Radiation hazard indices in the application of phosphogypsum mixtures as a building material: proposal for a Brazilian regulation

Marcelo Francis Máduar,Barbara Paci Mazzilli,Marcelo Bessa Nisti

doi:10.15392/bjrs.v7i3.839

Marcelo Francis Máduar, Barbara Paci Mazzilli + Show 1 more

Open Access

https://doi.org/10.15392/bjrs.v7i3.839

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Abstract

Phosphogypsum (PG), a by-product from the phosphoric acid industry, is being worldwide stockpiled, posing environmental problems. Viability of the PG safe re-use in civil construction has been studied, as PG can contain natural radionuclides in significant concentrations. We propose a policy for using PG as a building material, limiting the total concentration of 226Ra plus 228Ra by mixing PG with natural gypsum. It was concluded that PG from the largest Brazilian deposits could be used without any dilution, when the sum of the activity concentrations of 226Ra and 228Ra does not exceed 150 Bq kg-1. For higher values, the approach is to mix PG with increasing amounts of natural gypsum, so that the final concentration does not exceed 1000 Bq kg-1. We show that PG re-use in such a way is feasible in terms of radiological protection and recommended to minimize PG piles environmental impact

Highlights

Occurring radionuclides are present in several natural resources
In Brazil, the main producers of phosphate fertilizers are responsible for the production of approximately 12 million tons of PG per year, which is stored in stacks, posing major environmental concern
For the 40K concentrations, 50 Bq kg-1 was adopted for all PG/gypsum mixtures, as no analyzed PG in Brazil presented concentration above this value [27]

Summary

Introduction

Occurring radionuclides are present in several natural resources. High concentrations of these radionuclides are found in geological materials, mainly igneous rocks and some ores. Human activities that exploit such resources can lead to an increase in the concentration of these radionuclides, giving rise to materials that are known as ”Naturally Occurring Radioactive Material” — NORM. A typical example is the mining and processing of phosphate rock to produce phosphoric acid, phosphate fertilizers and animal feed. Use of sulfuric acid in the process generates calcium sulfate precipitate (CaSO4·n H2O), known as phosphogypsum, which is considered a residue due to its content of impurities. In Brazil, the main producers of phosphate fertilizers are responsible for the production of approximately 12 million tons of PG per year, which is stored in stacks, posing major environmental concern

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