Characterization of the submarine disposal of a Bayer effluent (Gardanne alumina plant, southern France): I. Size distribution, chemical composition and settling rate of particles forming at the outfall

The submarine discharge of the high pH clarified Bayer effluent of the Gardanne alumina plant (Marseille region, France) leads to the formation of concretions at the outfall 324 m underwater and to a plume of white particles. The bulk chemical composition of the concretions has been determined by SF-ICP-MS. Mg and Al are the major elements measured with concentrations of a few hundred mg g(-1). Ca and S are also found at concentrations in the range of mg g(-1). Among the measured trace elements there is a specific interest in As and V because of environmental concerns pointed out by regulation authorities. Their concentrations are of tens to thousands mg g(-1), respectively. Concentrations of the other elements are in the range of a few ng g(-1) to few hundreds mg g(-1). In order to constrain the dispersion of particles in the environment and to understand how chemical elements can be scavenged from or released to seawater, the size distribution of particles composing the concretions has been measured by settling rate experiments and, for each size class of particles, their chemical composition has been determined. For example, As and V are mainly associated to particles with mean diameters between 15.6 and 63 mm and settling rates around 96 m d(-1). Overall, all the main elements (Mg, Al, Ca, S) composing concretions are associated to this size class of particles which represents 5-60% of the total concretion mass. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The submarine discharge of high pH clarified Bayer effluent from the Gardanne alumina plant in the Marseille region of France leads to the formation of concretions underwater, with major elements including Mg, Al, Ca, and S, as well as trace elements such as As and V. These elements are mainly associated with particles with diameters between 15.6 and 63 mm, representing 5-60% of the total concretion mass.