One of the best ways to scrub CO2 is with calcium and oxygen. Seawater has the biggest testament to this, as the ocean floor is completely covered in substances called calcium carbonates. This is the same mineral that small animals use to make seashells. It forms as a result of underwater volcanic eruptions, which spew thousands of tonnes of Co2 into the ocean. This is really the most efficient and effective way to get rid of CO2, as our oceans have been doing it for tens of thousands of years. If you counted up all the CO2 that's locked into calcium carbonates and released it into the atmosphere, our air would have more CO2 in it than Venus (which, as you know, has a runaway greenhouse effect resulting in temperatures of well over 1000 degrees). In fact, the only real difference between Earth and Venus in that respect is that Earth is 75% Ocean (on the surface). There are two power plants in the EU that are pumping their CO2 into a process similar to this. One pumps CO2 in liquid form straight underwater to the ocean floor, where it stays and slowly "dissolves" into seashells. The other one, in Germany, is pumping CO2 into the ground where they are hoping it will seep into saltwater aquifers and precipitate there.