Phosphate deposits

In the remote Negev desert region of Israel, oil shale is being burned in a duidized-bed combustor to supply process heat and produce electric power. Unlike the Estonian kukersite, this oil shale is lean, about 63 L/1, but is being mined to access an undedying phosphate deposit (26). 

In addition to the formation of scale or corrosion of metal within boilers, auxiliary equipment is also susceptible to similar damage. Attempts to prevent scale formation within a boiler can lead to makeup line deposits if the treatment chemicals are improperly ehosen. Thus, the addition of normal phosphates to an unsoftened feed water ean eause a dangerous eondition by elogging the makeup line with preeipitated calcium phosphate. Deposits in the form of calcium or magnesium stearate deposits, otherwise known as "bathtub ring" can be readily seen, and are caused by the eombination of ealcium or magnesium with negative ions of soap stearates. 

Traditionally, stabilization of unstable treated water generally is provided by simply lowering the treated water pH slightly or by using a threshold phosphate technique. Neither of these techniques is particularly suitable for boiler FW makeup because an alkaline FW is required and rapid reversion of the polyphosphate will take place under hot FW conditions, thus leading to phosphate deposits in the pre-boil-... 

In particular, where polyphosphate is added either to the MU waterline (say, as a stabilizer against the risks of after-precipitation) or to the FW line or FW tank (as a precipitating treatment for residual hardness), there is some risk of FW line phosphate deposits developing. Such deposits are likely to be primarily composed of hard, intractable calcium phosphate [tricalcium phosphate Ca3(P04)2] scale, but they may include magnesium phosphate [Mg3(P04)2] and other insoluble phosphates and hydroxides. The risk of precipitation and subsequent deposition is increased where the pH is below 8.3, if the FW line is particularly long, or when the FW temperature is high. 

To minimize the risk of phosphate deposits, all efforts should be made to keep residual FW hardness levels to an absolute minimum (good softening ). 

The type of membrane cleaning required depends on both the type and degree of fouling experienced, but typically it is either organic (bacterial slimes, natural organics, or process foulants and nutrients) or inorganic (silica, carbonate, sulfate, or phosphate deposits). 

Radiographic studies show calcium-phosphate deposits in joints and/or cardiovascular system Bone biopsy of the iliac crest... 

The major effect of hyperphosphatemia is related to the development of hypocalcemia and damage resulting from calcium phosphate deposits. 

Historically, phosphate deposits with an average uranium content of 0.01% are the only type of deposit from which significant quantities have been recovered, mostly in... 

According to a literature survey conducted by Shahalam [28], the contents of various chemicals found in the natural mined phosphate rocks vary widely, depending on location, as shown in Table 1. For instance, the mineralogical and chemical analyses of low-grade hard phosphate from the different mined beds of phosphate rock in the Rusaifa area of Jordan indicate that the phosphates are of three main types carbonate, siliceous, and silicate-carbonate. Phosphate deposits in this area exist in four distinct layers, of which the two deepest - first and second (the thickness of bed is about 3 and 3.5 m, respectively, and depth varies from about 20 to 30 m) - appear to be suitable for a currently cost-effective mining operation. A summary of the data from chemical analyses of the ores is shown in Table 2 [28]. 

Fluorine for industrial use is almost exclusively obtained from fluorite. There are many possible fluorite-ore types. It occurs as fissure-fill and manto-replaced types, and in pegmatites, residual/eluvial deposits, carbonates and phosphate deposits. It is a gangue mineral in many base metal deposits, but due to stringent trace metal requirements often can t be economically beneficiated to a saleable product. Most fluorite ores are selectively mined, and ore from some minor vein deposits is then upgraded to a saleable product by sorting. 

In the second stage, as the needle-like calcium phosphate deposits radially grow out of the vesicles, the surrounding collagen fibres become mineralized. 

The process known in industry as "parkerizing" consists essentially of a treatment of an iron object with an acidic phosphate soln which results in depositing a thin layer of cryst iron phosphate on the surface of iron. When applied to sintered iron projs, the "parkerizing" process decreased only slightly the friction of proj s in the bore, because the amt of phosphate deposited on the surface was so small that it was completely removed even before the proj left the bore. The use of this method did not improve the penetration of armor by AP projs... 

While the standard, modem chemical treatment programs used today almost always contain a synergistic blend of polymers and other organic inhibitors, they often may not contain a specific calcium phosphate deposit control agent (as it would increase the cost of the program). This situation reinforces the need for vigilance. 

Additionally, as with risks of calcium phosphate deposition, modem trends to the reuse of wastewaters can sometimes introduce high sulfates into cooling systems via the makeup supply. 

Typically, these low PO4 programs have been designed to operate at higher pH levels than stabilized phosphate programs, which reduces the risk of pH upsets and iron phosphate deposition. 

The formation of tricalcium phosphate in a cooling system is primarily a net result of system pH, calcium concentration, temperature, and phosphate concentration factors. An increase in any of these factors leads to an increased risk of phosphate deposition. 

In almost all instances of biological mineralization fibrous proteins represent the bulk of the organic matrix. In the past, this phenomenon has been interpreted to mean that proteins such as collagen, keratin or elastin are the key elements in mineralization by providing nucleation sites and at the same time offering structure and space for oriented crystal growth. However, with the advance in the field of biomineralization this model came under severe attack. At present, there is no universal concept which could explain all the intriguing facets of phosphate deposition in cellular systems. 

Matthews, J. L., Martin, J. H., Kennedy III, J. W., and Collins, E. J. An ultrastructural study of calcium and phosphate deposition and exchange in tissues. In Hard tissue growth, repair and remineralization (eds. K. Elliott and D. W. Fitzsimons), pp. 187-211. Amster-dam-London-New York Elsevier-Excerpta Medica-North-Holland 1973. 

Differential 31P 1H CPMAS technique has been applied to study mineral crystals of calcium phosphate deposited during osteoblast calcification in cell culture.198 The samples harvested after 8 days of culture represent the minerals formed at the very early stage of calcification, in... 

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