“Calcium hydroxide” “lime” “slaking”
224850499
Effects of organic additives on calcium hydroxide crystallisation during lime slaking
Abstract Organic compounds, often used in cement systems as admixtures, may affect the crystallisation and carbonation kinetics of Ca(OH)2, an important phase of hydrated cement. Here, we investigated changes in Ca(OH)2 morphology in the presence of 3 organic compounds, commonly encountered in cement and lime based materials: sucrose, pectin and calcium lignosulfonate. The additives were introduced either before or after lime slaking to determine the influence of temperature. Ca(OH)2 crystals and supernatant solutions were characterised at time of slaking and after 6 months of ageing using scanning electron microscopy, X ray diffraction and optical emission spectroscopy. Our results indicate that the morphology of Ca(OH)2 crystals is modified by the characteristics of the organic molecules which promote formation of Ca(OH)2 with habits that can result in faster carbonation, an effect that is detrimental to cement used in reinforced concrete. These effects are enhanced when the additives are introduced before slaking, likely as a result of thermal degradation.
Cecilia Pesce Giovanni L Pesce Marco Molinari Alan Richardson
101925474
Effect of Lime Slaking Conditions on Activity of Calcium Hydroxide
In order to prepare the lime milk with high activity and good dispersion,the influence of operating parameters including the slaking temperature,mass ratio of H2O and lime,aging time on the activity of Ca(OH)2 was researched.The slaked lime products were characterized by laser particle analyzer and scanning electronic microscope.The results show that the optimizing conditions are that the slaking temperature is 84 ,the mass ratio of H2O and lime is 5:1 without the need for aging.Under this condition,lime milk can reach a higher activity and have a better dispercenty.
Guo Zhiwei
26261838
Kinetics and Mechanism of Calcium Hydroxide Conversion into Calcium Alkoxides: Implications in Heritage Conservation Using Nanolimes.
Nanolimes are alcohol dispersions of Ca(OH)2 nanoparticles used in the conservation of cultural heritage. Although it was believed that Ca(OH)2 particles were inert when dispersed in short chain alcohols, it has been recently shown that they can undergo transformation into calcium alkoxides. Little is known, however, about the mechanism and kinetics of such a phase transformation as well as its effect on the performance of nanolimes. Here we show that Ca(OH)2 particles formed after lime slaking react with ethanol and isopropanol and partially transform (fractional conversion, a up to 0.08) into calcium ethoxide and isopropoxide, respectively. The transformation shows Arrhenius behavior, with apparent activation energy Ea of 29 4 and 37 6 kJ mol( 1) for Ca ethoxide and Ca isopropoxide conversion, respectively. High resolution transmission electron microscopy analyses of reactant and product phases show that the alkoxides replace the crystalline structure of Ca(OH)2 along specific [hkl] directions, preserving the external hexagonal (platelike) morphology of the parent phase. Textural and kinetic results reveal that this pseudomorphic replacement involves a 3D diffusion controlled deceleratory advancement of the reaction front. The results are consistent with an interface coupled dissolution precipitation replacement mechanism. Analysis of the carbonation of Ca(OH)2 particles with different degree of conversion into Ca ethoxide (a up to 0.08) and Ca isopropoxide (a up to 0.04) exposed to air (20 degC, 80% relative humidity) reveals that Ca alkoxides significantly reduce the rate of transformation into cementing CaCO3 and induce the formation of metastable vaterite, as opposed to stable calcite which forms in untransformed Ca(OH)2 samples. Similar effects are obtained when a commercial nanolime partially transformed into Ca ethoxide is subjected to carbonation. Such effects may hamper/delay the strengthening or consolidation effects of nanolimes, thus having important implications in the conservation of cultural heritage.
