Fractionation and fluxes of metals and radionuclides during the recycling process of phosphogypsum wastes applied to mineral CO2 sequestration

Abstract

The industry of phosphoric acid produces a calcium-rich by-product known as phosphogypsum, which is usually stored in large stacks of millions of tons. Up to now, no commercial application has been widely implemented for its reuse because of the significant presence of potentially toxic contaminants. This work confirmed that up to 96% of the calcium of phosphogypsum could be recycled for CO2 mineral sequestration by a simple two-step process: alkaline dissolution and aqueous carbonation, under ambient pressure and temperature. This CO2 sequestration process based on recycling phosphogypsum wastes would help to mitigate greenhouse gasses emissions. Yet this work goes beyond the validation of the sequestration procedure; it tracks the contaminants, such as trace metals or radionuclides, during the recycling process in the phosphogypsum. Thus, most of the contaminants were transferred from raw phosphogypsum to portlandite, obtained by dissolution of the phosphogypsum in soda, and from portlandite to calcite during aqueous carbonation. These findings provide valuable information for managing phosphogypsum wastes and designing potential technological applications of the by-products of this environmentally–friendly proposal.This work was supported by the Government of Andalusia through two research projects 'Characterization and modelling of the phosphogypsum stacks from Huelva for their environmental management and control (P10-RNM-6300)' and 'Phosphogypsum: from the environmental assessment as a waste to its revaluation as a resource (P12-RNM-2260)'. M. Contreras expresses her gratitude for the contract by The Fellowship Training Program of the University Teaching Staff; reference AP2010-2746, financed by the Spanish Ministry of Education, Culture and Sport (MECD). RPL also thanks to the Spanish Ministry of Science and Innovation and the 'Ramon y Cajal Subprogramme' (MICINN-RYC 2011). VMF would like to thank the funding action of 'V Plan Propio de la Universidad de Sevilla 2014' and the Spanish Ministry of Economy by funding the project MAT2013-42934-R. The technical staff of the ICMSE (CSIC/US) and of the CITIUS-Universidad de Sevilla has to be acknowledged for his kind help on the analyses of the samples. This is a publication No. 91 from CEIMAR Publication Series.Ciencias IntegradasCiencias de la Tierr