Abstract
Ferric hydrate has been extensively applied for the removal of various types of pollutants from wastewater because of its low cost and high efficiency. However, its wide-scale application has been greatly restricted by high-dose and low-adsorption capacity. Therefore, a novel Ca-doped ferrihydrite adsorbent has been synthesized and used for the enhanced removal of fluoride from wastewater in the presence of other co-existing ions. At 5 mg/L initial fluoride concentration and pH 5, the removal efficiency of fluoride approached to 97.5% and remained stable. Similarly, with the increase of dose from 100 to 300 mg/L, the fluoride removal linearly increased to 98% and remained plateau at neutral pH. Also, the presence of co-existing ions such as NO3-, SO42-, Cl-, and natural organic matter has not significantly influenced the removal performance of the adsorbent. Fluoride removal best fit the pseudo-second-order reaction kinetics and Langmuir isotherm model. The prepared adsorbent exhibited a maximum adsorption capacity of 53.21 mg/g for fluoride uptake from water. The SEM-EDX confirmed the doping of Ca onto the ferrihydrite where the elemental peaks of Ca and Fe emerged at the energy value of about 3.6 Kev and 7.1 Kev respectively in EDX analysis. In addition, SEM results of Ca-doped ferrihydrite adsorbent illustrated that a large microplates type of products was acquired after synthesis. The regeneration results confirmed that adsorbent could retain their original adsorption capacity after five regeneration cycles. The current study suggested that Ca-doped ferrihydrite has the application potential for the enhanced adsorption of fluoride from the water phase.
Highlights
Fluoride is an essential element for the growth of the skeleton and teeth in the human body (Pillai et al 2020; Tao et al 2020)
The structural morphology and elemental constituents of the as-synthesized Ca-doped ferrihydrite were evaluated by SEM-EDX analysis Fig. 2(a, b)
The SEM results of Ca-doped ferrihydrite adsorbent illustrated that a large microplates type of products was acquired after synthesis Fig. 2b
Summary
Fluoride is an essential element for the growth of the skeleton and teeth in the human body (Pillai et al 2020; Tao et al 2020). It can cause various health problems, if used in excessive amounts. Fluoride is an important element for flora and fauna; its presence in high concentration can adversely affect the various biological process in plants (Gao et al 2020). Around two hundred million people are living in regions with elevated fluoride concentrations in drinking water (Amini et al 2008; Gao et al 2020). As per WHO guidelines, the permissible level of fluoride content in drinking water is 1.5 mg/L (santé et al 2004)
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