To reduce the negative effects of lizardite on the flotation of pentlandite,chemical suppliers amino trimethylene phosphonic acid(ATMP) was tested as a potential depressant for lizardite. Micro-flotation test results indicated that the flotability of pentlandite restored in pentlandite-lizardite system by the addition of ATMP. The adsorption and ICP results indicated that ATMP interacted with the Mg species of lizardite surface meanwhile a part of the Mg ions were dissolved from lizardite surface. XPS tests illustrated that ATMP changed the surface characteristics of lizardite mineral and the Mg/Si atomic ratio decreased on lizardite surface. Zeta potential measurements demonstrated that the lizardite zeta potential was changed from positive to negative after interacting with ATMP, which caused the electro-steric repulsion between pentlandite and lizardite particles, and thus the pentlandite floatability was restored.