Fly ash-brine interactions: Removal of major and trace elements from brine

Abstract

Fly ash and brine contain major and trace elements such as Na, Cl, Ca, SO₄, K, Mg, P, Si, Al, Fe, Mn, Cr, V and Ti in significant quantities. This study focuses on the leachability of species from fly ash and the removal of major and trace species from brine as the two waste streams interact. Another objective is to evaluate the effect of the interactions on the brine quality. Batch reaction tests were carried out on two different fly ashes and brine at different L/S ratios and different reaction times, and the supernatant analysed for major and trace species. Chemical analysis revealed that the unreacted brine solution contained high concentration of species such as Na, K, Ca, Mg, Cl and SO₄, while species such as As, Ba, Cd, Co, Cr, Mn, Pb and Ti were present in trace quantities.

Analysis of the supernatants after the batch reaction tests (fly ash-brine interaction experiments) revealed that major species such as Na, Mg, Cl and SO₄, and trace elements such as As, Co, Pb, Zn, Ni and Cu were significantly removed from the brine solution while Ca, Ba, Sr, Cr and Mo were leached into the brine solution from the fly ashes. The removal of species from the brine solution was most prominent at L/S ratio 1:1. This indicates that the L/S ratio of the ash-brine system has a significant effect on the release of species from fly ash or the removal of species from brine solution. The final pH of the fly ash-brine solutions and the contact times were also observed to have a significant effect on the leaching from fly ash as well as the removal of major and trace species from the brine. The study also showed that some contaminant species can be removed from brine solution using fly ash.

Keywords:

• Brine
• fly ash
• batch reaction test
• chemical interactions
• leaching
• major and trace species
• brine quality
• mineralogy
• chemical composition
• coal combustion

Acknowledgments

We express our gratitude to SASOL-ESKOM ash-brine co-disposal study initiative for providing financial support to perform this study, SASOL-Secunda R&D and ESKOM-Tutuka R&D who provided the fly ash samples used for this study, and the Chemistry Department of the University of the Western Cape, South Africa for the assistance provided during this study.