Effect of Exhausted Coffee Ground Particle Size on Metal Ion Adsorption Rates and Capacities

Abstract

Spent coffee grounds (SCGs) are common waste products that can be used as low-cost adsorbents to remove contaminants from water. SCGs come in a range of particle sizes based on how they were ground to brew coffee. However, few studies have investigated how SCG particle size influences the adsorption rate and capacities of metal ions. In this study, SCGs were washed under alkaline conditions, creating exhausted coffee grounds (ECGs). ECGs were sieved into four particle size ranges (106–300, 300–500, 500–710, and 710–1000 μm). Monocomponent batch adsorption experiments were conducted with each size fraction using 0.3 mM Pb2+, Cu2+, Zn2+, and Ni2+ at pH 5.5 to examine the effect of particle size on the adsorption rates and capacities. The initial adsorption rates for all the four metal ions were 8–12 times higher for the smallest ECGs compared to the largest ECGs. Slower initial adsorption rates with increasing particle size were due to intraparticle diffusion of metal ions into the porous structure of ECGs. However, the equilibrium adsorption capacities for each metal ion and the surface acidic group concentrations were similar across the range of particle sizes studied, suggesting that grinding ECGs does not substantially change the number of adsorption sites. The equilibrium adsorption capacities for Cu2+ and Pb2+ were 0.18 and 0.17 mmol g–1, respectively. Zn2+ and Ni2+ had lower adsorption capacities of 0.12 and 0.10 mmol g–1, respectively. The time needed to reach equilibrium ranged from less than 2 h for Zn2+ and Ni2+ adsorption onto the smallest ECGs to several hours for Pb2+ or Cu2+ adsorption onto the largest ECGs. Future adsorption studies should consider the effect of ECG particle size on reported adsorption capacities, particularly for shorter experiments that have not yet reached equilibrium.

Recent advances on sustainable removal of emerging contaminants from water by bio-based adsorbents

“…Repurposing waste materials such as coffee grounds, fruit peels, and eggshells effectively adsorbed contaminants and heavy metals from water and other industrial effluents in the past, contributing to sustainable waste management and pollution control measures. [61][62][63] Sea materials have been revealed to be good bio-adsorbents, utilizing their inherent capabilities to adsorb pollutants and toxins from numerous sources. These eco-friendly bio-adsorbents provided a sustainable and economical option for water treatment and environmental remediation activities by utilizing materials such as seaweed, seashells, and marine algae.…”

The Bioactive Substances in Spent Black Tea and Arabic Coffee Could Improve the Nutritional Value and Extend the Shelf Life of Sponge Cake after Fortification

“…Currently, the awareness of the general farmers and consumers of terms including sustainable development and circular bioeconomy helped in mitigating this problem, and agri-food waste is now accepted as a valuable resource and re-entered the supply chain via recycling, valorization, energy recovery, and other uses. ,− In this context, there have been studies on the use of used spent coffee and tea leaves in the field of livestock nutrition, agricultural compost, or production of biogas, or valorized for their bioactive molecules. ,,− However, there is a lack of research on the use of spent tea and coffee in the production of novel foods. − …”