Electronic waste is one of the hazardous waste concerns which pose threat to the both developed and developing countries in terms of environmental pollution. Generation of electronic waste is increasing year by year globally and it is important to treat the e-waste properly. Electronic waste contains materials such as Al, Ag, Cu including hazardous materials such as lead in various electronic waste products. In this work integrated circuit chips, header pins and edge connectors from modem e-waste are selected for the investigation due to the availability of precious metals in them. Experiments were conducted on these selected components by acid leaching followed by elemental analysis by ICP-OES. The components for the acid leaching were removed from PCBs of computer modem boxes by de-soldering method. The acid leaching experiment on header pin was conducted using 200ml of HNO3 solution. The leaching experiment on IC chip was carried out using aqua regia solution containing 25ml of HNO3 and 120 ml of HCl. The precipitation was done using sodium metabisulfite (Na₂S₂O₅). The elements in output residue obtained from acid leaching were identified using ICP-OES. Concentration of silver was found to be highest with the value of 64.40 mg/l among all the other elements present. Similarly, in header pins residue the concentration of silver was found to be 14.18 mg/l and copper 7.68 mg/l. The silver present in the IC chip ash was found to be 13.99 mg/l and the concentration of copper was 7.77 mg/l.
2. M. Anandhan, M. Muhaidheen, J. Thanikachalam and S. Balamurugan
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Keywords: Acid Leaching of E-Waste Scraps.
Cite this Article: M. Anandhan, M. Muhaidheen, J. Thanikachalam and S.
Balamurugan, Investigation on Acid Leaching of E-Waste Scraps Obtained from
Modem Boxes, International Journal of Mechanical Engineering and Technology,
10(5), 2019, pp. 98-104.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=5
1. INTRODUCTION
The electronic industry is the world’s largest and fastest growing manufacturing industry. The
United States ranked first in e-waste generation, generating 11.7 million tonnes of e-waste
annually. China ranked second with 6.1 million tonnes of e-waste every year. India is the fifth
largest generator of electronic waste in the world. Indian electronic waste output has jumped 8
times in the last seven years that is 1.85 million tonnes reported by The Associated Chambers
of Commerce & Industry of India, 2016 [1].
Fırat Burat et al, 2019 [2] investigated the precious metal recovery from floor sweeping
waste at jewellery shops by physical and physiochemical method. The gold Au and silver Ag
are the primary metals explored in their work. Garima Chauhan et al, [3] reviewed
conventional practices for metal recovery and analysed the technical feasibility of metal
recovery from waste electronic and electrical equipment. They have investigated a novel
method to recover metals from PCBs. R. Cayumil et al, [4] proposed a method to recover
metals from pyro-metallurgical process. They also demonstrated recovery of valuable materials
from printed circuit boards by using high temperature pyrolysis. Luis a et al, [5] developed a
comprehensive process for the recovery of critical and value metals from electronic waste. They
have discussed the separation of metals from magnetic and non-magnetic fractions. From the
results they have concluded that anaerobic extraction is the efficient alternative for the recovery
of critical materials from electronic waste. Diaz et al, [6] discussed and explored essential
strategies to recover metals from waste gadgets by electrochemical method. Yunji Ding et al,
[7] investigated the rapid generation of precious metals from e-waste. They have discussed the
overview of various methods to recover the metals. They have studied the environmental
impacts and sustainable recovery of precious metals with high recovery rate. Hyunju Lee et
al, [8] focused on selective recovery of copper and iron from fine materials of electronic waste
processing. They have achieved leaching efficiency of approximately 90% of Fe and 98% of
Cu by using H2SO4 and HNO3 acids. Yan Lu et al, [9] Proposed the importance to reuse metals
from Waste PCBs without negative impacts to nature and human wellbeing. Long meng et al,
[10] investigated recycling of printed circuit boards to recover Cu and Zn from waste using
super-gravity separation. They have reported that super gravity separation method is most
efficient and optimal method to recover metals from PCBs. They have also suggested methods
to control the waste generated during the recovery of heavy metals. Fangfang Wang et al, [11]
proposed a novel method utilising vibrated gas-fluidized bed to recover metals from residue
with a size of 0.5 mm. They have reasoned that the vibrated gas-strong fluidized bed had higher
efficiency to recover metals from residue. Zhi-Yuan Zhang et al, [12] discussed an
environment friendly ball milling process for recovery of valuable metals from e-waste.
Xiang-nan Zhu et al, [13] investigated the effective recovery of metals from WPCBs green
floatation technology in waste printed circuit boards. They have achieved 47% of copper yield
from this technology for the effective recovery of metals. Arda Işıldar et al, [14] discussed
latest technological developments, global state of electronic waste and its management to
recover metal from various types of electronic waste.
They also discussed the methods to recover metals from e-waste such as physical,
pyrometallurgical and hydrometallurgical processes. Artem Golev et al, [15] reviewed the
3. Investigation on Acid Leaching of E-Waste Scraps Obtained from Modem Boxes
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current situation with e-waste management in Australia, and focused the material flows and
metal recovery of valuable metals from waste printed circuit boards. They have reported that e-
waste in Australia is estimated up to 10 kt per year (2014) with huge potential for metal
recovery. Sebastian Gamez et al, [16] investigated the precious metal recovery from waste
printed circuit boards using thiosulfate leaching and ion exchanging resin.
