calcium hydroxide

calcium hydroxide
Name	Calcium hydroxide
Othernames	Slaked lime; Hydrated lime; Pickling lime
Formula	Ca(OH)2
Molar mass	74.093 g·mol−1
Appearance	White crystalline powder or colorless crystal
Density	2.211 g·cm−3 (solid)
Melting point	Decomposes at 580 °C
Solubility	Slightly soluble in water (1.65 g·L−1 at 20 °C)
Hazard	Corrosive; causes skin and eye irritation

calcium hydroxide

Calcium hydroxide is an inorganic compound commonly known as slaked lime or hydrated lime. It appears as a white powder or colorless crystal and is the principal product of adding water to calcium oxide derived from limestone. Widely used across industries, it plays roles in construction, water treatment, chemical synthesis, agriculture, and cultural technologies.

Chemical properties and structure

Calcium hydroxide is an ionic solid composed of Ca2+ cations and hydroxide (OH−) anions, adopting a layered crystal structure analogous to the brucite prototype; typical X-ray diffraction investigations reference methods similar to those used for Diamond or Graphite studies. Its basicity is strong in aqueous solution, forming alkaline suspensions historically characterized alongside studies of Sodium hydroxide and Potassium hydroxide in 19th-century inorganic chemistry; equilibrium and acid–base titrations often compare its dissociation to reactions explored in classic texts alongside Sulfuric acid and Hydrochloric acid. Solubility is limited and temperature-dependent, a feature that parallels solubility data compiled for salts like Calcium carbonate and Magnesium hydroxide. Thermal decomposition produces calcium oxide and water, a reversible reaction conceptually related to high-temperature processes investigated in studies of Cement and Portland cement manufacture. The compound participates in carbonate equilibria with atmospheric Carbon dioxide to yield calcium carbonate, a process analogous to carbonation phenomena observed in archaeology at sites such as Pompeii and Machu Picchu conservation projects.

Preparation and production

Industrial production begins with calcination of quarried Limestone (chiefly composed of Calcite and Aragonite) to produce calcium oxide, a process historically linked to lime kilns like those discussed in accounts of Industrial Revolution infrastructure and 19th-century engineering referenced alongside works on Isambard Kingdom Brunel. Hydration of calcium oxide yields calcium hydroxide in processes comparable to hydration steps described for Cement kilns in modern Portland cement plants. Large-scale plants employ rotary kilns and slaking towers similar in engineering scope to installations used by companies with histories akin to LafargeHolcim or CEMEX. Smaller-scale preparation, as in traditional lime slaking for mortar used in restoration projects at Notre-Dame de Paris or St Paul's Cathedral, follows long-established empirical procedures dating back to classical construction practices described in treatises from the era of Vitruvius and the Renaissance.

Uses and applications

Calcium hydroxide is multifunctional: in construction, it is a primary component of lime mortar and renders used in conservation of monuments like Westminster Abbey and Chartres Cathedral. In water and wastewater treatment, it is applied for pH correction and softening, a role paralleled in treatment systems in major urban utilities such as those in London, Paris, and New York City. In the food industry, it is used for nixtamalization of maize—an ancient process tied to cultures around Teotihuacan and Mesoamerica—and in sugar refining alongside technologies developed in industrial centers like Liverpool and Bristol. In agriculture it adjusts soil pH, the same agricultural interventions discussed in agrarian reforms during the eras of Thomas Jefferson and Justus von Liebig; in flue-gas desulfurization it contributes to sulfur capture in systems referenced in studies of emissions control at power plants such as those in Pittsburgh and Bełchatów Power Station. It also serves as a reagent in inorganic synthesis, leather processing in historical contexts like the Industrial Revolution, and niche uses in art conservation projects at institutions including the Louvre and the Metropolitan Museum of Art.

Safety and handling

Calcium hydroxide is corrosive: contact can cause skin and eye burns and inhalation of dust can irritate respiratory passages; workplace controls draw on occupational safety frameworks developed by agencies such as Occupational Safety and Health Administration and European Chemicals Agency. Personal protective equipment standards recommended by groups like American National Standards Institute and protocols used in labs at universities such as Harvard University and University of Cambridge apply; emergency response follows guidelines similar to those published by National Fire Protection Association and Centers for Disease Control and Prevention. Storage requires dry conditions to prevent carbonation; handling procedures mirror those for other alkaline solids used in industrial operations of multinational firms such as BASF and Dow Chemical Company.

Environmental impact

Environmental effects stem from alkalinity and particulate release: runoff can raise pH in aquatic systems affecting organisms monitored in studies at locations like the Great Barrier Reef and Chesapeake Bay. Production emits carbon dioxide during limestone calcination, contributing to greenhouse gas inventories assessed in reports by the Intergovernmental Panel on Climate Change and mitigation efforts explored by organizations like the International Energy Agency. Carbonation of calcium hydroxide in the environment sequesters CO2 to form calcium carbonate, a process investigated in carbon capture and utilization research programs at institutions such as Massachusetts Institute of Technology and ETH Zurich. Remediation strategies and regulatory frameworks are informed by policy discussions from bodies including the United Nations Environment Programme and regional agencies like the Environmental Protection Agency.

Occurrence and history

Natural analogues of calcium hydroxide are rare, but modern awareness traces to medieval and classical uses of lime in Roman engineering projects such as aqueducts and mortars of Ancient Rome and plasterwork in Ancient Egypt. Advances in systematic chemistry during the 18th and 19th centuries, involving figures and institutions like Antoine Lavoisier, Justus von Liebig, and the early laboratories of the Royal Society, clarified its composition and reactivity. Industrialization expanded lime production alongside developments in kiln technology central to the Industrial Revolution and infrastructure growth in cities like Manchester and Glasgow. Ongoing research into sustainable production and applications connects modern scientific centers including Stanford University, Imperial College London, and multinational corporations pursuing low-carbon technologies.

Category:Calcium compounds