Phosphate onto calcium carbonate

Published reports discussing the influence of calcium carbonate solid surfaces on the phosphate ion concentration in natural water (2, 3) include 1)solubility product-based calculations 5) iTspontaneous precipitation experimehts from highly supersaturated solutions 7j 9) 3) adsorption of phosphate onto calcium carbonate (10, 11, 12, 13), These experiments have provided useful information, but several have not included activity coefficient or ion pair corrections in their analyses, seriously limiting the applicability of the results. 

Calcium carbonate (calcite) scale formation in hard water can be prevented by the addition of a small amount of soluble polyphosphate in a process known as threshold treatment. The polyphosphate sorbs to the face of the calcite nuclei and further growth is blocked. Polyphosphates can also inhibit the corrosion of metals by the sorption of the phosphate onto a thin calcite film that deposits onto the metal surface. When the polyphosphate is present, a protective anodic polarization results. 

Hydroxyapatite (HA) coating on the surface of the hip stem and the acetabular cup is the most recent advancement in artificial hip joint implant technology. This substance is a form of calcium phosphate, which is sprayed onto the hip implant. It is a material found in combination with calcium carbonate in bone tissue, and bones can easily adapt to it. When bone tissue does grow into HA, the tissue then fixes the hip joint implant permanently in position. These HA coatings are only used in press-fit, noncemented implants. 

Phosphate is also ubiquitous as a minor component within the crystal lattices of other minerals or adsorbed onto the surface of particles such as clays, calcium carbonate, or ferric oxyhydroxides (Ruttenberg, 1992). Therefore, in general, transport of these other particulate phases represents an important transport pathway of P as well. 

Most common ions (sodium, calcium, nitrate, phosphate, chlonne, bromide, and iodine) found in natural or wastewater are not really adsorbed onto activated carbons. An exception is fluoride that can be removed by activated carbon as well as by activated alumina. Table 24.6 gives some indications of the adsorption potential of some inorganic cations and anions onto carbonaceous porous material. 

Tea stains are dry films of tea scum adhering strongly onto the surface of porcelain cups. They are complex mixtures of organic material from the oxidation of soluble tea components interspersed with calcium carbonate crystals [196]. Other metal ions, either from tap water or from tea leaves, are also present, and may form complexes with polyphenolic tea components. Strong complexing agents such as phosphates or phosphonates are capable of extracting the earth alkali metal ions to loosen the polymeric framework and support the action of the bleach systems. 

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