『Abstract
The dynamics of trace elements from phosphate rock ore to the
environment in a phosphoric acid plant located in SW Spain and
the impact of phosphogypsum wastes were investigated through total
digestion and BCR-sequential extraction. Based on total concentration,
element transfer factors as criteria for examining the potential
environmental risk of waste with respect to ore rock were calculated,
and it was observed that most trace elements are only transferred
into phosphogypsum at rates of 2-12％. However, based on those
concentrations that are likely to be most readily mobile in the
environment, phosphogypsum acts as a higher emission source of
contaminants than the original rock. About 100 million tonnes
of phosphogypsum are stack-piled in a dump of 1200 ha over salt-marshes
of an estuary formed by the confluence of the Tinto and Odiel
rivers. Phosphogypsum has been applied, at the recommended rate
of 20-25 t/ha since 1978-2001, to improve fertility and reduce
Na saturation in agricultural soils of the Guadalquivir river
valley (140 km2). Phosphogypsum capacity as a source
of mobile contaminants in three environmental scenarios (water
leaching, exposure to oxidising and reducing conditions) was quantified
by combining sequential extraction and waste mass. The amounts
of mobile contaminants that could be released for every tonne
of phosphogypsum are approximately 7×102 g Sr, 1.1×102
g Fe, 55g Y, 30g Ce, 12g Cr, 11g Ti, 5g Zn, 4g each of Cu and
Pb, 3g each of V and Cd, 2g each of As and Ni and 1g U. Multiplying
these amounts by 100 Mt and 20-25 t/ha, it is possible to calculate
risk assessments of phosphogypsum for both estuarine zones, e.g.
in a hypothetical stack collapse and waste spilling, and agricultural
soils, respectively.』
1. Introduction
2. Materials and methods
2.1. Environmental setting
2.2. Sample collection and preparation
2.3. Procedures
2.3.1. pH determination
2.3.2. Total elemental analysis
2.3.3. Sequential extraction method
2.3.4. Chemical analysis and quality control
3. Results
3.1. Quality assurance
3.2. Geochemical characterization
3.3. Sequential extraction data
4. Discussion
4.1. Dynamics of contaminants from phosphate rock to phosphogypsum
4.2. Dynamics of contaminants from phosphogypsum to the environment
4.2.1. Risk to estuarine zones
4.2.2. Risk to agricultural soils
5. Conclusions
Acknowledgements
References