The froth flotation process is a commonly used method for the concentration of ores. In this process, the ore particles are selectively attached to air bubbles, which are then removed as froth, while the gangue particles (unwanted materials) sink to the bottom. The choice of ores concentrated by this process depends on their physical and chemical properties.

The given list of ores includes cassiterite, galena, zinc blende, chromite, hematite, and copper iron pyrites. Let's analyze each ore and determine whether it can be concentrated by froth flotation.

1. Cassiterite:
Cassiterite is the primary ore of tin. It has a high density and is often associated with sulfide minerals. Cassiterite can be easily concentrated by the froth flotation process due to its surface properties and affinity for air bubbles.

2. Galena:
Galena is the primary ore of lead. It has a relatively high density and is usually associated with sulfide minerals. Galena can also be concentrated by froth flotation, as it exhibits good floatability.

3. Zinc Blende:
Zinc blende, also known as sphalerite, is the primary ore of zinc. It is a sulfide mineral with a relatively high density. Zinc blende can be concentrated by froth flotation due to its surface properties and ability to form stable froths.

4. Chromite:
Chromite is the primary ore of chromium. It is a spinel mineral with a high density. However, chromite does not exhibit good floatability and is not typically concentrated by froth flotation. Alternative methods, such as gravity separation or magnetic separation, are used for chromite concentration.

5. Hematite:
Hematite is an iron oxide ore with a high density. However, it does not have good floatability and is not concentrated by froth flotation. Hematite is usually concentrated using gravity separation or magnetic separation techniques.

6. Copper Iron Pyrites:
Copper iron pyrites, also known as chalcopyrite, is a copper and iron sulfide mineral. It has a relatively high density and can be concentrated by froth flotation. Chalcopyrite is often the primary ore for copper extraction.

In summary, out of the given ores, three can be concentrated by froth flotation: cassiterite, galena, and zinc blende. Chromite, hematite, and copper iron pyrites are not typically concentrated by this process due to their surface properties and floatability.