STUDY ON EFFECTIVE METHODS FOR NOBLE METALS EXTRACTION FROM E-WASTE- A REVIEW

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1 ISSN: X CODEN: IJPTFI Available Online through Review Article STUDY ON EFFECTIVE METHODS FOR NOBLE METALS EXTRACTION FROM E-WASTE- A REVIEW 1 Dr.N.Gomathi*, 2 Rupesh P L Professor, School of Computing & Veltech Technology Incubator, Veltech University, Chennai-62, India. Id: Assistant Professor, School of Mechanical Engineering, Veltech University, Chennai-62, India. rupeshkumar221@gmail.com Received on Accepted on: Abstract Electronic waste is a mixture of end-of-life electronic products collected from various sources. These wastes are highly complex in composition, phase, and physiochemical properties. The metals which are embedded in the electronic waste can be recovered in order to reduce the risk in potential supply of strategic raw materials and environmental concerns. Some of the state of art technologies with the maximum recycling potential to recover gold & silver were discussed in this paper. This review paper also deals with some of the methodologies to extract copper & zinc. These methods have been selected based on their potential in the secondary supply of metals into the market with reduced operational costs, especially when dealing with solutions of low ion concentrations. Keywords: Copper, Electronic Waste, Electro leaching, Electro Deposition, Gold, Silver. Introduction Globally, production of electrical & electronic equipment is one of the fastest growing manufacturing activities. Used/discarded electrical or electronic devices destined for reuse, resale, recycling or disposal was considered as electronic waste or e-waste. Adverse human health effects & environmental pollution were caused due to informal processing of e-waste. Recycling of electronic wastes from industrial & domestic areas of sources is needed to avoid environmental pollution. E-waste contains both hazardous & noble metals. The demand on metals, especially more precious metals and more scarce metals has been increased due to the development of electronic industry along with the increased growth of waste electrical & electronic equipment (WEEE). In current, the annual generation rate of electrical & electronic waste is around 10 million tones in European Union. Every year, generation of WEEEis a significant risk to human health and environment. Manufacturing of refractory materials, fabrication of many industrial and machine parts IJPT April-2017 Vol. 9 Issue No Page 5547

2 such as clutch phasing, brake linings etc. uses metals like copper in the form of powder. A large amount of solid waste containing heavy metals such as zinc & lead is generated by industrial activity. Electric arc furnace dust, household alkaline batteries are some of the zinc rich by products. A critical survey on WEEE treatment has been performed based on numerous investigations and abundant studies. Incineration, Acid bath & landfill leach into ground water were some of the current disposal methods which make air pollution & also spoils the ground water. Usage of hazardous substances such as Lead, Mercury, Cadmium, and Chromium etc. has been restricted in electrical & electronic equipment by European Union (EU) legislative. The collection & recycling of such equipments is also promoted by EU. Some of the environmental benefits offered by recycling of PCB s are Energy savings Reduction of metals obtained from traditional extractive metallurgical process and Reduced CO 2 emissions Usage of recycled metals compared to virgin metals leads to energy savings. Table 1 shows the variation of energy savings depending upon the type of metal extracted. Some of the metals such as Lead, Zinc, Copper, Mercury, Cadmium, Polychlorinated Biphenyls, Polycyclic Aromatic Hydrocarbons, and Dioxins has high level of contamination in to water and soil and spoil the atmosphere. Table 1. Variation of energy savings depending upon the type of metal extracted. Recycling Process-A Review Type of metal Variation of energy (%) Copper 85 Steel 74 Lead 65 Zinc 60 Precious metals >80 The recycling process of E-waste comprises the following steps: 1. To disassemble and segregate E-wastes collected at different areas is sent to pretreatment plant 2. Removal of cables, plastics, wires and glass is done in this process 3. They are sent to the Heavy Duty Shredder for shredding after the removal of cables and capacitors from the PCBs 4. In order to reduce the PCB s size, the shredded PCBs are sent to the Hammer Mill and for the separation of Ferrous and Non-Ferrous Metals, they are fed to the Magnetic Separator IJPT April-2017 Vol. 9 Issue No Page 5548

3 5. To separate Aluminum from non-ferrous metals, they are fed to the Eddy current Separator 6. The Electrostatic Separator separates the conductors (copper), semiconductors (extrinsic silicon), and nonconductors (woven glass reinforced resin) from the remaining Non-Ferrous Metals after the removal of Aluminum 7. To extract the noble metals such as copper, Silver and gold, crushed E-Waste material are fed to the leaching tank 8. Electro Deposition and Electro generative process are the methods through which the complete recovery of noble metals is achieved. Some of the selective methods based on percentage of metals extracted and considering environmental policies has been discussed in this review paper. Effective Extractive Methods- A Review Recovery of gold using electro generative process Gold can be recovered from e-waste by hydrometallurgical process as it has wide applications in jewelry manufacturing and electronic industries. The hydrometallurgical process comprises the following steps Cyanidation Adsorption on activated carbon/ Cementation onto Zinc dust Ion Exchange resin Electro winning [5] Fig. 1 Electro generative process for gold extraction. Factors such as elimination of the external power resource, ease of operation and scale up system as well as its operating cost made the Electro generative method as a best method to recover maximum amount of gold from chloride solution instead of cyanide solution. Fatemeh Salehi Karoonian et al[7] has investigated the electro deposition of gold in a batch reactor containing solutions of HAuCl 4 salt and sodium chloride as a supporting electrolyte through an electro generative process. In this process, IJPT April-2017 Vol. 9 Issue No Page 5549

