The ants are in the upper center of the photo and tiny, only about 2mm long. They have collected this flotsam and jetsome. At first I thought it was just a pile of dust in the corner and swept it away but in a few hours the'd collected a new pile. I really can't tell what any of it is. For scale the pile is 3cm wide.
CLOSED: Tiny Busy Ants
This looks like a 'kitchen midden' - these may include discarded food scraps, ant corpses, and other detritus. Some species of small ants seek out and scavenge in the middens of larger species.