Effective recycling of Cu from electroplating wastewater effluent via the combined Fenton oxidation and hydrometallurgy route

An entire recycling of spent Al-bearing cathode powder as giniite sphere and lithiophophate plate with leaching-hydrothermal-precipitation process

Spent lithium battery is a polymetallic waste, and valuable to be recovered as Li-bearing chemical with the barriers of impurities separation, especially Fe and Al. Here in, Li-rich cathode powder was manually disassembled from spent battery, and then recovered as lithiophosphate plate in consideration of effective separation of impure Fe/Al. The powder comprised of 23.2% Fe, 3.2% Al, 5.5% Li and 19.6% P, and then dissolved by azotic acid as Li-rich solution. When the solution was heated to 190°C for 10 h with the supplementary of saccharose, more than 99.9% Fe and 98.9% Al were removed as spherical giniite particles, in accordance with the rest of Fe/Al at the concentrations of 2.1 and 14 mg/L, whilst the loss of Li was less than 1.5%. But without saccharose, the Fe/Al removals only achieved by 99.2% and 52.1%. It is also found that the Fe/Al/Li removal achieved by 99.6%, 96% and 25.3% after adjusting the solution to pH 2.7 by NaOH. After hydrothermal treatment, the rest Li can be recycled as lithiophosphate plate by pH adjustment, in contrast to the recovery efficiency of 98.5% Li. Such method raised a facile route to effectively separate impure Fe/Al from Li-rich cathode powder, and showed promising application in the industrial recovery of spent battery.

Revitalizing contaminated lands: A state-of-the-art review on the remediation of mine-tailings using phytoremediation and genomic approaches

The mining industry has historically served as a critical reservoir of essential raw materials driving global economic progress. Nevertheless, the consequential by-product known as mine tailings has consistently produced a substantial footprint of environmental contamination. With annual discharges of mine tailings surpassing 10 billion tons globally, the need for effective remediation strategies is more pressing than ever as traditional physical and chemical remediation techniques are hindered by their high costs and limited efficacy. Phytoremediation utilizing plants for remediation of polluted soil has developed as a promising and eco-friendly approach to addressing mine tailings contamination. Furthermore, sequencing of genomic DNA and transcribed RNA extracted from mine tailings presents a pivotal opportunity to provide critical supporting insights for activities directed towards the reconstruction of ecosystem functions on contaminated lands. This review explores the growing prominence of phytoremediation and metagenomics as an ecologically sustainable techniques for rehabilitating mine-tailings. The present study envisages that plant species such as Solidago chilensis, Festuca arundinacea, Lolium perenne, Polygonum capitatum, Pennisetum purpureum, Maireana brevifolia, Prosopis tamarugo etc. could be utilized for the remediation of mine-tailings. Furthermore, a critical evaluation of the organic and inorganic ammendments that optimize conditions for the remediation of mine tailings is also provided. The focus of this review extends to the exploration of environmental genomics to characterize microbial communities in mining sites. By delving into the multifaceted dimensions of phytoremediation and genomics for mine tailings, this study contributes to the ongoing efforts to revitalize contaminated lands for a sustainable and environmentally friendly future.

Near-complete recycling of real mix electroplating sludge as valuable metals via Fe/Cr co-crystallization and stepwise extraction route

In electroplating sludge, iron (Fe) and aluminum (Al) are common impurities that need to be separated before recycling valuable heavy metals. However, the traditional Fe/Al separation process often leads to significant losses of heavy metals. To address this issue, a new approach was developed to sequentially separate Fe/Al and recycle chromium (Cr) and nickel (Ni) from real electroplating sludge. The sludge contained 4.5% Cr, 1.2% Al, 1.1% Ni, and 14.6% Fe. Initially, the sludge was completely dissolved in a mixture of hydrochloric and nitric acids. The resulting acid solution was then heated to 160 °C for 10 h with the addition of saccharose. This hydrothermal treatment led to the hydrolysis and crystallization of 98.3% of Fe, 31.8% of Cr, 1.1% of Al, and 4.9% of Ni, forming akaganeite-bearing particles. It was observed that the excessive amount of saccharose also improved the removal of Cr, Al, and Ni, but decreased the removal of Fe. After the hydrothermal treatment, the remaining supernatant was adjusted to different pH levels (1.9, 2.9, and 4.5, respectively), and then Al, Cr, and Ni were stepwise extracted using di-(2-ethylhexyl) phosphate acid (P204). The recycling efficiencies achieved were 97.4% for Al, 61.2% for Cr, and 89.3% for Ni. This approach provides a promising method for the stepwise separation of Fe/Al and the recycling of heavy metals from electroplating sludge.