4 three-dimensional (Porous graphite (PG) and 80 ppi reticulated vitreous carbon (RVC)) and two-dimensional (Stainless steel and copper sheets) cathodes were used along with zinc as an anode. It was observed that after 90 min operation of the reactor from a 500 mg L-1 Au(III) in 0.2 M NaCl and 0.4 M NaH 2 PO 4 solution, the deposition of gold was more than 99% when RVC is used as the cathode material, at ph 7. Table 3 shows the percentage of deposited gold observed in the above study with usage of different cathode materials such as PG, Stainless steel, Copper and RVC. Table 3. Percentage of gold deposited using different cathodes. Cathode Materials % of gold recovered RVC > 99% PG 59% Stainless steel 53% Copper 43% Table 3 also shows that to recover the metal from dilute solutions in an efficient and low-cost process, a threedimensional cathode material like RVC is needed. Extraction of Silver & Copper Fig. 2 Electroleaching combined with Electrowinning. The extraction process of silver from electronic scrap consists of following steps: Dissolution of gold, silver, tin, copper and nickel from gold plated parts in aqua regia without additional heating. Reaction temperature was raised about 80 C due to the exothermal reaction of metals dissolution in aqua regia. All of the metals presentedin the e-scap entered the solution in the form of chlorides at the optimum reaction temperature of C, while all other non-metal parts remained insoluble. Purification of metal solution from tin is done by the hydrolysis of tin chloride with the formation of tin acid in the form of voluminous deposit and could be separated from solution IJPT April-2017 Vol. 9 Issue No Page 5550

5 Dr.N.Gomathi*et al. /International Journal of Pharmacy & Technology Most of the metals dissolves in aqua regia but the strong chemical resistance of silver to aqua regia prevents its dissolution. This may lead to the formation of a thin protecting layer of AgCl, as a product of the initial silver dissolution. The refining process of silver from AgCl can be done by dissolution of precipitate in aqueous ammonia followed by reduction with hydrazine hydrate Silver powder which is recovered from the above process had the quality of 99.9% or higher. From the above process, recovery of copper metal is also possible through electro winning process. In order to extract copper selectively from the waste, a leaching reagent is needed ideally to only react with copper. While other metals present in the waste should be inert to the leaching solution. In a research of Zhi Sun [3], the three types of leaching solutions with air flow rate of 70 L/h were selected which is shown in Table 4 Table 4. Types of Leaching solutions. S.No. Constituents Temperature Solid to liquid ratio Ammonium (7.55 wt %) with 196 g/l ammonia Room temperature for 4 Solution 1 carbonate h Sulfuric acid (25 wt %) with 1.2 times the Solid to liquid ratio is Solution 2 80 C for 4 h stoichiometric amount of H 2 O 2 1g/5 ml Salt aluminum chloride (25 wt %) with 1.2 Solution 3 80 C for 4 h times the stoichiometric amount of H 2 O 2 The results obtained from the above research shows that highest copper selectivity of 95.5% is shown in ammonia solution while in sulfuric acid solution; it becomes 26.6% and only 0.2% in the salt solution. The above result shows that leaching of copper selectively prior to other metals is possible with the usage of ammonia solution as leaching agent. A possible amount of solution with more than 70 g/l of copper can be obtained which is high enough for electro winning process. Conclusion Over the past few decades, numerous research papers dealing with several hydrometallurgical and electrochemical processes in order to recover the noble metals have been published, but this review paper shown importance on the best methods to recover the noble metals in high percentage. These methods have been selected from the study of various research papers based on the following factors: IJPT April-2017 Vol. 9 Issue No Page 5551

6 Maximum recovery of noble metals Minimum effect on environment Dr.N.Gomathi*et al. /International Journal of Pharmacy & Technology Recovery of more than 95% of noble metals such as gold, silver and copper has been observed from the above reviewed methods. Acknowledgement This material is based upon the work supported by the Department of Science and Technology & Veltech technology Incubator, Certificate of Registration of societies S.no.488 of References 1. Chin Yean Yap and Norita Mohamed, Electrogenerative Processes for Environmental Applications- Review, Clean 2008, 36 (5 6), pp N. Gomathi and I. Sridevi, Recovery of noble metal from E-waste using leaching, electro deposition and electro generative process, Der Pharma Chemica, 2015, 7(4):pp Zhi Sun, Y. Xiao, J. Sietsma, H. Agterhuis, and Y. Yang, A Cleaner Process for Selective Recovery of Valuable Metals from Electronic Waste of Complex Mixtures of End-of-Life Electronic Products, Environmental Science & Technology 2015, 49, pp Pascaline Guillaume, Nathalie Leclerc, Franc ois Lapicque, Clotilde Boulanger, Electroleaching and electrodeposition of zinc in a single-cell process for the treatment of solid waste, Journal of Hazardous Materials 2008, 152, pp S.G. Viswanath and Sajimol George, Electrowinning of copper powder from copper sulphate solution in presence of glycol and sulphuric acid, Indian Journal of Chemical Technology 2011, 18, pp Dimitrijevi, Silvana; Truji, Vlastimir; Ivanovi, Aleksandra, Recycling of Precious Metals from E-scrap, Iran. J. Chem. Chem. Eng. 2013, 32(4), pp Fatemeh Salehi Karoonian, Mohammad Etesami, and Norita Mohamed, Electrodeposition of Au on Reticulated Vitreous Carbon From Chloride Media by an Electrogenerative Process, International Journal of Electrochemical Science 2012, 7, pp IJPT April-2017 Vol. 9 Issue No Page 5552