How do I get rid of alkali in my basement cement?

I i don't have much experience with that but there's a product call Creteclean, as at Home Depot. From my quick research it sounds like a waterproofing issue, that once cleaned off, may need to seal the concrete. Maybe a dehumidifier would help.

Efflorescence is what you have. Moisture in the in the wall reacting with the salts in the concrete. You would need to wire brush off what you can. Clean the surface with a 50/50 mix of vinegar and water. Patch any damaged areas woith concrete patch. The use Drylock waterproofing paint. If it comes back you have an exterior moisture problem.

Alkaline in Cement is usually caused by either: Coooer or Iron in the aggregates. Commonly: pouring over nails and other demolition will cause Spots in Concrete, Cement or Mortar. Best way to rid yourself of this is alot like as I just responded to a Woman with Yellow Spots (Rust) coming through Linoleum. You need to remove the Source of the Rust.

1. Use A Small Masonry Hole Saw, 3/4 inch, without the Center Bit, to remove a Very Tiny Area of the Cement enough to get at the rusty nails.

2. Remove any nails that are rusty (by prying these up with a Sharp Flathead Screwdriver and a Board as the Fulcrum) And clean the area with ajax or pine sol.

3. If the Nail is essential to structure, Screw in a Galvanized Steel Screw of a Size equivalent to a 12D nail into the Spot where the Rusty Nail was.

4. Pour Cement into that hole, Smooth it and proceed to the next spot.

Once you do those, then you seal the entire as Kelli M. Said.

Yes, these are all good answers above. Find the source of the efflorescence and treat it first.