Lanthanum-functionalized lignocellulosic wastes for the arsenate and fluoride depollution of water: Antagonistic adsorption and interfacial interactions

The cleaning of water polluted by toxic geogenic compounds is challenging and demands novel, sustainable and low-cost adsorbents. To address this environmental problem, agricultural wastes functionalized with lanthanum have been studied for the depollution of arsenate and fluoride in aqueous solution. A simple and straightforward approach was utilized to anchor lanthanum on the surface of avocado seed, cauliflower stem, and macadamia nut shell wastes with the aim of effectively removing these toxic water pollutants and avoiding the microorganism growth on the biomass and its degradation during prolonged equipment operation. The adsorption mechanism using these modified biomass samples was endothermic and multi-ionic, involving up to two arsenate and three fluoride ions that can interact with the biomass surface functionalities. The simultaneous adsorption of these pollutants was antagonistic, and the co-anion concentration inhibited the adsorption of target geogenic pollutants. Overall, the fluoride adsorption properties of these modified lignocellulosic wastes were better than those for arsenate. The antibacterial activity of the lanthanum-modified biomass samples may enable for their use in packed-bed columns for long-term water treatment processes. The adsorption and antimicrobial properties of these functionalized biomass residues are promising for the implementation of efficient and economic processes for purifying water contaminated by arsenate and fluoride.