Effect of inorganic anions on hydrothermal removal of impurities Fe/Al from Cu-bearing polymetallic leachate

Hydrometallurgy recycling of heavy metals from electroplating sludge is of hot spot in recent decades. Such recycling was tedious in the separation of impure Fe/Al prior to heavy metals from acid leachate after sludge dissolution. Herein, a facile hydrothermal route was developed to separate Fe/Al from Cu-bearing leachate. The results showed that when the leachate was directly hydrothermally treated at 160 °C in the presence of nitrate and ethanol, Al/Cu were stable in the leachate, but nearly 100% Fe was removed as hematite nanoparticles. With the addition of chloridion, the removal efficiencies of Fe/Al/Cu did not change apparently, but the corresponding precipitate was akageneite, not hematite. By replacing chloridion with sulfate, nearly 100% Fe and 98.6% Al were separated as natrojarosite/natroalunite block, while the Cu loss was only 1.7%. However, with the supplementary of phosphate, the Fe/Al removal achieved nearly 100%, but the Cu removal also achieved by 92.6%. The thermodynamic analysis showed that Cu was precipitated rapidly via the phosphate/Cu oxyhydroxide route by adding phosphate but removed slightly via the coordination route on the Fe/Al precipitates with the addition of nitrate, chloridion, and sulfate. In summary, Fe was effectively separated as hematite, akageneite, natrojarosite, and phosphate halite, in the presence of nitrate, chloridion, sulfate, and phosphate, separately. But the removal of Al as natroalunite and AlPO4 only started by adding sulfate and phosphate, respectively. Such results enabled a short hydrometallurgy process to effectively recycle heavy metals from electroplating sludge.

Efficient separation of impurities Fe/Al/Ca and recovery of Zn from electroplating sludge using glucose as reductant

Electroplating sludge (ES), a hazardous waste containing heavy metals and Fe/Al/Ca impurities, is conventionally disposed of in landfills. In this study, a pilot-scale vessel with an effective capacity of 20 L was applied to recycle Zn from real ES. The sludge contained 6.3 wt% Fe, 6.9 wt% Al, 2.6 wt% Si, 6.1 wt% Ca, and 17.6 wt% Zn and was treated using a four-step method. First, ES was dissolved in nitric acid after washing in a water bath at 75 °C for 3 h to produce an acidic solution with Fe, Al, Ca, and Zn concentrations of 4527.2, 3116.1, 3357.7, and 21,275 mg/L, respectively. Second, the acidic solution was added with glucose at an Mglucose/Mnitrate ratio of 0.08 and hydrothermally treated at 160 °C for 4 h. During this step, nearly 100 % Fe and 100 % Al were simultaneously removed as a mixture containing 53.1 wt% Fe2O3 and 45.7 wt% Al2O3. This process was repeated five times, during which the Fe/Al removal and Ca/Zn loss rates remained unchanged. Third, the residual solution was adjusted with sulfuric acid, and over 99 % Ca was removed as gypsum. The residual Fe, Al, Ca, and Zn concentrations were 0.44, 0.88, 52.59, and 31,177.1 mg/L, respectively. Finally, Zn in the solution was precipitated as ZnO with a concentration of 94.3 %. Economic calculations showed that each 1 t of ES processed created revenue of about $122. This is the first study of high-value metal resource recovery using real electroplating sludge at the pilot scale. This work highlights the pilot-scale application of resource utilization of real ES and provides new insights into the recycling of heavy metals from hazardous waste.

Perspective on pH adjustment in hydrometallurgical recycling of valuable metals from waste

pH adjustment was considered a simple step in the hydrometallurgy process, but its complicated operation was ignored in the past. In some industrial applications, the leachate pH was slowly adjusted by a diluted alkaline solution, with the defects of doubling the leachate volume and causing droplet hydrolysis/coagulation. Up to date, promising routes have been developed for rapid pH adjustment, especially in sealed high-temperature/pressure vessels. New routes emerged in some redox/decomposition reactions of nitrate/urea and organics. Such reactions did not start and/or were slow at room temperature but started spontaneously at high temperatures to generate/consume free H⁺. This induced pH adjustment in a rapid and homogeneous way.

