Water pollution by heavy metals is a serious global issue due to their high toxicity, non-biodegradability, and persistence in the environment. Human activities such as mining, metal production, electronics electroplating, agriculture, and metallurgical waste disposal are the main contributors to the increased concentrations of hazardous metals. Long-term exposure to hazardous heavy metals can cause irreversible damage to various biological systems [1]. Among these, cadmium (Cd) is a toxic heavy metal that can contaminate water systems due to its higher solubility compared to other heavy metals. Therefore, according to the Environmental Protection Agency and the World Health Organization, the level of cadmium concentration in water should be in the range of 4.0-10.0 mg/L. Excessive exposure to cadmium can cause health problems. In many regions, cadmium levels are above safe limits. That’s why it’s important to detect and then remove Cd(II) ions from industrial wastewater [2].
Technologies such as ion exchange, solvent extraction, membrane-based processes, and precipitation are used for heavy metal removal from industrial effluents. However, all of these methods have some limitations in term of technical and economic feasibility. This has led environmentalists to focus on developing better, cheaper, and more effective removal techniques that use biological materials. Biosorption is an alternative method for heavy metals removal from water, replacing the above-discussed techniques [3].
The aim of this study is to provide an alternative to existing techniques in terms of efficiency, economy, and sustainability. In this study, buckwheat hulls, have been used for the efficient removal of Cd(II) from aqueous media. The sorption capacity and removal percentage of Cd(II) on buckwheat hulls were examined using batch sorption experiments with different parameters such as contact time, solution pH, biosorbent dose, temperature, and initial Cd(II) concentration. The results obtained were examined for isotherm, kinetic, and thermodynamic study. SEM, EDX, FTIR, and pH of point of zero charge confirmed the favorable biosorption surface characteristics. The maximum Cd(II) sorption by buckwheat hulls was 97.5% at pH 5, initial Cd(II) concentration of 10 mg/L, contact time for 180 min, sorbent dose of 0.1 g, temperature of 25 °C, and agitation speed 150 rpm. A kinetic study shows that the pseudo-second-order (R\(^{2}\)=0.999) is suitable for this sorption process. The isotherm study shows that the Langmuir model (R\(^{2}\)=0.998) is the best to explain experimental data, with a maximum sorption capacity of 44.44 mg/g. The thermodynamic parameter shows that the removal of Cd(II) by buckwheat hulls is an exothermic and non-spontaneous process.
These results showed that buckwheat hulls are suitable for the effective removal of metals from the aqueous media.