Recovery of Metals from Electronic Waste (Research Paper Sample)

RECOVERY OF METALS FROM ELECTRONIC WASTE AND SCALE-UP OF THE DEVELOPED PROCESS
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Recovery of Metals from Electronic Waste and Scale-Up of the Developed Process
Introduction
The production of electronic and electrical equipment is one of the major global manufacturing activities. Electronic equipment such as personal computers, mobile phones, polychlorinated biphenyls (PCBs), light-emitting diodes (LEDs), refrigerators, and liquid crystal displays (LCDs) have resulted in the production of huge amounts of electronic waste (e-waste). Today, it is estimated that 20 to 50 million tonnes of e-waste are produced every year (Debnath, Chowdhury and Ghosh, 2015). E-waste constitutes more than 5% of the solid waste generated globally, and the volume is expected to increase by 300% every year in developing countries (Debnath, Chowdhury and Ghosh, 2015). The increase in the production of e-waste has been a major health and environmental concern.
Most electrical and electronic equipment contain Printed Circuit Boards (PCBs) that are made of toxic metallic and non-metallic elements such as mercury, lead, brominated flame retardants, beryllium, arsenic, sulphur, and cadmium. Thus, if e-waste is discarded in the open, it can cause severe health and environmental hazards. However, PCBs are usually incinerated or dumped in open landfills resulting in serious environmental damage when the hazardous compounds leach into the soil and water or toxic gasses are released. The toxic substances are potentially harmful to the human nervous and respiratory systems (Hester & Harrison, 2009). Also, electronic equipment contain high amounts of precious metals such as silver (0.15wt %), copper (20wt %), palladium (0.01wt %), and gold (0.04wt %). Therefore, the disposal of e-waste also leads to the loss of these precious metals (Kurwara, 2010).
The proper treatment of e-waste is both profitable and environmentally worthwhile. Thermal, hydrometallurgical, and pyrometallurgical processes are currently being used to treat and recycle e-waste. However, these methods continue to be challenged by ecological, technical, and economic issues. The significant concern of e-waste disposal has accelerated research on the development of an economically and environmentally viable method of treating e-waste. The bio-hydrometallurgical process is an important method of recovering metals from electronic waste. It is environmentally sustainable and has can significantly lower energy requirements and operational costs (Debnath, Chowdhury and Ghosh, 2015). This paper addresses the recovery of metals from electronic waste, and the development of a sound method of managing e-waste.
Literature Review
Various studies have been carried out to establish a sustainable management process of e-waste, fueled by the statistical significance of e-waste. Nierderkom and Huzar et al (1984) were the pioneers of metal recovery from e-waste. The developed a method of recovering gold from used electrical contactors. They estimated that low voltage electrical contactors contained more than 700 tonnes of gold, and these contactors became redundant overtime. Through chemical and mechanical processing, their average rate of recovery of gold from the used contactors was 95%. Although several other researchers (Dunning B.W. et al) developed processes of recovery of metals from e-waste, Mellon and Mathews et al (1991) were the first to attempt the estimation of computer waste disposal and methods of recycling. In the Rio de Janeiro Earth Summit (1992), the sustainability of resources and precautionary principles were discussed. In the same year, the Basel Convention resolved to forbid the export and subsequent dumping of hazardous electronic waste into developing countries unless a number of conditions were met. Among the conditions was that the exporting country had to obtain written permission from the importing country and also had to guarantee that the toxic compounds would be treated in an eco-friendly manner. 171 countries ratified the treaty. Boswell et al (1995) published research on the recycling of e-waste through processes that laid emphasis on the concept of disassembly or de-manufacturing.
Hesselbach (2001) studied a recycling strategy that combined process and product oriented benchmarking in order to achieve economic efficiency. Furthermore, Chandra et al (2004) attempted to recover gold from e-waste through dissolution of electronic material in thiosulphate solutions. This was a viable and sustainable alternative method to cyanidation as a gold recovery method from ores. Gramatyka et al (2007) researched the current and developing status of electronic and electrical waste recycling in Europe with focus on the environmental and health impacts of e-waste. The study investigated the use pyrometallurgical processes of recycling e-waste and recommended the use of advanced recycling methods such as hydro- and bio-metallurgical methods of electronic scrap treatment.
Hischier et al (2011) in their paper titled “Does WEEE recycling make sense from and environmental perspective?” found that the dismantling and sorting activities of e-waste recycling companies are of little or no interest. According to them, the main impacts occur in the processes applied to recover secondary raw materials from the waste. They examined the recycling of computers, telecommunication equipment, and consumer electronics in Switzerland though the take-back and recycling systems. The two systems are the primary e-waste recycling methods in Switzerland. They concluded that recycling was the best eco-friendly method of e-waste recycling.
Youseff (2012) states that computers and mobile phones comprise the highest percentage of e-waste since they are the most widely used. They contain the highest amounts of precious metals as shown in the table below.
Metal by %

Key Boards

Personal Computers

Printed Circuit Boards

Car electronics

Typical copper ore

Recycling efficiency %

Au

0.005

0.001

0.008

0.007

0.00001

99

Ag

0.05

0.009

0.3

0.12

0,00034

80

Pd

0.0002

0.0004

-

-

0,04

60

Zn

3

1.2

1.5

1

0.12

60

Cu

13

7

25

20

0.8

90

Sb

0.3

0.5

0.06

0.08

-

70

Bi

<0.0003

<0.0004

0.17

0.01

-

6

Ni

0.16

0.2

0.5

0.3

-

0

Pb

0.3

1.5

-

1

-

5

Al

18

11

3

-

-

80

Fe

3

<0.1

5

5

-

80

In 2014, the United Nations Environmental Programme (UNEP) in its publication titled “Recycling – From E-Waste to Resource”, established that the various elements that comprise electronic waste are harmful to human health. The disposal of lead into the open can result in lead poisoning that may impair verbal and cognitive abilities and in severe cases, can result in paralysis and even death. Arsenic was established to interfere with cell communication and growth which may lead to diabetes, cancer, and cardiovascular diseases. Chromium is carcinogenic and causes skin disease while cadmium influences the metabolic activity of the body resulting in weakened bones and bone pain. The economic and social burden of dealing with and treating the diseases caused by electrical and electronic waste is huge. As such, the paper recommended that governments and private entities should establish environmentally viable ways of recycling e-waste to prevent these hazardous effects on human health. Muammer et al (2016) comprehensively reviewed the chemical and physical processes of e-waste recycling such as electrostatic, gravity, froth flotation, and magnetic separation. They also laid out the advantages and demerits of each of the processes. The purpose was to establish a cleaner e-waste management process with focus on extracting valuable metallic substances from the waste.
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