Since the Iron Council is the most complicated of these three encounters (and because it has two alternate, or hard modes, we'll discuss it last. Of course, as a warrior you'll either be tanking or DPSing in these fights... there's simply no alternative role for warriors... but there's more to it than that in each case. Let's start with Kologarn.
Kologarn is not a terribly complicated fight for a DPS warrior. You park yourself at his belt, switch between targeting the arms and his torso (you can hit all three from the belt) and go nuts. Usually (in my experience anyway) the raid leader will call for DPS to shift depending on whether or not you're going for an achievement or not - it's very possible to kill Kologarn merely by shifting DPS from his right arm to his torso repeatedly until he is dead.
It is very important as someone in melee range to not stand there when you get Focused Eyebeam. The strategy I'm used to implementing when I am targeted by this ability is to move immediately to the back of the room you engage Kologarn in then follow the wall until the beam stops targeting me, but regardless of how your particular raid deals with it, it can be very easy to get tunnel vision and focus on your DPS to the exclusion of paying attention to the area around you. This ability of Kologarn's means that if you do this, you will get yourself and somebody else killed. There's enough damage being thrown around in this fight between the Stone Shouts, Shockwaves, and the Rubble's Stone Nova abilities without a DPS forgetting to move during Focused Eyebeam.
As a tank, you will have other things to occupy you. On 10 man, you can have one tank for Kologarn and one tank to pick up the rubbles spawned when the Right Arm dies, but on 25 man you'll want at least two tanks for the torso itself to allow the Crunch Armor debuff from Kologarn's Overhead Smash to fall off. (As far as I can tell, on ten man the debuff falls off on its own, I've solo tanked Kologarn in 10's twice recently and have been told this was patched in after release.) If you are tanking Kologarn you must stay within melee range. If his aggro target isn't in reach of his Overhead Smash he'll cast Petrifying Breath on the raid. That would be bad, very very bad in fact. 15k (20k heroic) damage raid wide every second will most likely wipe your raid in two seconds at the minimum.
Meanwhile, if you're not tanking Kologarn's body, then tanking his arms is fairly unimportant: they just do their thing, and the Right Arm will most likely be focused down every time it appears. However, when it goes down there's another job for a tank. You'll have to pick up the four adds it spawns, the rubbles, and get them away from the rest of the raid as quickly as you can. (We usually just have everyone move away from the rubble tank, who sits around where the arm was, but other raids most likely have other strategies.) All a tank has to do is keep the Rubbles and their Stone Nova at least 10 yards away from the rest of the raid. Rubbles can be stunned by a Shockwave and the ranged DPS can pretty easily AoE them down so long as they don't get close, so warriors are a reasonably good choice to tank these.
Auriaya is a fight that can see DPS and tanking warriors utilized in several roles. If you're a warrior tank, you'll either be tanking Auriaya or one of the adds she starts the fight with (2 on normal, four on heroic). Even if you're a DPS warrior, depending on how many tanks your raid has available you may find yourself throwing on a shield and blowing all of your tanking cooldowns to hold a Sanctum Sentry just long enough for your raid to get a real tank to taunt it off of you. (Not that I've ever found myself panicking and wishing I'd switched my spec to prot, oh my no.) The Sentries aren't terribly complicated. Spread them out so that the Strength of the Pack buff doesn't stack up (many a tank has died on this pull when all four are close and get the buff, we often use a bubbled pally or a DK blowing all his cooldowns to survive getting the attention of all four buffed adds at once) and then they get burned down by focus fire (or offtanked if you're out for an achievement).
If a warrior is tanking Auriaya herself then he can break the fear effect of her Terrifying Screech and interrupt her Sentinel Blast more or less by her/himself. If not, then a DPS warrior is an excellent choice to break fear and pummel her Sentinel Blast - when I DPS on this fight I often dedicate myself to this role, and it's possible as a warrior to catch every fear and break every cast solo. Since you'll want to have at least a few higher armor characters standing stacked on the tank to absorb Sonic Screech (it's physical damage, so not only is it split between everyone in its path, it's mitigated by armor) fury warriors are an excellent choice for pummel duty. Arms warriors would have to switch stances, taking a lot more of their DPS time, but they can serve in a pinch. (My own raid stacks everyone in front of Auriaya to maximize the spread of Sonic Screech, but not all raids do this.)
The final complication for this fight is the Feral Defender. Due to the way warriors DPS (Bladestorm/Whirlwind) we can often accidentally help contribute to the Defender dying in the raid, which is very very bad. When the Defender dies, he spawns a void zone-like effect right where he died which is quite capable of killing a raid fairly quickly if they don't move out of it. If a warrior tank is outside of the raid he can taunt the Defender then Conq and Shockwave it to try and keep it in place until it can be killed safely, but it should be admitted that a DK with Death Grip is probably the best choice to yank the Defender out prior to death.