for froth flotation, the ground ore is mixed with water to form a slurry and the desired mineral is rendered hydrophobic by the addition of a surfactant or "collector" chemical (although some mineral surfaces are naturally hydrophobic, requiring little or no addition of collector). the particular chemical depends on the nature of the mineral to be recovered and, perhaps, the natures of those that are not wanted. as an example, sodium ethyl xanthate may be added as a collector in the selective flotation of galena (lead sulfide) to separate it from sphalerite (zinc sulfide). this slurry (more properly called the "pulp") of hydrophobic particles and hydrophilic particles is then introduced to tanks known as "flotation cells" that are aerated to produce bubbles. the hydrophobic particles attach to the air bubbles, which rise to the surface, forming a froth. the froth is removed from the cell, producing a concentrate ("con") of the target mineral.