Abstract: A common method for remediating heavy metal contaminated soil in acidic mining areas is to use comprehensive soil remediation agents, including slaked lime and biochar, which can effectively alleviate soil acidity and immobilize soil heavy metals. The use of biochar or hydrochar can simultaneously remediate soil acidity and adsorb and immobilize heavy metals, but the pore properties and surface functional group activity of hydrochar need to be enhanced by targeted activation to strengthen the heavy metal adsorption capacity. A hydrochar activation process combining physical activation and chemical activation was designed from the needs of soil acidity treatment and heavy metal adsorption and immobilization, which effectively strengthened the pore structure of the sludge hydrochar and enhanced the surface functional group content to strengthen the adsorption and immobilization of common heavy metals in the mining area, and at the same time, Ca(OH)₂ and CaCO₃ were explored as the activators to reduce the high cost and the risk of further soil contamination by exogenous metal ions brought by common activation methods. The experimental results showed that the activated sludge hydrochar significantly increased the adsorption of zinc, copper, lead, cadmium and chromium, and the adsorption of chromium could reach up to 85.09 mg/g. At the same time, the use of slaked lime, which is one of the common soil remediation agent formulations, as an activator could increase the utilization rate of the chemicals. The cost analysis of the sludge hydrochar activation process showed that the activator used in the activation process cost less, the environmental risk was smaller, and the activation process had lower running cost. A green, efficient and economic solution for the targeted activation of sludge hydrochar and the development of heavy metal remediation agent for acid mine soil is provided.