Purpose <p>Heavy metal contamination poses a critical environmental challenge and biochar is a promising remediation material. The goal was to explore a preferable material among peanut shell biochar (BC), potassium phosphate-modified biochar (BCKP) and magnesium chloride-modified biochar (BCMg) to remediate contaminated environment.</p> Methods <p>Characterization of BC and batch adsorption experiments were conducted to investigate the adsorption performance of biochar for Cd²⁺ or Pb²⁺ in aqueous solution. A soil incubation experiment was carried out to assess the immobilization efficiency of BCKP and BCMg on Cd and Pb in soil. Cd²⁺ or Pb²⁺ in solution, TCLP-Cd and TCLP-Pb in soil, as well as fractions of Cd and Pb in soil were determined.</p> Results <p>The specific surface area of BCKP increased by 29.4% compared to BC. In binary Cd²⁺ / Pb²⁺ solution, BCKP exhibited equilibrium adsorption capacities of 9.82&#xa0;mg·g⁻¹ for Cd²⁺ and 118.60&#xa0;mg·g⁻¹ for Pb²⁺, respectively. BCKP reduced soil TCLP-Cd by 33.1% and decreased soil TCLP-Pb by 63.66% within 45 days. The immobilization efficiency was achieved with 3% BCKP for Pb (63.7%) and 1% BCKP for Cd (64%) compared to the control. In the soil with 1%BCKP, the residual fraction of Cd increased by 72.2% and that of Pb increased by 35.7% through the conversion of acid-soluble, reducible, and oxidizable fractions.</p> Conclusion <p>BCKP exhibited a superior adsorption performance and a significant immobilization efficiency among the three biochar under the laboratory conditions. It suggests that phosphate-modified peanut shell biochar should be established as a highly efficient amendment for the adsorptive immobilization both in solution and soil contaminated by Cd and Pb. However, its long-term stability and field-scale applicability in different type of soil require further investigation.</p> Graphical abstract <p></p>