One thing people are supposed to learn in high-school
chemistry class is that you have to balance the equation.
Stuff that starts out on one side of the equation doesn't
just disappear; it has to wind up on the other side of
the equation in one form or another.
For centuries, the carbon-fuel industry has pretended
that CO2 just disappears. This is nonsense, and it
can no longer be tolerated. CO2 is a bad thing, and
it is cumulative (on any relevant timescale).
Hypothetically, it is possible to write a balanced CO2
equation with non-disastrous end products as follows:
CO2 + CaSiO3 --> ... --> CaCO3 + SiO2
CO2 + wollastonite --> limestone + sand
This happens naturally on a timescale of hundreds of
years. Alas that is nowhere near fast enough to be
relevant.
Hypothetically you could speed this up so that it
becomes relevant, as follows: Every time you mine
a ton of coal you also mine 10 tons of wollastonite,
grind it to a fine powder, and dump it in the ocean.
That hypothesis has a fatal flaw: the cost of mining
wollastonite (or any similar mineral) is comparable to
the cost of mining coal, on a ton-for-ton basis. So
balancing the equation increases the cost of burning
coal by an order of magnitude.
That's never going to happen, because even a small
increase in the cost of burning coal will make it
economically non-competitive with solar energy.
Similar arguments apply to other fossil carbon fuels.
Similar arguments apply to other sequestration schemes.
Balancing the equation is not a problem for biofuels
*provided* you don't use appreciable amounts of fossil
carbon in the course of producing the biofuel.