This article bothered me more than it should. After some reflection wondering why I think it breaks into a few things, some of which have already been mentioned.
Firstly, the author's casual disregard of the Laws of Thermodynamics in critiquing the implications of scaling up such technology is rather surprising given he holds a PhD in Geology. ThurberMingus already pointed out that the energy required to turn CO2 back into C + O2 would be AT LEAST (2nd Law, entropy sucks) as much as was generated by its first burning. Of course as Devac says it may hold up should you have a huge quantity of renewable energy at your finger tips, but while someone in the world is burning coal, then any energy you use to reverse the oxidation process of coals is going to be greater than was generated so you are simply going to make matters worse.
Secondly, the reason for getting excited about this apparently is that other sequestering technologies trialled by among others the author's former employer, Shell, are very expensive. So some discussion on why they are would be helpful. The general challenge with sequestering as I understand it is a combination of three tricky things: 1) CO2 in the atmosphere is very spread out, it doesn't collect conveniently in the corner of the room (Again, 2nd Law). 400 parts per million means you have to process through an awful low of air. The density of air is 1.2 kg/m3 of which by weight CO2 is 0.06% or 0.7g. So to even collect 1T of CO2 in the air - you need to get through 1.4 million cubic metres of air - fair enough a jet engine can suck this much up in half an hour or so, but that is hardly a cost effective machine. 2) Once you have collected the air you then have to scrub the CO2 out from it using some form of chemical reaction, so this air needs to be put through a reactive liquid or surfaces that can remove at a high degree of efficiency. If you can only scrub out 50% of the CO2 for example then you would need another 1.4million cubic metres of air to suck into your reactor. 3) Then in order to sequester the CO2 you need to take it into an inert non gaseous form through pressure, temperature, solvent or chemical transformation.
So based on these three challenges, this tech seems only to speak for problem 3). Of course if you put your reactor on the chimney of a power plant, 1) and 2) become much easier, but then you can't solve the energy problem with renewables. This is starting to sound a bit more like that perpetual motion machine I have in my attic or the cold fusion reactor in my car.
In any case the article is not specific on what problem the tech is trying to solve so hard to place it.
Finally the closing comment states "The international research team from Germany, China, the United States and Australia believes this is a first step toward an abundant and inexpensive method to remove carbon dioxide from the atmosphere and repurpose it as solid coal." Well they would wouldn't they, research funding is so vital to their daily bread. In the end though I am left wondering whether articles like this just give enough of an excuse for folks to simply have faith in technology solving everything rather than confronting the tough choices now. Don't get me wrong, sequestering is going to be a vital tool. But like Applewood I feel, nature has provided us with both plants and the oceans - both huge carbon sinks, that promise more than reversing the combustion process.
Maybe I have got the wrong impression here, so please jump in and correct me. Wanted to test whether what was bothering me about this is just me.