Calcium oxalate precipitation

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)...

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

The calcium carbonate precipitate was removed by filtration, and the filtered solution was found to contain 1,436 g of fructose as determined by optical rotation. A small amount of calcium bicarbonate was present as an impurity in solution and was removed by the addition of oxalic acid solution until a test for both calcium and oxalic acid was negative. The insoluble calcium oxalate precipitate was removed by filtration. 

If the kidneys remove too many calcium ions from the blood, the equilibrium position in the kidneys shifts to the right. Solid calcium phosphate can form in the kidneys, producing kidney stones. Kidney stones, which are painful, can also form as the result of calcium oxalate precipitating in the kidneys. Precipitates of other compounds can affect different areas of the body gallstones in the gall bladder and gout in the joints are two examples. 

This reaction shows calcium chloride reacting with oxalic acid to produce calcium oxalate and hydrochloric acid. The calcium oxalate is the kidney stone. Calcium oxalate precipitates out of the urine in the kidneys of all individuals. Normally, the solids formed are grain size and do not cause prob-... 

Fig. lc. Electronmicrograph of isolated sarcoplasmic reticulum membranes loaded with calcium oxalate46. The preparation was negatively stained with potassium phosphotungstate. Size and shape of the calcium oxalate precipitates differ considerably. Fine particles which are present on the surface of most vesicles are clearly visible. In all pictures the length of the bars measures 0.1 pm... 

Nitric Acid and Organic Matter. The use of the mixed acids to digest organic matter may result in explosions. Explosions with vegetable oil,19 milk, calcium oxalate precipitates from plants,21 rat carcasses,22 finely ground plant material,21 and animal tissues21 have been documented. 

Some precipitates are deposited slowly and the solution is in the state of supersaturation for a considerable time. Thus, when calcium oxalate is precipitated in the presence of larger amounts of magnesium ions, the precipitate is practically pure at first, but if it is allowed to remain in contact with the solution, magnesium oxalate forms slowly (and the presence of calcium oxalate precipitate tends to accelerate this process). Thus, the calcium oxalate precipitate becomes contaminated owing to post-precipitation of magnesium oxalate. Post-precipitation often occurs with sparingly soluble substances which tend to form supersaturated solutions, they usually have an ion in common with the primary precipitate. Another typical example is the precipitation of copper or mercury(II) sulphide in dilute acid solution, which become contaminated, if zinc ions are present, by post-precipitation of zinc sulphide. Zinc ions alone may not be precipitated with sulphide ions under identical circumstances. 

Once all the solution has been filtered, immediately remove the filter paper to a large watch glass. Pour the filtrate back into the beaker, place a new piece of filter paper on the funnel, and filter this solution through again as above. Repeat a third time with the third piece of filter paper. This third filter cake may be thick and milky. Calcium oxalate precipitate causes this color and causes the filter to clog. If this occurs, the third filter cake should be discarded. 

Calcium salts, such as calcium oxalate, precipitate in urine specimens during and after collection. Specimens may be collected in a container containing acid to prevent calcium salt precipitation. A commonly used acid is HCl, 6 mol/L, with 20 to 30 mL added to the container for a 24-hour collection (1 to 2 mL for a random specimen). The safety of the patient and the patient s family in handling such a container may be a concern. The measured urinary calcium concentration must be corrected for the dilution by the acid solution when the urinary volume is low. The specimen should be kept well mixed during collection. Specimens collected without acid should be acidified and allowed to stand for 1 hour before thorough remixing and aliquot-ing. Some have questioned the ability of postcollection acidification to redissolve all of the calcium salts with or without heating. ... 

Calcium oxalate precipitates when solutions of calcium hydroxide and oxalic acid are mixed ... 

The impedance of the on-line precipitate collector. This is particularly im] when the collection of a relatively large amount of precipitate is inteh befoit dissolution, or when a small capacity Altering device is used to limit dispersion. Thus, with a nylon membrane filter of 0.45-/xm pore and 5 mm diameter the highest tolerable flow-rate was found to be only 0.3 ml min in the collection [ of a calcium oxalate precipitate [10]. 

D. Enhanced elimination. Maintain high-volume urine flow (3-5 miykg/h) to help prevent calcium oxalate precipitation in the tubules. Oxalate is removed by hemodialysis, but the indications for this treatment are not established. 

An example is given in Fig. 4, which shows partial thermogravimetric curves (dehydration only) obtained from calcium oxalate precipitates prepared at different initial reactant concentrations. Curve 1 represents dehydration curves typically obtained from samples of COM of different morphologies formed by heterogeneous nucleation (including compact crystals and dendrites) curve 2 is... 

By determining the mass loss due to dehydration (rfwi and dm2 in Fig. 4), it is possible to quantitatively determine the phase composition of mixtures of crystal hydrates provided it was qualitatively ascertained by some other method (for instance, by X-ray powder diffraction). This method has been used to determine the influence of various experimental parameters on the phase composition of calcium oxalate precipitates. Several examples are given in Figs. 5-9. 

FIG. 5 Schematic presentation of changes of the average water content in crystalline calcium oxalate precipitates as a function of the initial reactant concentrations, [Ca] = [Ox]. Time of aging in contact with the mother hquid was from 10 min to 3 h. c denotes reactant concentrations corresponding to S, as defined in Section n.A (i.e., at c > c, homogeneous nucleation prevails). (Adapted from Ref. 44.)... 

In other words, some calcium oxalate precipitates from the solution. The solution now contains less calcium oxalate. You conclude that calcium oxalate is less soluble in a solution of calcium chloride than in pure water. 

In the chapter opening, we mentioned that calcium oxalate precipitates to form kidney stones. The same salt would precipitate in the body if oxalic acid (a poison) were accidentally ingested, because ion is present in the blood. (See Figure 18.3 for another example of a precipitation.) To understand processes such as these, you must understand the conditions under which precipitation occurs. Precipitation is merely another way of looking at a solubility equilibrium. Rather than ask how much of a substance will dissolve in a solution, you ask Will precipitation occur for given starting ion concentrations ... 

A semi-quantitative test for the estimation of urinary calcium excretion. It consists of adding oxalic acid and ammonium oxalate in acetic acid to the urine and assessing the degree of turbidity of the calcium oxalate precipitate. 

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