An Emission-Free Vacuum Chlorinating Process for Simultaneous Sulfur Fixation and Lead Recovery from Spent Lead-Acid Batteries

Physicochemical reactions in e-waste recycling

Electronic waste (e-waste) recycling is becoming a global concern owing to its immense quantity, hazardous character and the potential loss of valuable metals. The many processes involved in e-waste recycling stem from a mixture of physicochemical reactions, and understanding the principles of these reactions can lead to more efficient recycling methods. In this Review, we discuss the principles behind photochemistry, thermochemistry, mechanochemistry, electrochemistry and sonochemistry for metal recovery, polymer decomposition and pollutant elimination from e-waste. We also discuss how these processes induce or improve reaction rates, selectivity and controllability of e-waste recycling based on thermodynamics and kinetics, free radicals, chemical bond energy, electrical potential regulation and more. Lastly, key factors, limitations and suggestions for improvements of these physicochemical reactions for e-waste recycling are highlighted, wherein we also indicate possible research directions for the future.

Novel pathway of stabilized Cu2S volatilization by derivated CH3Cl

Stabilized heavy metals-containing phases and low chlorine utilization limit heavy metals chlorination reactions. The traditional method of adding chlorinating agents can promote heavy metals chlorination volatilization, but the limiting factor has not been resolved and more chlorides are emitted. Herein, a new reaction pathway to promote heavy metals chlorination volatilization through the transformation of stabilized heavy metals-containing phases and chlorine species by the addition of biomass at the sintering is first reported. The Cu volatilization efficiency increased sharply from 50.50% to 93.21% compared with the control, Zn, Pb, and Cd were nearly completely volatilized. Results show that the biomass carbonization process was more important for Cu chlorination volatilization. Stabilized heavy metals-containing phases were converted from Cu2S to CuO and Cu2O with the biochar and oxygen, increasing the activity of Cu. The chlorine species KCl reacted with CH3-containing groups to form CH3Cl, which reacted with CuO with a lower Delta G than HCl and Cl2, increasing the tendency for the conversion of CuO to CuCl. Cu chlorination volatilization process, following shrinking core kinetic model and controlled by chemical reactions. The outcomes fundamentally addresses the limiting step for heavy metals chlorination volatilization, supporting the incineration fly ash harmless treatment.

Novel PbO@C composite material directly derived from spent lead-acid batteries by one-step spray pyrolysis process

A one-step spray pyrolysis process is investigated for the first time in the field of spent lead-acid batteries (LABs) recycling. The spent lead paste that derived from spent LAB is desulfurized and then leached to generate the lead acetate (Pb(Ac)₂) solution, which is then sprayed directly into a tube furnace to prepare the lead oxide (PbO) product by pyrolysis. The low-impurity lead oxide product (9 mg/kg Fe and 1 mg/kg Ba) is obtained under the optimized conditions (the temperature of 700 °C, the pumping rate of 50 L/h, and the spray rate of 0.5 mL/min). The major crystalline phases of the synthesized products are identified to be α-PbO and β-PbO. In the spray pyrolysis process, Pb(Ac)₂ droplets are sequentially transformed into various intermediate products: H₂O(g)@Pb(Ac)₂ solution, Pb(Ac)₂ crystals@PbO, and the final PbO@C product. Owning its carbon skeleton structure, the recovered PbO@C product (carbon content of 0.14%) shows better performance than the commercial ball-milled lead oxide powder in battery tests, with higher initial capacity and better cycling stability. This study could provide a strategy for the short-route recovery of spent LABs.

