Hydrated lime (calcium hydroxide)

Calcium oxide reacts with water releasing a considerable amount of heat to form calcium hydroxide.

CaO + H2O => Ca(OH)2 + heat

The reaction requires about 320 gr. water for each kilogram of calcium oxide. Additionally, the heat released by the reaction usually causes a large amount of slaking water to evaporate. In practice, the process is steered so that the amount of water used is exactly equal to that required by the reaction and the subsequent evaporation. The result is a dry, powdery hydrated lime.

Lump lime is first pre-crushed and then stored in silos in grain sizes ranging from 0 to 10 mm. From there, the burnt lime is fed via a dosing unit into the first stage of the slaking plant where it is mixed with a precise quantity of water in two counter-rotating paddle shafts. The process is carried out under constant temperature control. Considerable heat is released by the reaction causing the water to boil. The mixing motion creates a sort of fluidized bed. The reaction causes calcium oxide particles to decompose resulting in the formation of fine calcium hydroxide.

The desired high-quality hydrated lime is then separated by means of an air-classifier. Depending on how the product will be used nekapur® 2 (building lime quality) or nekablanc® 0 (very fine hydrated lime for special applications) are produced.

Both products can be transported in bulk by rail or truck as well as bagged in bags of up to 25 kg. Similarly to other lime products, nekapur® 2 and nekablanc® 0 are available in big bags (around 800 kg), too.

Mixed with sand and a variety of additives and binders, nekapur® 2 is used for the production of plasters and mortars. Calcium hydroxide sets on contact with air by reacting with carbon dioxide (effectively the opposite process to calcination):

Ca(OH)2 + CO2 => CaCO3 + H2O.

The slaked lime used in this process should be of the desired grain size (not too coarse, not too fine). Under no circumstances should hydrated lime contain unslaked particles (reactive lime) that could result in the plaster cracking and eventually falling off. In addition, hydrated lime should be very white in colour.

nekapur® 2 – similarly to nekafin® 2 – is used to prepare milk of lime, a basic agent used for the neutralisation and treatment of industrial waste effluents.

Hydrated lime has been proven to have a positive effect on the durability of asphalt pavements. The use of a quantity of 1.5 to 2 % by weight of the pavement mixture has proved to be optimal. Calcium hydroxide improves the adhesion of bitumen to the surface of rock particles. The addition of calcium hydroxide also helps make the expanding components of mineral fillers innocuous.

nekablanc® 0 is also used in the form of milk of lime as a substitute for sodium hydroxide solution in the bleaching of paper pulp. Here calcium hydroxide acts as an alkaline activator for hydrogen peroxide. In order to prevent peroxide from decomposing the calcium hydroxide used in the process should be free of any heavy metals. The improved grain fineness of nekablanc® 0 enables calcium hydroxide particles to dissolve very rapidly.

The manufacture and processing of PVC materials involve the use of stabilizing chemicals such as acid scavengers; heavy-metal free systems often containing calcium stearate and calcium hydroxide are increasingly being used to this end. nekablanc® 0 meets the highest grain-fineness and purity requirements for direct use as calcium hydroxide or for the manufacture of calcium stearate.

nekablanc® 0 is also used as raw material for the production of a wide range of calcium compounds used for applications within the chemical industry for which highly pure calcium hydroxide is required.