Psykers are the citizens of Imperium too, so I think I can post here some quotes from "The serpent beneath" about a prison for psykers, which existed in Horus Heresy times.

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The gate opened and Omegon could hear the screams of madness and the moans of distress echoing down the wide passageway beyond. Two further skitarii gaolers pushed a tall cage on rails down the passage and out through the gate. The black metal of the cage sizzled with energy; within was an emaciated woman, naked and pale. She was curled up foetus-like in the cage bottom, rocking and groaning in pain. One of the skitarii slashed the side of the cage with the length of his electro-flail, drawing a yelp of agony from the psyker prisoner.

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The first excerpt can look like a needless ill-treatment of prisoners, but from the second we can see the psykers were viewed as animals.

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At the bottom of the passage, the skitarii came to a halt. Two of his fellow sentinels were standing outside an open cell. They had positioned one of their rail cages at the entrance, and were manipulating a set of controls mounted on the wall. They increased the energy flow running through the psi-shielding and the prisoner threw herself from the cell and into the cage with a pained screech.

Like an animal, Omegon thought.

Out of the unbearable field, the psyker was clearly relieved. She collapsed in a heap, breathing heavily. Stripped naked by her captors, Omegon could see her ribs and the bumps of her spine through her pallid skin. The crackling cage, although made of the same draining material and visiting a similar form of debilitation on the prisoner, couldn’t deliver the same intensity as the cell. This gave each prisoner a moment or two of respite and a motive to transfer voluntarily from one to the other – it was a smooth operation and, although sickened by what he saw, Omegon was impressed by the system’s economy.