Selective separation of silica from a siliceous-calcareous phosphate ore that had been sieved into different size fractions is investigated by a combination of chemical analysis,zeta potential measurement and FTIR and XPS techniques.Scrubbing is a better choice than flotation for removing silica from the coarse fractions.The P_2O_5 grade of the coarse fractions is increased to about 30%by scrubbing and the product yields are higher than those obtained by flotation.The silica in the fine fraction is separated by reverse flotation.An alkyl amine salt(DAH)is an effective collector and the P_2O_5 grade of the fine fraction can be increased by 7%to beyond 30%under acidic conditions.The higher zeta potential obtained using DAH suggests that it is more strongly absorbed onto the ore particles than the other cationic collectors. FTIR and XPS results confirm physical absorption of the cationic collector onto the ore surface.They also indicate that calcite is dissolved at low pH values,which increases the Si concentration on the ore surface. Selective separation of silica from a siliceous-calcareous phosphate ore that had been sieved into different size fractions is investigated by a combination of chemical analysis, zeta potential measurement and FTIR and XPS techniques. Scrubbing is a better choice than flotation for removing silica from the coarse The P_2O_5 grade of the coarse fractions is increased to about 30% by scrubbing and the product yields are higher than those obtained by flotation. The silica in the fine fraction is separated by reverse flotation. An alklamine amine salt (DAH) is effective collector and the P_2O_5 grade of the fine fraction can be increased by 7% to beyond 30% under acidic conditions. The higher zeta potential obtained using DAH suggests that it is more strong absorbed on the ore particles than the other low-level collectors. FTIR and XPS results confirm physical absorption of the cationic collector onto the ore surface. The same also that that calcite is dissolved at low pH values, which inc reases the Si concentration on the ore surface.