Abstract
Phosphogypsum, a waste byproduct derived from the production of phosphoric acid, is being worldwide stockpiled, posing concerns about the environmental problems originating from this practice. Considerations about the viability of the safe reuse of this material have been raised, among them its potential use as building material. However, as phosphogypsum can contain natural radionuclides in significant concentrations, using it as a building material has radiological implications, which presently prevent such application. In order to evaluate the feasibility of using phosphogypsum in the manufacturing of building elements such as bricks and plates, a comprehensive research was undertaken in Brazil, following a multiple approach. This research included studies related to: Brazilian phosphogypsum characterization; experimental determination of radon exhalation rate; and application of theoretical models to forecast both radon exhalation and external doses in dwellers. In this paper, a comprehensive review of the research carried out in Brazil is presented.
Highlights
The mining and processing of phosphate rock, which is processed to phosphoric acid, generate NORM containing residues
The use of building materials with elevated or technologically enhanced levels of natural radioactivity could in principle be a reason of higher external and internal doses for residents
It should be considered that the models for the evaluation of the external gamma dose, based on radiation indexes calculated for specific geometries of standard rooms, are intrinsically conservative, since they aim to establish criteria for the safe use from the radiological point of view, rather than determining exact values of the resulting indoors doses
Summary
The mining and processing of phosphate rock, which is processed to phosphoric acid, generate NORM containing residues. This intermediate is further processed into phosphate fertilizers and animal feeds. The phosphogypsum production reaches 160 million t [2], where the largest producers are located in the USA (as well as China, Africa and Middle East), especially in Florida, responding for 14 – 40% of the worldwide phosphogypsum production [3]. Brazil is the sixth largest phosphate rock producer, reaching 6.5 million t in 2016 [1]. Regarding to the planned and prospecting phosphate mines, two large projects are currently in process, both from Galvani/Yara industry: Serra do Salitre, expecting to produce 1.2 million t of phosphatic concentrate per year; and Santa Quitéria, whose phosphate deposits are associated with high concentrations of uranium and, its extraction is more complex and, by national legislation, demands a partnership with the Indústrias Nucleares do Brasil (INB)
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