Weakly Alkaline Phosphate-Free

Pyrite is not only one of the key compounds in Wachtershauser s theory, but could also have fulfilled an important function for phosphate chemistry in prebiotic syntheses. A group in Rio de Janeiro studied the conditions for phosphate sorption and desorption under conditions which may have been present in the primeval ocean. In particular, the question arises as to the enrichment of free, soluble inorganic phosphate (Pi), which was probably present in low concentrations similar to those of today (10 7-10 8M) (Miller and Keffe, 1995). Experiments show that acid conditions favour sorption at FeS2, while a weakly alkaline milieu works in an opposite manner. Sorption of Pi can be favoured by various factors, such as hydrophobic coating of pyrite with molecules such as acetate, which could have been formed in the vicinity of hydrothermal systems, or the neutralisation of mineral surface charges by Na+ and K+. 

Adsorption by Clays. — Owing to the possibility of chemical reactions between the clay and the adsorbed substances, the phenomena here are much more complicated than is ordinarily the case with many colloidal systems. According to Sullivan changes between the radicals are often involved. For instance when acid or neutral salts are adsorbed, sodium, potassium, and magnesium from the clay may be released or dissolved, while an equivalent amoimt of the adsorbed basic radical remains with the clay. The addition of alkaline solution is still more complicated. Not only may there be free alkali but basic solutions may be formed because of the hydrolysis of salts of a strong base and a weak acid, e.g., carbonates and phosphates. Three different reactions are now possible. First, the free alkali may react with the colloidal silica. Second, the silicate radical from the clay may form insoluble salts with the adsorbed base. Third, the sodium, potassium, or magnesium displaced from the clay may form soluble carbonates and phosphates, and these salts in turn be adsorbed by the clay constituents. These reactions are of great importance in the study of the fertilization of the soil. It has been claimed that the addition of lime not only neutralizes the undesirable acids, but also renders the potassium of the clay available for the plant. 

Waters may be alkaline due to the presence of a wide variety of salts of weak acids such as carbonates, bicarbonates, borates, silicates, phosphates, etc., and also due to the presence of weak and strong bases (due to contamination with industrial wastes). Ibe major portion of alkalinity in natural water is, however, caused by presence of bicarbonates that are formed in appreciable amounts when water containing free CO2 percolates through soils containing CaC03 and/or MgC03 ... 

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