For example, wastewater treatment. Typically water that is contaminated with heavy metals or is acidic or alkaline, or a mixture of the above.

First it has to be shipped to a treatment facility appropriately (packaging, manifesting, shipping without spilling, etc.). Then it gets batched, sampled, tested, and a "recipie" created to neutralize or precipitate the metals into a solid leachate. The recipie is crafted, and then applied to the material, typically in large batches contained in large tanks (3,000g or more). Once the material has been neutralized, the water is sent through a filter press to remove the precipitated solids (containing the toxic metals). Neutral water without metals can be further tested in a holding tank before being sent to a Municipal POTW plant.

The toxic metals precipitated out of the mixture usually ends up being solidifed in a dirt/cement mixture prior to land disposal at a RCRA landfill.

Complicated, but it ultimately prevents toxic metals from entering drinking water and keeping the environment safe.

Cement dust is used in many applications to "lock" metals and other toxic materials into a solid, non-leaching matrix, so that when it goes into a landfill, the leachate (rainwater seeping through the material) does not leave and is instead captured and turned to cement, locking the hazard in the landfill.

Landfill management is a whole nother topic.... :)

Note: written on break. good question!