Preparation and characterization of nano- Fe(OH)3, its composites with two natural zeolites, and granulation of them for nitrate removal from polluted water

The development of a cost-efficient, highly effective, and granular shape adsorbent is highly desired for nitrate removal. In this study, two different Fe(OH)3 nanoparticles with amorphous and crystalline structures, and nanocomposites were successfully synthesized using the ultrasonic-assisted co-precipitation. Both nanoparticles were scrutinized using FTIR, SEM, and XRD. Crystallized Fe(OH)3/zeolite nanocomposites were not efficient for nitrate removal;hence, the rest of the study was carried out with amorphous Fe(OH)3 nanoparticles (Am-Fe(OH)3). Clinoptilolite and analcime were acid-washed and used as a support for synthesized Am-Fe(OH)3 nanoparticles. Nanocomposites of clinoptilolite and analcime were abbreviated as Fe(OH)3/Clin and Fe(OH)3/Anc, respectively. The nanocomposites were characterized by BET, FTIR, SEM, EDS, and XRD techniques. Subsequently, granules of the above-mentioned nanocomposites were prepared using the wet gelation method and alginate. Two crucial features of pH and adsorbent:alginate ratio, were assessed and optimized as 11–12 and 1:3, respectively. The performance of granules were investigated regarding pH, time, and adsorbent dosage. Fe(OH)3/Clin and Fe(OH)3/Anc granules removed 96.82% and 34.02% of nitrate from a contaminated solution with initial concertation of 50 mg l−1. Overall, Fe(OH)3/Clin granule was an effective adsorbent for nitrate removal. The maximum adsorption capacity of Fe(OH)3/Anc and Fe(OH)3/Clin were 0.4443 mg g−1 and 5.6211 mg g−1 for 0.2 g of each adsorbent, respectively. Both adsorbents displayed good compatibility with the pseudo-second-order kinetic model.