2. MATERIALS AND METHODS
For this study the acid leaching experiments were performed on header pins, edge connectors
and integrated circuit chips. First the printed circuit boards are removed from computer modem
boxes manually. Then header pins, IC chips and edge connectors are identified and dismantled
by de-soldering method. The acid leaching experiments were conducted by using HNO3,
Na₂S₂O₅ and HCl with the equal amount of water. The header pins are highly precious metal
coated pins available in the PCBs in higher quantity. Header pins are normally 2mm of size
approximately of 15 numbers in a single board. In this experiment 4 number of PCBs were
taken for conducting the experiments. The edge connectors are chopped into small pieces to
recover the metals by acid leaching technique. The IC chips are also removed from the printed
circuit boards for precious metal recovery. The figure 2.1 shows the methodology followed in
this work for the E waste management.
Figure 2.1 Methodology of E waste treatment
4. M. Anandhan, M. Muhaidheen, J. Thanikachalam and S. Balamurugan
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Figure 2.2 Header Pins Figure 2.3 Edge Connector
Figure 2.4 IC Chips Figure 2.5 Acid Leaching
Figure 2.6 Metal Residue of Header Pins
2.1. Material identification
Most printed circuit boards are generally consisting of Copper, Iron, Silver, Lead, Palladium,
Mercury and Plastic. They are manufactured by drilling the holes and mounting the components
on the printed pattern of the substrate [4]. The header pins are conductive material which were
removed from the PCBs using cutting pliers and de-soldering set. The header pin base material
is made of brass and was coated with nickel followed by gold.
5. Investigation on Acid Leaching of E-Waste Scraps Obtained from Modem Boxes
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2.2. Experimental work
2.2.1. Metal recovery from header pins
In this experiment over 300 numbers of header pins are collected from printed circuit boards
for metal recovery. The weight of the total header pins is measured in a weighing balance and
found to be 78 g. First 200 ml of nitric acid (HNO3) and 200 ml of water were taken in a 500ml
beaker. Then the removed header pins are slowly poured into the beaker for the metal reaction.
Metal pins are allowed to remain in the beaker for 3 to 4 hours. Then it was filtered by light
cotton cloth. The collected metal residue weight is 0.965 g.
2.2.2. Metal recovery from edge connectors
For conducting the acid leaching experiment of edge connectors over 29 numbers are chopped
from the printed circuit boards. The weight of the edge connector is 14 g with the size of 2mm.
First the 200 ml of HNO3, and 100 ml of water were taken in the 500ml beaker. The edge
connectors are poured into the beaker and kept in the solution for overnight. Then the metal
residue is separated from the liquid. The liquid solution is filtered with light cotton cloth and
the heavy metal residue are collected from the top surface of the cotton.
2.2.3. Metal recovery from IC chips
For the IC chip experiment 45 no of IC chips are collected from modem box printed circuit
boards. The IC chips are removed in the PCBs by de soldering. The experiment was done by
heating the IC chips in pan for 1 or 2 hr and the ash was collected for further study. Then the
collected ash was completely allowed to cool for 2 hours. Then the ash is sieved to get the fine
ash. Then the collected ash was subjected into acid leaching experiment. The weight of the fine
sieved ash is found to be 117 g. The sieved ash was taken in the beaker. In the beaker 70 ml of
HNO3 and 200 ml of HCl 200ml were added and mixed manually for 5 hours. The solution is
then filtered using light cottons. After that 25 g of sodium metal bisulfite is added in the solution
and kept overnight for the reaction. Finally, powder is collected from beaker for conducting
further experiments.
3. TESTING
The testing was done by inductively coupled plasma spectrometry. For this experiment 500 ml
of blank solution was prepared using 10ml of HNO3 and 490ml of Millipore water. Then the
aqua regia solution is prepared by taking 1ml of HCl and 3ml of HNO3 in 100 ml beaker. Then
the 0.5g of sample is put into the above solution and the solution is heated up until we get the
solid solution. Then the solid residue is poured into the 50 ml SMF with the addition of blank
solution. The final sample is taken by the micropipette for 0.5ml in the 50ml SMF with the
addition of blank solution. The same procedure is repeated for all the other two samples.
3.1. Testing results
Table 3.0 shows the testing result of the three samples
6. M. Anandhan, M. Muhaidheen, J. Thanikachalam and S. Balamurugan
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Table 3.0 Results of IC P-OES
Materials Header pin recovery Incinerated IC chip ash
Leached IC chip
metal powder
Silver (Ag) 14.18 mg/l 13.99 mg/l 64.40 mg/l
Copper (Cu) 7.68 mg/l 7.77 mg/l 4.82 mg/l
Iron (Fe) 0.056 mg/l 0.035 mg/l 0.047 mg/l
Nickel (Ni) 0.094 mg/l 0.083 mg/l 0.082 mg/l
Lead (Pb) 0 0 0
Zinc (Zn) 0 0 0
The ICP experiment was carried out for three residue samples to identify the metal contents
present in the recovered powders of open pan heating of E waste.
4. RESULT AND DISCUSSION
The identification of metals using ICP–OES Inductively coupled plasma optical Emission
spectroscopy is done for collected ash and residues of leaching experiments. ICP experiments
identified the type of elements present in the header pins, edge connectors and IC chips removed
from modem e-waste. The silver concentration in the IC chip residue is 64.40 mg/l and is
highest among the all. Similarly, in header pin sample the silver concentration was found to be
14.18 mg/l and copper was 7.68 mg/l. The lead and zinc was not found in the output. Iron and
Nickel are found in very low quantity compared to that of silver. The silver present in the ash
obtained from open pan heating was found to contain 13.99 mg/l and copper 7.77 mg/l.
5. CONCLUSION
Precious metals and hazardous materials have been identified in the modem box select
components and thus recovery of these metals can be tried at the industrial scale using acid
leaching technique. The IC chips samples were found to have favourable recovery options
among the three components selected for the study. Thus, there is a feasibility to recover heavy
metals by developing and customizing such procedure for every E waste component. The
procedure can be adopted in large scale by industries by experimenting with prototype setup
for each type of E waste component.
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