Uptake of mercury by exhausted coffee grounds

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Abstract
In view of using low cost material for the removal of mercury from wastewaters, Exhausted Coffee Grounds (ECG), appropriately pretreated with NaOH 0.5 M, have been tested as a possible scavenger from 10 mgl‐1 Hg solutions characterized by ionic strength 0.1 M NaNO3 or 0,1 M NaCl, in the range of pH 3–11. The Hg uptake can be expressed in terms of a Lang‐muir relationship over the Hg concentration range 0.05–50 mgl‐1 in both pH value 3 and 11, respectively, the evaluated capacity being of the order of 80 mg/g, which is 10 times higher than that of the activated carbon. Sorption occurred also in presence of chlorides provided that the pH was adjusted to the range 10–11. Results of experiments performed on columns containing 2 g of ECG, while confirming the order of magnitude of the capacity value evaluated with batch experiments, showed an efficiency of Hg removal of about 99.9% for solutions at pH=3 and 99% for solutions at pH 11 after treatment of 540 and 160 bedvolumes, respectively. A recovery of 70% of mercury uptaken at pH 11 was possible by elution with 16 bed volumes of HC1 1 M; the same volume of HC1 1 M allows 85% of the mercury sorbed at pH=3 to be recovered.

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