Simultaneous Removal of Arsenate and Fluoride Using Magnesium-Based Adsorbents
Hajime Sugita, Kazuya Morimoto, Takeshi Saito, Junko Hara
Abstract
In this study, arsenate, As(V), and fluoride (F) were simultaneously removed from contaminated water using MgO, Mg(OH)2, and MgCO3 as Mg-based adsorbents, as existing studies only focus on their individual removal. The removal performance of As(V) and F followed the order MgCO3 < Mg(OH)2 < MgO. Under the test conditions, MgO and Mg(OH)2 met the environmental standards for As and F (0.01 and 0.8 mg/L, respectively), but MgCO3 did not. The As(V) removal performance was not significantly affected by an increase in the initial F concentration. It was concluded that As(V) was adsorbed and removed more preferentially than F by Mg-based adsorbents because a considerable amount of F remained even when the majority of As(V) was removed. Most arsenic (As)-adsorption data for MgO fit the Langmuir and Freundlich models, whereas those for Mg(OH)2 did not fit either model well. Additionally, the As-adsorption data for MgCO3 fit the Freundlich model but not the Langmuir model. Most of the F-adsorption data for the Mg-based adsorbents fit the Langmuir and Freundlich models. The removal mechanisms of As(V) and F using Mg-based adsorbents were assumed to be predominantly caused by ion-exchange and chemical-adsorption reactions on the adsorbent surface because no magnesium arsenate, magnesium fluoride, or magnesium hydroxide fluoride species were observed in the X-ray diffraction analysis. This research advances the sustainable As–F simultaneous treatment method using inexpensive adsorbents.