ORIGINAL PAPER Long-term brine impacted fly ash, Part II: Mobility of major species in the ash residues O. O. Fatoba • L. F. Petrik • R. O. Akinyeye • W. M. Gitari • E. I. Iwuoha Received: 14 May 2012 / Revised: 7 May 2013 / Accepted: 26 May 2013 / Published online: 28 June 2013 Ó Islamic Azad University (IAU) 2013 Abstract The leaching of major species from fly ash is a function of the pH of the solution in contact with the fly ash. The aim of this study was to determine the effect of the pH of the leachant on the leaching of species from the ash residues recovered after the long-term fly ash–brine inter- actions. Acid neutralization capacity (ANC) tests using solutions of different pH values ranging from the initial pH of the ash residues (11–12) to pH 4 were employed in the leaching experiments. The ANC tests revealed that the release of major species from the ash residues depended on the pH of the leachants except for Na and Cl, where the significant concentrations leached were independent of the solution pH. The concentrations of Al and Si in the ANC leachates were very high at pH below 6 while Ca, K, Sr, Mg and B were immediately mobilized from the brine impacted fly ash when in contact with de-ionized water, and leaching increased as the pH decreased. The concen- tration of SO 4 leached from the brine impacted ash residues at high pH was high, and the leaching increased with decrease in the pH of the leachant. This study shows that most of the major elements captured in the ash residues could be mobilized when in contact with aqueous solutions of various pH. This reveals that the co-disposal of fly ash and brine may not be the best practice as the major ele- ments captured in the ash residues could leach over time. Keywords Acid neutralization capacity (ANC)  Brine  Fly ash  Major species  Mobility  Co-disposal Introduction The combustion of coal to generate electricity is ongoing in most countries of the world, but the waste materials gen- erated during the combustion process are a major concern because of their environmental implications. Fly ash is one of the major solid wastes by-products generated during the combustion of coal. South African power utilities generate significant quantities (about 40 Mt) of fly ash annually of which the power stations operated by ESKOM South Africa generate 25 Mt of the fly ash annually (ESKOM Report 2013). Due to the large quantities of ash generated and the need for its careful disposal because of its chemical composition, many countries including South Africa have devised different methods of ash disposal. According to Sushil and Batra (2006), there are two different methods of fly ash disposal operated by power stations in India. These are wet and dry disposal techniques. South African power utilities employ dry and dense slurry disposal techniques. For instance, at Secunda power station, the ash is added from the hoppers to a stirring tank with continuous addition of brine (hyper saline wastewater generated from water treatment plants) to make a slurry with controlled density. This is then pumped continuously via pipes to the ash dam where the ash particles immediately settle out and the ash- water is either drained away via a penstock to the clear ash effluent dam, or percolates through the ash dam and is O. O. Fatoba (&)  L. F. Petrik  R. O. Akinyeye Environmental and Nano Sciences Research Group, Chemistry Department, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa e-mail: ofatoba@uwc.ac.za W. M. Gitari Department of Ecology and Resources Management, School of Environmental Sciences, University of Venda, Private Bag X5050, Thohoyandou 0950, Limpopo, South Africa E. I. Iwuoha Sensor Lab, Chemistry Department, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa 123 Int. J. Environ. Sci. Technol. (2014) 11:1641–1652 DOI 10.1007/s13762-013-0349-2