The way you were saying it, 'Dust' seems to be a substance that cannot be replenished by simply recharging. From what you're saying, if the character cannot passively generate the material, the guy will burn out. Even if he can retrieve some of it after an attack, the reacquistion rate will not be absolute. If it was, then there's no point in writing the character as such.

What you're proposing's not going to fly if everything is as you stated, I believe; also, reabsorbing it in the middle of a fight seems kinda... Difficult.
Then there's also the issue of diffusion. The longer he does without said reabsorption, the harder it is to gather everything. And, you know, things diffuse pretty damn fast.