# Assessment of Characteristics of Acid Mine Drainage Treated with Fly Ash
## 1 Introduction  
Mining activities exert an inherently high impact on the environment, and as such a common framework for responsible mining is urgently needed [1]. Among the various pollution sources related to mining activities, acid mine drainage (AMD) is created in areas that have previously been mined and that contain pyrite materials in spoil piles or mine shafts; iron pyrite in the tailings chemically reacts with oxygen and water, facilitated by the _Thibacillus_ sp. bacteria, resulting in the creation of AMD. Therefore, AMD is a dangerous industrial byproduct, highly acidic and rich in sulfates [2]. The recycling of this secondary waste may reduce environmental risks, as well as increase the economic profitability of the mining industry [3]. In any case, while mine waste piles accumulate, AMD is continuously formed, and this affects industrial environments well after closure of mining activities. In and around coal mines, the pollution of surface water by AMD and other mine effluents may have serious environmental implications [4; 5; 6]. In many industrial settings, the consequences of AMD are considered moderate to severe [7; 8]. There are various methods for treating AMD, such as using calcium carbonate, sodium hydroxide, sodium bicarbonate or anhydrous ammonia, as well as zeolite-adsorption processes. The fresh zeolite, for example, presents a high ammonia removal efficiency from mine effluents [9; 10; 11]. These chemicals raise the pH to acceptable levels and decrease the solubility of dissolved metals, but the cost of the treatment of AMD is usually very high since the latter is generated up to 300 m\({}^{3}\)/day for 2000 tons/day or less of mine production capacity [12]. On another note, fly ash is another deleterious byproduct generated by coal burning. Its toxicity potential (metal leaching) may be higher in low pH batches [13]. In the literature, neutralization of AMD has been attempted through various treatment systems, a simple one being the addition of lime. This method efficiently increases AMDpH value, but it necessitates large lime quantities and produces unstable secondary wastes. Other chemical [14; 15], biological and microbiological [16; 17; 18] methods have also been applied, but clogging due to metal hydroxide precipitation may interfere with the biological and microbiological activity [19]. As such, a satisfactory and economic solution for the long-term treatment of AMD is still needed. Ideally, the material applied should be an undesirable byproduct not used for any other application [20].  
Especially in India, which mostly depends on thermal power plants to meet its energy requirements, fly ash production is significant. India's total installed power-generation capacity was 350,162 MW in March 2019, out of which the thermal power plants contributed to 222,927 MW; i.e., 63.7% of the total power-generation capacity of India [21]. Fly ash is indeed an undesirable byproduct of coal combustion, disposed of in specially designed landfills in an environmentally safe manner. This waste has been proven to be appropriate for AMD treatment due to its alkaline properties [22; 23; 24; 25]. As an extravagant example, water quality from a stream heavily affected by AMD, with low macroinvertebrate productivity and diversity, significantly improved after impoundment works that directed waters from a fly ash pond to the stream. Species diversity and benthic production increased, and a few opportunistic fish feeding on insects appeared [26]. Focusing on these two kinds of toxic industrial waste, fly ash produced from a thermal power plant was characterized by its geochemical and mineralogical profile. Its suitability to successfully neutralize AMD pits was then assessed. These preliminary results may be utilized to manipulate fly ash to aid the neutralization of AMD, reducing its potential for metal mobilization.