Abstract: The influences of sodium hexametaphosphate on interfacial properties of fine minerals in coal flotation were investigated by many tests,including flotation,Zeta potential measurement,adsorptive capacity and theoretical calculations of extended DLVO.The flotation results showed that high content of kaolinite is unfavorable for coal flotation.An addition of 20% kaolinite decreased the coal recovery by 18.70%.At low concentration,sodium hexametaphosphate depressed the flotation of kaolinite,whereas it had little effect on coal flotation.At high concentration,sodium hexametaphosphate lost the selective inhibition ability.With 1000g/t sodium hexametaphosphate,the Zeta potentials of coal and kaolinite particles were shifted from -25mV,-39mV to -32mV and -57mV,respectively.As a result,the electrostatic repulsion between coal particles and kaolinite particle were enhanced.In addition,by adsorbing on the surface of kaolinite,sodium hexametaphosphate increased the steric hindrance repulsion and strengthened the dimensional stabilization effect when particles approached to each other.