Enhanced decomplexation of Cu-EDTA and simultaneous removal of Cu(II) by electron beam irradiation accompanied with autocatalytic fenton-like reaction: Synergistic performance and mechanism

Widely existing heavy metal complexes with high stability and poor biodegradability are intractable to be eliminated by conventional methods. In this study, electron beam (EB) irradiation characterized by rapidly producing strong oxidizing radicals was employed to effectively decompose Cu-ethylenediaminetetraacetic acid (Cu-EDTA) with almost complete elimination at 5 kGy. In terms of heavy metal removal, EB irradiation at relatively low doses was insufficient to remove copper ions, which was only 17.2% under 15 kGy. However, with the extra addition of 8 mM H₂O₂, such an irradiation dose could result in 99.0% copper ions removal. Mechanism analysis indicated that EB irradiation combined with spontaneously induced Fenton-like reactions were responsible for its excellent performance. The prime function of EB irradiation was to destroy the structure of Cu-EDTA with in-situ produced ·OH, and the subsequent released Cu-based intermediates could activate H₂O₂ to initiate autocatalytic chain reactions, correspondingly accelerating the degradation of complexes and the liberation of metal ions. Highly oxidative ·OH and O₂·^- were demonstrated as main active species acted on different positions of Cu-EDTA to realize gradual decarboxylation, synchronously generating low molecular weight compounds. XRD and XPS analysis showed that the released copper ions were mainly precipitated in the form of CuO, Cu(OH)₂ and Cu₂(OH)₂CO₃. In general, EB/H₂O₂ was an adoptable strategy for the disposal of such refractory heavy metal complexes.

Environmental behavior, human health effect, and pollution control of heavy metal(loid)s toward full life cycle processes

Heavy metal(loid)s (HMs) have caused serious environmental pollution and health risks. Although the past few years have witnessed the achievements of studies on environmental behavior of HMs, the related toxicity mechanisms, and pollution control, their relationship remains a mystery. Researchers generally focused on one topic independently without comprehensive considerations due to the knowledge gap between environmental science and human health. Indeed, the full life cycle control of HMs is crucial and should be reconsidered with the combination of the occurrence, transport, and fate of HMs in the environment. Therefore, we started by reviewing the environmental behaviors of HMs which are affected by a variety of natural factors as well as their physicochemical properties. Furthermore, the related toxicity mechanisms were discussed according to exposure route, toxicity mechanism, and adverse consequences. In addition, the current state-of-the-art of available technologies for pollution control of HMs wastewater and solid wastes were summarized. Finally, based on the research trend, we proposed that advanced in-operando characterizations will help us better understand the fundamental reaction mechanisms, and big data analysis approaches will aid in establishing the prediction model for risk management.

Activation of peroxymonosulfate by pyrophosphate for the degradation of AO7 at neutral pH

In the present study, pyrophosphate (PP) was used to activate peroxymonosulfate (PMS) for acid orange 7 (AO7) removal under neutral pH conditions. The removal rate of AO7 (20 mg/L) was 84% within the reaction time with a rate constant value of 0.0165 min^-1 under optimum conditions. Additionally, the effects of the concentrations of PMS and PP in solutions with various pH values and the coexisting inorganic anions on AO7 removal were measured. In addition, the performance of phosphate (P(V)) on PMS activation was compared with that of phosphite (P(III)) species. In contrast to P(III), the concentration of P(V) showed a positive correlation with the efficiency of AO7 decolorization. PMS activation in different types of buffer solutions was also examined, and the results indicated that the decolorization efficiency of AO7 induced by PP addition, and the buffer solution also contributed to PMS self-decomposition. Singlet oxygen (¹O₂) might be the primary reactive oxygen species (ROS) in the PP/PMS system in which AO7 is decolorized at an initial pH of 7.06, as indicated by quenching experiments and electron spin resonance (ESR) tests. Therefore, PP/PMS systems may be promising technologies for removing organic contaminants, particularly for PP-rich electroplating wastewater.

