Aqueous phosphate removal behavior of chemically synthesized vaterite nanoparticles: Isotherms and kinetic study

Abstract

Eutrophication is one of the most adverse impacts of nutrient contamination of water bodies. Recent studies have shown that the primary limiting factor for eutrophication is phosphorus. We developed a vaterite polymorph of porous calcium carbonate nanoparticle to remove phosphate ions in water. These nanoparticles were synthesized using calcium acetate and sodium bicarbonate in a water-ethylene glycol media at a temperature of 100°C in a reaction time of 24 hours and characterized by the X-Ray Diffraction and the Fourier transform infrared spectroscopy which show the presence of vaterite. Particle size was 25.5 nm, and the Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Analysis show the spherical vaterite nanoparticles and the presence of calcium, carbon and oxygen. The phosphate removal efficiency was tested with different concentrations of phosphate solutions (2 ppm – 80 ppm), pH levels (5 – 12), adsorbent dosages (0.05 g – 0.25g), and contact times (0 – 120 min). Ion chromatography was used to analyze phosphate in water samples. The maximum adsorption percentage of 100% was obtained with 50 mL of 2 mgL-1 phosphate solution and 0.15 g of the synthesized nanoparticle. Adsorption data were well fitted with the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model with R2 of 0.99 and 0.98 (Rate constant - 0.083 gg-1min-1), respectively. Phosphate adsorption is not influenced in the presence of F-, 𝑁𝑂3− and 𝑆𝑂4−2 as phosphate shows 100% removal in the presence of them. The study presents a viable option for removing excess phosphate and controlling eutrophication.