Secondary Metal Resources Research Articles

Development of an Integrated Process Flowsheet to Recover Valuable Metals from Waste Cathode Ray Tubes and Printed Circuit Boards

Electrical and electronic waste is considered a valuable stream of secondary metal resources because it contains metals such as copper, silver and gold. However, it is also classified as hazardous waste as it contains toxic heavy metals such as lead and cadmium. If electronic waste is not managed properly, the toxic metals may pose serious risks to the environment and human health, especially complex fractions such as printed circuit boards (PCBs) and cathode ray tubes (CRTs). The current study investigated a new process for the thermal treatment of CRTs and PCBs in an integrated flowsheet for metal recovery. Smelting tests were conducted to demonstrate that oxidative smelting of PCB concentrate and recycled CRT slag can produce a crude copper alloy with a grade of more than 95%. Another set of smelting tests was conducted to demonstrate that reductive smelting of CRT funnel glass and recycled PCB fume can produce a crude lead alloy with a grade of more than 95%. The investigations were undertaken in a pilot-scale top blown rotary converter (TBRC). The PCBs were smelted under mildly oxidising conditions at temperatures up to 1350 °C. The CRTs were smelted under mildly reducing conditions at temperatures up to 1250 °C. The study demonstrated that it is technically feasible to produce crude alloys of copper and lead from electronic waste, using an integrated process flowsheet.Graphical

Bioleaching Extraction of Valuable Metal From E-Wastes: A Mini Review

Abstract: Electrical waste (E-waste) is a significant global issue, with an annual generation of over 50 million tons, causing detrimental effects on both the environment and human health. However, E-waste is also known as a secondary valuable metal resource. Although hydrometallurgy and pyrometallurgy are still the preferred methods for metal recovery from E-wastes, bioleaching has gained significant attention as a promising alternative for metal recovery from E-wastes due to its sustainability, environmental friendliness, and cost efficiency. In this review, different chemical principles of bioleaching were first discussed. Major bacterial groups that can be applied in bioleaching were then introduced. The bioleaching procedures and applications have been summarized and analyzed. Finally, a few perspectives were made on potential future research on bioleaching.

Co-treatment of spent automotive catalyst and copper-bearing electroplating sludge to alloy platinum group metals with base metal matrices

Spent automotive catalyst (SAC) is an important secondary metal resource of platinum group metals (PGMs). However, the traditional smelting process for recovering valuable metals from SAC generally has the problems such as high reagents consumption and increased solid waste. Thus, a novel co-treatment process of SAC and copper-bearing electroplating sludge (CBES) was proposed in this study, where CBES was first used as the capture agent and fluxing material in the pyro-capture process of PGMs. The effects of separation behaviors of PGMs and copper under different smelting conditions were studied systematically. The optimum conditions for this process are as follows: m(CBES)/m(SAC) of 2.0, m(SiO2)/m(Al2O3) of 3.00, basicity of 0.80, 5.0 wt% Na2B4O7, oxidative temperature of 1460 ℃, oxidative time of 30 min, NC/Cu of 1.250, reductive temperature of 1300 ℃, and reductive time of 90 min. Under these conditions, the sulfur removal rate exceeds 99% while the recoveries of Pt, Pd, Rh and Cu are 99.26%, 98.53%, 99.96% and 97.60%, respectively. The addition of pure reagents is only about 47% of the total waste mass. Furthermore, the capture process of Cu-Fe alloy for PGMs was discussed, which can consist of three steps: reduction of copper and iron, mutual migration and collision of the reduced metal atoms, and alloying. Finally, the produced slag was synthesized into non-hazardous glass-ceramics material successfully. To sum up, this study achieved the efficient recycling of two hazardous wastes simultaneously.

Thermally Reduced Graphene Oxide Membranes Revealed Selective Adsorption of Gold Ions from Mixed Ionic Solutions.

