Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Cradle to cradle solution to problematic waste materials from mine and coal power station: Acid mine drainage, coal fly ash and carbon dioxide Godfrey Madzivire a,b,c, ⁎ , Ramogohlo M. Maleka a , Memory Tekere c , Leslie F. Petrik a a University of the Western Cape,Robert Sobukwe Road, Bellville, Cape Town, South Africa b Council for Geoscience, Mine Water & Solid Residues Management, Sustainable Resources and Environment Competency, 280 Pretoria Street, Silverton, Pretoria, 0084, South Africa c University of South Africa, Department of Environmental Science, 28 Pioneer Avenue, Florida Park, Roodepoort, 1709, South Africa ARTICLE INFO Keywords: In-situ carbonation Ex-situ carbonation Carbon dioxide sequestration Back filling Target water quality range ABSTRACT During mining, minerals such as FeS 2 are exposed to O 2 ,H 2 O, and microorganisms resulting in the oxidation and generation of acidic water. The acidic water causes chemical weathering of the adjacent rocks and leaching of potentially toxic metals and the resultant water is often termed acid mine drainage (AMD). Coal power stations produce an alkaline aluminosilicate waste material called fly ash (CFA). Modern waste resource management emphasises finding useful applications of waste generated from processes to achieve a green economy. CFA was, with additional lime and Al(OH) 3 used to treat AMD at a 80L pilot scale. Most of the physical and chemical parameters of the treated water were within South African target water quality range (TWQR) for irrigation. Carbonation of the water after treatment with CFA, lime and Al(OH) 3 produced water that was within the TWQR for irrigation with respect to all parameters and resulted in the sequestration of 15–123L of CO 2 per 80 L of AMD treated at standard ambient temperature and pressure. CO 2 reacted with Ca ions in the water and solid residues to form CaCO 3 . Carbonation improves the ease of disposal of CFA, the AMD quality as well as reducing the amount of CO 2 emissions by coal power plants through mineral carbonation. The solid residues from the overall process are suitable for the back filling of mine voids thereby preventing AMD generation by excluding air and water. This is an innovative cradle to cradle solution for the disposal of waste materials from coal mines and power stations. 1. Introduction Mining industries create economic benefit and they continue to play an important role in South Africa’s economy. However coal mining has a significant environmental impact of uncontrolled discharge of acidic water from both abandoned and operating mines. Acid mine drainage (AMD) is produced by chemical weathering of acid minerals such as pyrite in the presence of O 2 and H 2 O according to Eq. (1). + + → + + + + − 2FeS 7O 2H O 2Fe 2H 4SO 2 2 2 3 4 2 (1) The sulphuric acid generated causes chemical weathering of the surrounding rocks leaching potentially toxic metals and radioactive elements into water [1]. Pyrite is a common constituent in many ore bodies associated with coal and gold mining [2]. It is well known that 98% of South Africa gold is produced from the Witwatersrand formations which were formed from an ancient sea where rivers deposited their sediments as sands and gravels that became conglomerates containing gold and about 3% of pyrite. After gold extraction the pyrite normally ends up in mine waste dumps. However, during the rainy seasons the pyrite in the dumps is oxidised and causes the formation of sulphuric acid, which percolates through the dumps, dissolving heavy metals [2]. Gold occurs in association with pyrite (FeS 2 ) which accounts for about 3% of the Au bearing minerals [3]. Exposing the ore body and country rock to O 2 and H 2 O produces sulphuric acid and Fe (III) as shown in Eq. (1). The Witwatersrand goldfields also have strata with neutralizing minerals such as dolomite Ca Mg(CO 3 ) 2 and CaCO 3 . These minerals not in sufficient proportions to neutralise the acidity caused by the oxidation of pyrite, but result in AMD with elevated concentration of Ca and Mg ions. The acidic pH of the mine water discharging from mine voids makes it unsuitable for domestic, agricultural and industrial use [4,5]. The mine water is also unsuitable to be released into the environment and thus poses a liability to the mining company. There- fore, it is essential to treat the mine water before it can be released to the environment. Various mine water treatment technologies can be broadly classified http://dx.doi.org/10.1016/j.jwpe.2017.08.012 Received 11 April 2017; Received in revised form 25 July 2017; Accepted 21 August 2017 ⁎ Corresponding author at: Environment and Water Unit, Council for Geoscience, 280 Pretoria Road, Silverton, Pretoria, South Africa. E-mail address: gmadzivire@geoscience.org.za (G. Madzivire). Journal of Water Process Engineering xxx (xxxx) xxx–xxx 2214-7144/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Madzivire, G., Journal of Water Process Engineering (2017), http://dx.doi.org/10.1016/j.jwpe.2017.08.012