Enhanced green remediation and refinement disposal of electrolytic manganese residue using air-jet milling and horizontal-shaking leaching

The reclamation and reuse of electrolytic manganese residue (EMR) as a bulk hazard solid waste are limited by its residual ammonia nitrogen (NH4+-N) and manganese (Mn2+). This work adopts a co-processing strategy comprising air-jet milling (AJM) and horizontal-shaking leaching (HSL) for refining and leaching disposal of NH4+-N and Mn2+ in EMR. Results indicate that the co-use of AJM and HSL could significantly enhance the leaching of NH4+-N and Mn2+ in EMR. Under optimal milling conditions (50 Hz frequency, 10 min milling time, 12 h oscillation time, 400 rpm rate, 30 ℃ temperature, and solid-to-liquid ratio of 1:30), NH4+-N and Mn2+ leaching efficiencies were optimized to 96.73% and 97.35%, respectively, while the fineness of EMR was refined to 1.78 µm. The leaching efficiencies of NH4+-N and Mn2+ were 58.83% and 46.96% higher than those attained without AJM processing. The AJM used strong airflow to give necessary kinetic energy to EMR particles, which then collided and sifted to become refined particles. The AJM disposal converted kinetic energy into heat energy upon particle collisions, causing EMR phase transformation, and particularly hydrated sulfate dehydration. The work provides a fire-new and high-efficiency method for significantly and simply leaching NH4+-N and Mn2+ from EMR.

Bioleaching of heavy metals from metal tailings utilizing bacteria and fungi: Mechanisms, strengthen measures, and development prospect

Recovering key metals from secondary sources is an indispensable strategy for preventing metal shortages and reducing the risk of toxic releases into the environment. Metal mineral resources continue to be depleted and the global supply chain will face metal scarcity. The use of microorganisms for metal transformation plays an important role in the bioremediation of secondary resources. It shows great potential for development due to its compatibility with the environment and possible cost effectiveness. The results of the study show that the influence of bioleaching processes and effects are mainly analyzed from microorganisms, mineral properties and leaching environmental conditions. In this review article, we elucidate light on the role and mechanisms of fungi and bacteria involved in extracting different metals from tailings, including acidolysis, complexolysis, redoxolysis, and bioaccumulation. Key process parameters that affect the efficiency based bioleaching are discussed, providing referenceable pathways to improve leaching efficiency. The investigation concludes that exploitation of the functional genetic role of microorganisms and their optimal growth conditions can achieve efficient leaching of metals. It was found that the improvement of microbial performance was achieved at the level of mutagenesis breeding, mixed culture microorganisms, and genetics. Moreover, control of leaching system parameters and removal of passivation films can be achieved by adding biochar and surfactants in the leaching system as an effective means to improve tailings leaching. Knowledge about cells with minerals and their detailed interactions at the molecular level is still relatively scarce and the field could be deepened and this area needs to be further explored in the future. The challenges and the key issues associated with the bioleaching technology development are elaborated as a green and effective bioremediation strategy for the environment and prospects for imminent are also highlighted.

Recovery of rare earth elements from waste phosphors via alkali fusion roasting and controlled potential reduction leaching

Waste phosphors, which contain the quantity of rare earth and toxic metals, need to be recycled for both environmental protection and the sustainable development of rare earth resources. Due to the magnesium-aluminum spinel structure, it is difficult to extract cerium and terbium from waste phosphors. In this study, a facile process for recovering rare earth elements from waste phosphors was developed. First, the waste phosphors were alkali roasted to destroy the aluminum-magnesium spinel structure in the blue and green powders. NaOH was found to be a more suitable additive than Na₂CO₃, NaHCO₃, and K₂CO₃ for alkali roasting. Then, the roasted slag was washed with water to remove the aluminum and controlled potential reduction leaching was conducted. FeCl₂ was used as the reductant (dosage of 0.04) in the 3 mol·L^-1 HCl solution at a leaching temperature of 50 °C for 60 min. The leaching efficiencies of Y, Eu, Ce, and Tb were up to 99.1 %, 99.4 %, 98.6 %, and 98.8 %, respectively. The reduction leaching process obeys the shrinking core model and depends on the diffusion. This process can effectively improve the leaching efficiency of rare earth elements from waste phosphors and provides theoretical and technical support for the recycling of waste phosphors.

