Fe3O4-chitosan magnetic particles derived from water treatment sludge for enhanced copper adsorption

Chitosan modifies water treatment sludge to form magnetic particles that have enhanced copper (Cu2+) adsorption performance. Batch and column experiments tested the adsorption performance of the Fe3O4–chitosan modified and Fe3O4 non-modified adsorbents under Cu2+ concentrations ranging from 200 to 1000 mg L-1. Fe3O4 magnetic particles achieved a maximum particle adsorption capacity of 145 mg g-1 at 1000 mg L-1 in batch testing. Fe3O4–chitosan particles under the same test and concentration reached 280 mg g-1 at 1000 mg L-1. Isotherm analysis showed strong agreement with the Langmuir model with R2 > 95. Fe3O4–chitosan adsorbent showed a maximum capacity (Cmax) of 247.8 mg g-1 with R2 > 0.9998. Kinetic analysis indicated pseudo-second order behavior (R2 > 0.99). The Fe3O4–chitosan adsorbent rapidly chemisorbs Cu2+ and increases its rate constant (k₂) from 0.117 g mg-1 h1 to 0.536 g mg-1 h-1. Column experiments conducted using 1 g and 2 g of adsorbent at influent concentrations of 800 mg L-1 to 2000 mg L-1 demonstrated longer breakthrough times and improved resistance for the Fe3O4–chitosan particles. Traditional column models (Thomas, Yoon–Nelson, Adams–Bohart) provided a limited fit (R2 ≤ 0.65). The Thomas model provided the best overall fit and most reliable prediction of breakthrough behavior. This study addresses the gap of traditional adsorbents being costly or unsustainable and provides a solution to recycle sludge water instead of disposing of it in landfills. This research introduces a novel approach to recycling industrial sludge by using chitosan as a biopolymer.