Enhancing composition and heavy metals combined with humic substances by adding black tourmaline during composting

Humic substances (HSs) extracted from compost play an important role in remediating heavy metals pollution of soil. Adding mineral additive is widely considered as a practical way to enhance the synthesis of HSs and immobilize heavy metals during composting process. Meanwhile, it is a prosperous field to search more mineral additive related to local conditions. Therefore, three dosages of Black Tourmaline (TM) were applied into initial feedstocks to investigate its effect on the composition of HSs and heavy metals combined with HSs. Results demonstrated that TM shortened the maturity period and promoted the transformation from degradable organic substances to stable structures. The variation of spectral parameters such as SUVA(254), SUVA(280), A(4)/A(1), Pi, n and specific values of FTIR provided evidences for the degradation of aliphatic carbon and the formation of aromatic carbon. Meanwhile, adding TM increased the HA-Cu and HA-Zn, and thus decreased the bioavailability of heavy metals. Therefore, TM is beneficial for improving composition of HSs and reducing toxicity of compost, and 10% is suggested in this research. To further, more specific additive amounts of TM should be investigated to get more details about the application of TM in composting technology.