Alkalinity is defined as the capacity of a water to neutralize strong acids. In natural waters, this capacity is generally attributable to bases such as HCO 3 −, CO 3 2 and OH − as well as to species often present in small concentrations such as silicates, borates, ammonia, phosphates and organic bases. Carbonate alkalinity of process waters in mineral processing may change as a result of the seasonal climatic changes, the fresh water source and the amount of recycled process water. Any mineral processing plants in general and flotation plants in particular will have process waters with different alkalinities. Therefore, carbonate alkalinity should be of concern in flotation. The effect of alkalinity on the flotability of quartz with an amine-type collector and with sodium oleate, in the presence of calcium ions at alkaline pH values was studied. It was observed that as the alkalinity of the process water increased, the flotability of quartz decreased both with an amine type collector and with sodium oleate.