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PCBRec process: Waste Printed Circuit Board (WPCB) Recycling with Molten Salts

Periodic Reporting for period 1 - PCBRec (PCBRec process: Waste Printed Circuit Board (WPCB) Recycling with Molten Salts)

Reporting period: 2017-02-01 to 2017-07-31

Every year about 400,000 tons of waste printed circuit boards (PCBs, see Figure 1 for an example) are collected in Europe representing a large resource of precious, critical and other metals such as gold, platinum, palladium, copper and solder; often in concentrations significantly higher when compared with their ores i.e. copper (0.5–1% copper), gold (1–10 g/ton gold).

PCBs are used to mechanically support and electrically connect electronic components. They are used in almost all electronic equipment such as televisions, computers or mobile phones.
Waste PCB are difficult to recycle as tyres are designed to be durable and tough. This durability and toughness of tyres is a result of their composite nature made of resin, glass fibre, copper clad boards, solder and electronic components.
Composite Recycling Ltd (CRL) developed a patented PCB recycling process, which uses molten salt at temperatures of 350-400°C. The technology uses whole PCBs, significantly reducing capital and operational costs compared to other processes, who shred the PCBs and while doing so loose precious and other metals. Moreover, the PCBs are recycled within 15 minutes. Combined these two advantages result in an economic process.

Composite Recycling Ltd’s PCB recycling technology (PCBRec) offers many significant advantages over current technologies, which is also the unique selling proposition (USP):

1. Yields: over 95% recycling rate of copper, steel and solder [1, 2] greatly exceeding the recovery rates of current technologies of 70-80% [4].
1. PCBRec boosts the recycling yields of technology metals (indium, tantalum, etc.) to 50-80%. Moreover, aluminium, solder and steel is separated and recovered in metallic form rather than incomplete as by typical metallurgical processes.
2. Critical and special metals: for the first time, metals such as indium and tantalum will be recyclable.
3. All types of PCBs: high value (motherboards; high gold content) and low value (TVs; low gold content) PCBs.
4. No shredding: energy efficient process - no prior opening of lithium batteries or mobile phones resulting in cost savings.
5. Simple process from established industries: no moving parts, low capital cost. Easy to operate.
6. Continuous process: large throughputs are possible.
7. Scalability: Easy scale up: doubling the salt volume, doubles throughput. Modular technology, allowing further capacity increases in a systematic fashion.

The main objective of the study, establishing the technical, environmental and the economic feasibility of the PCBRec process on a commercial scale has been achieved.
At the core of the PCBRec technology lies the innovative, patented, U-shaped reactor containing molten salt as shown in the Figure below. The process operates as follows:

1. Whole, un-shredded PCBs with components present are added to charging vessel 1 and inerted with nitrogen.
2. The PCBs are charged with conveyor belt 3 into molten salt 4 (400-450°C). The PCBs decompose and separate into vapor, glass, metals and other materials. The operating temperature is high enough to melt the solder connecting the electronic components to the PCBs and to decompose the PCB resin. Vapors are not emitted from leg B allowing continuous access to leg B, as the molten salt seals the pyrolysis chamber from leg B.
3. The lighter solids (steel, copper) collect in area C below the molten salt but above the molten metal D (solder) and are removed intermittently from chamber 5 by removal device 6-7.
4. The vapours from the decomposition of the PCB resin are continuously removed from chamber 5 by line 8 and condensed to pyrolysis oil (P-oil) 9. The non-condensable gases (e.g. propane) 10 may provide energy for the burners 11 making the process self-sustaining.
5. Solder, molten at the operating temperature, collects in area D being much denser than the molten salt and is removed by 6-7 for metal recovery by specialized companies.
6. Gold, palladium and other dense metals partially settle in area E from where they can be removed by 6-7 or are suspended within the salt. Note: Indium is present as Indium Tin Oxide (ITO) in LCD screen will be suspended within the salt.
7. The recycling of metals from LCD screens, batteries and ASR is similar to PCB recycling. However, PCBs are the most difficult waste to treat due to their complexity.
fig-2-chamber.png