Overview
Chwastowski and colleagues compared spent coffee grounds with activated spent-coffee-ground biochar as sorbents for Cd(II), Mn(II), and Pb(II) in prepared aqueous solutions. This is mitigation evidence, not coffee occurrence evidence: the source reports removal capacity from spiked water matrices and should not contribute to coffee product concentration pools.
Key numbers
The batch adsorption tests used 20 cm3 metal-ion solution at 100 mg/dm3 with sorbent masses from 0.2 g to 0.5 g. The authors modeled adsorption with Langmuir, Freundlich, and Temkin isotherms and reported that Langmuir gave the best fit across tested metals and sorbents.
Table 1 reports Langmuir maximum adsorption capacities. Activated spent coffee grounds (A-SCG) had qmax 19.56 mg/g for Cd(II), 19.40 mg/g for Mn(II), and 22.25 mg/g for Pb(II). Untreated spent coffee grounds (SCG) had qmax 12.97 mg/g for Cd(II), 10.99 mg/g for Mn(II), and 13.58 mg/g for Pb(II). The text summarizes these as about 19.6 mg/g Cd(II), 19.4 mg/g Mn(II), and 22.3 mg/g Pb(II) for A-SCG, respectively 51%, 77%, and 64% higher than SCG.
The Langmuir RL values were below 1 for all metal-sorbent combinations, which the authors interpreted as favorable adsorption. For A-SCG, Table 1 reports RL 0.0392 for Cd(II), 0.0435 for Mn(II), and 0.0961 for Pb(II). For SCG, the corresponding RL values were 0.0718, 0.1553, and 0.1726.
The kinetic analysis found that the linear pseudo-second-order model best described adsorption for both sorbents and all three metals. The authors reported that adsorption equilibrium occurred early, on average about 30 minutes for concentrations below 200 mg/dm3. At 300 mg/dm3 initial concentration, the first-5-minute average adsorption rates for A-SCG were 1.51 mg/g/min for Cd(II), 1.15 mg/g/min for Mn(II), and 1.24 mg/g/min for Pb(II), which were 2.0, 1.6, and 2.3 times the corresponding SCG rates.
Methods (brief)
The spent coffee grounds were 100% Arabica coffee, brewed at 100 C, washed three times with distilled water, dried, screened to 0.2-0.4 mm, and dried again. Activated spent coffee grounds were produced by pyrolysis in a laboratory fluidized-bed reactor using CO2 as the fluidizing medium. The pyrolysis run lasted about 3 hours, followed by a 30-minute hold after reaching the target temperature.
The authors characterized the sorbents with SEM-EDX, FTIR, BET measurements, and CHN analysis. BET analysis reported A-SCG surface area of 6.8 m2/g. Stock solutions of Cd(II), Mn(II), and Pb(II) were prepared from cadmium sulfate, manganese sulfate, and lead nitrate salts. This design tests sorbent performance under controlled aqueous conditions, not native metal concentrations in coffee, coffee grounds, food, or beverages.
Related evidence
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