sustainable recycling of a lead battery by directly producing lead grid and value added paste...
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Sustainable recycling of a lead battery by directly producing lead grid and value added paste precursor for a new battery
R Vasant Kumar
Department of Materials Science & Metallurgy
University of Cambridge, UK
Acknowledgements
Seref Sonmez, Vega Kotzeva, Jiakuan Yang, Lilia Sanchez, Richard Darby, Yingjun Liu, David Zou, of Department of Materials Science
Lei Wang, Nigel Williams of the Business School
Maggie Wilkinson & Zlatka Stoeva of Cambridge Enterprise
Lead Battery (> 80 % Lead Usage)
Lead Batteries- Leaders in Recycling
Consumer Product Recycling Rate
Plastic bottles 10 – 35 %
Glass containers 25 – 35 %
Steel Cans 50 – 60 %
Aluminium Cans 50 – 70 %
Lead batteries 70 – 95 %
Current Method - Pyrometallurgy
*For 10,000 tpy plantCapital: $4-5MEnergy: 14,000MWH*Independent Consultants
Lead Recycling
50 % of Pb from waste battery (Pb alloy grid + Pb paste)
Pb + Pb oxides + PbSO4 (smelted at 1450 K) → Pb + CO2 + SO2
Done either in independent units or with primary smelting units
Energy: 4 - 10 kWh/Kg of Pb + pollution Energy from a battery < 35 Wh/Kg
Environmental Issues
Lead fuming is intensified at T > 500oC Vapours and dust of Pb/PbO and gaseous
SO2/SO3 in the vicinity of smelters Smelter slags may contain up to 5 % Pb
and such slags can release Pb by weathering
Na slags that can fix most of the sulfur dissolve Pb even more readily
Some Other Recent Advances
Leaching (fixes S with soda ash, usually incompletely) – Precipitation – Smelting (SO2 & C penalty)
Leaching (powerful reagents) – Electrowinning (capital and power intensive) @ 2 - 12 kWh/Kg to produce metallic electrodeposited Pb
Shipping!
Battery Manufacture
Lead is then chemically oxidised to PbO for the battery industry
PbO is electrochemically reduced to Pb and oxidised to PbO2 to make anode and cathode
Current recycling processes are unsustainable from energy considerations
Recycling> 2- 10 KWh/kg; Energy available from a battery < 50 Wh/kg
Table 1 Range of Compositions from a dry lead battery paste
Material Wt %
Lead sulphate 55-65
Lead dioxide 15-40
Lead monoxide 5-25
Metallic lead 1-5
Carbon black, plastics, fibres, other sulphates
1-4
Lead containing Organic
Crystalline Compounds
PbO Precursor
New
A new process for recycling lead battery waste
→
↓↑
→
Special Leaching/Crystallization Process
Lead Battery
Combustion/Calcination Process
Manufacturing Lead Battery
Waste Battery
Paste
New Paste
Patent: PCT/GB2007/004222; WO2008/056125RV Kumar, S Sonmez and V Kotzeva
A new process for recycling lead battery waste
→
Paste
Pb GridHeat Energy from pasterecycling
New Grid
New Paste directly from paste recycling
Kettle
Waste Battery
New lead Battery
Green PB Recycling Process
Patent: PCT/GB2007/004222; WO2008/056125RV Kumar, S Sonmez, V Kotzeva
Leaching
Combustion-Calcination
SpentLead grid
MetallicLead
Energy
PbO leaching with citric acid solution
PbO + C6H8O7·H2O → [Pb(C6H6O7)]·H2O + H2O
Molar Ratio: PbO/ C6H8O7·H2O= 1:1Temperature: 20 ℃Solid/Liquid=1/3; concentration of citric acid monohydrate : 23.9 wt%Magnetic stirring speed : 500rpmReaction time : 60min
0
10
20
30
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50
0 5 10 15 20 25 30 35 40 45 50 55 60 65
Reacti on Ti me/ mi n
Temp
erat
ure/
℃
0
1
2
3
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6
0 10 20 30 40 50 60
Time / mins
Tem
pera
ture
Ris
e / °
C
1.5 : 1 1.25 : 1 1 : 1
Leaching of battery paste
Ratio ofPaste/reagent
PbO2 leaching experiment with citric acid solution
Filtration of Crystalline lead citratePb recovery 99.9 %
Leaching solid products and recovery ratio
239.2g/mol 415.32g/mol
PbO2 + C6H8O7·H2O + H2O2→ [Pb(C6H6O7)]·H2O + 2H2O +O2↑
PbSO4 leaching experiment with citric acid solution
