Abstract
Phosphogysum (PG) or agricultural gypsum, a solid waste from the phosphate fertilizer industry, is used as soil amendment, especially on soils in the Cerrado region, in Brazil. This material may however contain natural radionuclides and metals which can be transferred to soils, plants and water sources. This paper presents and discusses the results of physical and chemical analyses that characterized samples of PG and compares them to the results found in two typical soils of the Cerrado, a clayey and sandy one. These analyses included: solid waste classification, evaluation of organic matter content and of P, K, Ca, Mg, and Al concentrations and of the mineralogical composition. Natural radionuclides and metal concentrations in PG and soil samples were also measured. Phosphogypsum was classified as Class II A - Not Dangerous, Not Inert, Not Corrosive and Not Reactive. The organic matter content in the soil samples was low and potential acidity high. In the mean, the specific 226Ra activity in the phosphogypsum samples (252 Bq kg-1) was below the maximum level recommended by USEPA, which is 370 Bq kg-1 for agricultural use. In addition, this study verified that natural radionuclides and metals concentrations in PG were lower than in the clayey Oxisol of Sete Lagoas, Minas Gerais, Brazil. These results indicated that the application of phosphogypsum as soil amendment in agriculture would not cause a significant impact on the environment.
Highlights
The main raw material in Brazilian phosphoric fertilizer industries is the apatite, of which approximately 80 % are of igneous origin (Canut, 2006)
Radionuclides and metals concentrations in PG were lower than in the clayey Oxisol of Sete Lagoas, Minas Gerais, Brazil. These results indicated that the application of phosphogypsum as soil amendment in agriculture would not cause a significant impact on the environment
Results from solid waste classification tests showed that PG was considered neither corrosive nor reagent, according to ABNT norms
Summary
The main raw material in Brazilian phosphoric fertilizer industries is the apatite, of which approximately 80 % are of igneous origin (Canut, 2006). The most commonly used process in the production of phosphoric fertilizers is the attack of the phosphate rock with concentrated sulfuric acid and water. In this case, the main products from chemical reactions are phosphoric acid (H3PO4), and simple superphosphate (SSP). The annual world production is estimated to be 150 million tons, approximately 12 million tons of which are produced in Brazil (Mazzilli et al, 2000). At present, this material is stored in piles near the factories. This practice represents a potential risk of contamination, mainly to organisms and hydrological systems in the surroundings of the storage sites
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