Synthesis of a perovskite-type catalyst from Cr electroplating sludge for effective catalytic oxidization of VOC

Catalytic reduction of nitrogen monoxide using iron-nickel oxygen carriers derived from electroplating sludge: Novel method for the collaborative emission decrease of polluting gases

The valorization of electroplating sludge (ES) for high added value presents greater economic and environmental benefits than conventional treatment methods such as thermal processing, solidification, and landfill. Inspired by the mechanism of chemical looping combustion (CLC), this study developed a novel cost-effective method for denitrification by preparing FeNi-OCs from ES to achieve the synergistic reduction of CO and NO emissions. The phase structure, micromorphology, and valence state changes of the FeNi-OC catalyst during the CO-catalyzed reduction of NO and the pathway for catalytic denitrification using FeNi-OCs were analyzed. Results showed that CO could reduce FeNi-OCs to FeNi, and the reduced FeNi was subsequently oxidized back to FeNi-OCs by NO, a process analogous to CLC. During experiments, the simultaneous consumption of CO and NO gases was observed at 350 °C. This phenomenon was highly pronounced at 600 °C, where the CO and NO concentrations decreased from initial values of 8550 and 470 ppm, respectively, to 6719 and 0 ppm, respectively, with conversion rates of 21.41 % and 100 %, respectively. Hence, synergistic emission reduction was achieved. Further experiments also indicated that the addition of 1.5 % ES during iron ore sintering could substantially reduce the CO and NO concentrations in the sintering flue gas from 1268.32 and 244.81 ppm, respectively, to 974.51 and 161.11 ppm, respectively.

Approaches for electroplating sludge treatment and disposal technology: Reduction, pretreatment and reuse

Electroplating sludge (ES) has become an obstacle to the sustainable development of the electroplating industry. Electroplating sludge has a large storage capacity, with a high concentration of soluble pollutants (heavy metals), which has great potential to harm the local ecosystems and human health. Although much research has been done in this area, there seems to be no mature and stable solution. Therefore, the latest technologies for the reduction, pretreatment and reuse of electroplating sludge are emphatically introduced based on the analysis of the characteristics of electroplating sludge and its impact on the ecological environment. The factors hindering the treatment and disposal of electroplating sludge are pointed out, and reasonable and feasible suggestions to solve this problem are proposed. The solidification and removal mechanism of heavy metals in electroplating sludge is emphatically analyzed. The physicochemical and separation processes of heavy metals, as well as thermal treatment technique are discussed. Finally, it is proposed to establish a database of the physicochemical properties and elemental content of electroplating sludge to achieve its systematic treatment and digestion. We hope that this paper can help solve the problem of electroplating sludge and promote the sustainable development of the electroplating industry.

Analysis of soil pollution characteristics and influencing factors based on ten electroplating enterprises

The electroplating industry encompasses various processes and plating types that contribute to environmental pollution, which has led to growing public concern. To investigate related soil pollution in China, the study selected 10 sites with diverse industrial characteristics distributed across China and collected 1052 soil samples to determine the presence of industrial priority pollutants (PP) based on production process and pollutant toxicity. The factors influencing site pollution as well as proposed pollution prevention and control approaches were then evaluated. The results indicate the presence of significant pollution in the electroplating industry, with ten constituents surpassing the risk screening values (RSV). The identified PP consist of Cr(VI), zinc (Zn), nickel (Ni), total chromium (Cr), and petroleum hydrocarbons (C10-C40). PP contamination was primarily observed in production areas, liquid storage facilities, and solid zones. The vertical distribution of metal pollutants decreased with soil depth, whereas the reverse was true for petroleum hydrocarbons (C10-C40). Increase in site production time was strongly correlated with soil pollution, but strengthening anti-seepage measures in key areas can effectively reduce the soil exceedance standard ratio. This study serves as a foundation for conceptualizing site repair technology in the electroplating industry and offers a reference and methodology for pollution and source control in this and related sectors.

Low-energy production of a monolithic catalyst with MnCu-synergetic enhancement for catalytic oxidation of volatile organic compounds

Producing a low-cost catalyst by a low-cost method is one of the hottest topics in the field of catalytic oxidization of volatile organic compounds (VOCs). In this work, a catalyst formula with a low-energy requirement was optimized in the powdered state, and verified in the monolithic state. An effective MnCu catalyst was synthesized at a temperature as low as 200 °C. Removals were all bigger than 88% for toluene, ethyl acetate, hexane, formaldehyde, and cyclohexanone at a low temperature of 240 °C. The MnCu catalyst was then loaded on a honeycomb cordierite, which was also effective for toluene removal at 240 °C. After characterizations, active phases were Mn₃O₄/CuMn₂O₄ in both the powdered and monolithic catalysts. The enhanced activity was attributed to balanced distributions of low-valence Mn and Cu, as well as abundant surface oxygen vacancies. The obtained catalyst is produced by low energy and effective at low temperature, which suggests a perspective application.

