The　purpose　of　this　study　is　to　design　the　oxygen-rich　biochar　through　torrefaction　for　the　detoxification　of　toxic　metals　in　agricultural　wastewater.　The　optimum　operation　parameters,　kinetic,　isotherm,　and　thermodynamic　study　are　investigated.　The　influence　of　torrefaction　biochar　on　toxic　metal　adsorption　is　analyzed　by　using　site　energy　distribution　theory.　The　adsorption　mechanism　is　analyzed　by　Fourier　transform　infrared　spectroscopy　(FTIR)　and　X-ray　photoelectron　spectroscopy　(XPS).　Two-dimensional　FTIR　analysis　and　density　functional　theory　(DFT)　calculations　are　further　used　to　inquire　the　prior　interactional　sequence　between　surface　functional　groups　and　poisonous　metals.　The　results　indicate　that　the　sorption　mechanism　of　Cr(VI)　is　ascribed　to　the　adsorption-coupled　reduction　mechanism　that　some　redox-active　components　provide　electrons　for　Cr(VI)　reduction.　Surface　complexation　is　mainly　the　Cu(II)　sorption　mechanism　with　a　small　content　of　Cu(II)　reduction　to　Cu(I).　The　catechol　hydroxyl　group　is　the　main　form　of　phenol-OH　on　the　TBC　surface.　©　2022　Elsevier　Ltd