The recovery of gold from water is an important research area. Recent reports have highlighted the ultrahigh capacity and selective extraction of gold from electronic waste using reduced graphene oxide (rGO). Here, we made a further attempt with the thermal rGO membranes and found that the thermal rGO membranes also had a similarly high adsorption efficiency (1.79 g gold per gram of rGO membranes at 1000 ppm). Furthermore, we paid special attention to the detailed selectivity between Au3+ and other ions by rGO membranes. The maximum adsorption capacity for Au3+ ions was about 16 times that of Cu2+ ions and 10 times that of Fe3+ ions in a mixture solution with equal proportions of Au3+/Cu2+ and Au3+/Fe3+. In a mixed-ion solution containing Au3+:Cu2+:Na+:Fe3+:Mg2+ of printed circuit board (PCB), the mass of Au3+:Cu2+:Na+:Fe3+:Mg2+ in rGO membranes is four orders of magnitude higher than the initial mass ratio. A theoretical analysis indicates that this selectivity may be attributed to the difference in the adsorption energy between the metal ions and the rGO membrane. The results are conducive to the usage of rGO membranes as adsorbents for Au capture from secondary metal resources in the industrial sector.

Treating waste with waste: Metals recovery from electroplating sludge using spent cathode carbon combustion dust and copper refining slag

Electroplating sludge is a hazardous waste and secondary metal resource because of its heavy metal content, which poses a huge threat to environmental safety if not properly disposed. An innovative process of oxidizing roasting followed by water leaching and smelting reduction to recover Cr, Cu, and Ni from electroplating sludge was proposed in this research, in which other two hazardous wastes of spent cathode carbon combustion dust and copper refining slag were co-treated. The NaF from spent cathode carbon combustion dust could convert Cr2O3 to Na2CrO4 using the oxidizing roasting process, resulting in a Cr recovery through the subsequent water leaching. The Na2CrO4 formation was promoted by CaO owing to it transferring the Cr spinel phase of FeCr2O4 [1+] to CaCrO4 and then to Na2CrO4. Under optimal conditions, the Cr recovery reached 97.1 %, and most ‘F’ was solidified into CaF2. In the next smelting reduction of the leaching residue, the Cu and Ni were recovered mainly in the form of Cu-Ni alloy. The addition of copper refining slag promoted their recovery, due to it modifying the molten slag and alloy structures and increasing the Cu-Ni alloy separation from molten slag. Some generated high-melting-point Cu-Ni-Fe and Ni-Fe alloys were converted to a Cu-Ni alloy with a low melting point in presence of Co from the copper refining slag, simultaneously with which the Fe was transferred out from Cu-Ni-Fe and Ni-Fe alloys and combined with Co to form a Fe-Co alloy. It increased Cu-Ni alloy droplets aggregation from molten slag and decreased their contents in the residual slag. Under optimized conditions, the Cu and Ni contents in the residual slag decreased to 0.37 and 0.06 wt%, respectively. Besides, the residual slag mainly composed of CaO, CaF2 and SiO2 could be used to prepare building materials rendering it harmless.

Comparation on the methods of removing impurity metals from copper powder of waste printed circuit boards

Copper powder of waste printed circuit boards (WPCBs), an important secondary metal resource, is usually processed by copper concentrate pyrometallurgy system to recover valuable metals. However, metals such as Pb, Sn, Zn and Al in copper powder of WPCBs are harmful to copper smelting system. Therefore, a two-stage leaching process was proposed to remove impurity metals from copper powder, and different routes were screened. Copper powder was firstly leached in the hydrochloric acid to remove Al, and then the Al-removed residue was treated to recover Sn and Pb by two routes, i.e., acid oxidation leaching or alkaline pressure oxidation leaching, respectively. The results showed that more than 97.15% of Al in copper powder was removed by the hydrochloric acid leaching. In HCl system adding H2O2, the leaching ratios of Pb and Sn reached 91.07% and 94.67%, respectively. In the alkaline pressure oxidation leaching system, the leaching ratios of Pb and Sn were 86.63% and 93.80%, respectively. In general, the separation and recovery of valuable metal resources in the WPCB copper powder were realized, and Cu was further enriched, providing high-quality raw materials for copper pyrometallurgy.

