Do they have to be repolished?
Was the counter previously sealed?
I suggest adding a layer of bees wax on your counter. You can apply a layer of wax and let it soak in with a heat gun. Don't use the heat gun too close, but you'll see the change as it penetrates the concrete. It's the variation in color that adds character
Were they sealed when installed? If so check into resealing, if not take Pam's (from Mount Shasta) advice and use bees wax as she say's.
You need to clear well and seal with a good wet look or color enhancing stone sealer. I would recommend contacting a tile installer or a granite manufacturer for product recommendations.
Resealing should bring back the shine.
You need to seal it like you do grout except with a concrete sealer then use a paste wax, buff and wax, buff until you get a nice build up. You will need to do it every year for several years until the build up protects the concrete from your cleaners and wiping. Then you will need to not use your countertops while you are restoring. You can do it ... But it will be daunting.
If you google how to reseal a cement countertop you should get many hits. I have included a link to one Instructable. If you do not want to do this yourself get in touch with someone who does this for a living. You need to clean seal and re-wax the cement. Just using wax on the cement is not going to do the job. Good luck :)
Sand off the existing finish with an electric sander. Use the finest grit available. Wipe up all the dust. Coat with two coats of Marine Varnish. Follow the directions very carefully on the can.
Not only will your counter shine like mad, it will repel water and hold up to the most viscous stains for years!
Hint. That dust will go everywhere. Wear a mask and 'tent' the space as closed in as possible to keep the mess in place. in then seal with 2-3 Varathane (marine varnish)Will seal and keep your shine for years to come. Let cure thoroughly btwn coats. 1-2 days each..