Haven't read anything about it in a while but I believe the conclusion was it wouldn't work, basically because it would take way too much iron to even start to make a dent.

There wasn't a real conclusion because the tests were always small. Governments became afraid of triggering toxic blooms and otherwise messing up coastal ecosystems and then being liable for damages, so they put a moratorium on testing [1]. Then in 2012 someone illegally tried it again anyway, with mixed results [2].

Basically it's like most geoengineering projects - everyone is too afraid of negative consequences to really try anything at scale, so instead we get endless inconclusive studies. Personally, I think we're going to pretty quickly get to the point where we need to make decisions about what negative consequences are acceptable to prevent complete environmental catastrophe.

[1] https://www.nature.com/articles/453704b

[2] http://www.planetexperts.com/two-years-russ-george-illegally...

That wasn't the conclusion. It'd make a dent, but not sufficient by itself. The real reason is people are skeptical of the wisdom of geoengineering in general. But I think we will almost certainly have to look at it.

This is what I read as well. Couple this with planting 1e12's trees, maybe aerosol injection and possibly buy some time.