Towards a better understanding on adsorption mechanism of various heavy metal with phosphorus rich hydrochar

The heavy metal contents in many rivers and groundwater exceeds safety standards, and hydrochar stands out among many functional materials for environmental protection applications as its efficient and low−cost. The influence of endogenous phosphorus in the adsorption and the forms of heavy metal combined with phosphorus are not always fully explored. Thus, the purpose of this study was to clarify adsorption mechanism as well as the biological risks. The physisorption and chemisorption likely coexisted during adsorption of Pb(II) and Hg(II), while physisorption dominated Cd(II) adsorption. The adsorption isotherms of three heavy metal were well fitted with the Langmuir model with capacity of 466.45, 339.48, and 264.19 mg·g−1, respectively. The ion−exchange was the dominant mechanism for Pb(II) and Cd(II) adsorptions. The precipitations were mainly phosphate and carbonate, respectively. On the contrary, formation of complexations was considered as the dominant mechanism for Hg(II) adsorption. Thus, the contribution of phosphorus in adsorption was: Pb(II) > Cd(II) > Hg(II). Using CMHCC to remove heavy metal not only had great effect, but also little harm of eutrophication caused by endogenous phosphorus release for the proportion of bioavailable phosphorus decreased. It's worth noting that the biological risk of CMHCC@HM was: CMHCC@Pb > CMHCC@Cd > CMHCC@Hg. The present study explored the role of endogenous phosphorus in the adsorption of different heavy metal, and the forms of heavy metal and phosphorus. The study improved the effect of hydrochar endogenous substances on heavy metal adsorption.