Langmuir the ACS journal of surfaces and colloids
Carlos Rodriguez-Navarro Irene Vettori Encarnacion Ruiz-Agudo
137688992
Microstructural Changes of Lime Putty during Aging
AbstractThe microstructural development of lime putty is widely recognized and commonly associated with an increase in quality. Many heritage institutions encourage the systematic application of lime putties in conservation; however, all the issues associated with age are not fully understood. Changes occur during storage underwater, which traditionally took place in pits to prevent carbonation. The properties of mortars, plasters, and decorative finishes formed from lime putties are intimately linked to manufacturing parameters such as storage time. The hydration of calcium oxide was investigated using an environmental scanning electron microscope with particular attention to the nucleation of calcium hydroxide crystals on the surface of calcium oxide. Crystal modifications were monitored. The results obtained confirm and quantify the influence of slaking time in the microstructure of lime putties that is also reflected in the current referred special characteristics of the mortars produced with them, su.
Maria Goreti Margalha Antonio Silva Maria do Rosario Veiga Jorge de Brito Richard James Ball Geoffrey C Allen
53586981
Dolomitic limes: evolution of the slaking process under different conditions
Abstract Dolomitic lime based pastes were prepared in order to study the evolution of the compounds during the slaking process. Thermal studies as well as X ray diffraction and FT IR spectroscopy were used to confirm the formed compounds. The rate of the hydration of calcium and magnesium oxides has been determined under different conditions: atmospheric conditions, CO 2 rich and enclosed environment without CO 2 Also the lime powder evolution without water added was studied. Whereas CaO hydrates at a higher rate, MgO is very dependent by its particle size distribution and stirring. The paper also focuses on the carbonation process. Given that carbonation is the most usual hardening process in lime pastes, its knowledge is necessary to understand the mechanical behavior of these pastes. In an excess of water, calcium hydroxide carbonates giving calcite if exposed to CO 2 In lime powder, another mechanism has been established through vaterite formation. Magnesium hydroxide does not carbonate under normal conditions. In a CO 2 atmosphere nesquehonite (MgCO 3 *3H 2 O) has been checked found as a result of carbonation.
J Lanas Jose Ignacio Alvarez
115422371
Method and apparatus for lime milk in line arranged for producing a fiber web machine in connection with the PCC in line manufacturing process
A method and apparatus for in line production of milk of lime into an in line production process of PCC arranged in connection with a fibrous web machine. In the solution, lime is slaked in a slaking apparatus at a temperature of at least 80 degrees. The produced milk of lime is cleaned by separating excessively large calcium hydroxide particles immediately prior to introducing the milk of lime into the production process of PCC. The milk of lime is introduced into the in line production process of PCC located in the production line of the end or intermediate product of the fibrous web machine.
Olavi Imppola Esko Kukkamaeki Jouni Matula Paeivi Solismaa
101093675
Issledovanie tekhnologicheskikh vozmozhnostei polucheniia novogo sorbenta mikrokristallicheskogo gidroksida kal'tsiia
In this article there was confirmed the possibility of obtaining domestic lime sorbent on the basis of the microcrystalline calcium hydroxide corresponding to their physical and chemical properties to the best foreign analogues. There were analyzed the parameters of the traditional technological process of lime slaking. In the laboratory conditions there was developed a damping technology, allowing to get the lime sorbent with large adsorption surface.
A M Gonopol'skii O E Papovian
140286038
Production of calcium carbonate from waste sludge
A method of producing calcium carbonate from a waste sludge containing calcium carbonate and at least one silicate mineral. The method comprises the steps of: (i) incinerating the sludge to an ash in which at least 60 of the calcium carbonate present in the sludge is converted to free calcium oxide which is unreacted with the silicate mineral(s) (ii) optionally slaking the ash to convert at least a portion of the free calcium oxide therein to calcium hydroxide, (iii) treating either the ash from step (i) or the slaked ash from step (ii) with an aqueous solution of a polyhydroxy compound to provide a solution of dissolved calcium hydroxide, (iv) separating insoluble material from the solution of calcium ions obtained in step (iii) (v) dispersing carbon dioxide through the solution obtained from step (iv) so as to produce calcium carbonate, and (vi) separating the calcium carbonate produced in step (v) The silicate mineral may be kaolin. The invention allows the production of metakaolin substantially devoid of free lime as an additional product stream.
