Variation of heavy metal speciation during the pyrolysis of sediment collected from the Dianchi Lake, China

Sediment samples with high organic carbon were collected from the Dianchi Lake in China and thermally treated using a method analogous to biochar production. The speciation of the heavy metals Cu, Cd, Pb, and Zn in sediment and thermally treated sediments (TTSs) were analyzed by European Community Bureau of Reference (BCR) sequential extraction methods. Heavy metal bioavailability and eco-toxicity were assessed by risk assessment code. This study demonstrates that BCR sequential extraction methods and risk assessment code can be used as valuable tools to assess heavy metal mobility, bioavailability and eco-toxicity. Compared to biochar derived from biomass, TTSs had different characteristics, which may contribute to the formation of organo-mineral complexes. The heavy metals Cu, Cd, Pb, and Zn speciated in TTSs show different patterns from that of the sediment and pyrolysis temperature has a great influence on the fractional distribution of heavy metals. Those different distributions may attribute to the geochemistry of the sediment and the different physicochemical characteristics of heavy metals. In order for the safe application of thermally -treatment sediments (TTSs) as a soil amendment, further studies such as field experiments may be required.