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[Display omitted] • Modification by Fe and Si produces novel Fe-containing silicate in biochar. • Fe introduced in biochar promotes Si dissolution to enhance precipitation of CdSiO 3. • Synergistic effect of Fe and Si in biochar on Cd adsorption was identified. • The Cd removal effect using Fe/Si modified biochar is controlled by chemical reaction. The interaction mechanisms of silicon (Si) and active ingredient iron (Fe) on cadmium (Cd) removal are still unknown. Herein, the Fe/Si modified biochar (Fe/Si-BC) was synthesized to enhance Cd removal by pre-immersion of Fe and ball milling loading of Si. Detailed characterizations indicated that Fe and Si were successfully introduced into Fe/Si-BC, resulting in the formation of a new metallic silicate (Ca 2.87 Fe 0.13 (SiO 3) 2). The maximum Cd adsorption capacity of Fe/Si-BC (31.66 mg g−1) was 3.6 times and 2.5 times higher than that of Fe-BC (8.89 mg g−1) and Si-BC (11.03 mg g−1), respectively, deriving from an enhancement of Si dissolution induced by Fe introduction. The dissolved Si could capture and combine Cd to form CdSiO 3 precipitation, which was strongly supported by the random forest regression and correlation between dissolved Si content and Cd adsorption capacity. This study advances the mechanistic insights into synergistic functions of Si and Fe in Cd removal. [ABSTRACT FROM AUTHOR]