Adsorption of fluorine from lepidolite hydrometallurgy wastewater by aluminum modified zeolite

Abstract Fluoride contamination is a serious environmental problem in lepidolite hydrometallurgy wastewater. The treatment of the fluoride-bearing wastewater is facing a great challenge due to the presence of co-existed ions including lithium (Li+), rubidium (Rb+), silicate (SiO32−), sulfate radical (SO42−) and so on. However, aluminum-modified zeolite (Al@zeolite) of sufficient hydroxyl group and high adaptability have exhibited unique advantages for fluoride elimination from lepidolite hydrometallurgy wastewater. Al@zeolite was prepared on natural zeolite by an atmospheric process, and it was then used for the adsorption of fluorine from fluoride bearing wastewater produced by lepidolite hydrometallurgy process. The results of material characterization confirmed the successful immobilization of aluminum within the zeolite pores, and indicating the formation of zeolite-Al-OH. The zeolite host significantly enhanced the chemical stability of Al@zeolite against pH changes with a wide pH of 2.0–10.0. The adsorbent possessed a surface area of 33.46 m2/g and demonstrated excellent capacity and selectivity for fluoride adsorption. It is pertinent to mention that maximum adsorption of 98.6% has been observed with a pH value of 6.0 with 20 min time duration with fluoride dosage of 20 mg/L, and the equilibrium concentration dwindled to 0.4 mg/L. The results of fluorine adsorption showed that fluoride uptake onto Al@zeolite agreed well with the pseudo-first-order kinetic model and the Langmuir isotherm model. The reusability of the substance was evaluated for up to eight cycles following consecutive regeneration with 0.2 mol/L AlCl3. The exhausted Al@zeolite was effectively regenerated through a simple alkaline treatment for recycling. The above results verified that Al@zeolite is a new kind of efficient defluoridation adsorbent for lepidolite hydrometallurgy wastewater with practical application prospect.