Lime water precipitation

Because early enzyme preparations were tissue extracts, enzyme activity was always associated with the presence of albuminous bodies, and physiologists wondered whether the enzymes were themselves albuminous bodies or were merely associated with them. As early as 1861, Ernst Briicke in Vienna prepared an extract of pig s stomach that rapidly digested fibrin in acid solution. Briicke added phosphoric acid and then lime water, precipitating pepsin along with colloidal calcium phosphate. When he dissolved the precipitate in acid, Briicke obtained a solution that, while very dilute, still digested fibrin. Briicke applied a series of tests that various authors had said should be positive for protein in solution, but the solution showed no trace of protein. ... 

A more constrained opportunity for nitrate bioremediation arose at the US-DoE Weldon Spring Site near St. Louis, Missouri. This site had been a uranium and thorium processing faciUty, and treatment of the metal had involved nitric acid. The wastestream, known as raffinate, was discharged to surface inpoundments and neutralized with lime to precipitate the metals. Two pits had nitrate levels that requited treatment before discharge, but heavy rains in 1993 threatened to cause the pits to overflow. Bioremediation by the addition of calcium acetate as a carbon source successfully treated more than 19 million liters of water at a reasonable cost (75). 

Gold Lime Softening. Precipitation softening accompHshed at ambient temperatures is referred to as cold lime softening. When hydrated lime, Ca(OH)2, is added to the water being treated, the following reactions occur ... 

More recendy, the molten caustic leaching (MCL) process developed by TRW, Inc. has received attention (28,31,32). This process is illustrated in Eigure 6. A coal is fed to a rotary kiln to convert both the mineral matter and the sulfur into water- or acid-soluble compounds. The coal cake discharged from the kiln is washed first with water and then with dilute sulfuric acid solution countercurrendy. The efduent is treated with lime to precipitate out calcium sulfate, iron hydroxide, and sodium—iron hydroxy sulfate. The MCL process can typically produce ultraclean coal having 0.4 to 0.7% sulfur, 0.1 to 0.65% ash, and 25.5 to 14.8 MJ/kg (6100—3500 kcal/kg) from a high sulfur, ie, 4 wt % sulfur and ca 11 wt % ash, coal. The moisture content of the product coal varies from 10 to 50%. 

In a study of crystal precipitation of calcium carbonate during the batch carbon-ation of lime water, individual crystals and agglomerated particles were observed as shown in Figure 8.18(a), (b) and (c), respectively (Wachi and Jones, 1991b). 

In an undated letter to J. G. Gahn, which was probably written in 1774, Scheele stated that he had precipitated alum with lime water. "When I had the right proportion of the lime water to the acid in the alum, said he, I got a precipitate of alumina and gypsum (calcium sulfate) in the solution, . . and I found neither lime or gypsum in the clear solution, but pure water (18). Thus it is evident that Scheele was at that time unaware of the presence of potash in alum. 

To detect elderberry coloring in. port [ nd. Other red wines, aeetete of lead is the simplest test, With pure red wine it throws down a greenish-grey precipi-, tate. A deep blue precipitate isthe result of elder berries, logwood, and bilberries, Brazil wood. and red sunders are thrown down red. Lime water destroys the color imparted by beet... 

Calcium Pyroarsenite, Ca2As205, is a white powder obtained by slowly precipitating a solution of arsenious acid with excess of lime-water, or by adding calcium chloride or sulphate to aqueous ammonium arsenite, and heating the precipitate to 105° C.7 If the product is dried in the air at the ordinary temperature, the monohydrate is obtained. At red heat calcium arsenate is formed. The pyroarsenite is only slightly soluble in water, 100 parts dissolving 0-025 to 0-030 part of the salt. It is more soluble in the presence of alkali chlorides and some ammonium salts, such as the nitrate, sulphate, acetate and succinate.8 It also dissolves in dilute acids. 

Treat with lime water. Glucose, unlike fructose, yields no precipitate. 

Fulminating silver was prepared in 1788 by Berthollet who precipitated a solution of nitrate of silver by means of lime water, dried the precipitated silver oxide, treated it with strong ammonia water which converted it into a black powder, decanted the liquid, and left the powder to dry in the open air. Fulminating silver is more sensitive to shock and friction than fulminating gold. It explodes when touched it must not be enclosed in a bottle or transferred from place to place, but must be left in the vessel, or better upon the paper, where it was allowed to dry. 

Lime water. Excess of lime water is added to a little of the tannin solution in a flat porcelain dish, any formation of precipitate or coloration being noted, as well as the variations occurring therein after some time. 

Detection of Red Wood Extract.—A dilute aqueous decoction of the substance is treated with lime water the colouring matter of the cochineal separates as a violet precipitate if the liquid remains coloured, the presence of red wood is indicated. 

By the respiration of animals, healthy air is not merely rendered mephitic but it also suffers another ohange, for after the mephitic portion is absorbed by solution of caustic alkali, the remaining portion is rendered salubrious and although it occasions no precipitate in lime water, it nevertheless extinguishes flames, and destroys life. 

As discussed in Chapters 5 and 7, the use of lime to precipitate calcium arsenates is a common method for removing inorganic As(V) from water or flue gases. Calcium arsenates were also once extensively used in pesticides (Chapter 5). The compositions of some calcium arsenates, such as johnbaumite (Ca5(As04)3(0H) Table 2.5), resemble the very common phosphate mineral, apatite (Ca5(P04)3(F,Cl,0H)), where arsenate replaces phosphate. Some lead arsenates, such as mimetite (Pb5(As04)3Cl Table 2.5), also have crystalline structures that are related to apatite. Mimetite may occur in oxidized lead-rich hydrothermal deposits. 

Precipitation refers to the process of adding one or more chemical reagents to water so that dissolved contaminants are transformed (precipitated) into insoluble solids (precipitates) (US EPA, 2002b, 17). The precipitates can then be collected and removed from the water by filtration, flotation, centrifugation, or other methods. For arsenic in water, precipitation typically involves reactions between arsenic oxyanions and dissolved cations. A common example is the precipitation of calcium arsenates from the addition of lime to a wastewater containing dissolved As(V). 

Downstream processing may consist of several operations such as liming to precipitate the metabolite as the calcium salt, washing of the precipitate with water to remove soluble impurities, acidification using strong acids to convert the salt in its free acid form. The acidic liquor may be demineralized using IER, decolorized using active carbons, concentrated under vacuum, and finally crystallized. 

GO Bubble carbon dioxide slowly into a test tube of lime water. A white precipitate forms at once but very soon redissolves and the solution then remains clear. 

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