Adsorptive removal of dissolved Iron from groundwater by brown coal - A low-cost adsorbent

Iron (Fe) contamination in groundwater is a widespread issue, necessitating the implementation of efficient removal methods to ensure the provision of safe drinking water. To contribute to the development of effective and sustainable solutions for addressing Fe contamination problems, this study investigated the potential of natural brown coal (BC) as a cost-effective adsorbent for removing dissolved Fe from groundwater. The study also explored the regeneration and reusability potential, as well as the effects of operational parameters, including pH, temperature, adsorbate concentration, and competitive ions, on the adsorption process. The equilibrium data fitted very well with the Langmuir model (R² = 0.983), yielding a maximum adsorption capacity of 1.41 mg g^-1. The adsorption kinetics were well described by the pseudo-second-order kinetic model. Notably, higher solution pH, Fe concentration, and temperature values led to higher Fe removal. The adsorption process exhibited endothermic behaviour, accompanied by an increase in randomness at the interface between the BC and the Fe. The BC was easily regenerated and maintained good adsorption capacity after four cycles of adsorption and regeneration. However, the presence of high-valent cations could affect its performance. Fourier-transform infrared spectrometry, coupled with structural and aqueous solution elemental analyses, revealed a synergetic adsorption mechanism, comprising ion-exchange with mono and divalent basic cations and complexation with functional groups. Overall, these findings highlight the potential of brown coal as a cost-effective adsorbent for Fe removal from groundwater.