Synthesis of Fe-layered double hydroxide from bittern and its nitrate-ion removal ability

Abstract

AbstractNitrate contamination of surface waters and groundwater is one of the main problems associated with agricultural activities worldwide, and there is an urgent need to develop effective materials and processes to remove efficiently excess nitrate from aquatic environments. Bittern is a seawater resource that contains large amounts of Mg2+ and Ca2+, and its utilization has received much recent attention. In this study, an Fe-type layered double hydroxide (Fe-LDH) product was prepared from bittern with the addition of an inexpensive agent (FeCl3) for nitrate removal. The greatest nitrate removal was obtained for synthesis conditions of pH 8.5–9.5 at 50°C for 0.5 h. The equilibrium adsorption capacity of the product for nitrate was measured and fitted with the Langmuir and Freundlich isotherm models. The experimental data better fit the Langmuir model than the Freundlich model. The calculated maximum adsorption capacity for nitrate was 0.40 mmol g–1, which was greater than those of other reported nitrate adsorbents. The product removed nitrate ions from a highly saline solution. The order of interference of anion species for nitrate removal was CO32– > SO42– > Br– > NO2– > Cl– > F–. The pH of the solution and removal of nitrate increased with increasing solution temperature because of ion exchange between the Cl– in Fe-LDH and the NO3– in the solution. Nitrate ions were repeatedly adsorbed and desorbed. The prepared Fe-LDH is expected to be a new inorganic anion exchanger for the removal and recovery of nitrate ions from aquatic environments.