methods of gold extraction----------------

about gold extraction

1. CHEMICAL AND BIOLEACHING METHODS FOR GOLD EXTRACTION FROM E-WASTE Supervisor: Dr. Sana Zulfiqar Supervisee: Sundas Hamid Department: Environmental Sciences (Chemistry)

2. INTRODUCTION When electric equipment(EE) reaches the end of its lifecycle, it becomes electronic waste (E-waste). A total of 54 different product types are classified as E-waste, and these are grouped into six categories. ( Forti et al., 2020) The volume of global E-waste production between 2010 and 2019 was steadily rising, from ∼ 33.8 million tonnes to ∼ 53.6 million tonnes. It is expected to reach 74 million tonnes by 2030 . ( Ghimire & Ariya , 2020) 2

3. PERCENTAGE COMPOSITION OF DIFFERENT ELEMENTS IN E-WASTES Precious metals makeup more than 70% of mobile phones and PCBs that are widely used for chemical stability and have conductive properties . ( Rawat et al., 2019) et al., 2019). 3

4. 4 Diagram showing the E-waste recycling and adverse effect in environment

5. Research focus 5 In this research, the efficiency and environmental impact of recovering gold from waste printed circuit boards (WPCBs) using both chemical methods (Aqua regia and nitric acid) and chitosan -based bioleaching methods are investigated . C hitosan based bioleaching is more sustainable and innovative method. Chitosan is a naturally occurring biopolymer obtained from crustacean shells like chitin and has a well-known property of forming a complex with metal ions Chitosan (C6H11NO4 ) n was established to be important as a bio-adsorbent ( Liu et al., 2021)

6. SIGNIFICANCES The main significance of this research is to find out the effectiveness of E-waste management, helping to alleviate the burden on landfill capacity and environmental pollution. The Managing E-waste aligns a circular economy by recycling and reusing valuable components, reducing the demand for new raw materials, and promoting sustainable production and consumption. Educating the public, businesses, and policymakers about the importance of E-waste recycling and gold recovery is an essential aim . Extracting gold from E-waste helps to recover this valuable metal, reducing the need for mining and its associated environmental and social impacts. 6

7. AIMS AND OBJECTIVES To extract gold from E-wastes by sustainable and environment friendly method. To compare and evaluate the gold extraction efficiency from chemical and bioleaching method using chitosan . To explore the potential of bioleaching method, as an environmental friendly and economically efficient technology for extracting metals from E- wastes. To explore the scalability and practical applications of chitosan bioleaching for industrial use, and drive greener innovation in e-waste management. 7

8. METHODOLOGY Diagram showing the various stages involved in the sampling of WPCB 8

9. 9 Flow chart illustrating the step-by-step process for extracting gold from WPCB

10. Chemical leaching using Aqua Regia ( Elomaa et al. 2017) Representation of chemical extraction process of gold, detailing the steps from initial raw material treatment to the final recovery stages 10

11. Possible chemical reactions Primary leaching: Secondary leaching: 11

12. Chemical leaching using Nitric Acid Possible chemical reactions ( Tatariants et al., 2018) Chemical extraction process of gold from Random access memory module (RAM) 12

13. 2. Biological Leaching Preparation of Chitosan ( Mathew et al., 2020 ) Flow diagram depicting the process of chitin and chitosan preparation from prawn waste shells 13

14. Experimental setup illustrating the biological method for extraction of gold, showcasing the different concentrations and conditions Bui et al., 2021 14

15. Chitosan Adsorption Treatment of leached solution G1 with chitosan Incubate at 25°C for 24 hours Formation of chitosan -gold complex Filter to obtain the solid phase contained gold. ( Riaz et al., 2018). 15

16. Characterization techniques SEM employ in order to analyze the morphology of the samples EDS to analyze elemental composition of the recovered sample FTIR identify the chemical bonds and functional groups in the sample AAS Evaluate the precise measurement of metal content 16

17. RESULTS SEM,EDS results of S1 sample Elements Common oxidation states Weight% Atomic% O -2 17.50 57.99 Cl -1, +1, +3, +5, +7 16.81 25.15 Au +1, +3 4.34 1.17 Pb +2, +4 61.34 15.70 17

18. SEM/EDS results of S2 sample Elements Common Oxidation states Weight% Atomic% O -2 7.9 51.64 Au +1, +3 92.02 48.36 18

19. Biological Method SEM/EDS results of chitosan 19

20. SEM/ EDS of WPCB Powder Elements Common oxidation states Weight% Atomic% C -4, -3, -3, -1, 0, +1, +2, +3, +4 48.86 80.61 O -2 9.43 11.68 Cl -1, +1, +3, +5, +7 8.00 4.47 Au +1, +3 2.22 0.22 Pb +2, +4 31.49 3.01 20

21. SEM/EDS Analysis of Sample G1 (Residue) 21

22. SEM/EDS of G4 Sample (Residue) SEM of GA sample (Filtrate of G1+chitosan) 22

23. FTIR of Chitosan Wave Number Functional Group Literature Peaks Reference 1024 CO stretch 1021 (Bandara et al., 2018) 1373 CH 3 amide group 1384 (Liu et al., 2015) 1560 -NH 2 1559 (Li et al., 2013) 1653 -C=O stretch 1633 (Ren et al., 2017) 2922 CH 2 stretch 2889 (Pokhrel et al., 2016) 3437 OH-NH stretch 3450 ( Rasulu et al., 2019) 23