Efficient separation and recovery of lithium through volatilization in the recycling process of spent lithium-ion batteries

Spent lithium-ion batteries (LIBs) comprise different kinds of valuable metals with recovery and reuse value. Aiming to address the difficulty of recycling lithium from spent LIBs through conventional pyrometallurgy, a new method of high-efficiency separation and recovery of lithium through volatilization is proposed. In this new method, spent LIBs as the raw material, copper slag as the only flux and CaCl₂ as an additive are utilized to recover lithium from spent LIBs. Under the optimal conditions, the volatilization rate of Li was 96.87%. During the smelting process, lithium is volatilized into the gas phase in the form of LiCl, where lithium can be recycled from the dust. In light of the experimental results, the addition of CaCl₂ contributes to the formation of LiCl. The kinetics study showed that the volatilization of LiCl was controlled by an interfacial chemical reaction, and the apparent activation energy was 42.57 kJ/mol. In addition, Li₂CO₃ could be obtained from lithium-containing dust using a precipitation process. This method achieves efficient separation of lithium during the reduction smelting process. The phase transformation and kinetics of the separation process were investigated, and reaction mechanism was revealed. Importantly, the novel process provides new ideas and perspectives for the separation of lithium from spent LIBs through a pyrometallurgical process.

Evaluation of a green-sustainable industrialized cleaner utilization for refractory cyanide tailings containing sulfur

In order to achieve the clean treatment of refractory cyanide tailings containing sulfur, a novel microwave-assisted chlorination thermal treatment recovery technology was proposed in this paper. On the basis of studying the mineralogy of cyanide tailings, the treatment capacity of common chlorinated agents for refractory cyanide tailings containing sulfur was compared. CaCl₂ as the best chlorination agent, gold recovery and chlorine removal rates were 85.2% and 95%, under the optimal conditions. The specific action mechanism of CaCl₂ in the process of microwave roasting was studied. Under the action of microwave, CaCl₂ accelerated decomposition into chlorine-containing gas and rapidly diffused in cracks caused by thermal stress to ensure gold volatilization and chlorination. Finally, the approach and mechanism of removing residual harmful substances in roasting slag were proposed based on the environmental assessment of roasting slag. Environmental pollution and corrosion of building materials can be effectively avoided in the later transportation and secondary utilization of roasting slag.

An infinite life cycle assessment model to re-evaluate resource efficiency and environmental impacts of circular economy systems

Challenges exist in life cycle assessment (LCA) to evaluate resource efficiency and environmental impacts of circular economy systems. Rules attributing recycling benefits/burdens are inconsistent, causing system boundary ambiguity. Besides, LCAs covering one or several life cycles fail to capture the complete resource path, which leads to unfair assessment results for the primary life cycle. This paper develops an infinite life cycle assessment model, which integrates LCA, substance flow analysis, and a state transition matrix into an infinite-life-cycle framework. On this basis, algorithms are formulated to quantify the resource efficiency and attribute environmental impacts following the principle of whole first, then allocation. Our model is demonstrated by a case study of lead-acid batteries. Results show that the resource efficiency of lead in the infinite life cycle assessment model is at least 118.75% higher than that of primary lead derived from the typical finite life cycle models. Measured by the index of environmental toxicity potential, environmental impacts are transferred from the primary product life cycle to recycled product life cycles, with the range fluctuating from 66.26% to 68.12%. Our model enables scholars to make more reasonable assessments for circular economy systems based on traditional LCA adjustment. From the infinite-life-cycle perspective, sustainable production policies should focus on increasing the recycling rate of waste products rather than limiting the exploitation of natural resources.

Effective separation and recovery of Zn, Cu, and Cr from electroplating sludge based on differential phase transformation induced by chlorinating roasting

Heavy metals in electroplating sludge (ES) are usually amorphous and easily released in the environment. Especially for the ES containing multiple heavy metals, owing to the complex composition and lack of effective disposal method, it has been storage for a long time. In order to avoid environmental pollution, effective treatment methods are very urgent and necessary. Here, chlorinating roasting method was developed to enlarge the phase difference of heavy metals to fulfill the utilization of ES containing multiple heavy metals (Zn, Cr, and Cu). When CaCl₂ was used as additive, Zn and Cu were volatilized to the gas phase, while Cr was oxidized to Cr(V)/(VI) and retained in the solid phase with readily leachable state. The recovery percentage of Zn, Cu, and Cr can reach 99%, 98%, and 96% respectively by chlorinating roasting for 4 h at 1000 °C with the CaCl₂ addition proportion of 100%. After further extraction and purification, the purity of Cr and Zn can reach 92% and 99% respectively. Moreover, the mechanism of the differential phase transformation induced by chlorinating roasting was analyzed by the method of thermodynamics and kinetics. The kinetic reaction equation of the ZnCl₂ and CuCl₂ volatilization process can be described by phase boundary reaction and the function is G(α) = 1-(1-α)^1/3. This work provides a simple and effective method for the treatment of ES containing multiple heavy metals.

