Potential of easily prepared low-cost rice husk biochar and burnt clay composite for the removal of methylene blue dye from contaminated water

Abstract

The textile industry is one of the most significant and rapidly growing industries. However, it consumes a large amount of processed water and produces highly contaminated discharge water and consequently has a significant influence on the environment. Therefore, presently, it is necessary to remove dyes from wastewater. In this study, we examined the adsorption of methylene blue dye on a rice husk char–burnt clay composite. At a total residence time of 50 min, the rice husk was burned at 200 °C at a heating rate of 10 °C min⁻¹. Subsequently, the produced RHBC was pulverised, and a composite was created by combining it with burnt clay that was burnt at 400 °C in a weight ratio of 9 : 16. FTIR, SEM, XRF and BET surface area analysis were performed to characterize the adsorbent. Both batch and column adsorption studies were conducted to identify the variables influencing the adsorption process. The favorable removal of MB in certain media is defined by the point of zero charge of RHBC/BC, which was analyzed to be 6.8. The optimum RHBC/BC dosage was 0.25 g, pH = 7, contact time = 50 min, initial MB concentration = 10 ppm and temperature = 10 °C, resulting in the excellent removal efficiency by the adsorbent of 97.11%. It was discovered that the pseudo-second-order model, which had a value of R² = 0.9994 and low error function values best described the kinetics of the adsorption process. The Langmuir isotherm model had the largest R² (0.9936) and low values for the models of error, making it the best fit. The applicability (n = 2.094 L g⁻¹) and physisorption nature (E_s = 0.6368 kJ mol⁻¹) of the process were both confirmed by the Freundlich and D–R isotherm plots, respectively. As evidenced by the negative values of the thermodynamic parameters, i.e., ΔG and ΔH, the adsorption was exothermic and spontaneous, respectively. The column study also revealed the direct relation between % removal and bed height as well as dye concentration used. However, an increase in flow rate resulted in a decrease in the % removal of dye. The results of the BDST model are consistent with the experimental data, as confirmed by the high regression coefficient values. The desorption experiment revealed that 90% of RHBC/BC could be recycled. Also, the impact of various ions on the adsorbent efficiency was studied. The experiment was carried out using an environmental sample and the results showed a high percentage of removal of dye of greater than 90%. The high adsorption (>90%) and desorption efficiencies (=90%) imply that RHBC/BC has potential to be exploited as a reliable, quick, and low-cost adsorbent for stripping MB dye from industrial effluents, especially in the textile industry. The originality of the current study is that no work has been documented on the explicit use of an RHBC/BC composite as an adsorbent to eliminate methylene blue dye specifically to date.