Silico-manganese fumes waste encapsulated cryogenic alginate beads for aqueous environment de-colorization

Safe and economical disposal of ultrafine silico-manganese fumes (SMF), a waste, generated during steel production operation is a challenge for environmental chemists. Herein, SMF waste was encapsulated into alginate, lyophilized to form cryogenic SMF beads (cSMFB). The cSMFB was characterized and its adsorptive potential was tested in the removal of methylene blue (MB), methylene green (MG), crystal violet (CV) and celestine blue (CB) from aqueous environment. The cSMFB having respective Brunauer-Emmett-Teller (BET) surface area and Barrett, Joyner, and Halenda (BJH) pore diameter of 59.88 m²/g and 18.58 Å was developed. Fourier transform infra-red (FT-IR) analysis revealed bands at 1630 and 1412 cm⁻¹, attributed to asymmetric and symmetric stretching vibrations of carboxylate ions, characteristic of alginate (used to encapsulate SMF). Also, the bands at 1092 and 1031 cm⁻¹ corresponding to carbohydrate rings of alginate were present. A band ascribed to metal oxides was appeared at 467 cm⁻¹. The encapsulation of SMF waste in alginate was further confirmed by X-ray photoelectron spectroscopy (XPS) (with peaks at binding energies 34, 284.7, and 532 eV ascribed to Na 2p, C1s, and O 1s), X-ray diffraction (XRD) (with 2θ peaks at 13.5 and 22.2° for sodium alginate), and energy-dispersive X-ray (EDX) analyses. The cross-sectional image of pristine cSMFB showed highly porous rough and uneven surface. Thermogravimetric (TGA-DTA) analysis of cSMFB sample revealed the five stages total weight loss of ∼17.5% between 40 and 800 °C. Alkaline pH (pHi range: 6–8) favored the adsorption of dyes, while the equilibration time at Cₒ: 50 mg/L was varied between 480 and 600 min. The adsorption of dyes was possibly governed through electrostatic interaction, coordinate bond formation, and cationic interchange.