Highly efficient LaMO3 (M = Co, Fe) perovskites catalyzed Fenton's reaction for degradation of direct blue 86

Perovskite-structured catalysts LaMO₃ (M = Co, Fe) were successfully synthesized and attempted to catalyze hydrogen peroxide (H₂O₂) for the degradation of Direct Blue 86 (DB86), a carcinogenic phthalocyanine dye. The heterogeneous Fenton-like reaction revealed that the oxidative power of the LaCoO₃-catalyzed H₂O₂ (LaCoO₃/H₂O₂) process was higher than that of LaFeO₃/H₂O₂. When LaCoO₃ was calcined at 750 °C for 5 h, 100 mg/L of DB86 could be completely degraded within 5 min via LaCoO₃/H₂O₂ system under H₂O₂ 0.0979 mol/L, initial pH 3.0, LaCoO₃ 0.4 g/L, and 25 °C. The oxidative LaCoO₃/H₂O₂ system has a low activation energy (14.68 kJ/mol) for DB86 degradation, indicating that it is a fast reaction process with highly favorable at high reaction temperatures. For the first time, a cyclic reaction mechanism of catalytic LaCoO₃/H₂O₂ system was proposed based on the evidence of coexisting Co^II and Co^III on the LaCoO₃ surface and the presence of HO^• radicals (major), O₂^•- radicals (minor), and ¹O₂ (minor). LaCoO₃ perovskite catalyst was reusable and still maintained reactive with a satisfactory degradation efficiency within 5 min even after five consecutive uses. This study shows that the as-prepared LaCoO₃ is a highly efficient catalyst for phthalocyanine dye degradation.

A review on fabricating functional materials by electroplating sludge: process characteristics and outlook

As the end product of the electroplating industry, electroplating sludge (ES) has a huge annual output and an abundant heavy metal (HM). The effective disposal of ES is attracting increasing attention. Currently, the widely used ES disposal methods (e.g. landfill and incineration) make it difficult to effectively control of HMs and synchronously utilise metal resources, leading to a waste of metal resources, HMs migration, and potential harm to the environment and human health. Therefore, techniques to limit HMs release into the environment and promote the efficient utilisation of metal resources contained within ES are of great interest. Based on these requirements, material reuse is a great potential means of ES management. This review presents an overview of the process flows, principles and feasibilities of the methods employed for the material reuse of ES. Several approaches have been investigated to date, including (1) additions in building materials, (2) application in pigment production, and (3) production of special functional materials. However, these three methods vary in their treatment scales, property requirements, ability to control HMs, and degree of utilisation of metal resources in ES. Currently, the safety of products and costs are not paid enough attention, and the large-scale disposal of HMs is not concordant with the effective management of HMs. Accordingly, this study proposes a holistic sustainable materialised reuse pattern of ES, which combines the scale and efficiency of sludge disposal and pays attention to the safety of products and the cost of transformation process for commercial application.

Ball milling transformed electroplating sludges with different components to spinels for stable electrocatalytic ammonia production under ambient conditions

Electroplating sludge is classified as hazardous waste, but it is also a potential raw resource since it contains plenty of transition metals. However, the component of electroplating sludge is unstable, which hinders recycling. This work investigates the possibility to synthesize spinels with stable catalytic performances by different electroplating sludges. The obtained catalysts are used in electrocatalytic N₂ reduction to produce ammonia. As a result, CuCr₂O₄, ZnCr₂O₄, and NiCr₂O₄ spinels are successfully synthesized by a ball-milling and calcination method. These spinels result in ammonia yields of 7.30-8.86 μg h^-1 mg^-1_cat. Among the three spinels, CuCr₂O₄ shows the highest yield of 8.86 μg h^-1 mg^-1_cat at -0.9 V. Its faradaic efficiency reaches 0.57%. In addition, no by-product N₂H₄ is detected, indicating a high selectivity. The catalytic process is carried out by both distal and alternating pathways, in which metal doping and oxygen vacancy function as binding sites for N₂ adsorption and reduction. Above results indicate that electroplating sludges with unstable components are feasible to produce spinels for stable electrocatalytic ammonia production under ambient temperature. This is in favor of high-value-added utilization of hazardous waste, and devotes to circular economy.

Recycling electroplating sludge as a monolithic catalyst for effective catalytic purification of volatile organic compounds

Electroplating sludge had a high content of heavy metals and usually lacked high-value-added utilization. In this work, Cu-containing sludge was used to synthesize a spinel catalyst, which was applied in catalytic oxidization of toluene. As a result, the sludge-derived spinel removed 50% of toluene (1000 ppm, 9600 h^-1) at 280 °C. In comparison, a reagent-synthesized spinel with a similar component removed 50% of pollutant at 294 °C. The sludge-derived spinel also showed a stable performance for over 50 h at 370 °C. Even when the initial concentration was increased to 5000 ppm, or the gas hourly space velocity was increased to 40,000 h^-1, the temperature for 50% removal was only increased to 303 °C. According to characterizations, surface oxygens of the sludge-derived spinel were more active than those in the reagent-synthesized one. Besides, the former had more active surface oxygens (207.9 μmol/g) than the latter (183.1 μmol/g). Furthermore, the sludge-derived spinel was coated on a monolithic honeycomb, which were also effective in catalytic oxidization of toluene. The main results of this work were in favor of high-value-added utilization of hazardous solid waste and promoting its real industry application.