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Chapter 55.4.13 Disposal and valorisation options for phosphogypsumDescriptionToday, all plants in the EU practice land disposal [154, TWG on LVIC-AAF] since disposal tothe sea is no longer accepted.Many of the important considerations in the design and construction of gypsum disposal areasare based on the necessity to keep both the gypsum and the acidic stack effluent within a closedsystem. To avoid pollution of the subsoil and groundwater by acidic and contaminatedphosphogypsum leachate and run-off (process water and rainwater), stringent preventivemeasures are necessary, such as seepage collection ditches, intercept wells, natural barriers andlining systems. Furthermore, to prevent or minimise pollution of the surrounding area and watersystems, it is necessary to make provisions for any effluent overflow. The effluent requiresappropriate treatment, such as immobilisation of soluble P 2 O 5 and trace elements byneutralisation, before it can be released from the system. Besides applying control during thebuild-up of a gypsum stack, the run-off from gypsum stacks will require treatment for manyyears after the acid plant has ceased production.A third and interesting way of dealing with the phosphogypsum disposal problem is to improvethe quality of the gypsum, so that it can be used as a resource like natural gypsum and flue-gasdesulphurisation gypsum. Many examples of phosphogypsum usage exist. Table 5.10 gives anoverview of phosphogypsum applications. It should be noted that different commercialapplications require different types of gypsum.In the past, not all efforts to use the gypsum have been successful, mainly because of qualityconsiderations. In most cases, the radioactivity aspects of the gypsum have presented aparticular problem. Also the residual acidity or P 2 O 5 content of the gypsum is an importantfactor. Application of phosphogypsum requires the production of clean pure gypsum.Anhydrite CaSO 4DihydrateCaSO 4·2 H 2 OHemihydrateCaSO 4·½ H 2 OConstructionFloor screed cement (assetting regulator)Cement (as settingregulator)Plaster (stucco),plasterboard, ceiling tiles,gypsum blocks, floorscreedAgricultureSoil conditioner as asource of calcium andsulphur carrier and fillerin insecticides and as afiller in the production offertiliserSoil conditioner carrierand filler ininsecticides, and as afiller in the productionof fertiliserAs a source of calcium andsulphurIndustrialuses/otherFiller/pigment in a varietyof applicationsFiller/pigment in avariety of applications,production ofammonium sulphateand sulphuric acidFiller/pigment in a varietyof applicationsTable 5.10: Overview of phosphogypsum applications[29, RIZA, 2000]Achieved environmental benefits• valorisation of the phosphogypsum would be the desirable solution.Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 247