Removal of nitrate ion from aqueous solutions by functionalization of nano clay: preparation, characterization and mechanistic performance

Nitrate, as one of the primary pollutants, is found in agricultural drainage water, and human and animal excrement. Nitrate causes damage to water environments and endangers human health. It is clear that the research is very important for the development and improvement of existing methods for treating water containing high concentrations of nitrate. This study was conducted aimed to investigate the possibility of using a batch system of nanoclay modified with the organic surfactant hexadecyltrimethylammonium bromide (HDTMA-Br) to remove nitrate anion as a model pollutant from drinking water containing this pollutant. This study was conducted on laboratory and batch reactor scale. Removal efficiency of different pH 4–9, contact time 15–60 min, nanoclay adsorbent concentration modified with organic surfactant HDTMA-Br 0.5–1.5 g/dL and nitrate concentration 25–75 mg/L was investigated. Nitrate concentration was measured by ultra-violet spectrophotometer. Based on the scanning electron microscopy, the particles have a uniform shape with high porosity and the diameter of the nanoclay particles modified using the organic surfactant HDTMA-Br was 1.6 nm. Based on the X-ray diffraction analysis, the modification process changed the base distance in the nanoclay structure from 17 to 24 Å. The best conditions for removal of 25 mg/L of nitrate (100% efficiency) included contact time of less than 15 min, optimum temperature of 20°C, optimum pH 4 and concentration of 1 g/dL of nanoclay modified using organic surfactant HDTMA-Br with the surface of the surfactant was 40% of the cation exchange capacity. The maximum nitrate adsorption capacity was 94.33 mg/g by following the Langmuir isotherm (correlation coefficient of 0.9960) and second-order adsorption kinetic (correlation coefficient of 0.9988). The results showed that the modified nanoclay adsorbent is a suitable, cheap and efficient method for removing nitrate from drinking water. Nanoclay adsorbent modified with the organic surfactant HDTMA-Br is used as a strong adsorbent to remove nitrate from aqueous media due to its high adsorption capacity and reusability for at least 4 cycles of recycling.