Desalination Property of Various Calcined Layered Double Hydroxides from Seawater

Abstract— Now, approximately 20% of farmland in the world becomes salt damage soil with unsuitable properties for agriculture. In general, salt was removed from soil by flushing out with rain water due to the improvement of soil permeability using gypsum and so on. However, there are arid and semi-arid areas with an insufficient supply amount of rain water to remove salts from soil. In this study, a novel method to capture salt in soil using various calcined layered double hydroxides (LDHs) as a desalination agent was attempted to estimate desalination property from seawater. 4 kinds of LDH with the different M²⁺/M³⁺ ratios are prepared using 2 kinds of Mg²⁺ and Ca²⁺ as M²⁺ and 2 kinds of Al³⁺ and Fe³⁺ as M³⁺. The desalination ability of these calcined LDHs was investigated using seawater. As a result, the decrease of salinity was confirmed using all samples. Among these samples, the calcined Mg-Al LDH with Mg/Al = 3.45 and Ca-Fe LDH with Ca/Fe = 2.35 indicated the highest desalination property, due to the decrease of Cl^- and SO₄^2- from seawater, by reconstruction reaction. Ca-Fe LDH was calcined at various temperatures and the desalination ability at different calcined temperatures was also evaluated. It was found that the desalination ability of calcined LDH depends on the calcination temperatures and Ca-Fe LDH calcined at 500℃ indicated the highest desalination ability.