Gypsum Waste Minimisation
Presented at the 3rd Annual WARMNET Conference “Tackling Waste 2006”,
Nottingham, 6th and 7th July 2006
Rosemary Greaves
Department of Materials
Prof. Alan Atkinson
Dr. Mark Tyrer
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Presentation Outline
• The gypsum waste minimisation project
• Titanogypsum by-products
• Alternative approaches
• The ammonia process
• Experimental & analysis
• Conclusions & further work
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Gypsum
Calcium Sulfate Dihydrate CaSO4.2(H2O)
• Vital component of many construction materials
• In the UK demand outstrips domestic supply [1]
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Impetus For Work
• Sponsors landfill ~75kt of by-product gypsum per annum
– Red titanogypsum
– Construction site waste
• Disposal costs have escalated
– EU landfill directive [2]
– Increased landfill tax
Minimise and reuse gypsum wastes
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The Gypsum Waste Minimisation Project
Research Partners
Sponsors
Imperial College London
Huntsman Tioxide
•
•
•
Professor Alan Atkinson
Dr Mark Tyrer
Rosemary Greaves
Lafarge Plasterboard
Coventry University
•
•
•
Dr Peter Claisse
Dr Esmaiel Ganjian
Seema Karami
Funding
EPSRC
University of Birmingham
•
•
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Dr Gurmel Ghataora
Waliur Rahman
Miniwaste Faraday Partnership
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Titanogypsum By-products
By-product of TiO2 production from ilmenite (FeTiO3)
Waste Acid
Calcium Oxide
Calcium Hydroxide
Partial
Neutralisation
Complete
Neutralisation
Carbon Dioxide
White Gypsum
Red Gypsum
Effluent to Drain
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Red Titanogypsum
Fe(OH)3
Mass per gram
(mg/g)
Fe(OH)2
Element
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Routes to Red Gypsum Minimisation
Precipitate metal salts prior to gypsum formation
• Wastewater contains a complex combination of
impurities
• Focus on colour
• Use simplified solution based on sponsor’s analysis
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[H2SO4]g/l
[Fe2+]
pH
142.10
36.12
~2.5
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Eh (Volts)
Pourbaix Diagram [3]
pH
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Eh (Volts)
Oxidise
pH
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Eh (Volts)
Increase pH
pH
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Ammonia Addition Process [4]
H 2 SO 4  NH 4 OH 
 ( NH 4 ) 2 SO 4  H 2 O
• Regeneration of NH3
• Iron content 160g/kg
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0.42g/kg
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Titration Experiments
How does pH effect
precipitation?
1. Produce Analogue:
– H2SO4
– FeSO4.7(H2O)
2. Titrate aqueous ammonia
(NH4OH)
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Precipitation of Iron
pH 4.7
6.3
6.8
7.0
7.6
8.2
8.7
Samples taken at various pH
• Centrifuged
• Solids filtered from solution
• Iron concentration of solution analysed
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Spectrophotometry
1. Reduce to iron (II)
2. Chelate
–
1,10-phenanthroline
3. Illuminate
–
–
–
l=515nm
Visible
monochromatic
Intensity a concentration
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Data Analysis
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Effect of pH on Iron Removal
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Conclusions and Future Work
• Alkalizing the solution causes iron to precipitate
• Concentration of iron decreases with pH
• Precipitates must be analysed
• Perform a Comparison with alternative techniques
• Analyse resultant gypsum samples
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References
1.
Hillier, J. A., L. E. Taylor, et al. (2004). United Kingdom
Minerals Yearbook 2004, British Geological Survey.
2.
European Council Directive 1999/31/EC on the Landfill of
Waste. 1999.
3.
Roine, A., HSC Chemistry 5.1 for Windows, Outokumpu
Research Oy.
4.
Hyvrard, F. and P. Muller, Method for Treating and
Upgrading Effluents Containing Metalic Sulphates Using an
Ammonia Addition Step. 2004: US. p. 5.
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