Phosphogypsum stacking: A new approach and case study

Keywords: phosphogypsum, stacking, environmental issues, environmental solutions, environmental impact mitigation.

The process of producing phosphoric acid from the reaction of phosphate rock and sulphuric acid generates significant amounts of calcium sulphate, a by-product that is commonly referred to as ‘phosphogypsum’. Phosphogypsum can be used in a wide variety of applications, but from the large quantity produced annually worldwide, only a small part of it finds a commercial use. The majority of the rest has to be stored in large stacks or, in some cases, discharged into water bodies or used as backfilling material in open-pit mines.

On land, phosphogypsum can be stored by stacking in wet or dry forms. If not adequately designed, the disposal of phosphogypsum may become a significant source of environmental impact such as highly acidic seepage water and leaks of impurities (including heavy metals, fluoride compounds and various naturally-occurring radioactive elements) into the ground and groundwater. The release of carcinogenic radon gases may also potentially occur. In addition, the stability of the stacks has to be carefully studied and dust emissions from the stacks might also be a problem.

However, most of these potentially harmful issues can be mitigated, or avoided, by using adequate environmental management tools.

The environmental impact of phosphogypsum stacks depends on the type of hazard posed by the materials they contain and by the site-specific conditions. Thus, studying the specific characteristics of the phosphogypsum and the specific hydrogeological conditions present on the site leads to the development of powerful predictive models (contaminant dispersion model, dust dispersion model, stability model, etc.), which can then be used to design more efficient and environmentally effective stacking methods. When applied to existing stacks, these innovative methods may also help to define mitigation solutions.

These methods have been applied successfully to an existing dry stack of phosphogypsum in Belgium, leading to cost-effective solutions and sustainable reductions of environmental issues.

V. Dardenne, J. Peret and S. Plainchamp, Aquale sprl, 5380 Noville-les-Bois, Belgium.

24 pages, 5 figures, 5 plates, 4 tables