Resource utilization of hazardous Cr/Fe-rich sludge: synthesis of erdite flocculant to treat real electroplating wastewater

Cr/Fe-bearing sludge is a hazardous solid waste, produced at mass production in smelting, plating and surface finishing industries. Such waste is commonly treated by chemical detoxification and safety landfill, whereas only a few Cr-rich sludge is recycled as a tanning reagent. In this study, a novel route was developed to recycle Cr/Fe-bearing sludge as erdite-bearing flocculant for wastewater treatment. Results showed that two sludges were irregular aggregates, one of which contained 1.6 wt.% Cr (short for LS) and the other contained 4.2 wt.% Cr (HS). After hydrothermal treatment, stable Cr(III)/S-bearing product was formed from the Cr(VI) reduction in the sludges. Conversely, erdite was generated in nanorod form with diameter and length of 200 nm and 0.5-1 μm from LS, respectively, whereas grew radially to 1.5-2.5 μm for HS. The two erdite-bearing products were spontaneously hydrolysed to Fe/S-bearing flocs and showed similar performance in the treatment of real electroplating effluent with 91.55, 1.94 and 0.25 mg/L of Zn, Ni and Cr, respectively. For instance, by adding 1 g/L product of LS, the release of Cr from the products did not occur, and the residual Zn, Ni and Cr in the effluent was 0.25, 0.65 and 0.17 mg/L, respectively, which met the discharge standard of the electroplating industry. With the two converted products, the residual Zn/Ni/Cr concentrations were apparently lower than those of the raw sludges and other common reagents (e.g. polymeric ferric sulphate, activated carbon and diatomite). Thus, such erdite-bearing products could serve as a flocculant and then be applied in electroplating wastewater treatment.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Stepwise extraction of Fe, Al, Ca, and Zn: A green route to recycle raw electroplating sludge

Electroplating sludge is a hazardous waste produced in large quantities in the electroplating industry during production. It is rich in heavy metal resources and can be recovered as value-added heavy metal products. To recover Zn in electroplating sludge, Fe/Al/Ca impurities were effectively removed as hematite, boehmite, and calcium sulfate, respectively, via a facile hydrothermal method with reduction of nitric acid by addition of glucose. After the sludge was dissolved in nitric acid, the generated solution contained 6.1 g/L of Zn, 2.2 g/L of Fe, 2.5 g/L of Al, and 2.9 g/L of Ca. First, approximately 100% Fe was extracted as hematite nanoparticles containing 94.6 wt% Fe₂O₃ after the solution was treated at 190 °C for 6 h. Second, when the temperature was elevated to 270 °C, nearly 99% Al was isolated as boehmite particles containing 95.2 wt% Al₂O₃. Third, more than 98% Ca was removed as anhydrite, which contained 95.9 wt% CaSO₄, by adding sulfuric acid. During the steps, the total loss of Zn was less than 3%, and 5.75 g/L of residual Zn was recovered as zincite containing 92.2 wt% ZnO by adjusting the pH to 8. The dissolved Fe, Al, and Ca impurities were successfully removed as purified hematite, boehmite, and anhydrite, respectively, through the stepwise separation method by adjusting reaction temperatures and pH. The high content of Zn in the electroplating sludge was finally purified as zincite.

The Tolerance of Anoxic-Oxic (A/O) Process for the Changing of Refractory Organics in Electroplating Wastewater: Performance, Optimization and Microbial Characteristics

In order to investigate the tolerance of an anoxic-oxic (A/O) process for the changing of refractory organics in electroplating wastewater, optimize the technological parameters, and reveal the microbial characteristics, a pilot-scale A/O process was carried out and the microbial community composition was analyzed by high-throughput sequencing. The results indicated that a better tolerance was achieved for sodium dodecyl benzene sulfonate, and the removal efficiencies of organic matter, ammonia nitrogen (NH4+-N), and total nitrogen (TN) were 82.87%, 66.47%, and 53.28% with the optimum hydraulic retention time (HRT), internal circulation and dissolved oxygen (DO) was 12 h, 200% and 2–3 mg/L, respectively. Additionally, high-throughput sequencing results demonstrated that Proteobacteria and Bacteroidetes were the dominant bacteria phylum, and the diversity of the microbial community in the stable-state period was richer than that in the start-up period.