Simultaneous separation and immobilization of Cr(VI) from layered double hydroxide via reconstruction of the key phases

Layered double hydroxide (LDH) is one of the key host phases of Cr(VI) in the natural environment and chromite ore processing residue (COPR), causing serious pollution by Cr(VI). Therefore, efficient extraction or immobilization of the incorporated Cr(VI) in LDH is urgently needed. In this work, simultaneous separation and immobilization of Cr(VI) in LDH by using MgCl₂·6H₂O under thermal treatment is innovatively proposed. Cr was volatilized as CrCl₃ and was immobilized as MgCr₂O₄ accounted for 62.2% and 37.8%, respectively, under the optimal condition (the mole ratio of Cl/Cr is 9, 700 °C and 120 min). The underlying reaction mechanisms are as follows: (i) HCl produced by MgCl₂·6H₂O accelerates the destruction of Cr(VI)-LDH layer structure, completely exposing the incorporated Cr(VI), (ii) Cr(VI) is reduced to Cr(III) by Cl^-, part of which is directly immobilized as MgCr₂O₄, and the other part generates CrCl₃, which is volatilized or further combined with Mg²⁺ to form MgCr₂O₄. The total Cr leaching concentration of the practical COPR sample treated by this method dramatically decreases from 421 to 0.7 mg/L, well below the landfill standard limit (4.5 mg/L). This work provides an attainable strategy for thorough remediation of COPR and inspires the treatment of heavy metal-containing LDH.

One-step extraction of high-purity CuCl2·2H2O from copper-containing electroplating sludge based on the directional phase conversion

The recovery of heavy metals is a vital way to turn electroplating sludge into resources and reduce its environmental hazards. However, the complex compositions of the polymetallic electroplating sludge severely limit the selective recovery of metal resources such as copper. In this study, we took a kind of copper-containing electroplating sludge (C-ES) as an example present and investigated the process of copper extraction. The copper and other metals were directional converted through an accurate phase transformation process carried out by chlorination combined with thermal regulation. Eventually, the copper was selectively recovered in the form of CuCl₂·2H₂O, while the rest of the metals were converted into stable metal salts or oxides. The HCl solution was the best regulator for selective copper recovery. Under the optimal conditions, the recovery of copper approached 97% and the purity of the CuCl₂·2H₂O product was about 95%. The kinetic reaction equation of the CuCl₂ volatilization process can be described by Power Low, G(α) = α^1/15. The economic estimate based on experimentation indicates the profit of recycling CuCl₂·2H₂O is about $23.2/kg. This work provides a novel, simple, and efficient approach to the selective recovery of heavy metal from polymetallic solid wastes.

Organic Electroactive Molecule-Based Electrolytes for Redox Flow Batteries: Status and Challenges of Molecular Design

This is a critical review of the advances in the molecular design of organic electroactive molecules, which are the key components for redox flow batteries (RFBs). As a large-scale energy storage system with great potential, the redox flow battery has been attracting increasing attention in the last few decades. The redox molecules, which bridge the interconversion between chemical energy and electric energy for RFBs, have generated wide interest in many fields such as energy storage, functional materials, and synthetic chemistry. The most widely used electroactive molecules are inorganic metal ions, most of which are scarce and expensive, hindering the broad deployment of RFBs. Thus, there is an urgent motivation to exploit novel cost-effective electroactive molecules for the commercialization of RFBs. RFBs based on organic electroactive molecules such as quinones and nitroxide radical derivatives have been studied and have been a hot topic of research due to their inherent merits in the last decade. However, few comprehensive summaries regarding the molecular design of organic electroactive molecules have been published. Herein, the latest progress and challenges of organic electroactive molecules in both non-aqueous and aqueous RFBs are reviewed, and future perspectives are put forward for further developments of RFBs as well as other electrochemical energy storage systems.

