Vol.:(0123456789) 1 3 Biomass Conversion and Biorefinery https://doi.org/10.1007/s13399-021-01996-8 ORIGINAL ARTICLE Comparative experimental and mathematical analysis on removal of dye using raw rice husk, rice husk charcoal and activated rice husk charcoal: batch, fxed‑bed column, and mathematical modeling Niladri Saha 1  · Lopamudra Das 1  · Papita Das 1  · Avijit Bhowal 1  · Chiranjib Bhattacharjee 1 Received: 2 July 2021 / Revised: 22 September 2021 / Accepted: 24 September 2021 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract A methodology involving rice husk (RH), rice husk charcoal (RHC), and activated rice husk charcoal (ARHC) as an efec- tive adsorbent to eliminate malachite green dye from aqueous solution using adsorption process by varying the pH, initial dye concentration (mg/L), contact time, temperature, and adsorbent doses (g/L). The surface characteristics were observed under scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy was used to identify the chemical bonds present on the adsorbent surface. Data obtained from adsorption system at equilibrium condition were ftted to isotherm models such as Langmuir and Freundlich model where it was found that unlike raw RH and RHC equilibrium, data for ARHC ftted best to Langmuir model with 1000 mg/g as maximum adsorption capacity at 303 K, indicating homo- geneous monolayer adsorption by the mesopores. The adsorption kinetics for all three adsorbents were observed to ft the pseudosecond-order model better. The negative value of ΔH and ΔS obtained from the thermodynamic study indicates that the process is exothermic and involves an associative mechanism respectively. Boyd plot was used to understand the mass transfer mechanism. Moreover, fxed-bed column studies were performed using ARHC as the adsorbent. At diferent experi- mental conditions such as inlet fow rate (Q), initial dye concentration (C 0 ), bed height (L b ), and pH, it was observed that the adsorption capacity (k d *) of MG dye on ARHC in a fxed bed continuous fow in a column mode, ranged between 0.008 and 0.177 (g/g). Present investigation and comparison with other reported adsorbents concluded that RH, RHC, and ARHC can be used as efcient and environment-friendly adsorbents for the removal of dissolved malachite green from contaminated water. However, ARHC was proved to be the best-suited candidate among the three adsorbents. Keywords Isotherm · Kinetics · Thermodynamics · Mass transfer · Fixed bed column · Mathematical modeling 1 Introduction Industrial wastewater contains a wide variety of pollutants that can cause severe damage to the environment if dis- charged into ponds, lakes, rivers, or seas without any treat- ment. They not only pollute the water body or the aquatic environment but also deplete the groundwater table causing contamination in drinking water. Among such chemicals, dye is used in several sectors like textile, cosmetic, plastic, paper, leather, and pigment industries. Synthetic dyes like alizarin, amaranth, Congo red, gentian violet, malachite green, methyl red, methylene blue, Sudan, tartrazine, and Tropaeolin are found to be harmful not only for aquatic species but also extremely toxic for humans. The toxicity of the dyes and their subsidiary chemicals extends from tropical irritation to carcinogenicity and mutagenicity, depending on the exposure[1]. Malachite green (MG) is used as a primary contami- nant in this study. It is a commonly used dye for textile, paper, and fshery. It is a triphenylmethane dye. Oomycete Saprolegnia and Ichthyophthirius multifiliis are algae that infect fsh eggs. MG is actively used to treat such algal con- taminations in commercial aquaculture. Malachite Green also has efective antibacterial properties and is a popular treatment in freshwater aquaria. Application of malachite green in the aquaculture industry is illegal though it is an inexpensive and efective antibacterial, topical fungicide, and parasiticide. The reason being, malachite green is read- ily absorbed by fsh and metabolically reduced to lipophilic * Niladri Saha niladrianjan@gmail.com 1 Jadavpur University, Kolkata, India