The effect of carbonization temperature on the capacity and mechanisms of Pb(II) adsorption by microalgae residue-derived biochar

This study investigated the adsorption characterizations and mechanisms of lead (Pb) on biochar-derived microalgae residue (MB) produced at different pyrolytic temperatures. Six different MB samples were prepared from Chlorella sp. (CB) and Spirulina sp. (SB) in the temperature range of 200-600 degrees C, and microalgae residue power (MP) was used as a control. The effect of pH, adsorption kinetics and isotherms were studied for the different MBs, and a chemical analysis of Pb2+-loaded MP and MB was performed by SEM-EDS, XRD, XPS, FTIR, and Boehm titration. The results showed that Pb2+ adsorption on MP and MB was a monolayer chemical adsorption process. Precipitation with minerals, metal ion exchange, oxygen/nitrogen-containing functional groups (OFGs/NFGs), and coordination of Pb2+ with pi electrons jointly contributed to Pb2+ adsorption on MP and MB. More specifically, the contribution of each mechanism depended on the pyrolytic temperature. The contribution of surface complexation and ion exchange decreased with increasing pyrolytic temperature due to the loss of OFGs/NFGs and decreasing metal ion content, while the contribution of precipitation and Pb2+-pi interaction significantly increased. Overall, precipitation with minerals and ion exchange dominated Pb2+ adsorption on MP and MB, which accounted for 65.20-74.40% of the total adsorption capacity. Surface precipitation contributed to a maximum adsorption capacity for high-temperature CB and SB (600 degrees C) of up to 131.41 mg/g and 154.56 mg/g, respectively. In conclusion, MB adsorbents are a promising material for the remediation of heavy metal-bearing aquatic environments.

Automated summary

This study investigated the adsorption mechanisms and properties of lead on biochar-derived microalgae residue produced at different pyrolytic temperatures. The results showed that precipitation with minerals and ion exchange were the main mechanisms for Pb adsorption, with the contribution of each mechanism depending on the pyrolytic temperature. Surface precipitation contributed to the maximum adsorption capacity for high-temperature CB and SB.