Hydrated lime suspension

Synonyms kalsomine hydrated lime suspension calcium carbonate suspension. 

The hydrolysis process, ie, reaction with water, for lime is called slaking and produces hydrated lime, Ca(OH)2. Calcium hydroxide is a strong base but has limited aqueous solubiHty, 0.219 g Ca(OH)2/100 g H2O, and is therefore often used as a suspension. As an alkaH it finds widespread iadustrial appHcatioa because it is cheaper than sodium hydroxide. 

Many kinds of absorbents have been tested for wet FGD. From the points of view of a low-cost, easily available raw material with high absorption efficiency and, consequently, a smaller device requirement and lower operation costs, hydrated lime may be the best. In the wet GFD process by absorption with Ca(OH)2-in-water suspension as the absorbent, the following reactions are generally considered to occur in the liquid phase ... 

Calcium oxide (CaO, lime, quicklime, unslaked lime) is differentiated from calcium hydroxide [Ca(OH)2, slaked lime, hydrated lime] and limestone (CaC03, calcite, calcium carbonate, marble chips, chalk) by formula and by behavior. A saturated solution of calcium oxide in water is called limewater and a suspension in water is called milk of lime. 

Derivation (1) Mined from natural surface deposits. (2) Precipitated (synthetic) by reaction of calcium chloride and sodium carbonate in water solution or by passing carbon dioxide through a suspension of hydrated lime (Ca(OH)2) in water. 

The thermal decomposition of limestone - which was reported by Cato in 184 bc -at about 900 °C produces calcium oxide (lime, technically called quicklime ) (CaCOj CO2 + CaO). This is an important basic step in glass and ceramics production, and quicklime in combination with clay is also a cheap essential raw material for the cement industry. For the estimated worldwide production of cement in 1994, the consumption of limestone was about 1420x10 (metric) tons. Quicklime reacts with water to calcium hydroxide Ca(OH)2. Hydrated lime is a dry calcium hydroxide powder, while slaked lime is an aqueous suspension of calcium hydroxide particles in water. Both forms are the cheapest industrial alkaline chemical and are frequently used together with limestone as a neutralizer for acids, for example in flue gas desulfurization (see below) (Oates 1998). The annual global production of lime and lime compounds is estimated to exceed 300x10 tons, with highest amounts in China, followed by the USA, the former Soviet Union, Germany, Japan, Mexico and Brazil (Oates 2002). 

Bordeaux mixture is produced by mixing hydrated lime (9 to 12 g/1), copper sulfate (5 to 7 g/1) and cold water to produce a colloidal suspension of tetracupric sulfate. When sprayed on foliage, the mixture covers the leaves with a tenacious film which slowly releases soluble copper [30.7, 30.8]. It is effective against many fungi and insects. 

Dime slury is a form of lime hydrate in aqueous suspension that contains considerable free water. 

Milk-of-lime is a dilute lime hydrate in aqueous suspension which has the consistency of milk. 

Slaked lime is a hydrated form of lime, available as a dry powder, putty, or aqueous suspension. 

The aim of the experiments was to obtain stationary values for SO2 separation. Initially, the hold-up was sprayed with water to obtain stationary temperatures after cooling the particles and to conserve the used calcium hydroxide during the unsteady start-up phase. At the steady-state temperature the injection was suddenly switched to suspension. The SC>2-concentration at the outlet then decreased. The suspension consisted of lime hydrate (DIN 1060-CL90, DIN EN 12518) and water. The suspension injection had to be held constant until the SC>2-concentration was constant. After achieving steady state the injection was stopped, and this caused an increase in SC>2-concentration at the outlet up to the initial value. The same procedure was started after a few minutes in order to obtain a new measuring point at a higher suspension injection rate. 

After filtration, addition of sodium sulphide to the clear solution effects the precipitation of the three metals, cobalt, nickel, and manganese, as sulphides. Digestion with the calculated quantity of ferric chloride oxidises the manganese sulphide to sulphate, which passes into solution. The residue consists of cobalt and nickel sulphides, which are washed and converted into their soluble sulphates by roasting. The sulphates are extracted with water, and converted into chlorides by addition of calcium chloride solution. Their separation is effected g.s follows The requisite fraction of the chloride solution is precipitated with milk of lime, and the insoluble hydroxides of nickel and cobalt thus obtained are oxidised to the black hydroxides by treatment with chlorine. The. washed precipitate is then introduced into the remainder of the chloride solution, and the whole is well stirred and heated, when the black hydrated oxide of nickel passes, into solution, displacing tlm Remainder of. the cobalt from the solution, into. the precipitate.. The final product is thus a suspension of hydrated peroxide.of cobalt,in p. solution of nickel chloride, from which idle cobalt precipitate is removed by filtration, washed, and ignited, to the black oxide. 

Caloium Hydrate—Slacked lime—Colds hydras (Hr,)—CaH,0,—74 —is formed by the action of H,0 on CaO, If the < uantity of H,0 used be one-thirtl that of the oxide, Uxe hydrate remains as a dry, white, odorless powder alkaline iu taste and reaction more soluble in cold than in hot H. O. If the <)uantity of H,0 be greater a creamy or milky liquid remains, cream or milk of Hme a solution holding an excess iu suspension. With a sufficient quantity of H,0 the hydrate is dissolved to a clear solution, which is fime water—Liquor colds (C. 8. Hr.). The solubility of CaH,0, is diminished by the presence of alkalies, and is increased by sugar or man nice Ltq, calc, saccharatus (Hr,). Solutions of OaH,0, absorb CO, with formation of a white deposit of CaCO,. 

Reactivity to water is measured by the rate of release of the heat of hydration [13.3, 13.5, 13.6], or by the rate at which an aqueous suspension produces hydroxyl ions (which are neutralised at pH 9.2 by hydrochloric acid) [13.4]. A large number of reactivity tests have been used [13.7-13.11], The relationships between some of those test methods (for a high-calcium quicklime) are given in Fig. 13.1 (N.B., the relationships for other limes may differ significantly from those given). 

The suspension is then treated in an external reactor with fresh milk of lime containing further magnesium oxide. The magnesium hydrogen sulfite and sulfate react with calcium hydroxide, forming magnesium sulfite and sulfate, which are recycled, and precipitate calcium sulfite hemi-hydrate and gypsum (29.12,29.13). 

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