Stepwise recycling of Fe, Cu, Zn and Ni from real electroplating sludge via coupled acidic leaching and hydrothermal and extraction routes

Copper recovery by solvent extraction for nanoparticle synthesis from waste motherboards

Printed circuit boards, which make up part of waste from electrical and electronic equipment, contain elements that can be economically reused, such as copper, silver, gold, and nickel, as well as metals that are harmful to the environment and health, such as lead, mercury, and cadmium. Thus, through recycling this scrap, materials that would otherwise be discarded can be reinserted as secondary raw materials to produce new consumer goods through urban mining. In this context, the synthesis of nanoparticles shows promise as it allows the reinsertion of these materials in the manufacture of new products. Therefore, this study used obsolete computer motherboards as a secondary material to obtain copper to produce nanoparticles of this metal. From a solution based on the leach liquor of this scrap, a purification route using solvent extraction was defined and applied to the real leach liquor. Applying the hydroxyoxime extractant at a dilution of 20% (v/v) in kerosene, A/O of 1/1, 298 K, and 0.25 h of contact during extraction, and stripping in H2SO4 (2 M), 298 K, 0.25 h, W/O ratio of 3/1, and two theoretical countercurrent stages, a solution containing more than 95% of the copper in the leach liquor could be obtained with less than 1% of contaminants. From this purified liquor, nanoparticles containing copper and metallic copper oxides and hydroxides were produced, with an average size of 84 nm, at pH 11, 3 h of hot stirring, volume of 0.015 L of ascorbic acid (0.50 M) and 0.015 L of precursor solution (0.03 M Cu), and temperature (343 K).

Research on Resource Recovery and Disposal of Copper-Containing Sludge

Copper-containing sludge is a common by-product of industrial activities, particularly electroplating and metal processing. This type of sludge contains high concentrations of heavy metals such as copper, which can pose a potential threat to the environment. Therefore, its treatment and disposal require special attention. Due to its efficient mass and heat transfer characteristics, the suspended state technology has shown significant potential for application in a number of key processes, including the drying, decomposition, and reduction of copper-containing sludge. This paper presents an in-depth analysis of the current status of the application of the suspended state technology in the treatment of copper-containing sludge. Based on this analysis, a device for the treatment of copper-containing sludge in the suspended state was designed, through which the characteristics of copper-containing sludge in the oxidative decomposition and reduction phases are investigated. The research objects were gas concentration, temperature, contact state, and particle size time. Orthogonal experiments were initially employed to investigate the relationship between the influencing factors and the conversion rate of copper oxides. This was followed by a single-factor influence study, which led to the determination of the optimal process parameters for the decomposition experiments of the Cu-containing sludge in an oxidizing atmosphere. The 100 μm Cu-containing sludge was reacted with 10% O2 gas at a flow rate of 1 m/s for 3 min under the condition of 900 °C. The process parameters were then determined as follows: The research objects were gas concentration, temperature, contact state, and particle size time. Orthogonal experiments were employed to investigate the relationship between the influencing factors and the copper conversion rate. This was followed by a single-factor influence study, which determined the optimal process parameters for the copper-containing sludge reduction experiments. The 200 μm copper-containing sludge was reacted for 5 min at a flow rate of 7% carbon monoxide at a flow rate of 1.5 m/s under the condition of 800 °C.

Approaches for the Treatment and Resource Utilization of Electroplating Sludge

The disposal of electroplating sludge (ES) is a major challenge for the sustainable development of the electroplating industry. ESs have a significant environmental impact, occupying valuable land resources and incurring high treatment costs, which increases operational expenses for companies. Additionally, the high concentration of hazardous substances in ES poses a serious threat to both the environment and human health. Despite extensive scholarly research on the harmless treatment and resource utilization of ES, current technology and processes are still unable to fully harness its potential. This results in inefficient resource utilization and potential environmental hazards. This article analyzes the physicochemical properties of ES, discusses its ecological hazards, summarizes research progress in its treatment, and elaborates on methods such as solidification/stabilization, heat treatment, wet metallurgy, pyrometallurgy, biotechnology, and material utilization. It provides a comparative summary of different treatment processes while also discussing the challenges and future development directions for technologies aimed at effectively utilizing ES resources. The objective of this text is to provide useful information on how to address the issue of ES treatment and promote sustainable development in the electroplating industry.

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.

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.

Research status of soda residue in the field of environmental pollution control

High-quality soda ash (Na2CO3) is mainly produced using the ammonia-alkaline method, generating a significant amount of industrial waste called soda residue. In China, the annual production of soda residue exceeds 10 million tons. The large-scale open-air storage of soda residue not only occupies land but also causes severe pollution to the surrounding environment. Soda residue displays characteristics such as strong alkalinity, high reactivity, and a well-developed pore structure, making it a valuable raw material for producing environmentally functional materials. This article provided an overview and summary of soda residue, including its sources and hazards, basic properties, applications in environmental management (wastewater treatment, flue gas desulfurization, and soil remediation), and associated risks. The limitations of using soda residue in "waste to waste" technologies were also analyzed. Based on this analysis, the article suggests focusing on simultaneous removal of heavy metal ions using soda residue, safely disposing of and acquiring resources from metal-laden sludge, efficiently dechlorinating soda residue, using soda residue for contaminated soil solidification, stabilization, and assisted remediation, controlling pollution via green and circular utilization approaches, and assessing long-term risk.

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.

Recovery of copper from electroplating sludge using integrated bipolar membrane electrodialysis and electrodeposition

Electroplating sludge, though a hazardous waste, is a valuable resource as it contains a large amount of precious metals. In this study, copper was recovered from the electroplating sludge using a technology that integrates bipolar membrane electrodialysis (BMED) and electrodeposition. The experimental results showed that Cu²⁺ in the electroplating sludge was successfully separated and concentrated in the BMED system without adding any chemical reagents; the concentrated Cu²⁺ was recovered in the form of copper foil in an electrodeposition system. Current density clearly affected the Cu²⁺ separation and concentration in the BMED system; the current density, solution pH and Cu²⁺ concentration drastically affected the Cu²⁺ electrodeposition ratio and the morphology and purity of the obtained copper foil. Under the optimised experimental conditions, 96.4% of Cu²⁺ was removed from the electroplating sludge and 65.4% of Cu²⁺ was recovered in the foil form. On increasing the number of electroplating sludge compartments from one to two and three, the current efficiency for recovering Cu²⁺ increased from 17.4% to 28.5% and 35.2%, respectively, and the specific energy consumption decreased from 11.3 to 6.7 and 5.3 kW h/kg of copper, respectively. The purity of the copper foil was higher than 99.5%. Thus, the integrated technology can be regarded as an effective method for recovering copper from electroplating sludge.