ICNSCET19- International Conference on New Scientific Creations in Engineering and Technology
INVESTIGATION ON SUSTAINABLE EXTRCTION OF
PRECIOUS METALS AND RARE ELEMENT FROM E-WASTE
M. Anandhan, S. Balamurugan
mechanical engineering, mepco schlenk engineering college,[email protected]
mechanical engineering, mepco schlenk engineering college, [email protected]
Abstract Mobile phone Printed Circuit Boards (PCBs) are collected from local sources were used for recovering copper by electro deposition process, using a glass reactor setup of working volume 10 liters and aqua regia for dissolution.
Copper rod was used as the anode and stainless steel rod as the cathode for the deposition process. Five mobile phone PCBs were adopted both for the dissolution and deposition processes. Metal powder has dissolved and the maximum metal powder deposited was 14.25gm in 120 minutes, which is equal to 10% of maximum recovery of metal powder from the PCBs. The maximum power consumption is found to be 0.0200 kWh for 14.25gm of metal powder recovered. The maximum metal powder recovered in 120 minutes of the deposition process can be considered as the optimum for the 6 L of dissolved solution.
There is scope to refine the process and scale it up, if proper funding and facilities are made available.
India has two types of electronic waste market called organized and unorganized market. 90% of the electronic waste generation in the country lands up in the unorganized market. Electronic waste accounts for 70% of the overall toxic wastes which are currently found in landfills which is posing threat to soil contamination and other natural resources. Abhishek Kumar awasthi et al, 2017 investigated the laws and policies on proper e-waste collection, treatment and recycling from India and china. Discussed the problems involved in the illegal shifting of e-waste from china to India. Yan lu et al, 2016 proposed the importance of precious metals from printed circuit boards and its hazardous nature to the environment. Also they reported the technological innovation and improvements of living standards have results in large amounts of waste electric and electronic equipment. Huan Li et al, 2018 reviewed the hydrometallurgical recovery of metals from waste printed circuit boards. Approached the current status and perspectives of printed circuit boards and its harmful metals such Pb, Cr, As, Cd and Hg and some economical valuable metals Cu, Sn, Au, Ag and Pd. Ata akcil et al, 2015 studied various technologies involved in the e-waste recovery from printed circuit boards by cyanide leaching, non-cyanide leaching. Like there are several recycling technologies have been developed to recover precious and valuable metals through thiourea, thiosulphate, aqua regia and iodine leaching methods.
Oyuna Tsydenova et al, 2011 summarizes the existing knowledge on the chemical hazards associated with recycling and other end-of-life treatment options of waste electrical and electronic equipment. The review describes exposure to chemicals, workplace and environmental pollution associated with the three major e-waste management options, that are recycling, incineration and landfilling. Ionela Birloaga et al, 2013 investigated the process of leaching from waste printed circuit boards in order to recover gold by thioureaction. The amount of gold yield from this reaction is 69% and 75% Cu was removed by a double oxidative leaching treatment of waste printed circuit boards with particles size smaller than 2mm. Robinson Torres et al, 2016 studied the effect of oxidants such as air, ozone, and peroxide hydroxide. He has achieved the copper extraction up to 90% by pre-treatments with peroxide. This study was focusing on copper leaching from electronic waste for the improvement of gold recycling. L. Flandinet et al, 2012 developed a new approach for recycling waste printed circuit boards using molten salts. Molten salts and specifically molten KOHNaOH eutectic is used to dissolve glasses, oxides and to destruct plastics present in wastes without oxidizing the most valuable metals. Vinh Hung Ha et al, 2010 deals with the leaching of gold from the printed circuit boards of waste mobile phones using an effective and less hazardous system. The method was conducted by copper-ammonia-thiosulfate solution, as an alternative to the conventional and toxic cyanide leaching of gold. The obtained data on this method will be useful for the recycling of gold from waste mobile phones. Young Jun Park et al, 2009 studied the recovery of high purity precious metals from printed circuit boards by conducting the experiment using aqua regia solution. The precious metals palladium, gold and silver are recovered through liquid to liquid extraction, aqua regia leaching technique and precipitation method. The study shows promising method to recover precious metals from wastes selectively because of metal yield weight percentage was 96% that is tested from SEM. Muammer Kaya, 2016 provided a comprehensive review of various physical and chemical processes for electronic waste recycling, their advantages and shortfalls towards achieving a cleaner process of waste utilization with special attention towards extraction of metallic values. St. Kontogianni et al, 2017 investigated the occupational health and safety conditions in Hellenic solid waste management facilities. The proposed research work asked questions with facility safety officers and conducted interviews to detect risk level parameters of sanitary landfills, recycling plants and transfer stations. Andre Canal Marques et al, 2013 provided a comprehensive review and environmental problem related to recycling of printed circuit boards. Furthermore studied the structure and materials presented in the printed circuit boards to minimize the impact from recycling. R. Vijayaram et al, 2013 conducted various experiments to extract materials from discarded printed circuit board by leaching technique. In addition to obtained the highest percentage of copper (92.7%) extracted from aqueous regia solutions so the indeed results taken from scanning electron microscope for H2 SO4, HNO3 and HCl solutions.
