Calcium oxalate

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

Caldum chloride test. Add CaCl2 solution to a neutrai solution of an oxalate a white precipitate of calcium oxalate is formed, insoluble in acetic acid, but soluble in dil. HCl. 

Of nutrient chelates in the human diet, oxalates and phytates are the most common. OxaUc acid (8), found principally in spinach, rhubarb leaves, beet leaves, some fmits, and mushrooms, is a primary chelator of calcium. Oxalate present in pineapple, kiwifmit, and possibly in other foods, occurs as calcium... 

Ftiedel-Crafts acetylation of cyclohex ibenzene gave 4-cyclohexylacetophenone which was used as an iatermediate for the preparation of 2,4-dioxo-4-substituted-l-butanoic acid detivatives useful ia treating utinary tract calcium oxalate lithiasis (98). 

The sodium formate process is comprised of six steps (/) the manufacture of sodium formate from carbon monoxide and sodium hydroxide, (2) manufacture of sodium oxalate by thermal dehydrogenation of sodium formate at 360°C, (J) manufacture of calcium oxalate (slurry), (4) recovery of sodium hydroxide, (5) decomposition of calcium oxalate where gypsum is produced as a by-product, and (6) purification of cmde oxahc acid. This process is no longer economical in the leading industrial countries. UBE Industries (Japan), for instance, once employed this process, but has been operating the newest diaLkyl oxalate process since 1978. The sodium formate process is, however, still used in China. 

Quantitative Analysis. OxaUc acid is precipitated as calcium oxalate from a solution containing oxaUc acid, and the calcium oxalate obtained is then weighed. If there are no organic substances other than oxaUc acid present, oxaUc acid can be titrated quantitatively with potassium permanganate. 

The common treatment methods are acidification, neutralization, and incineration. When oxahc acid is heated slightly in sulfuric acid, it is converted to carbon monoxide, carbon dioxide, and water. Reaction with acid potassium permanganate converts it to carbon dioxide. Neutralization with alkahes, such as caustic soda, yields soluble oxalates. Neutralization with lime gives practically insoluble calcium oxalate, which can be safely disposed of, for instance, by incineration. 

Millet Jelly Production. Starch powder is heated together with oxahc acid and hydrolyzed to produce millet jelly. Oxahc acid functions as a hydrolysis catalyst, and is removed from the product as calcium oxalate. This apphcation is carried out in Japan. 

Calcium Oxalate. The monohydrate [5794-28-5], CaC2 04-H2 0, mol wt 128.10,is of importance principally as an intermediate in oxahc acid manufacture and in analytical chemistry it is the form in which calcium is frequentiy quantitatively isolated. Its solubihty in water is very low, lower than that of the other aLkahne-earth oxalates. The approximate solubihties of this and several related salts are indicated in Table 6. 

Fig. 5. pM vs pH for M = Ca(II), L = EDTA, in the presence of excess oxalate. Sohd lines A, B, C represent 100%, 10%, and 1% excess EDTA, respectively. Broken lines indicate sohd—solution equihbria of calcium oxalate in the presence of dissolved oxalate. 

Sugar Processing. Dispersants are used in the production of cane and beet sugar to increase the time between evaporator clean outs. Typical scales encountered include calcium sulfate, calcium oxalate, calcium carbonate, and silica. Dispersants are fed at various points in the process to prevent scale buildup, which would interfere with efficient heating of the vessels. Only certain dispersants, conforming to food additive regulations, can be used, since a small amount of the dispersant may be adsorbed on the sugar crystals. 

Calcium oxalate monohydrate Calcium phosphate (dibasic) Calcium pyrophosphate Calcium sodium phosphate Calcium sulfate Calcite... 

Figure 6.15 Predicted and experimental calcium oxalate agglomerate size distributions (Hartel and Randolph, 1986)...

The crystal growth rates can be directly determined from the second and third moment as described above. The calculated rates for calcium oxalate here are in the range 0.75 x 10 to 4.7 x 10 m/s. Literature values for the growth rate of calcium oxalate monohydrate vary considerably 1.08 x 10 m/s (Kavanagh, 1992), 3.4 X 10 to 5.0 x 10 m/s (Garside etal., 1982) and 2.8 x lO to 1.11 X 10 m/s (Nielsen and Toft, 1984). The values obtained from the experiments are therefore within the range of the literature data. It should be borne in... 

Figure 6.20 Growth rate of calcium oxalate versus supersaturation at 21 °C (Zauner and Jones, 2000a)...

For stirrer speeds of 4.2, 8.4, 16.7, 25 and 33.4Fiz, agglomeration kernels obtained in this study vary from 0.01 to 183 s . Unfortunately, no other measured data for agglomeration of calcium oxalate analysed using Smoluchowski s kernel were found in the literature. The corresponding values reported by Wojcik and Jones (1997) for calcium carbonate, however, cover a range from 0.4 to 16.8s-. ... 

Figure 8.4 Scale-up of continuous calcium oxalate precipitation, volume mean size L43 (300 ml, 4.3 1 and 121 0.04 M, 7.5 min, id). (Zauner and Jones, 2000h)...

Figure 8.6 Mean particle for calcium oxalate precipitation after Zauner and Jones, 2000b)...

The reactor has been successfully used in the case of forced precipitation of copper and calcium oxalates (Jongen etal., 1996 Vacassy etal., 1998 Donnet etal., 1999), calcium carbonate (Vacassy etal., 1998) and mixed yttrium-barium oxalates (Jongen etal., 1999). This process is also well adapted for studying the effects of the mixing conditions on the chemical selectivity in precipitation (Donnet etal., 2000). When using forced precipitation, the mixing step is of key importance (Schenk etal., 2001), since it affects the initial supersaturation level and hence the nucleation kinetics. A typical micromixer is shown in Figure 8.35. 

Aquilano, D. and Franchini-Angela, M., 1985. Twin laws of calcium oxalate trihydrate (COT). Journal of Crystal Growth, 73, 558-562. 

Bramley, A.S., Hounslow, M.J. and Ryall, R.L., 1996b. Aggregation during precipitation from solution. Kinetics for calcium oxalate monohydrate. Chemical Engineering Science, 52, lAl-lSl. 

Brecevic, Lj. and Kralj, D., 1989. Factors influencing the distribution of hydrates in calcium oxalate precipitation. Journal of Crystal Growth, 97, 460M68. 

Brecevic, Lj., Skrtic, D. and Garside, J., 1986. Transfomiation of calcium oxalate hydrates. Journal of Crystal Growth, 74, 399-408. 

Brown, C.M., Ackemiann, D.K., Puricli, D.L. and Finlayson, B., 1991. Nucleation of calcium oxalate monoliydrate use of turbidity measurements and computer-assisted simulations in characterising early events in crystal formation. Journal of Crystal Growth, 108, 455 64. 

Collier, A.P. and Hounslow, M.J., 1999. Growth and aggregation rates for calcite and calcium oxalate monohydrate. American Institute of Chemical Engineers Journal, 45, 2298-2305. 

Doiiiiet, M., Joiigeii, N., Lemaitre, J. and Bowen, P., 2000. New morphology of calcium oxalate triliydrate precipitated in a segmented flow tubular reactor. Journal of Materials Science Letters, 19, 749-750. 

Donnet, M., Jongen, N., Lemaitre, J., Bowen, P. and Hofmann, H., 1999. Better control of nucleation and phase purity using a new segmented flow tubular reactor Model system Precipitation of calcium oxalate. In 14th International Symposium on Industrial Crystallization. Cambridge, U.K., September 12-16, Institution of Chemical Engineers, CD ROM, pp. 1-13. 

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