Utilizing mining dam bottom sludge as a novel adsorbent for AuO removal from wastewaters: Batch and column studies

Abstract In this study, the adsorption of Auramine O (AuO) dye using bottom sludge (BS) was investigated in batch and continuous systems. The BS was characterized by EDX, BET, XRD, DLS, ζ-potential, SEM, FTIR, helium pycnometer, and mercury porosimetry. The kinetic and isotherm data were fitted to pseudo-second-order and Langmuir models. The maximum amount of adsorption calculated from the Langmuir isotherm model was 5.09 mg/g. Thermodynamic studies showed that adsorption was endothermic and occurred spontaneously. Thomas, Clark, and Yoon-Nelson models were suitable (R2 > 0.95 for all these models) to explain the dynamic behavior of AuO-BS in the column system. Increased bed depth increased breakthrough time, while the breakthrough time declined with increased initial AuO concentration and flow rate. Optimum conditions were determined for the batch system as 4 g of BS dose, 100 rpm agitation speed, and 90 min reaction time; optimum conditions for the column system were 3 cm bed depth, 0.14 mL/min flow rate, reaction time of 181 h; and optimum conditions for both systems were 100 mg/L AuO concentration, 20 °C reaction temperature and pH 6.18 (natural). Under these conditions, the amounts of AuO adsorbed in batch and column systems were calculated as 2.06 mg/g (89.75%) and 2.63 mg/g (47.13%), respectively. The studies showed that efficient remediation of AuO from aquatic environments is possible with BS.