Recovery of gold from waste mobile phone circuit boards and synthesis of nanomaterials using emulsion liquid membrane

In recent years, waste mobile phones have become popular as electronic waste due to the huge amount, serious pollution with improper disposal and high resource value. It is imperative to realize the recycling of resources in waste mobile phones. The application of emulsion liquid membrane in the recovery of gold and synthesis of nanomaterials from waste mobile phone printed circuit boards (WMPCBs) was studied. The components of the emulsion liquid membrane, effects of 7 factors on the extraction rate and the morphology of the synthesized nanomaterials were explored. The results show that it is possible to extract 99.79% of Au(III) from WMPCBs leachate with kerosene as diluent, Span80 as surfactant, methyl isobutyl ketone(MIBK) as carrier, ascorbic acid solution as stripping agent and liquid paraffin as membrane stabilizer. The external phase pH and the internal phase concentration had a greater influence on the extraction efficiency of Au(III) among 7 factors. The morphology of the synthesized product was affected by the concentration and type of the surfactant. It provides a new idea to connect recovery from waste with deep processing, extending the waste mobile phone recycling process chain and achieving high-value utilization of waste mobile phone secondary metal resource products.

Applications of molten salt and progress of molten salt electrolysis in secondary metal resource recovery

Molten salt is an excellent medium for chemical reaction, energy transfer, and storage. Molten salt innovative technologies should be developed to recover metals from secondary resources and reserve metals from primary natural sources. Among these technologies, molten salt electrolysis is an economic and environment-friendly method to extract metals from waste materials. From the perspective of molten salt characteristics, the application of molten salts in chemistry, electrochemistry, energy, and thermal storage should be comprehensively elaborated. This review discusses further directions for the research and development of molten salt electrolysis and their use for metal recovery from various metal wastes, such as magnet scrap, nuclear waste, and cemented carbide scrap. Attention is placed on the development of various electrolysis methods for different metal containing wastes, overcoming some problems in electrolytes, electrodes, and electrolytic cells. Special focus is given to future development directions for current associated processing obstacles.

Thermodynamic Evaluation on the Removability of Impurity Elements during the Recycling of Secondary Metal-resources by Re-melting

Thermodynamic Evaluation on the Removability of Impurity Elements during the Recycling of Secondary Metal-resources by Re-melting

Mechanical activation to enhance the natural floatability of waste printed circuit boards

The metal in the waste printed circuit boards (WPCBs) is an excellent secondary metal resource. WPCBs were ground to dissociate, and impurities in the dissociated product were removed by gradient flotation to recover valuable metals in this study. The effects of crushing methods on size composition and dissociation state of the crushed products were studied. Then the gradient flotation experiment was designed to verify the natural floatability of ground materials. Grinding test shows that impact crushing has greater grinding fineness (−0.074 mm) than shear crushing, which is 42.14% and 26.18% respectively with 5 min grinding. The flotation test results illustrate that the natural floatability of impurities increases with the grinding fineness, that is, the yield of floats increases without flotation reagents. For impact crushing and shear crushing, the floats yields are 38.48% and 31.75% respectively, accompanied by 70.53% and 65.46% impurity removal for ground materials with 5 min grinding. Subsequently, 21.61% and 26.35% of impurities can be further removed with the aid of collector. Finally, the recovery of Cu in concentrate reaches 67.84% and 65.75%, respectively. FT-IR proves that the excellent floatability of particles is caused by the significant hydrophobic group. Mechanical grinding has been proved to have double effects of improving dissociation and natural floatability.

Recovery of Copper and Precious Metals and Separation of Lead from Flue Dust of Electronic Waste Processing

ABSTRACTThe flue dust generated during the processing of e-waste is valuable as a secondary metal resource. In this study, a process of selective metal recovery from flue dust through the magnetic separation and the leaching process were developed. All the experiments were carried out at atmospheric pressure below 60°C. A continuous four-step process was carried out for the selective recovery of Al, Cu, Au, and Pb, using NaOH, H2SO4, CH4N2S, and HNO3 as leaching reagents in the four steps, respectively. As a result of this continuous recovery process, leaching efficiencies of 57.3% for Al, 98.0% for Cu, 75.2% for Au, and 77.5% for Pb were obtained.

