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Gypsum Waste Minimisation
Rosemary GreavesDepartment of Materials
Prof. Alan AtkinsonDr. Mark Tyrer
Presented at the 3rd Annual WARMNET Conference “Tackling Waste 2006”, Nottingham, 6th and 7th July 2006
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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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• 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
Impetus For Work
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The Gypsum Waste Minimisation Project
Sponsors
Huntsman Tioxide
Lafarge Plasterboard
Funding
EPSRC
Miniwaste Faraday Partnership
Research Partners
Imperial College London• Professor Alan Atkinson• Dr Mark Tyrer• Rosemary Greaves
Coventry University• Dr Peter Claisse• Dr Esmaiel Ganjian • Seema Karami
University of Birmingham• Dr Gurmel Ghataora • Waliur Rahman
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Titanogypsum By-products
By-product of TiO2 production from ilmenite (FeTiO3)
White Gypsum Calcium Oxide
Red Gypsum Calcium Hydroxide
Carbon Dioxide
Waste Acid
Partial Neutralisation
Complete Neutralisation
Effluent to Drain
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Red Titanogypsum
Fe(OH)3
Fe(OH)2
Mas
s pe
r gra
m
(g/
g)
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
[H2SO4]g/l [Fe2+] pH
142.10 36.12 ~2.5
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Pourbaix Diagram [3]E
h (V
olts
)
pH
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OxidiseE
h (V
olts
)
pH
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Increase pHE
h (V
olts
)
pH
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Ammonia Addition Process [4]
OHSONHOHNHSOH 2424442 )(
• Regeneration of NH3
• Iron content 160g/kg 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
Samples taken at various pH • Centrifuged• Solids filtered from solution• Iron concentration of solution analysed
pH 4.7 6.3 6.8 7.0 7.6 8.2 8.7
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Spectrophotometry
1. Reduce to iron (II)
2. Chelate – 1,10-phenanthroline
3. Illuminate– =515nm– Visible– monochromatic
Intensity 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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