Efficient removal of Sr ions from water utilizing a novel Ni-/Fe-doped spongy apatite through fixed bed column system: optimization and realistic application

Abstract

The removal of strontium metal ions from aqueous solutions and raw groundwater using synthetic spongy apatite was studied based on the experimental parameters of the continuous fixed bed column system. Novel Ni-/Fe-doped spongy apatite of carbonate fluorapatite composition was synthesized as an effective adsorbent and ion exchanger bed of high adsorption capacity for strontium ions in water. Based on the mathematical parameters, the best removal percentage of strontium (83.7%) from aqueous solutions was obtained after treatment of 6.6 L at optimum conditions of pH6, 3 cm bed height, 5 mL/min flow rate and 15 mg/L initial concentration. Under the previous conditions, the breakthrough time was attained after 1200 min. The total amount of adsorbed strontium in the column system is about 1446 mg, and the equilibration uptake capacity of spongy apatite is about 347.8 mg/g within the limitations of the studied parameters. The regeneration studies reflected the suitability of spongy Ni-/Fe-doped carbonate fluorapatite to be used effectively for five cycles in the removal of strontium contaminants. The operating adsorption mechanisms and the column performance were addressed based on Thomas, Adams–Bohart and Yoon–Nelson mathematical kinetic models. Ni-/Fe-doped spongy apatite column system was applied in a realistic purification of groundwater samples from strontium pollutants in Quseir area, Egypt (Wadi El Nakheil well and Wadi El Ambagi spring). The obtained results reflected the efficiency of the synthetic material in the decontamination of strontium ions and other metal ions from raw water.