Estimation of obsolete cellular phones generation: A case study of China

Rapid development of electronic technique has led to decreasing lifespan of electronic products. Meanwhile, the amount of waste electrical and electronic equipment (WEEE) is rapidly growing in recent years especially in China. The generation amount of WEEE is one of the basic information for waste management. In our study, the generation of obsolete cellular phones and metals containing of cellular phones were estimated from 1997 to 2025. The future average possession in per 100 inhabitants of cellular phones was predicted using logistic model. Moreover, the lifespan distribution of cellular phones was analyzed using Weibull distribution. Meanwhile, the generation amount of obsolete cellular phones and its metals containing were estimated by using population balance model (PBM) and substance flow analysis (SFA), respectively. The estimated results indicate that the average possession in per 100 inhabitants will reach to 111.2 and 118.3 units in 2020 and 2025, respectively, which is about two times higher than the average possession in 2010. In addition, the total possession amount of cellular phones are expected to exceed 1.64 billion units in 2025. Moreover, the estimated results show that 781 million units obsolete cellular phones were generated in 2015, and the number will grow up to 877 and 937 million units in 2020 and 2025, respectively. In 2025, the total weight of annual generation amount of obsolete cellular phones will exceed 140Gg. The precious metals such as silver, gold contains in obsolete cellular phones will reach 56,250 and 28,130kg, respectively, in 2025. The obsolete cellular phones are the typical secondary metal resources especially for precious metals. In order to improve the recycling efficiency, it is necessary to establish a comprehensive system of waste management.

Research progress in biohydrometallurgy of rare metals and heavy nonferrous metals with an emphasis on China

In the past decade, progress in the field of biohydrometallurgy had been significant. A total of 17 novel biomining microorganisms were discovered, and eight copper heap bioleaching plants and 11 gold biooxidation plants were established or expanded. In this review, it was summarized the physiological properties of the newly isolated biomining microorganisms and three novel microbial ecological methods for studying microbial community dynamics and structure. In addition, biohydrometallurgy research on rare metals such as uranium, molybdenum, tellurium, germanium, indium, and secondary rare metal resources, as well as heavy nonferrous metals such as copper, nickel, cobalt, and gold has been reviewed, with an emphasis on China. In future, further studies on bioleaching of chalcopyrite, rare metals, secondary resources from waste, and environmental pollution caused by resource utilization are necessary. Zijinshan heap bioleaching plant restarted operation in 2012 with capacity of 30,000 ton·year−1. The average copper grade is 0.308 %. The ore particle size is 40 mm accounting for 80 %. The heap height is 8 m. The solution pH is controlled at 1.5–1.7, and redox potential is maintained at 730–760 mV. After 185 days leaching, copper leaching rate of more than 76 % and iron leaching rate of <6 % are achieved.

Biohydrometallurgy of secondary metal resources: a potential alternative approach for metal recovery

AbstractResearch on biohydrometallurgy of secondary metal resources is primarily focused on the leaching of valuable metals. For secondary metal resources biological processing can be an economically more effective and environmentally friendlier alternative to traditional hydrometallurgical and pyrometallurgical processes. Therefore, biohydrometallurgy is a rapidly evolving biotechnology that has already provided revolutionary solutions to old problems associated with recovery of metals by conventional pyrometallurgy and chemical metallurgy. This review evaluates various processes of recovery of metals from waste materials and commercial applications are discussed. Case studies and future technology directions are reviewed. © 2013 Society of Chemical Industry

Electroplating sludge metal recovering with vitrification using mineral powder additive

Electroplating sludge is a potential secondary metal resource. In this study, vitrification process was employed to recover the metal from plating sludge, and the mineral powder additive was used to improve the recovery efficiency of vitrification process. Plating sludge was collected from an industrial Ni electroplating workshop in Taiwan. Mineral powder composed of dolomite, limestone, and cullet was employed as the reductant additive to improve the efficiency of producing metallic ingot in the vitrification process. The metals Al, Ca, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were analyzed with an atomic adsorption spectrometer (AAS). Ni, Fe, and Cr are potential candidates for recovery using the vitrification process due to their relatively high mass content. To determine the optimal efficiency, vitrification processes were performed with additive to sludge mass ratios of 5:5, 6:4, 7:3, 8:2, and 9:1. The results indicate that the optimal metal recovery efficiency of Ni, Fe, and Cr was achieved at an additive to sludge ratio of 8:2. In addition, the toxicity characteristic leaching procedure (TCLP) test results for the slag meet the Taiwan EPA's regulated level of Cr(VI), Cr, Pb, and Cu. To examine the changes in microstructure, the crystalline phases of slag were analyzed with XRD. The XRD patterns show that the appearance of pseudowollastonite improves the metal recovery efficiency, whereas the appearance of diopside and quartz decreased efficiency. The preliminary economic analysis indicated that the vitrification was not only a feasible but also a cost-effective technology for the electroplating sludge treatment in this study. However, the practical application should further depend on the building cost of the plant and financial support from the government.

