Calcium carbonate biological precipitation

Biological production of lactic acid is complicated primarily due to economical considerations arising from product inhibition and the required downstream processing of dilute aqueous product streams. The standard method of biological lactic acid production is the anaerobic fermentation by Lactobacillus in a batch reactor [7]. The conventional process requires the base to be added to the reactor to control the pH and the use of calcium carbonate to precipitate the lactate. This process produces a lactate salt that must be acidified (usually by sulfuric acid) to recover the lactic acid, with calcium sulfate as an undesirable by-product. 

Aragonite. Calcium carbonate is a common deposit in shallow tropical waters as a constituent of muds, or in the upper part of coral reefs where it precipitates from carbon dioxide-rich waters supersaturated with carbonate from intense biological photosynthesis and solar heating. Deposits of ooHtic aragonite, CaCO, extending over 250,000 km in water less than 5 m deep ate mined for industrial purposes in the Bahamas for export to the United States (19). 

Oceanic surface water is everywhere supersaturated with respect to the two solid calcium carbonate species calcite and aragonite. Nevertheless carbonate precipitation is exclusively controlled by biological processes, specifically... 

The main components of marine sediments are inorganic aluminosilicate minerals which are usually accumulated on the sea floor by river and other geological activities, and also skeletons and shells of marine organisms (mainly calcium carbonate and silica) [2]. Of course, some metal salts or particulates which precipitate from seawater form new minerals, e.g. manganese nodules [2]. The chemical compositions of the three principal types of sediments in the ocean are shown in Table 12 [105], Most of the sediments found in the deep-sea floor are mixtures of these three principal minerals. Study of the sediments in the oceans and seashores can provide important data related to geochemical, oceanographical or biological circulation and deposition of elements, formation and distribution of marine sediments, and exploitation of marine resources. 

Aizenberg, J. 1996. Stabilization of amorphous calcium carbonate by specialized macromolecules in biological and synthetic precipitates. Advanced Materials, 8 222-5. 

Experimental studies of authigenic apatite precipitation. Mechanisms and rates of authigenic apatite formation in the early diagenetic environment are difficult to resolve, because of the wide variety of biological, chemical, and physical factors that can affect its formation. Experimental studies of apatite formation under controlled conditions have provided important information for placing constraints on modes and rates of CEA authigenesis. Examples of such studies include those of Ames (1959), who documented nucleation of CEA on calcium carbonate Gulbrandsen et al. (1984), who documented rates of CEA formation in seawater Jahnke (1984), who evaluated the... 

Oceanic surface water is everywhere supersaturated with respect to the two solid calcium carbonate species calcite and aragonite. Nevertheless, calcium precipitation is exclusively controlled by biological processes, specifically the formation of hard parts (shells, skeletal parts, etc.). The very few existing amounts of spontaneous inorganic precipitation of CaC03(s) come from the Bahamas region of the Caribbean. 

The mineral adsorbs Cl and NO3 ions poorly and reversibly, whilst S04 is precipitated at the mineral surface. Phosphates are preferentially adsorbed on calcium carbonate. Soils which contain CaCOj show pH values ranging from about 7 to 8.4, due to the formation of calcium hydrogen carbonate. The formation of this compound is accelerated in biologically active soils, with a high production of carbon dioxide. Calcareous soils have a soil solution dominated by Ca + ions, and this limits swelling of soil days and prevents the dispersion of finer particles in the soil. If Ca predominates on the exchange complex of soils, the pH value is maintained above 5.5. 

Lake trophic status can also affect calcium carbonate. Increased productivity in lakes can lead to biological CO2 consumption, consequent increased pH, and precipitation of calcium carbonate. Under the right circumstances this can be preserved in the sediment (Kelts Hsli, 1978 Dean, 1981 1999). 

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