Multiple hazardous elements in nanoparticulate matter from a Caribbean industrialized atmosphere

Modern microscopy studies are capable of revealing ultra-fine particles (UFPs) and nanoparticles (NPs) that are produced in the processes related to traffic vehicular, industrial, metropolitan, and marine aerosol dry deposition in the coastal zones. Especially, secondary aerosol passages complexes categories of NPs and UFPs, which can be accumulated on construction compounds and by dry deposition, encourages multiples monuments deterioration routes. The advanced electron microscopies method is one of the most utilized in environmental studies. Between the different industrial areas in the world, the Caribbean area is the most relevant symbols of air quality due to climatic conditions with strong winds, but this study shows that regionally the most industrialized region does not have an adequate air quality. In the present work, electron microscopy analyses are used to describe of the extent of ultra-fine particle and nanoparticles in walls in contact to weathering. Numerous phases were recognized by advanced mineralogy methods. Thanks to the new analytical procedure it was feasible to understand NPs and UFPs; the occurrence of potential hazardous elements (PHEs), most of them as minerals but also combined in multiple accumulations with Al-Cr-Fe-K-Mg-Pb-Si-Ti-Zn amorphous; and carbonaceous phases.

Cleaner Recycling of Spent Lead-Acid Battery Paste and Co-Treatment of Pyrite Cinder via a Reductive Sulfur-Fixing Method for Valuable Metal Recovery and Sulfur Conservation

This study proposes a cleaner lead-acid battery (LAB) paste and pyrite cinder (PyC) recycling method without excessive generation of SO2. PyCs were employed as sulfur-fixing reagents to conserve sulfur as condensed sulfides, which prevented SO2 emissions. In this work, the phase transformation mechanisms in a PbSO4-Na2CO3-Fe3O4-C reaction system were studied in detail. Furthermore, the co-treatment of spent LAB and PyCs was conducted to determine the optimal recycling conditions and to detect the influences of different processing parameters on lead recovery and sulfur fixation. In addition, a bench-scale experiment was carried out to confirm the feasibility and reliability of this novel process. The results reveal that the products were separated into three distinct layers: slag, ferrous matte, and crude lead. 98.3% of lead and 99% of silver in the feed materials were directly enriched in crude lead. Crude lead with purity of more than 98 wt.% (weight percent) was obtained by a one-step extraction. Lead contents in the produced matte and slag were below 2.7 wt.% and 0.6 wt.%, respectively. At the same time, 99.2% total sulfur was fixed and recovered.

Effective Extraction of Cr(VI) from Hazardous Gypsum Sludge via Controlling the Phase Transformation and Chromium Species

Through controlling the phase transformation and chromium species under hydrothermal condition, the Cr(VI) was extracted fully from hazardous Cr(VI)-containing gypsum sludge, with a very high efficiency of more than 99.5%. Scanning transmission electron microscopy, X-ray absorption fine structure, and density functional theory calculation results revealed that the dissolution-recrystallization of CaSO₄·2H₂O into CaSO₄ was the key factor to fully release the encapsulated Cr(VI). Moreover, the mineralizer (persulfate salt) provided H⁺ and SO₄^2- ions, the former made an acidic condition to transform the released CrO₄^2- into the specie (Cr₂O₇^2-) with less similarity to SO₄^2-, which further prevented the recombination of the released Cr(VI) with gypsum; and the latter was essential to accelerate crystal growth of calcium sulfate so as to enhance Cr(VI) extraction. This work would provide an instructive guidance to fully extract heavy metals from hazardous solid wastes via the control of crystal transformation and the pollutant species.

Toward sustainable and systematic recycling of spent rechargeable batteries

A comprehensive and novel view on battery recycling is provided in terms of the science and technology, engineering, and policy.