A preliminary categorization of end-of-life electrical and electronic equipment as secondary metal resources

End-of-life electrical and electronic equipment (EEE) has recently received attention as a secondary source of metals. This study examined characteristics of end-of-life EEE as secondary metal resources to consider efficient collection and metal recovery systems according to the specific metals and types of EEE. We constructed an analogy between natural resource development and metal recovery from end-of-life EEE and found that metal content and total annual amount of metal contained in each type of end-of-life EEE should be considered in secondary resource development, as well as the collectability of the end-of-life products. We then categorized 21 EEE types into five groups and discussed their potential as secondary metal resources. Refrigerators, washing machines, air conditioners, and CRT TVs were evaluated as the most important sources of common metals, and personal computers, mobile phones, and video games were evaluated as the most important sources of precious metals. Several types of small digital equipment were also identified as important sources of precious metals; however, mid-size information and communication technology (ICT) equipment (e.g., printers and fax machines) and audio/video equipment were shown to be more important as a source of a variety of less common metals. The physical collectability of each type of EEE was roughly characterized by unit size and number of end-of-life products generated annually. Current collection systems in Japan were examined and potentially appropriate collection methods were suggested for equipment types that currently have no specific collection systems in Japan, particularly for video games, notebook computers, and mid-size ICT and audio/video equipment.

Recycling of gold from electronics: Cost-effective use through ‘Design for Recycling’

With over 300 tonnes of gold used in electronics each year, end-of-life electronic equipment offers an important recycling potential for the secondary supply of gold. With gold concentrations reaching 300-350 g/t for mobile phone handsets and 200-250 g/t for computer circuit boards, this “urban mine” is significantly richer than what is available in primary ores. However, the “mineralogy” in scrap products is much different than in the conventional ores in a gold mine: Up to 60 different elements are closely interlinked in complex assemblies and sub-assemblies, and this requires specialised metallurgical processes with extensive offgas treatment to recover gold and a wide range of other metals cost effectively and in an environmentally sound way. Moreover, the logistics to “excavate” and “haul” the scrap products to the concentrator and further to the smelter are much more challenging than in the primary supply chain. Currently, only a small portion of old products is collected and directed into state-of-the art recycling chains. Significant improvements are needed here to fully utilise this secondary metal resource. The importance of the gold content of scrap electronics to the economics of recovery of gold and many other valuable metals is not always appreciated and this impacts on the “design for recycling” approach in selecting materials for new products, particularly in the European Union where the WEEE Directive aims to provide a closed loop economy. With a lower carbon footprint than primary-mined gold, recycled gold represents an important “green” source. The challenges faced in recycling electronic scrap to achieve a closed loop economy are discussed.

An overview study of chlorination reactions applied to the primary extraction and recycling of metals and to the synthesis of new reagents

Energy intensive classical metallurgical processes, the depletion of high-grade ores and primary sources push the scientific and technical communities to treat lean and complex ores as well as secondary metal resources for the recovery of valuable metals. Chlorination technique could be a suitable technology for this purpose. This paper summarizes laboratory experimentation of chlorination processes developed for the extraction of tantalum and niobium from their bearing materials, the upgrading of chromite, the treatment of sulfide concentrates, and the decontamination of jarosite, as well as for the synthesis of potassium ferrate. Each investigation started by a thermodynamic study of different systems (M–O–Cl, M–S–Cl, M = metal) including the calculations of the standard free energy of chlorination reactions and phase stability diagrams of these systems. The kinetics of these chlorination reactions was studied by thermogravimetric analysis. The effects of total gas flow rate, temperature, individual reactant partial pressures, etc., on the chlorination reaction rate were investigated. Besides, experiments were also conducted in tubular furnaces. Several different qualitative and quantitative analyses methods were used to evaluate the selectivity and performance of the chlorination processes. The results reported in this paper show the advantages of the chlorination technology in terms of energy saving, selectivity of the processes, and recovery rate of valuable metals. They also demonstrate the possibility to treat lean raw materials, to improve the decontamination of wastes, to generate environmentally safer residues, to engineer new compounds, etc.