Clean Technologies

This study investigates the removal of copper and zinc at environmentally relevant concentrations from aqueous solutions using barista coffee waste in both standalone and blended forms (with rice husk biochar). A fixed-bed horizontal column adsorption study was conducted to determine the effects of contact time, adsorbent type, and initial metal concentration on the removal efficiency. As far as we are aware, this study is the first to focus on eliminating low concentrations in accordance with World Health Organization (WHO) guideline levels, employing a horizontal fixed-bed column setup. Adsorption equilibrium was achieved around six hours after initiation and resulted in a high percentage of metal removal (up to 96.71%). Ground coffee waste performed better for lower initial metal concentrations (2.5 ppm copper and 10 ppm zinc), although a mixture of coffee waste and biochar performed better at concentrations greater than 5 ppm for copper and 25 ppm for zinc. Experimental results were applied to the Thomas model to determine the efficiency of the adsorbents. Results indicated it was linear with a good correlation coefficient (R² = 0.94). The experimental data also fitted the pseudo-first-order reaction kinetic with a higher correlation coefficient (R² = 0.93) than the second-order reaction kinetics. The experimental and calculated values were very similar for the first-order reaction kinetic. The metal adsorption was affected by both external mass transfer and intra-particle diffusion mechanisms. This study developed an engineered solution to remove heavy metals from wastewater using widely available ground coffee waste as an effective adsorbent.

The increasing emphasis on green chemistry has led numerous researchers to focus on environmentally friendly solvents for mineral extraction. Among them, deep eutectic solvents (DESs) have garnered significant attention due to their eco-friendly, non-toxic, and biodegradable properties. These solvents possess comparable physicochemical properties to conventional ionic liquids but are more cost-effective and environmentally friendly. While DESs have been widely studied for extracting metals from synthetic minerals and end-of-life products, its use with primary ores and associated wastes remains relatively unexplored. This study aims to bridge that gap by assessing the effectiveness of choline chloride- and ethylene glycol-based DESs in extracting rare earth elements from primary feedstocks with varied grades and mineralogy, including sub-economic ores, monazite flotation tailings, and acid-crack and leach residue. The study also examines the practical challenges in preparing DES and assesses the applicability of the solvents for primary materials. By examining both solvent preparation challenges and the variable responses of different feed materials, this work provides a high-level scoping analysis to better understand the suitability and limitations of DES for primary resource extraction. This study highlights the challenges with physical properties and mineral breakdown in using DES.

Oranges are widely consumed worldwide and are highly valued both for their nutritional properties and their economic importance. In Mexico, particularly in the northeastern citrus-producing region, large amounts of peel are generated during industrial processing, representing a significant source of agro-industrial waste. This byproduct is naturally rich in compounds of interest, including flavonoids, polyphenols, and pectin, which motivates the development of sustainable recovery strategies. In this work, orange peel biomass was valorized using ultrasound-assisted extraction in combination with deep eutectic solvents (DESs). Among the evaluated formulations, the choline chloride–lactic acid DES at a 1:10 molar ratio produced the highest overall extraction yield (43.88% by dry weight/mass). The 2:1 formulation, however, was the most efficient for the recovery of phenolic compounds, reaching 4.12 mg GAE/g, and exhibited the greatest antioxidant activity (2.55 mmol Trolox/g) and the strongest antimicrobial response against clinically relevant microorganisms. This same DES ratio enabled the highest quantification of key phenolics such as naringin (1150.29 µg/g), caffeic acid (139.41 µg/g), and ferulic acid (379.96 µg/g). For polysaccharide extraction, the 1:1 DES ratio was the most effective, achieving a pectin yield of 48.24%. Overall, the findings demonstrate that DES, particularly when combined with ultrasound, offers a green and efficient approach for the integrated recovery of pectin, phenolic antioxidants, and antimicrobial compounds from citrus byproducts, contributing to environmentally sustainable biorefinery strategies.