[eber]

I believe the cycle they are referring to is:

2 CO2 + H2O + CaSiO3 -> Ca^2+ + 2HCO3- + SiO2

and

Ca^2+ + 2HCO3- -> CaCO3 + CO2 + H2O

https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cyc...