Abstract: A highly stable oxidation layer is formed on the surface of pyrite after heavy oxidation, which significantly affects the adsorption of flotation reagents and increase the difficulty of the flotation recovery of pyrite. In order to realize the effective flotation recovery of heavily oxidized pyrite, the effect of oxalic acid and ultrasonic pretreatment on the floatability of heavily oxidized pyrite and the adsorption of copper ions on surface was investigated. The results of micro-flotation experiments showed that the flotation of pyrite after treated by oxalic acid pretreatment was not ideal. Even when the dosage of oxalic acid reached 2.5 g/L, the recovery of pyrite was still only 44.68%. After adding copper ions, the recovery of pyrite only increased to 48.13%. However, the recovery of pyrite significantly increased after treated with ultrasonic pretreatment. The recovery reached 79.72% when the ultrasonic power was 100 W. After adding copper ions, the recovery reached 84.77% when the ultrasonic power and time was 60 W and 2 min, respectively. This indicated that pyrite could be effectively recovered at low ultrasonic power after adding copper ions. The main reason was that the shedding degree of oxidized species on pyrite surface was low after treated by oxalic acid pretreatment. However, large amounts of hydrophilic iron oxides/hydroxides and sulfates was detached from the surface after treated by ultrasonic pretreatment, thus increasing the active sites for the adsorption of copper ions and promoting the adsorption of collectors on the surface of pyrite.