Reversing the Greenhouse effect by chemically pulling CO2 out of the atmosphere A team of scientists at Trent University (Ontario, Canada) have demonstrated a method of creating Magnesite, from Magnesium, water, and atmospheric CO2. The resulting material holds half its weight in CO2. That's the good news. The bad news is we emit 40 billion tons of CO2 into the atmosphere each year... so 80 billion tons of Magnesite per year would be needed to be net carbon neutral.

https://www.forbes.com/sites/trevornace/2018/08/15/scientists-develop-lab-made-mineral-that-will-suck-co2-from-the-atmosphere/#593da6225d78