Abstract
For about 20 years, between the 60 ’s and the 80 ’s of the last century, in the Passo a Campalto area (Lagoon of Venice - Italy) about 400,000 m3 of phosphogypsum (PG) were deposited at the border of the lagoon and next to urban areas without any environmental control. These materials are a by-product formed during the wet processing of phosphate rocks by sulphuric acid and have a significant environmental impact due to their abundance and their chemical-physical and radiochemical characteristics. The PG contains both chemical elements, which are considered dangerous for the ecosystems and natural radionuclides whose concentrations are much higher if compared to those typical for the Earth’s crust. These discarded materials caused for many years the dispersion of radionuclides in the environment due to the tidal erosion, the re-suspension of radioactive inhalable dusts, the uncontrolled radon exhalation and the bioaccumulation of some radionuclides in the lagoon environment. After a decision of the appointed authorities, the Venice Water Authority (Ministry of Infrastructure and Transport), planned a permanent safety control of the site resulting in the complete isolation of the entire volume of contaminated materials from the environmental system. The entire project was specific for the particular features of the site and it required the improvement of analytical, sampling and measurement techniques in order to verify the effectiveness of the safety action. The radon assessment, in particular the check of the effectiveness of the inhibition of radon exhalation, is part of a more complex study, covering many other aspects of the management of a permanent disposal; they will be the object of further notes. The ultimate results of this study prove the efficacy of the intervention: radon concentrations in air and exhalation values from the restored area, measured during surveys, have been proved to be well in agreement with those of non contaminated soils.
Highlights
For about 20 years, between the 60’s and the 80’s of the last century, debris, hazardous waste and phosphogypsum were deposited without any environmental control and without considering the impact in the subsoil and lagoon waters [1]
For about 20 years, between the 60’s and the 80’s of the last century, in the Passo a Campalto area (Lagoon of Venice - Italy) about 400,000 m3 of phosphogypsum (PG) were deposited at the border of the lagoon and next to urban areas without any environmental control. These materials are a by-product formed during the wet processing of phosphate rocks by sulphuric acid and have a significant environmental impact due to their abundance and their chemical-physical and radiochemical characteristics
The radioactive equilibrium, existent among the various members appertaining to the decay series of 232Th and 238U contained in the phosphate rock, is disrupted and the radionuclides are partitioned into various phases according to their physical and chemical properties [2,3,4]
Summary
For about 20 years, between the 60’s and the 80’s of the last century, debris, hazardous waste and phosphogypsum were deposited without any environmental control and without considering the impact in the subsoil and lagoon waters [1]. The area concerned can be divided into two distinct areas: the West sector, about 150,000 m2, which contains various types of waste and the East sector, about 70,000 m2, which contains phosphogypsum, a byproduct of the Porto Marghera phosphate fertiliser industries (volume of about 400,000 m3) and which is characterized by deep and marked erosion towards the lagoon. Phosphogypsum is an acidic by-product, formed during the wet processing of phosphate rocks by sulphuric acid. During this process, the radioactive equilibrium, existent among the various members appertaining to the decay series of 232Th and 238U contained in the phosphate rock, is disrupted and the radionuclides are partitioned into various phases according to their physical and chemical properties [2,3,4]. The characteristics of the phosphogypsum vary according to the raw material used during the production process, whose concentration of radionuclides that are found later in the residues strongly depends on
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