Ultrasound augmented leaching of nickel sulfate in sulfuric acid and hydrogen peroxide media

A comprehensive review on the ultrasound-enhanced leaching recovery of valuable metals: Applications, mechanisms and prospects

In recent two decades, ultrasound has been broadly applied to the hydrometallurgical leaching process to recover valuable metals within raw materials, aiming to solve the shortcomings of the conventional leaching process, including relatively low leaching recovery, long leaching duration, high reagent usage, high energy consumption and so on. The present work focuses on a comprehensive overview of the ultrasound-enhanced leaching of various metals, such as common nonferrous and ferrous metals, rare metals, rare earth elements, and precious metals, from raw metal ores and secondary resources. Moreover, the enhanced leaching mechanisms by ultrasound are discussed in detail and summarized based on the improvement of leaching kinetics, enhancement of the mass transfer and diffusion of lixiviants, and promotion of the oxidative conversion of metals from insoluble to soluble states. Lastly, the challenges and outlooks of future research on the leaching recovery for valuable metals with the assistance of ultrasound irradiation are proposed.

Ammoniacal leaching behavior and regularity of zinc ash

In this work, a new hydrometallurgical process was developed to treat zinc ash produced from the hot galvanizing industry. The theoretical analysis shows the feasibility of dissolving zinc ash in the NH3–NH4Cl–H2O system, and the dissolution products are predominantly composed of Zn (NH3)4 2+. The impacts of different experimental conditions were examined, and the leaching ratio of zinc was as high as 96.4% under the conditions of NH3/NH4 + ratio of 1:1, liquid/solid of 9:1, total ammonia concentration of 8 mol/L and the stirring speed of 250 rpm at 313 K for 120 min. The kinetics of the leaching process were investigated and the calculated apparent activation energy was approximately 4.69 kJ/mol, which indicated that the zinc ash leaching process was controlled by diffusion-controlled. As revealed by the determination of impurity ions, on one hand, there were fewer impurities in the leaching solution, and the concentrations of Fe2+ and Pb2+ in solution are less than 0.02 mg/L and 0.05 mg/L respectively; on the other hand, there was no need for further impurity removal in this process. The proposed process has a certain application value in treating zinc ash.

Selective Leaching and Recovery of Er, Gd, Sn, and In from Liquid Crystal Display Screen Waste by Sono-Leaching Assisted by Magnetic Separation

We report a facile, economic, and ecofriendly method for selective recovery of Er, Gd, Sn, and In from liquid crystal display (LCD) screen wastes by ultrasound-assisted leaching, followed by magnetic separation. Thermodynamic analysis showed that the pyrophosphate ion is an excellent leaching agent for Er, Gd, and In at pH values below 8. Dissolved screen waste powder was subjected to leaching at room temperature using aqueous solutions of 0.05 M of sodium pyrophosphate (Na₄P₂O₇) as the leaching agent; hydrogen peroxide (H₂O₂) (3 v/v %) was added as an auxiliary reducing agent, and an ultrasonic source was used in the process. Once completed, magnetic separation was applied to the leached residue. The average contents of Er, In, Sn, and Gd in the LCD screen were found to be 477, 2422, 835, and 93 mg·kg^-1, respectively, of which 93, 97, 72, and 99% were selectively recovered from the waste material by this method at pH 3 after 2 h of leaching. The proposed method emerges as an easy and selective process for leaching Er from LCD screen wastes and concentrating In, Sn, and Gd in a separable magnetic solid.

Effectiveness of thermal treatment on Pb recovery and Cl removal from sintering dust

Sintering dust is considered as a hazardous waste material owing to its high heavy metal content. In this study, a new technology for the treatment of sintering dust via chlorination roasting was developed. The chlorination behavior of Pb at high temperatures was studied. The volatilization behavior of Pb and Cl was found using different analytical techniques, such as scanning electron microscopy and energy dispersive X-ray spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence, and atomic absorption spectroscopy. In addition, the thermodynamics and kinetics of the chlorination mechanism of Pb at high temperatures were studied. Thermodynamic analysis results showed that quartz and the chlorinating agent played key roles in the process of chlorination. Compared with KCl and NaCl, CaCl₂ showed superiority in the chlorination. The phase transformation of sintering dust at different temperatures was analyzed. The volatilization rates of Pb and Cl reached 98.69 % and 84.55 %, respectively. The study of kinetics showed that the volatilization of PbCl₂ was controlled by diffusion, and the apparent activation energy is 7.97 kJ/mol. Finally, chlorination roasting residue can be recycled for iron and steel metallurgy.

Ultrasound-assisted leaching of spent lithium ion batteries by natural organic acids and H2O2

Ultrasound-assisted bioacid leaching was examined for the extraction of valuable metals from spent lithium ion batteries (LIBs). In this work, organic acids in lemon juice were used as the leaching agent together with H₂O₂. Three effective factors, namely solid/liquid (S/L) ratio, lemon juice percentage, and H₂O₂ volume percentage, were optimized using Response Surface Methodology (RSM). The optimal conditions were found to be 0.98% (w/v) S/L ratio, 57.8% (v/v) lemon juice and 8.07% (v/v) H₂O₂ in the leaching liquor, achieving recovery of 100% Li, 96% Co and 96% Ni. Furthermore, the individual effects of ultrasound, H₂O₂ and lemon juice on metal recovery were studied and the results showed that without H₂O₂ or lemon juice, the metal recovery rates decreased greatly while the absence of ultrasound reduced recovery rates to a much smaller extent, indicating that both H₂O₂ and lemon juice were essential in the leaching process. The effect of time on the metals recoveries was examined and results showed that Li and Co recovery reached 100% with the leaching time of 35 min. The modified shrinking core modeling results suggested that chemical reaction was the rate controlling step.

Effectiveness of microwave-assisted thermal treatment in the extraction of gold in cyanide tailings

A new technology for treating cyanide tailings (CT) by microwave chlorination roasting was first proposed in this study. A green process with prospective environmental and economic significance was experimentally and theoretically established for the sustainable extraction of gold from CT. The microwave roasting behavior and trajectory of gold in different gold-bearing bodies under microwave-enhanced roasting and conventional roasting conditions were explored and compared by introducing the concept of thermal and non-thermal effects provided by the microwave field. At the same time, the superiority of microwave chlorination roasting was verified by a series of experiments. Under the same conditions of the roasting experiments, the energy consumption of conventional calcination was more than double greater than that of microwave roasting. Finally, the essence of microwave chlorination roasting in the treatment of CT was summarized as a non-polluting process.

Electrochemical Performance of β-Nis@Ni(OH)2 Nanocomposite for Water Splitting Applications

Investigation on the formation mechanism of the β-NiS@Ni(OH)₂ nanocomposite electrode for electrochemical water splitting application was attempted with the use of the hydrothermal processing technique. Formation of single-phase β-NiS, Ni(OH)₂ and composite-phase β-NiS@Ni(OH)₂ has been thoroughly analyzed by X-ray diffractometer (XRD) spectra. Three different kinds of morphologies such as rock-like agglomerated nanoparticles, uniformly stacked nanogills, and uniform nanoplates for β-NiS, Ni(OH)₂, and β-NiS@Ni(OH)₂ materials, respectively, were confirmed by SEM images. The characteristic vibration modes of β-NiS, Ni(OH)₂, and β-NiS@Ni(OH)₂ nanocomposites were confirmed from Raman and Fourier transform infrared spectra. Near band edge emission and intrinsic vacancies present in the nanocomposites were retrieved by photoluminescence spectra. The optical band gaps of the synthesized nanocomposites were calculated as 2.1, 2.5, and 2.2 eV for β-NiS, Ni(OH)₂, and β-NiS@Ni(OH)₂ products, respectively. The high-performance electrochemical water splitting was achieved for the β-NiS@Ni(OH)₂ nanocomposite as 240 mA/g at 10 mV/s from a linear sweep voltammogram study. The faster charge mobile mechanism of the same electrode was confirmed by electrochemical impedance spectra and a Tafel slope value of 53 mV/dec. The 18 h of stability was achieved with 95% retention, which was also reported for the NiS@Ni(OH)₂ nanocomposite for continuous electrochemical water splitting applications.

Roasting Pretreatment Combined with Ultrasonic Enhanced Leaching Lead from Electrolytic Manganese Anode Mud

A method of conventional roasting pretreatment combined with ultrasonic enhanced leaching with ammonium acetate was proposed to solve the difficult problem of lead in electrolytic manganese anode mud. The effects of concentration, liquid–solid ratio, temperature, leaching time and rotating speed on the leaching process under conventional and ultrasonic conditions were studied, and the lead leaching rate can be as high as 93.09% under optimized process parameters. A leaching kinetic model under conventional and ultrasonic conditions was established to explore the restrictive links of the leaching process. The results show that the leaching process under both conventional and ultrasonic conditions is controlled by diffusion, and the activation energies are 29.40 kJ/mol and 26.95 kJ/mol for the conventional and ultrasound enhance leaching processes, respectively.

Efficient cleaning extraction of silver from spent symbiosis lead-zinc mine assisted by ultrasound in sodium thiosulfate system

The process to fast recovery of silver from the spent symbiosis lead-zinc mine enhanced by ultrasound has been developed. A system composed of thiosulfate and the spent symbiosis lead-zinc mine under ultrasound radiation is researched and compared with regular methods to prove the superiority of ultrasound enhanced leaching. Oxygen is not provided by the usual way but by the cavitation of ultrasound, and the effect of ultrasonic enhanced leaching is more obvious than oxygen enhanced leaching effect. We are more authoritative by combining some valuable literature after conducting systematic experiments. The process mechanism was analyzed by fire assaying, XRD, XRF, SEM and EDS. The optimal conditions were found out through single factor experiments: stirring rate of 300 rpm, thiosulfate concentration of 75 g/L, leaching temperature of 303 K, PH of 5, leaching time of 2 h and the ultrasound power of 100 W. And the leaching rate is 77.34% under the best conditions. When the ultrasonic experiment has the same parameters as the normal, the leaching rate at five minutes under ultrasonic conditions was 73.88%, while the leaching rate was only 72.51% at two hours under normal conditions. The apparent activation energy under conventional and ultrasonic conditions is 12.47 kJ/mol and 12.35 kJ/mol, respectively, and it is proved that both are controlled by diffusion.