Recycling of valuable metals from spent lithium-ion batteries by self-supplied reductant roasting

The massive spent lithium-ion batteries (LIBs) need to be recycled due to their increasing decommission in recent years. This paper aims to propose an effective process that uses self-supplied reductant roasting and acid leaching to recover Lithium, Nickle, Cobalt and Manganese from spent LIBs. In the absence of external carbon resources, the waste membrane from spent LIBs was used as the reductant in the self-supplied reductant roasting. A thermodynamic analysis was conducted to judge the possible reduction reaction between the cathode material and waste membrane. Then, the effects of roasting temperature, roasting time and membrane dosage on the crystal structure and phase transformation of roasting products were investigated and optimized. After the roasting process, the valence state of metals in the cathode material decreased and the structure became loose and porous. Moreover, the layer structure of the cathode material was transformed into groups of Li₂CO₃, Ni, Co, NiO, CoO and MnO. Further, the reduction effect of cathode powders under each roasting condition was verified under the same leaching conditions. After leaching for 30 min, the leaching efficiencies of Li, Ni, Co and Mn were over 99% under the optimum roasting conditions. Finally, economic assessments proved that the proposed process is profitable. The whole process demonstrates an effective and positive way for recycling spent LIBs and making full use of their waste membrane, which promotes resource recovery and environmental protection.

High-efficiency leaching of valuable metals from waste Li-ion batteries using deep eutectic solvents

With the penetration of lithium-ion batteries (LIBs) into electric vehicles, the recycling of waste LIBs is inevitable from the perspective of health, economy and environmental protection. Herein is reported a novel green method for extracting valuable metals from the cathode of LIBs, in which the Deep Eutectic Solvent (DES) is used as leachate to dissolve electrode material waste. Mixing choline chloride (ChCl) and malonic acid is helpful to effectively improve the reduction ability of DES, resulting in superior leaching efficiency. At the lower temperature (100 °C), the leaching efficiency of cobalt and lithium reached up to 98.61% and 98.78%, respectively. X-ray absorption near edge structure (XANES) spectroscopy demonstrated that DESs could act as both leachate and reducing agent, which could destroy the covalent bonds of metal oxides to form a cobalt (II)-chlorine complex. This method is straightforward to operate and does not involve the additional reducing agents, which is held promise to bring economic and sustainable development prospects in the field of lithium battery development.

Towards a method for optimized extraction of soluble nutrients from fresh and composted chicken manures

A preliminary method for extraction of soluble nutrients from organic materials is presented that investigates important characteristics of design for efficient extraction. The study was conducted in Polyvinyl Chloride (PVC) columns (length: 50 and 100 mm, diameter: 87.5 mm) filled with fresh and composted chicken manures, packed to densities in the range of 0.2-0.6 g cm(-3). The columns were leached with distilled water. A total of 5 cm(3) of water per cm(3) of material was applied. Leachate collection was sequentially partitioned to enable determination of soluble nutrients throughout time, including: total dissolved nitrogen (TDN), water soluble phosphorus (P) and potassium (K). Waste material state, density of packing and lengths of column all significantly (P<0.05) affected the concentration of ions in the leachate. In general, longer contact time between the percolating water and the material resulted in higher (P<0.05) concentration of ions in the leachate. Cumulative TDN and water soluble-P were greater (P<0.05) in fresh manure leachates, compared with compost leachates. Although, compost leachates provided relatively greater (P<0.05) concentration of K. Salinity ionic concentration of leachates, determined as Na and Cl, was consistently greater from fresh manure as compared to that from mature compost. Fresh manure and mature compost were determined to provide different responses to nutrient leaching because of differences in physico-chemical characteristics. Saturated hydraulic conductivity in fresh manure columns reduced rapidly with application of water to the columns. The mechanisms involved in this process are discussed with the implication for nutrient extraction and use of leachate from chicken manure waste sources.