Adsorption of Hexavalent Chromium Ions Using Pine Sawdust Cellulose Fibres

Abstract

In developing countries, agriculture generates not only income but also waste. Therefore, it is essential to recycle this waste for different purposes. This study explored an affordable way to modify pine sawdust to treat chromium-containing wastewater, with successful outcomes. The biosorbent’s surface area was enhanced through pretreatment steps, including NaOH treatment, bleaching, and acid hydrolysis for cellulose fibre extraction. SEM–EDS, TEM, and XRD were used to study the chemical composition and morphology. XRD measurements also revealed a rise in the sizes of crystallites. FTIR results revealed shifts in bands (-OH), (-C-H), and (-COOH), suggesting their involvement in Cr (VI) ion adsorption. TGA/DTA indicated enhanced thermal stability for cellulose extracted from pine sawdust compared to untreated pine sawdust. The adsorption parameters for Cr (VI) ions were investigated through mass, pH, stirring time, and temperature studies. The optimal Cr (VI) adsorption conditions were 2.0 g mass, pH 6, 90 min stirring, 100 mg/L concentration, and 313 K temperature. The adsorption of Cr (VI) ions was best-fit to the Langmuir isotherm model (R2 = 0.9991, kL = 0.09). Pseudo-second-order kinetics (R2 = 0.9999) provided the best description for Cr (VI) biosorption on cellulose fibres (CF). The analysis results confirmed the isotherm and kinetics models. The negative thermodynamic parameters (ΔG° and ΔH°) indicated that the uptake of Cr (VI) ions on the adsorbent was exothermic and spontaneous.