of P204 remains minimal. Additionally, sodium hydroxide and hydrochloric acid are the two impactful chemicals on most environmental categories used in the solvent extraction operation. On average, the solvent extraction step accounts for 30% of the total environmental impacts associated with individual REOs. Finally, opportunities and challenges for an enhanced environmental performance of the REEs solvent extraction operation were investigated.

Life Cycle Analysis for Solvent Extraction of Rare Earth Elements from Aqueous Solutions

Recently Rare Earth Elements (REEs) have received increased attention due to their importance in many high-tech and clean energy applications. Although production of REEs is known to be heavy polluting, very limited environmental Life Cycle Assessment (LCA) studies have been conducted. This is particularly true for the solvent extraction of REEs from aqueous solutions, a key step in the REE production pathway. In this study, an LCA is carried out on a typical REE solvent extraction process using P204/kerosene. The material and energy flow data were based on production information collected from several solvent extraction facilities in Inner Mongolia, China. The life cycle inventory was developed using Simapro 7.1 and Ecoinvent 3, in combination with mass/energy balance and stoichiometry. Eco-indicator 99H was used for impact assessment and LCA results were used to evaluate and identify environmental hotspots of solvent extraction process. Moreover, challenges and opportunities for improved environmental performance of solvent extraction process were discussed.

Optimization and dissolution kinetics of vanadium recovery from LD converter slag in alkaline media

Alkaline roasting-alkaline leaching process was used to recover vanadium from LD (Linz Donawitz) converter slag. The independent leaching parameters investigated were liquid to solid ratio (L/S) (10–20 mL/g), temperature (40–60°C), NaOH concentration (1.0–3.0 M), and time (60–120 minutes). Response surface methodology (RSM) was utilized to optimize the leaching parameters and as a result, the most influencing parameter was found to be liquid to solid ratio. Based on the results, the optimum recovery condition (approx. 99%) was obtained with L/S ratio of 20, temperature of 40°C, NaOH concentration of 3.0M, and leaching time of 100 minutes, respectively. Furthermore, the kinetics of alkaline leaching process was investigated using shrinking core model (SCM) equations. It was found that the rate of vanadium leaching is controlled by a mixed controlling mechanism which is comprised of chemical reaction and diffusion through the solid product layer.

Modeling of Synergistic Effect of Cyanex 302 and D2EHPA on Separation of Nickel and Cadmium from Sulfate Leach Liquors of Spent Ni—Cd Batteries

A model was developed to predict the synergistic effect of Cyanex 302 and D2EHPA on co-extraction and separation of nickel and cadmium from sulfate leach liquors of spent Ni-Cd batteries with the aim of increasing separation efficiency. The stoichiometric coefficient of cadmium was determined for sole D2EHPA and three different D2EHPA to Cyanex 302 ratios by applying the slope analysis method. The experimental data of cadmium extraction in pH range of 0.5–3, temperature of 25, 40 and 60 °C and various proportions of organic solvents (D2EHPA and Cyanex 302) were used to propose correlations of distribution coefficient of cadmium by multiple linear regression. The equation was found via multiple linear regression for the estimation of distribution coefficient of cadmium and the result showed that the proposed correlation is in good agreement with the experimental values. The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined.