The effect of depressant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on the flotation separation of smithsonite from calcite was studied by micro-flotation and electro-kinetic tests. The micro-flotation results showed that good floatability of both smithsonite and calcite were achieved in the presence of sodium oleate. The depressant PBTCA selectively depressed calcite without interfering the floatability of smithsonite. The mixed minerals flotation results showed that efficiency separation of smithsonite from calcite was achieved using PBTCA as the depressant. Zeta potential measurements indicated that NaOl was able to adsorb on the PBTCA pre-treated smithsonite surface, but failed to adsorb on the PBTCA pre-treated calcite surface. (C) 2019 Elsevier B.V. All rights reserved.