Effective removal of nitrate and phosphate ions from water using nickel-doped calcium alginate beads

Water contamination by nitrate and phosphate ions remains a critical environmental and public health challenge, largely driven by agricultural runoff and industrial activities. In this study, the adsorption capacity of nickel-doped calcium alginate beads (Ni-CaAlg) as a novel adsorbent for the dual removal of nitrate and phosphate ions from water has been investigated. Incorporating nickel ions into the alginate matrix enhanced adsorption capacity and provided additional active sites, fostering electrostatic interactions with the target contaminants. The characterization including Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDX), Brunauer–Emmett–Teller (BET) analysis, and zeta potential measurement (pHpzc), confirmed the successful doping, structural integrity, and surface charge properties of the beads. Based on the findings, in the optimized conditions of pH 6, adsorbent dosage of 30 mg, and contact time of 120 min, the Ni-CaAlg beads had the highest adsorption capacities of 169.5 mg/g for nitrate and 238.1 mg/g for phosphate. The adsorption process followed a pseudo-second-order kinetic model and well-fitted with the Langmuir isotherm, confirming chemisorption and monolayer adsorption. The beads retained over 70 % of their initial adsorption capacity after ten adsorption-desorption cycles, underscoring their durability and reusability. These findings establish Ni-CaAlg beads as a promising and innovative solution for mitigating nitrate and phosphate contamination in water treatment systems.