Aqueous Brilliant Blue adsorption on Fe3O4@Kaolin: Adsorption Performance, Equilibrium, and Operational Parameters

Textile wastewater is a major contributor to global water pollution. Magnetically modified kaolin adsorbents calcined at 200-500 °C (Fe 3 O 4 @K) were prepared. They removed anionic dyes from water, raised neat kaolin’s capacity, supported Fe 3 O 4 , and reduced its aggregation. Calcination had minimal impact on surface area and pore structure. Fe 3 O 4 was deposited onto kaolin via FeCl 3 and FeSO 4 ‧7H 2 O co-precipitation at pH 10 using 25 % NH 4 OH. After drying and calcined at 200 °C, it was characterized by XRD, FT-IR, SEM-EDX, BET-surface area, and p H PZC . The adsorbent was magnetically removed from dye solutions. Fe 3 O 4 @K-200 and virgin-kaolin adsorbed Brilliant Blue (BB), Crystal Violet (CV), and Brilliant Green (BG), but only BB’s uptake significantly increased on Fe 3 O 4 @K-200 vs kaolin. Fe 3 O 4 promoted this anionic BB uptake. BB adsorption was evaluated as a function of adsorbent dose, pH, initial concentration, temperature, and contact time. Virgin-kaolin had a surface area of 18.91 m 2 /g, while Fe 3 O 4 @K-200 increased to 27.07 m 2 /g. Respective pore volumes were 0.031 and 0.06 cm 3 /g with an improved Fe 3 O 4 dispersion. Kaolin has a pore diameter of 1.08 nm while Fe 3 O 4 @K-200 has 1.01 nm. Adsorption isotherms from 283-318 K ( R 2 = 0.95-0.99) best fit the Langmuir model vs the Freundlich model. Maximum BB Langmuir capacities ranged from 88.48 to 103.23 mg/g at pH 5 and 1 g/L dosage after 90 min equilibrations under controlled conditions. Adsorption was spontaneous endothermic, with increased randomness, indicating favorable thermodynamic behavior for practical wastewater treatment applications. Fe 3 O 4 @K-200 is a promising low-cost, magnetically recoverable adsorbent for anionic dye removal.