99821923
Analysis on Effects of PEG on Effience of Calcium based FGD Sorbent
In the hydrated process,Calcium based flue gas desulfurization sorbent has poor dispersion,the small surface area and prefers to get group.The hydrated products were modified by adding different amount of PEG(PEG600,1500,2000).The results showed that with a hydration period of 30min and the water/lime molar ratio 1.4:1,the optimal amount of PEG600 added was 3 wt%,the particle size of hydrated products was uniform with the average particle size 9.4mm,the surface area was 21.6 m2/g,and the desulfurization rate was improved from 61% to 91%.XRD,SEM,FT IR showed that lime was hydrated completely,lime slaking rate was high and the dispersion was improved,indicating calcium hydroxide was coating with PEG.
Zhao Jun-feng
96944896
Calcium Compounds, Survey
The chemical element calcium, Ca, atomic number 20, is an alkaline earth metal which is fifth in abundance among all elements (ca 4% and the third most abundant metal found in the earth's crust. It is too reactive to be found naturally in the free state, but its compounds are widespread as the minerals marble, CaCO3, limestone, CaCO3, calcite, CaCO3, dolomite, gypsum, anhydrite, CaSO4, fluorspar, CaF2, fluorapatite, Ca5F(PO4)3, hydroxylapatite, Ca5OH(PO4)3, selenite, and anorthite, CaAl2Si2O8. Lime stone calcium carbonate, is the most widely used of all rocks, as such for dimension stone or aggregate in concrete and road building, or as an industrial chemical and precursor of lime and hydrated lime. More than 90% of the lime consumed in the United States is used for basic or industrial chemistry. It is produced by thermal decomposition (calcination) of calcium carbonate. 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 it finds widespread industrial application as an alkali because it is cheaper than sodium hydroxide. Lime and hydrated lime are used in mortar, treatment of industrial wastes, and treatment of municipal and industrial water supplies. Fluorospar, CaF2, is used as a flux in metallurgical processes such as production of steel in the open hearth furnace. Calcium hypochlorite, Ca(OCl)2, bleaching agent, in contrast to bleaching powder, does not decompose on standing. Calcium sulfate occurs in large deposits as CaSO4, and as gypsum, The dihydrate is a functional additive in Portland cement to control setting time. Industrial phosphates including phosphate fertilizers, phosphoric acid, and calcium phosphates are obtained from the large deposits of fluorapatite found in Florida in the United States, and in Morocco. Calcium magnesium acetate (CMA) suggested formula CaMg2(C2H3O2)6, is an emerging bulk chemical. Calcium hydride, CaH2, is an effective reducing agent at high temperatures and has been used to reduce inorganic oxides to their metals. Ordinary glass, soda lime glass, is a complex mixture of silicates, chiefly those of sodium and calcium. Portland cement is obtained by calcining a mixture of substances to produce an appropriate ratio of the oxides CaO, MgO, Al2O3, Fe2O3, and SiO2. The chief raw materials of ceramic manufacture are clay, feldspar, and sand. Calcium ion shows some tendency to form complexes mainly through coordination with oxygen containing ligands. Calcium carbide is used to produce calcium cyanamide, CaCN2 (lime nitrogen) used as a fertilizer. Calcium cyanamide can be converted to calcium cyanide, used in cyanidation of metallic ores and production of sodium cyanide and ferrocyanides. Calcium cyanamide has also been used to make cyanamide, which in turn is the starting material for important industrial organic syntheses. Calcium hydride, CaH2, and anhydrous calcium sulfate (Drierite) CaSO4, are useful as drying agents. Biological functions of Ca(II) ion are numerous but may be classified in one of three categories: the formation of solid skeletal material such as bone, teeth, and shell; the stabilizing of protein conformation structure; and the most varied, the ability of Ca(II) to trigger certain physiological activities such as muscle contraction and the release of hormones. The recommended daily allowances of calcium are for children to 10 years of age, 360 800 mg; teenage children, 1200 mg; adults, 800 mg, increasing to 1200 mg during pregnancy and lactation. Cow's milk supplies ca 1.27 g/L of calcium in available form. Keywords: Calcium compounds; Calcium carbonate; Lime; Hydrated lime; Industrial wastes; treatment; Coordination chemistry; Calcium; Organic chemistry; Water supplies; treatment; Metallurgy; Biological function
Richard L Petersen Mark B Freilich Updated by Staff