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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.