Barium sulfate is an inorganic salt that is completely insoluble in water. It is used as a radiocontrast agent in medical imaging tests since it absorbs x-rays better than human tissues. When mixed with water, barium sulfate forms a heterogeneous mixture since it doesn't dissolve. Specifically, the solid particles form a suspension in the water. The solid is easy to separate from the water a couple of different ways. You could put the mixture in a centrifuge. The solid would be pressed down to the bottom of the tube and the water could simply be poured off the top. You could also pass the suspension through a paper filter using vacuum suction pressure. The water will pass through the paper and the solid will be collected in the paper filter.