Rice husk biochar (RHBC) and dairy manure biochar (DMBC) were prepared as sorbents for simultaneously removing Pb, Cu, Zn, and Cd from aqueous solutions. DMBC was more effective in removing all the four heavy metals than RHBC, with the removal capacities of above 486 mmol kg−1 for each metal, much higher than those of RHBC (65.5–140 mmol kg−1). RHBC showed stronger competition for metal removal than DMBC when the four metals coexisted, with Pb the least affected and Cd the most inhibited. When each metal was 1 mM in the multi-metal system, the metal removal by RHBC was reduced by 38.4–100%, much higher than that reduced by 2–40.9% for DMBC. The stronger competition for metals removal by RHBC was due to the fact that all metals competed only for the ionized phenolic-O− groups, while the removal of metals by DMBC resulted not only from the complexation with ionized hydroxyl-O− groups but also from the