Peggy Gunkel Grillon
University of New-Caledonia, New Caledonia
Title: Calcareous electrochemical precipitation, a new method to trap dissolved metallic contaminants in seawater
Biography
Biography: Peggy Gunkel Grillon
Abstract
The contamination of coastal waters by trace metals is an important worldwide concern since they may significantly affect marine ecosystems. A novel use of the calcareous deposit formed on a metallic structure is proposed to trap metallic contaminants in seawater. It is the same deposit that builds up in many tea kettles or water pipes in areas where calcium-rich water is the norm. Whereas the calcareous deposition is a common problem for many people, we transformed this problem into a solution to trap metals. The calcareous deposit is formed in seawater by imposing a current on a galvanized steel electrode. The working electrode’s potential reaches potential in the water reduction range. This reaction causes pH increase at the seawater/metal interface, inducing calcium and magnesium precipitation. A voluminous calcareous deposit composed of CaCO3 and Mg(OH)2 grows with polarization time. Experiments conducted in situ revealed that many metals can also be trapped. In order to better control and understand the mechanisms, lab-experiments were performed in artificial seawater. We first decided to study nickel trapping since nickel mining activities in New Caledonia are causing the subsequent pollution of local coastal waters. Artificial seawater was doped with NiCl2(s) and analysis revealed that Ni is trapped mainly as β-Ni(OH)2. Ni content increases with the initial Ni concentration in the electrolyte. Up to 24% in weight of Ni is trapped in the deposit after seven days of polarization. The calcareous deposit appears like a simple implementation with just a metallic structure immerged in seawater and connected to an electrical circuit which can be charged by renewable energy. This electrochemical method is thus a promising and cheap clean-up device for remediation of contaminated seawater.
