Abstract
We assessed the applicability of rice husk (RH) to remove cationic dyes, i.e., methylene blue (MB) and crystal violet (CV), from water. RH thermally treated at 75 °C showed a higher adsorption capacity than that at high temperatures (300–700 °C). For a suitable CV-adsorption model, a pseudo-first-order model for MB adsorption was followed by the kinetics adsorption process; however, a pseudo-second-order model was then suggested. In the qt versus t1/2 plot, the MB line passed through the origin, but that of CV did not. The Langmuir isotherm model was better than the Freundlich model for both dye adsorptions; furthermore, the adsorption capacity for MB and CV was 24.48 mg/g and 25.46 mg/g, respectively. Thermodynamically, the adsorption of both MB and CV onto the RH was found to be spontaneous and endothermic. This adsorption increased insignificantly on increasing the solution pH from 4 to 10. With an increasing dosage of the RH, there was an increase in the removal percentages of MB and CV; however, adsorption capacity per unit mass of the RH was observed to decrease. Therefore, we conclude that utilizing RH as an available and affordable adsorbent is feasible to remove MB and CV from wastewater.
Highlights
Effluents from textile, leather, cosmetics, paper, pulp and dye manufacturing industries are highly colored because they contain organic chemicals called dyes [1]
At 300 mg/L, the methylene blue (MB) adsorption by untreated rice was similar to that of rice husk (RH) treated at 75 ◦ C and 100 ◦ C, respectively, but was larger than that obtained under high temperatures (300–700 ◦ C)
These outcomes revealed that pyrolysis of the RH under high temperatures did not improve the adsorption of MB
Summary
Effluents from textile, leather, cosmetics, paper, pulp and dye manufacturing industries are highly colored because they contain organic chemicals called dyes [1]. The various types of dyes include methylene blue (MB) and crystal violet (CV). MB is an odorless, dark green powder that turns blue in an aqueous solution; it is used for dying cotton or silk, surgeries, and as a hair-colorant [2,3,4]. CV, a protein-based dye known as gentian violet, is used to enhance bloody-fingerprints and on adhesive tapes to prevent adhesion of powders on their sticky sides [6]. Disposal of colored wastewater into an aquatic environment causes reduced photosynthesis due to low light penetration [8], and mutagenesis in both aquatic organisms and humans [9]
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