PbSO4 +1.5 Na3C6H5O7.2H2O + C6H8O7·H2O → [Pb(C6H6O7) n ] ·H2O + + Na2SO4 + 2H2O
Molar Ratio: PbO2/ C6H8O7·H2O= 1:1Temperature: 20 ℃Solid/Liquid: 1/5Magnetic stirring speed : 500rpmReaction time: 60min
Leaching reaction conditions
101520253035404550
0 5 10 15 20 25 30 35 40 45 50 55 60 65
React i on Ti me/ mi n
Temp
erat
ure/
℃
1. Lead citrate synthesis from PbO:
2. Lead citrate synthesis from PbO2:
3. Preparation of sodium citrate from sodium hydroxide and citric acid:
4. Desulphurisation of PbSO4 by sodium citrate:
Reactions of Interest
Lead organic crystallites
Combustion - Calcination
Conversion of lead organic crystallites into PbO at relatively low temperatures (300- 500OC)
Source of Energy – Combustion of Organics embodied in the crystallites ( C-neutral)
Direct production of PbO raw material for battery manufacturing
Any ratio of PbO/Pb or PbO/PbO2 is achievable – Direct production of Anode or Cathode also possible
Energy for recycling 250 Wh/kg, of the same order of magnitude as energy from the battery 30 Wh/kg
Combustion product of PbO2 leaching productCombustion products at the different combustion temperatures in Stationary air atmosphere
At temperatures< 300 , amorphous ℃PbO structure At T > 350 , ℃crystalline PbO is the main product As T is increased, the ratio of PbO/ Pb increase
Thermal Analysis of organic precursor
DSC/DTA at Stationary air atmosphere 128.4 endothermic peak, dehydrate ℃peak 280.3 exothermic peak, 1st step ℃combustion 345.0 exothermic peak, 2th step ℃combustion Weight loss after combustion is 36.8%
Air flow at 100cm3 per minute 117.77 endothermic peak, dehydrate ℃peak 284.16 exothermic peak, 1st step ℃combustion 357.91 exothermic peak, 2th step ℃combustion 2427J/g heat release from combustion process873.27 endothermic peak, PbO ℃melting point Weight loss after combustion is 38.33%
Combustion product of PbSO4 leaching productCombustion products at the different combustion temperatures in Stationary air atmosphere
Combustion at different temperatures for 1 hour After 350 , weight loss is ℃constant at 37.6% Pb/PbO ratio is calculated from wt loss
15
20
25
30
35
40
45
50
250 300 350 400 450 500
Temperature(℃)
Loss
of
weig
ht(w
t%)
[Pb3(C6H6O7)2]·H2O → 3PbO
1019.6 g/mol 3*223.2 g/molIdeal weight loss = (1019.6-3*223.2)/1019.6 = 33.7%
[Pb3(C6H6O7)2]·H2O → 3Pb
1019.6 g/mol 3*207.2 g/molIdeal weight loss = (1019.6-3*207.2)/1019.6 = 39%
Results – Thermo Gravimetric Analysis–The graph below shows an example TGA analysis
–The progressive decrease in weight can be attributed to the
combustion/calcination of the lead citrate as it loses CO2 and H2O and
changes to PbO
–The differential of the curve allows for a more easy comparison between
cases
PbO by combustion-calcination
SEM TEM
The Green PB Process
For 10,000 tpy plantCapital: $1-1.5 MEnergy: 1750 MWH
Carbon Impact: 10,000 tpy plant
Acid from Renewable
sources
Acid from Non-
Renewable sources
Sustainability
Current methods: energy required for recycling- 2 to 10 kWh/kg; energy produced by the battery per cycle: 35 - 50 Wh/kg
Using our new process, energy produced by a lead battery is comparable to energy for recycling: 150 - 250 Wh/kg
Low-C impact from C-neutral source of energy embodied in the leaching reagent
Further Research Work at the University Further research
Tramp elements removal and recovery Low-cost industrial grade citric acid sourcing
and production Improved battery pastes for high energy/
power density batteries Lightweight Batteries via new materials for
grids and separators/electrolytes
CONCLUSIONS
Recycling of lead acid batteries is considered within the overall context of materials and energy sustainability
Direct recovery of lead as lead oxide is proposed
New research for high energy density lead acid battery is being carried out
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