24. FTIR of G1 sample with WPCB FTIR Analysis of G11 Sample (Without WPCB 24

25. FTIR Analysis of G4 Sample (With WPCB ) FTIR Analysis of G44 Sample (Without WPCB ) 25

26. AAS results The gold recovery efficiency of the biological extraction methods using chitosan treatment was quantified using Atomic Absorption Spectroscopy (AAS). The AAS results for the different methods, labeled G1 through G4, are summarized in table below. Samples Atomic adsorption results (AAS) G1 0.34% G2 0.17% G3 0.14% G4 0.005% G5 0% 26

27. Discussion Interpretation of Gold Extraction Efficiency Aqua regia has shown high efficiency in extracting gold in the analyzed samples as Sample S1 has a 4% gold composition. For Sample S2 when nitric acid was used as a solo leaching solution, a higher concentration of gold of 92% was achieved The AAS outcome confirms that chitosan has valuable role in bioleaching process and the optimization of the amount of HCl in the chitosan solution plays a crucial role (Bui et al., 2021) on leaching efficiency Environmental Impact Interpretation Hazardous Waste Generation Soil and Water Contamination Economic Viability Cost-Effectiveness Energy Efficiency 27

28. 28 Limitations Limited access to e-waste samples, especially those with high gold content Lack of sophisticated instruments like SEM-EDX and AAS for gold analysis Variations in chemical composition, recycling practices and environmental standards may limit the broader applicability of the findings . Conclusions This research compared two methods of gold extraction from e-waste: chemical leaching (using aqua regia and nitric acid) and bioleaching (using chitosan ). Nitric acid proved the most effective in gold extraction, but both chemical methods produced significant hazardous waste and toxic emissions. While bioleaching was less effective in terms of recovery rates, it was more environmentally friendly and aligned with sustainable practices. Economically, chemical methods offer short-term gains but involve higher costs due to environmental regulations. Bioleaching, although less efficient, provides a safer and more cost-effective alternative in the long term make it more concise.

29. Recommendations 29 Optimization of Bioleaching Process Development of Sustainable Practices Enhanced Safety Measures for Chemical Methods Policy and Regulation Further Research and Innovation

30. REFERENCES Forti, V., Balde, C. P., Kuehr, R., & Bel, G. (2020). The Global E-waste Monitor 2020: Quantities, flows and the circular economy potential. Ghimire , H., & Ariya , P. A. (2020). E-wastes: Bridging the knowledge gaps in global production budgets, composition, recycling and sustainability implications. Sustainable Chemistry , 1 (2), 154-182. https://doi.org/10.3390/suschem1020012 Rawat , K., Sharma, N., & Singh, V. K. (2022). X‐ray fluorescence and comparison with other analytical methods (AAS, ICP‐AES, LA‐ICP‐MS, IC, LIBS, SEM‐EDS, and XRD). X‐Ray Fluorescence in Biological Sciences , 1-20. https://doi.org/10.1002/9781119645719.ch1 Liu, F., Hua , S., Zhou, L., & Hu , B. (2021). Development and characterization of chitosan functionalized dialdehyde viscose fiber for adsorption of Au(III) and Pd(II). International Journal of Biological Macromolecules , 173 , 457-466. https://doi.org/10.1016/j.ijbiomac.2021.01.145 Elomaa , H., Seisko , S., Junnila , T., Sirviö , T., Wilson, B., Aromaa , J., & Lundström , M. (2017). The effect of the redox potential of aqua regia and temperature on the AU, CU, and FE dissolution from WPCBs. Recycling , 2 (3), 14. https://doi.org/10.3390/recycling2030014 Tatariants , M., Yousef , S., Denafas , G., Tichonovas , M., & Bendikiene , R. (2018). Recovery of gold, other metallic and non-metallic components of full-size waste random access memory. Journal of Cleaner Production , 172 , 2811-2823. https:// doi.org/10.1016/j.jclepro.2017.11.132 Mathew, G. M., Mathew, D. C., Sukumaran , R. K., Sindhu , R., Huang, C. C., Binod , P., Sirohi , R., Kim, S., & Pandey , A. (2020). Sustainable and eco-friendly strategies for shrimp shell valorization. Environmental Pollution , 267 , 115656. https:// doi.org/10.1016/j.envpol.2020.115656 Bui, T. H., Jeon , S., & Lee, Y. (2021). Facile recovery of gold from E- wastE by integrating chlorate leaching and selective adsorption using chitosan -based bioadsorbent . Journal of Environmental Chemical Engineering , 9 (1), 104661. https:// doi.org/10.1016/j.jece.2020.104661 Riaz , T., Zeeshan , R., Zarif , F., Ilyas , K., Muhammad, N., Safi, S. Z., Rahim , A., Rizvi , S. A., & Rehman , I. U. (2018). FTIR analysis of natural and synthetic collagen. Applied Spectroscopy Reviews , 53 (9), 703-746. https://doi.org/10.1080/05704928.2018.1426595 30

31. Recommendations 31 After thanking almighty ALLAH First and foremost, I would like to express my deepest gratitude to chairperson professor DR.sheikh saeed ahmad I am also immensely thankful to my supervisor dr.sana zulfiqar . University lab staff dr.irum and collegues Parents sister and husband.

32. THANK YOU 32