Utilization of coal fly ash and drinking water sludge to remove anionic As(V), Cr(VI), Mo(VI) and Se(IV) from mine waters

This study explores the potential of solid waste as effective and low-cost adsorbing materials to clean waters polluted by the mining sector. The selected adsorbents for our studies were drinking water sludge (SLG), coal fly ash (TB) and modified fly ash (TBFZ3). The adsorbates were the toxic oxyanions of As(V), Cr(VI), Mo(VI) and Se(IV). The studies were carried on in synthesized cocktail solutions (SCS) and real tailing pond waters (TPW). The investigation revealed that both TB and SLG contain very low non-leachable impurities, thus are suitable for most waste mining water treatment. The low temperature caustic liquor treatment of fly ash (TBFZ3) greatly improved the adsorption properties of original TB and made it even cleaner. The modification technique is simple and economic compared to other processes. The solution pH influences greatly and differently the adsorption process, depending on the nature of adsorbents and adsorbates and it must be monitored and controlled carefully. Excellent adsorption capacities were observed in both SCS and TPW matrices. The adsorption kinetics and adsorption capacity of the studied materials were remarkably enhanced in the high electrolyte containing TPW. The adsorption generally fits well the Langmuir and Freundlich isotherms.