Prediction of heavy metals adsorption by hydrochars and identification of critical factors using machine learning algorithms

•Four machine learning models are used to predict the adsorption of hydrochar.•Gradient boosting decision tree predicts the best performance with R2 of 0.93–0.98.•The process of heavy metal adsorption by hydrochar is mainly chemisorption.•The range of the C/H/O/N content of the optimal hydrochar is specified.