Radionuclides and heavy metal contents in phosphogypsum samples in comparison to cerrado soils

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 226 Ra 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

Radiological impacts of phosphogypsum

“…252 AE 26 Bq kg À1 (Jacomino et al, 2009). In Greece (Papastefanou et al, 2006) the 226 Ra concentration in PG varied between 261 and 688 Bq kg À1 , mean of 508 Bq kg À1 , whereas in Central Florida (Rutherford et al, 1994) 226 Ra content reached 2000 Bq kg À1 .…”

Sequential chemical extraction for a phosphogypsum environmental impact evaluation

“…Total contents of all chemical element concentrations were lower than the limits established by the National Environmental Council [5] and also lower than those obtained in an Idaho plant [6]. Lead (Pb) concentration in the PG sample is coincident with the upper limit concentration established by Brazilian Ministry of Agriculture, Fisheries and Livestock [7].…”

Use of nuclear technique in samples for agricultural purposes

“…Added to this, other distinguishing characteristics of clayey soil that tends to have a high concentration of organic matter and high cation exchange capacity compared to sandy soil. These properties imply to clayey soil increased capacity of retain elements (OLIVEIRA, 2008;JACOMINO et al, 2009). The z-score and u-scores tests show that the experimental results are within the confidence interval of 95%.…”

“…Although the PG is mainly composed of calcium sulphate dihydrate, it can provide high levels of impurities from the phosphate rock matrix as metals (Cd, Zn), rare earths, metalloids such as As, fluorides and radionuclides. The PG generation rate is of approximately 4.8tons per ton of phosphoric acid (JACOMINO et al, 2009). …”