Rust is the result of the reaction of iron with water to create a series of oxides.  Scientifically intriguing, aesthetically unsightly, especially when it ends up on your carpet.   If you have rust stains

Rust stains are difficult to remove and often require commercial rust removing products such as oxalic acid crystals.  Before using any such products read the warning label carefully and be sure you know what fiber material your carpet is made from.

Any rust removal attempts are going to be risky in terms of the welfare of your carpet so be sure to test any methods in an inconspicuous area before applying directly to the carpet.

Homemade Solution

Salt and lemon juice can sometimes remove rust from fabrics and may be worth exploring as an alternative carpet stain remover.  Sprinkle salt on the stain, squeeze enough lemon juice over the stain to cover it, and allow it to soak in the sunlight.  Keep in mind that lemon juice is known to lighten colors and could cause your carpet to lighten.  

Rust Warning

Chlorine bleach is known to set rust stains so even if the stain has marred a white t-shirt do not attempt to remove it with bleach.

Rust Prevention

Rust can be caused from the legs of your furniture.  If you are planning on steam cleaning your carpets, place a protective barrier between the furniture legs and your wet floor such as plastic wrap or wax paper.