Efficient adsorption of highly-concentrated Cr(VI) from aqueous solutions using tea residue-derived humic acid

The efficient capture and removal of toxic metals, for instance, Chromium (Cr(VI)) from aqueous environments is a critical issue, in environmental science and engineering. Developing cost-effective, eco-friendly and pH-adaptive adsorbent is essential for addressing this challenge. In this study, tea residue-based humic acid (T-HA) adsorbent was feasibly prepared via an alkali-soluble acid precipitation method for the optimal elimination of Cr(VI) from aqueous solutions. Results indicate that T-HA can be extracted from tea residues while the study of tea residue as an emerging biomass feedstock remains in the exploratory stage, yielding 1.47% through the proposed method. The highest adsorption capacity of T-HA for Cr(VI) was recorded as 27.32 mg/g, significantly 53.92% higher than that of untreated tea residue. The adsorption behavior adhered to pseudo-second-order kinetics (R 2 =0.999) and was consistent with the Freundlich isotherm model (R 2 =0.987), suggesting that chemical adsorption was the dominant mechanism. This study highlights the potential of T-HA for the valorization of tea residues and the purification of heavy metal-contaminated wastewater, contributing to sustainable resource utilization and environmental remediation. 1. Extraction of Humic Acid : Diagram showing the extraction process of humic acid (T-HA) from tea residue, which involving chemical treatments and thermal processes. 2. Characterization of T-HA : Images or graphs showing the characterization of the extracted humic acid, such as FTIR spectra, SEM images. 3. Adsorption Setup : Schematic of the adsorption experiment setup, showing a beaker or Column with Cr(VI) solution and the humic acid adsorbent. 4. Adsorption Process : Visual representation of Cr(VI) ions being adsorbed onto the T-HA, possibly showing the binding sites or mechanisms. 5. Efficiency Metrics : Graphs or charts displaying the adsorption efficiency, such as removal percentage over time, pH, oscillation intensity, adsorption isotherms, and kinetic studies. 6. Environmental Impact : suggesting the environmental benefits of using tea residue-derived humic acid for Cr(VI) removal, such as reduced waste and sustainable resource utilization. • Eco-friendly, low-cost and pH-adaptive adsorbent are obtained from waste tea residue. • Chemisorption plays a dominant role in the adsorption process. • Extracting humic acid from tea residues represents a promising approach for value-added utilization of waste tea residue.