Enhancement of Kaolin Adsorption Affinity Toward Phosphate by Sequestrating Naturally Abundant Ca/Mg From Seawater

Abstract

A facile and economical strategy is designed to enhance the adsorption affinity of kaolin toward phosphate by acquiring calcium (Ca) and magnesium (Mg) from seawater. The modified kaolin is prepared at different temperatures to obtain CaO/MgO with different surface properties. The different modified kaolins are comparatively characterized using X‐ray diffraction, zero charge, BET surface area, energy dispersive spectrometry, and X‐ray fluorescence spectroscopy. Solution pH slightly affected the removal of phosphate by modified kaolin in the range of 4–7. The maximum adsorption capacity of the modified kaolin sintered at 600 °C (KS600) was 4.07 mg g−1, which is eleven times higher than that of raw kaolin. The presence of SO42− or CO32− ions demonstrates a negative effect on adsorption, whereas the presence of Cl−, F−, or NO3− exerted a negligible effect on removal efficiency. Importantly, KS600 had the capacity to remove phosphate effectively in real sewage. The strong interaction between phosphate and CaO/MgO played a key role in the enhancement of phosphate adsorption. These results indicate that the abundant ocean resources could be used for environmental remediation.

Functionalization of kaolinite for removal of phosphate from urban sewage

“…Kaolinite [Al 2 Si 2 O 5 (OH) 4 ] has its negatively-charged surface, becoming this mineral an important adsorbent for cationic ions [11] . The functionalization of kaolinite with acid treatment [12] and bivalent trace elements can promote the removal of anionic molecules, such as PO 4 3− , present in the urban sewage [13] , [14] , [15] . Based on the functionalization of commercial kaolinite (CK) with bivalent trace elements, the functionalized kaolinite (FK) with Pb(II) was produced.…”

“…The value of 8.4 mg/g is higher than the removal capacities obtained for natural or functionalized kaolinite, i.e., CK used in this study (< 0.1 mg/g), kaolinite from Linthipe (ca. 0.15 mg/g) [12] , modified kaolinite with FeCl 3 (1.31 mg/g) [13] and modified kaolinite with seawater in different temperatures (4.07 mg/g at 600 °C) [15] .…”