Abstract
Biochar derived from coffee waste has been reported as a promising material for heavy metal sorption. However, if the intended use is environmental remediation, knowing the extent to which desorption may occur is critical. Thus, the objective of this work was to evaluate the efficiency of spent coffee ground (SCG) and coffee parchment (CP) biochars pyrolyzed at 700 °C under laboratory conditions, in the sorption of Cd and Pb from aqueous solutions, in a pH range from 2 to 10, and their retention after an induced desorption process with a 2.9 pH acetic acid solution. Both biochars were alkaline, and the initial pH of the solution had a large effect on the sorption capacity of SCG but a small effect on the sorption capacity of CP. The Pb sorption capacity was higher for CP (18.6 mg·g–1) than for SCG (11.4 mg·g–1), while both biochars had low Cd retention capacities (1.18 mg·g–1). Coffee parchment also showed the highest Pb retention (30% to 87%), while for Cd there was no difference between CP and SCG biochars. Our results showed that metal precipitation was the main mechanism for metal immobilization and CP biochar proved to be more reliable than SCG, mainly for Pb, due to its higher sorption capacity and lower metal release by desorption than SCG. These characteristics are particularly important for the use of biochar in environmental remediation. Besides that, the biochar production represents an eco-friendly destination for these feedstocks, contributing to the circular economy.
Highlights
The increase in environmental contamination by heavy metals due to anthropogenic activities is a global issue that requires attention
The Pb sorption capacity was higher for coffee parchment (CP) (18.6 mg∙g–1) than for spent coffee ground (SCG) (11.4 mg∙g–1), while both biochars had low Cd retention capacities (1.18 mg∙g–1)
Our results showed that metal precipitation was the main mechanism for metal immobilization and CP biochar proved to be more reliable than SCG, mainly for Pb, due to its higher sorption capacity and lower metal release by desorption than SCG
Summary
The increase in environmental contamination by heavy metals due to anthropogenic activities is a global issue that requires attention. Heavy metals pose high environmental risks due to their high toxicity and bioaccumulative potential (Xu et al 2018). Their persistence in the environment affects ecosystem productivity and the economy (Lahori et al 2017). Heavy metals such as Zn and Cu are nutrients; they become toxic at high levels. Other elements, such as Cd and Pb, do not have biological functions and are potentially toxic even at low levels (Nazir et al 2015). Prolonged human exposure to Cd and Pb can damage the bones and kidneys and negatively affect the central nervous system and fertility (Kumar et al 2020; Wang et al 2018)
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