CO2 seawater acidification by CCS-simulated leakage: kinetic modelling of Zn, Pb, Cd, Ni, Cr, Cu and As release from contaminated estuarine sediment using pH-static leaching tests

A modified pH-dependent leaching test with continuous pH control that employed CO2 to acidify a seawater-sediment mixture is used to address Zn, Pb, Cd, Ni, Cr, Cu and As release from contaminated estuarine sediments under the influence of acidification processes. Long-term (480 h) leaching experiments at pH values of 7.0, 6.5 and 6.0 are performed. The different evolutionary patterns of the redox potential and Fe release at pH = 6 with respect to the other pH values shows the need to assess the influence of the initial Fe content in seawater upon elemental release. Hence, assays at pH = 6.0 are conducted using natural seawater with Fe concentrations between 9.02 and 153 µg/L. A set of in-series reactions for trace elements, Fe and other ions associated with Fe is proposed to model a Fe/multi-ion-dependent mechanism for trace metal release. The maximum concentration of each contaminant that can be released from the sediment and the kinetic parameters of the proposed model are completed for the studied pH values, for good consistency between the experimental and simulated mobilisation of each studied element.This work was financially supported by the Spanish Ministry of Economy and Competitiveness, Project CTM 2011-28437-C02-01, ERDF included. M.C. Martín-Torre was funded by the Spanish Ministry of Economy and Competitiveness by means of F.P.I. fellowship No. BES-2012-053816