Inorganic precipitates

The majority of inorganic precipitants show poor selectivity. Most organic precipitants, however, are selective for one or two inorganic ions. Several common organic precipitants are listed in Table 8.4. 

Reactions for the Homogeneous Preparation of Selected Inorganic Precipitants... 

The dicyclobutanecarbonyl derivative (136.7 g) was dissolved in 200 ml of tetrahydrofuran and added dropwise to a suspension of 34.2 g of lithium aluminum hydride in 1 liters of tetrahydrofuran. The temperature of the mixture rose to reflux during the addition. Reflux was maintained for 2 hours after the addition was completed. After cooling, 110 ml of ethyl acetate was added dropwise, followed by 30 ml of water, followed by a solution of 53 g of ammonium chloride in 125 ml of water. The resulting mixture was filtered and the inorganic precipitate was washed with methanol. Evaporation of the combined filtrates gave 66 g of N-cyclobutYlmethyl-14-hYdroxydihydronormorphinone, melting point 229 to 231 . ... 

Figure 1. Histogram of measurements of molar U/Ca ratio in a number of samples of reef-building corals and one giant clam sample (after Edwards 1988). Also indicated is the U/Ca ratio of seawater. This illustrates the point that corals do not fractionate U from Ca by large amounts when they make their skeletons. U/Ca ratios of corals are similar to values from inorganically precipitated marine aragonite. Mollusks along with most other biogenic minerals exclude uranium. Note that the horizontal axis is on a log scale and that the U/Ca ratio of the clam is almost 5 orders of magnitude lower than that of the corals. This difference is the fundamental reason why there are difficulties with uranium-series dating of mollusks.

Magnesium may be precipitated from solution as MgNH4P04.6H20, a compound which has been widely used as a basis for the gravimetric determination of the element over many years. An examination of its use will serve to illustrate some of the problems associated with inorganic precipitations. The initial precipitation is made from a solution at pH = 11-12 by the addition of ammonium phosphate in excess. 

Figure 10. Summary of experimentally determined fractionation factors for Ca isotopes in the formation of foraminifera and coccolith shell carbonate, and for rapid inorganic precipitation of aragonite from an Mg-Ca-Cl solution. Data for the foraminifer G. ornatissima and the coccolith E. huxleyi are from De La Rocha and DePaolo (2000). Data on G. sacculifer are from Nagler et al. (2000). Data for O. universa and aragonite are from Gussone et al. (2003). Two of the forams and the coccolith E. huxleyi have similar fractionation behavior, with an overall fractionation factor of-1 to -1.5%o, and a small temperature dependence of about 0.02 per °C. The foram G. sacculifer appears to have a strongly temperature dependent fractionation factor.

The process produces no organic sludges or air emissions inorganic precipitates may be formed. 

Kitano, Y., Kanamori, N., Tokuyama, A, Influence of organic matter on inorganic precipitation. In Organic matter in natural waters, pp. 413. Hood, D. W. (ed.). Inst. Marine Sci., Univ. Alaska, 1970... 

In the presence of organic matter, inorganic precipitation of CaC03 is inhibited or accelerated depending on the nature of the dissolved constituents125-128. ... 

Bortnikova, S.B., Smolyakov, B.S., Sidenko, N.V. et al. (2001) Geochemical consequences of acid mine drainage into a natural reservoir inorganic precipitation and effects on plankton activity. Journal of Geochemical Exploration, 74, 127-39. 

Studies of oxygen isotopic fractionation in inorganic precipitates provide conflicting evidence for a correlation between fractionation and precipitation rate. A correlation between the isotopic composition of the inorganic precipitates and the proportion of carbonate in the carbonate-bicarbonate solution (Figure 3.16) was observed by McCrea (1950). He hypothesized that, when first formed, the calcium... 

In an attempt to compare isotopic fractionation in foraminifera to that in inorganic precipitates, Grossman (1984) presented tentative calcite-bicarbonate and aragonite-bicarbonate fractionation relations by combining the monomineralic results of Rubinson and Clayton with the temperature dependence obtained from the Emrich et al. relation. Grossman also redetermined the isotopic composition of the dissolved bicarbonate in Rubinson and Clayton s experiments. The 813C of... 

Fig. 3.17. Carbon isotopic enrichment factors for aragonitic (dots) and calcitic (circles) foraminifera and inorganic precipitates as a function of temperature. Shown are the inorganic precipitate data of Baertschi (1957)- circle with dot Emrich et al. (1970)- large dots and Rubinson and Clayton (1969) revised - see text aragonite - solid diamond, calcite - hollow diamond. (After Grossman, 1984.)...

One of the first comprehensive investigations of kinetic effects in isotopic fractionation was conducted by Turner (1982). Noting that calcite and low magnesian calcite inorganically precipitated in freshwater lakes were enriched in... 

---