Metal Recovery

8/13/2019 Metal Recovery

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MATERIALS RECYCLING

AND RECOVERY

Derek FrayDepartment of Materials Science

and Metallurgy

University of Cambridge


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TOPICS TO BE COVERED

Physical separation of materials

Treatment of Electronic Scrap to recovercomponents and valuable constituents

Use of scrap PVC to treat metallic residues


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SORTING


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MAGNETIC SEPARATION


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Eddy Current Sorting


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Melting of Aluminium Scrap

STEELMAKING


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STEELMAKING


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MELTING OF LEAD SCRAP


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TREATMENT OF

ELECTRONIC SCRAP


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KEY POINTS

Exponential demand for electronicequipment

Short life of computers

Small percentage of computers find re-use

Most electronic scrap is either land-filled or

melted Legislation is likely to require

manufacturers to take back equipment


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QUANTITIES OF AVAILABLESCRAP

50,000 tonnes of PCB scrap generated in

the UK 300,000 tonnes of PCB scrap generated in

Europe


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PERCENTAGE RECYCLED

Only 15% of the 50,000 tonnes per annumis subjected to any form of recycling, theremainder being consigned to landfill

Approximately 60% of the 42,500 tonnesper annum is landfilled within the total

redundant equipment package A significant proportion is exported

illegally


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APPROXIMATE COMPOSITION OF

PCB ASSEMBLIES

Glass-reinforced polymer 70% Copper 16%

Solder 5%

Iron, ferrite (from transformer coils) 5%

Nickel 1%

Silver 0.1% Gold 0.025%

Palladium 0.01%

Other (bismuth, antimony, tantalum, etc)


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Component Wt.

(by%)

Value ()

(by kg)

Intrinsic Value

( per kg)

Gold 0.025 12509 3.13

Palladium 0.01 26961 2.70

Silver 0.1 253 0.252

Copper 16 4.093 0.655

Tin 3 5.101 0.153

Lead 2 0.669 0.014

Nickel 1 10.815 0.108

Aluminium 5 1.538 0.077

Iron 5 0.208 0.01

Zinc 1 1.793 0.02

Total 7.12/kg

Value of components ~ 1.5 /kg


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OVERALL AIM

1. Recover value of components

2. Minimise chance of loss of precious metal

3. Recover solder

4. Recover copper

5. Recover bromine

6. Predominantly low temperature process- high energyefficiency

7. Low waste volume

8. Environmentally friendly


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80


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0

10

20

30

40

50

60

70

80

0 100 200 300 400

Time (min)

a

.me

tal

/L

Solder

Cu

Dissolution of solder and copper with

HBF4/ 0.3 M Ti(IV) at 60 deg. C usingoxygen sparge.


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LEACHING RESULTS

Lead and tin dissolved in the same ratio as in the

solder

About 70 g/l of metal was obtained in the

fluoroboric acid Temperature of dissolution was 20 30oC

Dissolution of copper was negligible

After dissolution of the solder, the components

were simply removed and electronically tested


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Divided electrowinning cell (flow cell, laboratory scale)


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Variation of concentrations of Sn and Pb in electrolyte asa function of electrolysis time.


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ELECTRODEPOSITED SOLDER


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ELECTRODEPOSITED COPPER

LEACHING AND


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LEACHING AND

ELECTROWINNING OFPRECIOUS METALS

Precious metals were leached with

hydrochloric acid and nitric acid and thenelectrowon


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RELEASE OF BROMINE

Boards after leaching were simplycombusted in air at 600oC

The bromine and hydrogen bromide were

collected in caustic soda

About 3.5% of the boards were bromine


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P r in ted c i rc u i t boa r d s

S o ld er

rem ov a l

S o ld er( r e - u s e )

Co m pon ents

S tr ipp ed

c i r c u it b oa r d s

R e -use or pre c ious

m eta l s reco very

C o p p e rC o p p e r

r e c o v e r y

B rom iner e c o v e r y

I n e r t r e s id ue s

B r o m i n e


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ECONOMIC ASSESSMENT

Cost of plant to process 10000

tonnes/annum of PCBs is 3m

Profit per tonne of material treated 90

Value of recovered components has not be

included as the value of components

fluctuates considerably. It could be as highas 1500/tonne


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COMBINATION OF PVC ANDSTEEL SCRAP AND RESIDUES


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GENERAL CONCLUSIONS

Conventional and novel metallurgicalextraction techniques can be applied to therecycling of a variety of wastes

In some cases it is possible to combine twowaste materials together to give useful

products

There are many other opportunities whichcan be investigated

Metal Recovery

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