II. MATERIALS AND METHODS
A. Printed circuit boards
Based on the available literature, the metallic elements are often covered with or encapsulated by various plastic or ceramic materials on PCBs. Huccuria (1) revealed that the general awareness on the potential hazardous nature of e-waste is rather poor, and that no attempt has been made to recover metals, in spite of the fact that the total e-waste generation is in tonnes per year. Hence, waste PCBs were collected from mobile phones by various local sources and used as source material for the present work. The collected mobile phone models are, LYF, YESTEL, NOKIA (MODEL 6030), SAMSUNG (SLIDE TYPE), and Bluetooth mobile the picture shown in Fig 1. The collected mobile phones are dismantled manually to separate the PCBs. The job safety analysis was conducted to the effective dismantling of components from mobile phone components. The each PCB is weighted before getting into the electrolytic process to know the variation after the treatment. There are 5 number of IC chips was found in the total no of five mobile phones.
B. Electrolytic reactor setup
A glass reactor of working volume of 10L was used for electrolytic process. The setup consisted of a copper rod of 14 mm diameter as the anode and stainless steel rod diameter 14 mm as the cathode for dissolution process. A direct current (DC) power supply 15A as given to the process by step down transformer and a multimeter was used to measure the current and voltage during the electrolytic process. The experimental setup adopted is shown in Fig. 2, which is based on the one reported by Huccuria et.al, (2017).
Fig. 1 Mobile phones
The experimental methodology has been carried out in three stages. The dismantling and preparation of source material (PCBs) as a first stage, followed by dissolution of metal present in PCBs into the prepared solution as a second stage and finally recovery of the dissolved metals from the solution by electrolytic process, at the third stage. Capacitors, ICs, joints, mountings, etc. were removed from the PCBs and sorted manually. The PCBs were then cut into pieces as small as possible, and the cut pieces were weighed. The weighed PCBs were then placed in the reactor. It was ensured that the cut pieces are in maximum contact with the copper anode to enhance the dissolution of the metal in the PCBs by improving the conductivity. The anode set was connected to the positive terminal of the rectifier and stainless steel rod was connected to the negative terminal of the step down transformer. Maximum possible current was set to carry out the experiment and the voltage was maintained such that to achieve maximum current and hence rate of dissolution. In the process, 6 liters of distilled water was taken in a container, then 500 ml concentrated nitric acid (HNO3) was added first and after that 300 gm hydrochloric acid (HCI) was added.
Fig.2 Experimental Setup of the electrolytic process
Nitric acid is steadily consumed during the dissolution and hence it has to be added periodically. Hydrochloric acid was added in the bath as it helps to maintain the electrical conductivity of the bath and hence the release of nitrate ions. Hydrochloric acid could not be used as it does not dissolve copper, but, it reacts with lead forming lead sulphate, which is water insoluble. The remains in the reactor were taken out, dried, weighed, and the weight loss in the scrap was calculated, which is equal to the amount of metals that have gone into solution. The current, voltage and time were measured so as to calculate the energy consumed for the dissolution of metals. The copper rod was polished by emery paper, cleaned with acetone and after drying the rod; its initial weight was noted. This stainless rod was connected to negative terminal (cathode) and copper rod was connected to positive terminal (anode) of the rectifier. Both electrodes were dipped in solution and an external supply was given. The copper ions in the solution move to the cathode for deposition.
III. RESULT AND DISCUSSIONS
a) Effect of electrolysis duration on dissolution and deposition process
In the different sets of experiments that were conducted for the dissolution and deposition processes the duration for the dissolution process was 3, 2, 1 hours and the initial amount of PCBs taken for the dissolution process was 350gm for every set of experiment. Weight of the dried sample of PCBs was noted after 5 hours of dissolution process and it was found that 122gm was dissolved in nitric acid bath. Weight of PCBs dissolved goes on gently increasing, with the rate of increase being higher during initial stages, and stabilizes at latter stages, within the range of duration considered. However, the weight of copper deposited in the stainless steel rod almost increases linearly with time, barring the initial stage. Initial weight of the stainless steel rod was noted for the deposition process and after the electro deposition of metal the deposited weight of metal in the stainless steel electrode was assessed by taking the weight. The duration for the deposition process was set as: 120, 90, 60, 30, 15 minutes. It was found that 14.25 gm of metal deposited during 120 minutes is the highest, among all the durations considered. It is found that the maximum metal recovered was 12% and achieved after 120 minutes, in 6 L of dissolved solution.
b. SEM characterization of metal powders
The SEM image shows that metal powder consists of close network in structures. The processed e-waste was physicochemically characterized by SEM analysis, which revealed the presence of the precious metal Ag, basic metals Cu, and Fe and toxic heavy metals. The analysis showed the presence of heavy metals in the structure of the heavy metals. Structure of deposit in the electrolytic process, the heavy metal is recovered from the cathode rod as a powder.
Fig. 3 SEM images for the collected powder
For the recovery of copper from E-waste (PCBs), the maximum duration for the dissolution process was found to be 3 hours for the dissolution of PCBs compounds and the maximum duration of electrolysis for deposition of copper was 120 minutes for 14.25 gm. The maximum power consumption was 0.0200 kWh for 14.25gm of metal recovered. Maximum metal recovered is 12% and it was achieved in 120 minutes using 6 L of dissolved solution. The performance of the process seems to depend on the choice of the electrolyte, the initial state of PCBs, duration and power consumed duration the dissolution and deposition stages. There is scope for improvement in the process and scaling it up, with the support for research from funding agencies, as laboratory investigation has its own limitations.
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