Filter materials for metal removal from mine drainage—a review

Lena Johansson Westholm 0 2 Eveliina Repo 0 2 Mika Sillanp 0 2 0 Responsible editor: Stuart Simpson 1 ) School of Business, Society and Engineering, Mlardalen University , P.O. Box 883, 721 23 Vsters, Sweden 2 Clinoptilolite (1-3 mm) A large number of filter materials, organic and inorganic, for removal of heavy metals in mine drainage have been reviewed. Bark, chitin, chitosan, commercial ion exchangers, dairy manure compost, lignite, peat, rice husks, vegetal compost, and yeast are examples of organic materials, while bio-carbons, calcareous shale, dolomite, fly ash, limestone, olivine, steel slag materials and zeolites are examples of inorganic materials. The majority of these filter materials have been investigated in laboratory studies, based on various experimental set-ups (batch and/or column tests) and different conditions. A few materials, for instance steel slag materials, have also been subjects to field investigations under real-life conditions. The results from these investigations show that steel slag materials have the potential to remove heavy metals under different conditions. Ion exchange has been suggested as the major metal removal mechanisms not only for steel slag but also for lignite. Other suggested removal mechanisms have also been identified. Adsorption has been suggested important for activated carbon, precipitation for chitosan and sulphate reduction for olivine. General findings indicate that the results with regard to metal removal vary due to experimental set ups, composition of mine drainage and properties of filter materials and the discrepancies between studies renders normalisation of data difficult. However, the literature reveals that Fe, Zn, Pb, Hg and Al are removed to a large extent. Further investigations, especially under real-life conditions, are however necessary in order to find suitable filter materials for treatment of mine drainage. - Working and abandoned mines world over are continuously discharging mine drainage into surface and groundwater bodies (Dybrowska et al. 2006; Perez-Lopez et al. 2007; Chockalingam and Subramanian 2009; Potgieter-Vermaak et al. 2006; Strosnider and Nairn 2010; Trumm and Watts 2010; Prasad and Mortimer 2011; Goetz and Riefler 2014) and the worldwide mining industry is facing enormous challenges with the mine drainage. Mining effluents are characterised by high concentrations of heavy metals and high acidity, a combination that in many cases causes severe environmental problems such as acidification and lethal poisoning of aquatic organisms (Chockalingam and Subramanian 2009). Mine drainage can, however, be treated before being discharged into recipients, e.g. through active or passive treatment methods (Johnson and Hallberg 2005); thus, the mining industry has to rely upon some of these methods (Batty and Younger 2004). The former are based on the addition of chemicals and/or energy, while the latter are based on treatment systems such as wetlands, permeable reactive barriers, inorganic media passive systems, reducing and alkalinity producing systems and re-use of waste materials (Johnson and Hallberg 2005). Passive treatment systems based on the flow of mine drainage through a filter material are advantageous in the sense, that they are regarded as low-cost solutions, thus interesting for the mining industry as well as for societies that have to deal with treatment of mine drainage. Scientists all over the world have therefore tested a large number of filter materials and scattered research has been presented on a wide variety of potential filter materials with regard to their metal sorption capacities in the first hand. Natural materials, e.g. minerals, rocks or organic compounds, have together with various by-products from the industrial or agricultural sectors, gained particular attention as attractive filter materials for the removal of heavy metals and, in some cases, also as alkalinity providers. Tested filter materials have proved to remove heavy metals, and different metal removal mechanisms taking place in the filter materials have been identified, e.g. adsorption, ion exchange, sulphate reduction (Robinson-Lora and Brennan 2009) and precipitation (Feng et al. 2004; Rios et al. 2008). A variety of investigations, e.g. laboratory investigations as well as field trials, have been described in the literature. Nonetheless, a compilation of data on the removal of heavy metals from mining wastewater using filter materials is lacking, even though there are a large number of reviews on filter materials and their capacities to remove heavy metals from wastewaters available, see for instance (Bailey et al. 1999; Wantanaphong et al. 2005; Nehdi and Tariq 2007; Ahmaruzzaman 2011; Iakovleva and Sillanp 2013). The overall aim with this paper is therefore to give an overview of the literature on heavy metal removal from mining drainage by different substrates. Further on, the aims are to discuss a possible normalisation of results, as well as to discuss whether the filter materials are beneficial for on-site treatment of mine drainage. Finally, the paper also might serve as a tool to help others to select suitable filter materials based on the findings presented in the literature, e.g. metal reduction capacity, availability and cost. Mine drainage, removal mechanisms, filter materials and experimental methods According to the literature reviewed, the filter materials can be divided into organic and inorganic materials. The first category includes materials such as peat and agricultural waste products. In addition, various organic polymeric materials have been investigated. The inorganic materials described in the literature include minerals and rocks and a variety of industrial waste products. These waste products have, from time to time, been deposited at landfill sites since there have been no use for them. At times when a shortage of natural resources has occurred, the industrial waste products have attracted attention as potential candidate materials for metal removal. Their potential to remove metals has just been one reason for the attention, in addition many filter materials a regarded as low-cost materials, easily available on a local scale. They are used in passive treatment systems that require a minimum of maintenance, which is another advantage compared to active treatment systems that might be in need of much maintenance as well as input of chemicals and/or energy (Johnson and Hallberg 2005). In this survey, steel slag materials and different types of ashes have been identified as potential filter materials for metal removal from mine drainage. Table 1 presents a variety of mine drainages that have been studied in the literature. From the table it can be seen that pH values vary depending on the elements mined and conditions at the mining sites. It has been suggested that mine wastewaters could be divided in to three categories according to their acid/base properties (Iakovlev (...truncated)