Transcript The work is described in more detail here

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
Page 1 of 19
© Imperial College London
Presentation Outline
• The gypsum waste minimisation project
• Titanogypsum by-products
• Alternative approaches
• The ammonia process
• Experimental & analysis
• Conclusions & further work
Page 2
© Imperial College London
Gypsum
Calcium Sulfate Dihydrate CaSO4.2(H2O)
• Vital component of many construction materials
• In the UK demand outstrips domestic supply [1]
Page 3
© Imperial College London
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
Page 4
© Imperial College London
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
•
•
Page 5
Dr Gurmel Ghataora
Waliur Rahman
Miniwaste Faraday Partnership
© Imperial College London
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
Page 6
© Imperial College London
Red Titanogypsum
Fe(OH)3
Mass per gram
(mg/g)
Fe(OH)2
Element
Page 7
© Imperial College London
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
Page 8
[H2SO4]g/l
[Fe2+]
pH
142.10
36.12
~2.5
© Imperial College London
Eh (Volts)
Pourbaix Diagram [3]
pH
Page 9
© Imperial College London
Eh (Volts)
Oxidise
pH
Page 10
© Imperial College London
Eh (Volts)
Increase pH
pH
Page 11
© Imperial College London
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
Page 12
0.42g/kg
© Imperial College London
Titration Experiments
How does pH effect
precipitation?
1. Produce Analogue:
– H2SO4
– FeSO4.7(H2O)
2. Titrate aqueous ammonia
(NH4OH)
Page 13
© Imperial College London
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
Page 14
© Imperial College London
Spectrophotometry
1. Reduce to iron (II)
2. Chelate
–
1,10-phenanthroline
3. Illuminate
–
–
–
l=515nm
Visible
monochromatic
Intensity a concentration
Page 15
© Imperial College London
Data Analysis
Page 16
© Imperial College London
Effect of pH on Iron Removal
Page 17
© Imperial College London
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
Page 18
© Imperial College London
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.
Page 19
© Imperial College London