Hydrated Lime, or Calcium Hydroxide [$Ca(OH)_2$], is a dry powder produced through the "Slaking" of Quicklime. The process begins with the Calcination of limestone (Calcium Carbonate) in a kiln at temperatures above $900$°C to drive off $CO_2$. The resulting Quicklime ($CaO$) is then mixed with a controlled amount of water in a "Hydrator."

Technically, the "Hydration Reaction" is highly Exothermic, releasing significant heat. The resulting powder is used in civil engineering for "Soil Stabilization," where it reacts with clay minerals to form "Calcium Silicate Hydrates"—the same compounds that give concrete its strength. In water treatment, it acts as a "Flocculant" and pH adjuster, neutralizing acidic waste streams and causing heavy metals to precipitate out of solution so they can be filtered.