Abstract
Dyes containing effluents constitute hazards to the environments and endanger human and aquatic lives. Although activated charcoal has been adjudged the best for adsorption treatment of wastewater, its regeneration and high cost have limited their applications, hence the quest for alternative adsorbent. Magnetic tuned biosorbent was prepared from sorghum husks by in situ co-precipitation of Fe3O4. It was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy. The biosorbent was then used for the removal of crystal violet (CV) and methylene blue (MB) dyes from aqueous solutions in a batch process. The effects of temperature, initial dye concentration, dosage, contact time as well as pH were investigated, and data obtained were analysed with appropriate kinetic and isotherm models. Response surface method was used for the optimization study of the adsorption using Box–Behnken experimental design. Pseudo-second-order kinetic model was the most appropriate model for both dyes with correlation coefficient (R2) > 0.9 and low % standard error values. The equilibrium data were best fitted with Langmuir isotherm with maximum adsorption capacity (Qmax) of 18.87 and 30.00 mg g−1 for CV and MB, respectively. The thermodynamic parameters for the adsorption processes showed that it was spontaneous, endothermic and random systems with free energy changes less than zero, enthalpy changes (∆H) of + 49.81 and + 51.18 kJ mol−1, entropy changes (∆S) of + 178.39 and + 177.34 J mol−1 K−1 for MB and CV dyes, respectively. Optimization studies revealed that 95% of the dyes are removable at 1.0 g adsorbent dosage and pH of 4.05 at 50 °C with initial dye concentration of 50 mg L−1. The prepared adsorbent is cheap, easily recycled and highly effective for the treatment of dye-contaminated water.
Highlights
Increased anthropogenic activities as a result of rapid urbanization and industrialization have led to the increase in environmental pollution with grave consequence in the quality of water available for industrial, agricultural and domestic use
Reduced light penetration due to the presence of the coloured pollutants will result in the loss of photosynthesis and upset the biological activities of the aquatic system which may lead to the destruction of aquatic species
Where Qe and Qt are respectively, while the amounts (mg k1 (min−1) is the g−1) of dye adsorbed per unit mass of adsorbent rate constant for the pseudo-first-order kinetics at equilibrium time and time t, Qt k2Q2e t 1+k2 Qe t where Qe and Qt are respectively, while the amounts of k2 (g mg−1 min−1) is dye the adsorbed per rate constant unit mass of adsorbent at equilibrium for the pseudo-second-order kinetics time and time t, Qt = 1∕ ln( ∗ t) (5) where α is the initial adsorption rate constant and the parameter β (g mg−1 min−1) is related to the extent of surface coverage and activation energy for chemisorptions
Summary
Increased anthropogenic activities as a result of rapid urbanization and industrialization have led to the increase in environmental pollution with grave consequence in the quality of water available for industrial, agricultural and domestic use. Synthetic dyes and pigments are used extensively industrially and in many other fields of technology, leading to generation of highly coloured waste effluents Reduced light penetration due to the presence of the coloured pollutants will result in the loss of photosynthesis and upset the biological activities of the aquatic system which may lead to the destruction of aquatic species. Methylene blue and crystal violet are cationic dye with various applications in chemistry, biology, medical science and dyeing industries, and they are highly toxic than other anionic dye (Gao et al 2016). Methylene blue is widely used as hemp, silk fabric, stained paper dyeing, bamboo and wood colouring as well as a chemical agent in printing and dyeing enterprises
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