Abstract
The ability of biochar to immobilize metals relies on the amount of functional groups at its surface but the contribution of each functional groups (e.g. carboxylic, phenolic) to metal bonding is poorly known. Using a new approach based on previous works on rare earth element (REE) interactions with humic substances, we aim at elucidating the relative contribution of these binding sites to metal sorption under various conditions (i.e. pH and ionic strengths, IS). Using batch experiments, REE sorption onto biochar was analyzed from pH 3 to 9 and IS 10−1 mol/L to 10−3 mol/L. Rare earth element patterns show a Middle REE (MREE) downward concavity at acidic pH and low ionic strength. These patterns are in good agreement with existing datasets quantifying REE binding with humic substances. Indeed, the MREE downward concavity displayed by REE-biochar complexation pattern compares well with REE patterns with various organic compounds. This similarity in the REE complexation pattern shapes suggests that carboxylic groups are the main binding sites of REE in biochar. Overall, our results indicate that the strength of the metal bonding with biochar increases when pH and IS increase, suggesting that biochar is more efficient for long-term metal immobilization at near neutral pH and high ionic strength.
Highlights
Biochar, the carbon-rich product of biomass pyrolysis, has sparked a broad interest due to its attractive potential for improving soil fertility, carbon sequestration and soil remediation (Beesley et al, 2011; Houben et al, 2013a; Lehmann and Joseph, 2009)
The biochar surface functional groups were measured with Fourier transform infrared spectroscopy (FTIR): 0.7 mg of biochar was gently mixed with 100 mg of KBr and the mixture were pressed into a pellet
The efficiency of biochar to sorb metals is critically dependent on the type of metalbinding sites at the surface of biochar particles
Summary
The carbon-rich product of biomass pyrolysis, has sparked a broad interest due to its attractive potential for improving soil fertility, carbon sequestration and soil remediation (Beesley et al, 2011; Houben et al, 2013a; Lehmann and Joseph, 2009). Rare earth elements are a group of seventeen elements presenting very similar and coherent chemical properties (Connelly et al, 2005) In this contribution, we will consider the fifteen lanthanides as REEs. Due to the unique properties of REEs, their partition coefficients (Kd; commonly used in estimating the potential sorption of dissolved metals by a solid phase) between humic substances and aqueous solution are highly sensitive to the heterogeneity of binding sites (i.e. the nature of the functional group involved) A new approach based on previous works on REE interactions with humic substances, was developed to provide new insight into the nature of the sorption sites responsible for metal binding to biochar under various pH and ionic strengths
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
