The key difference between quicklime and hydrated lime is that the quicklime (or burnt lime) contains calcium oxide whereas the hydrated lime (slaked lime) contains calcium hydroxide.
The major source for both quicklime and hydrated lime is the limestone. Therefore, like limestone, these compounds are also alkaline. We call quicklime as “burnt lime” because we produce it by the thermal decomposition of limestone. We call hydrated lime as “slaked lime” because we produce it by quenching quicklime with water.
What is Quicklime?
Quicklime is calcium oxide. We produce it by the thermal decomposition of limestone. Therefore, we call it “burnt lime”. Limestone contains calcium carbonate. We burn this material to above 825 °C. we call this process “calcination”. It liberates carbon dioxide forming quicklime. This substance is relatively inexpensive.
The chemical formula of the compound is CaO. Its molar mass is 56.07 g/mol. It appears as a white to pale yellow powder. Moreover, it is odorless. The melting point and boiling points are 2,613 °C and2,850 °C respectively. This compound is highly water soluble; it forms calcium hydroxide. The crystal structure of this compound is cubic.
There are many uses of this compound which includes its applications in basic oxygen steelmaking process, in the production of aerated concrete blocks, as a component in producing glass, organic chemicals, etc. Moreover, it is a key ingredient in producing cement.
What is Hydrated Lime?
Hydrated lime is calcium hydroxide. We call it “slaked lime” as well. This is because we produce calcium hydroxide via quenching calcium oxide with water. In addition to that, there are many other synonyms for this compound, i.e. caustic lime, builder’s lime, slack lime, pickling lime, etc. A saturated solution of calcium hydroxide is called “lime water”.
The chemical formula of this compound is Ca(OH)2. The molar mass of this compound is 74.09 g/mol. It appears as a white powder and is odorless. The melting point is 580 °C, and it decomposes upon further heating (it releases water vapor). However, the solubility of this compound in water is poor.
Hydrates lime is available as either a powder or as granules. However, the end product given from the production process appears as a dry, powder-like flour which has a light (mostly white) color. The uses of this compound are in flue gas treatment, neutralizing industrial wastewater, etc.
What is the Difference Between Quicklime and Hydrated Lime?
Quicklime is calcium oxide with the chemical formula CaO whereas, hydrated lime is calcium hydroxide with the chemical formula Ca(OH)2. This is the key difference between quicklime and hydrated lime. Furthermore, the molar mass of quicklime is 56.07 g/mol while the molar mass of hydrated lime is 74.09 g/mol. Moreover, the melting point and boiling point of quicklime are 2,613°C and 2,850°C respectively whereas the melting point of hydrated lime is 580°C, and it has no boiling point because it decomposes upon further heating (it releases water vapor). Moreover, there are many uses of both these compounds. Quicklime is useful in basic oxygen steelmaking process, in the production of aerated concrete blocks, as a component in producing glass, organic chemicals, etc. while hydrated lime is useful in flue gas treatment, neutralizing industrial wastewater etc.
The below infographic presents more details on the difference between quicklime and hydrated lime in tabular form.
Summary – Quicklime vs Hydrated Lime
We produce quicklime from limestone and hydrated lime from quicklime. The key difference between quicklime and hydrated lime is that the quicklime contains calcium oxide whereas the hydrated lime contains calcium hydroxide.
1. “Calcium Oxide.” Wikipedia, Wikimedia Foundation, 3 Aug. 2018. Available here
2. “Usage of Hydrated Lime (Calcium Hydroxide) & Quick Lime (Calcium Oxide) | Sodimate Inc.” Sodimate, 2 Jan. 2018. Available here