The sorption of heavy metals on thermally treated sediments with high organic matter content

• Sediment oxygen-containing functional groups decrease after pyrolysis.
• Cu(II) and Cd(II) sorption decrease with increasing pyrolysis temperature.
• Pyrolysis at 400 and 500 °C increases Pb(II) sorption.
• Small hydrated ionic radius of Pb(II) facilitate its diffusion into the pores.
• Treated sediments show higher sorption than natural adsorbents.

A sediment sample with organic matter higher than 60% was thermally treated and the sorption of Cu(II), Cd(II), and Pb(II) was investigated and compared to evaluate the potential use of sediments with high organic matter content to produce biochar. Cu(II) and Cd(II) sorption generally decreased with increasing pyrolysis temperature, concurred with decreased oxygen-containing functional groups of the adsorbents. Sediment particles pyrolyzed at 400 and 500 °C showed higher sorption to Pb(II) than other temperatures. The small hydrated ionic radius of Pb(II) may enable its close contact with solid particles and thus facilitated the diffusion of Pb(II) into the pores and the formation of cation–π bond with aromatic structures generated by pyrolysis. The sorption of heavy metals in thermally treated sediment showed comparable sorption to or higher sorption than natural adsorbents and biochars from biomass, suggesting their possible significant impact on the transport and risk of heavy metals.