Phosphate process

Nitric Phosphate. About 15% of worldwide phosphate fertilizer production is by processes that are based on solubilization of phosphate rock with nitric acid iastead of sulfuric or phosphoric acids (64). These processes, known collectively as nitric phosphate or nitrophosphate processes are important, mainly because of the iadependence from sulfur as a raw material and because of the freedom from the environmental problem of gypsum disposal that accompanies phosphoric acid-based processes. These two characteristics are expected to promote eventual iacrease ia the use of nitric phosphate processes, as sulfur resources diminish and/or environmental restrictions are tightened. 

Nonetheless, production and use of nitric phosphates ia Europe are continuing to grow. In general, nitric phosphate processes are somewhat more compHcated than sulfur-based processes and requite higher investment. In the past, several attempts have been made to estabHsh commercial acceptance of this type process ia the United States, but plant operations have been relatively short Hved because of low sulfur prices and resultant competition from sulfur-based processes. 

The majority of the fluorine ia the earth s cmst is present in the form of the phosphoms fluoride fluoroapatite [1306-05 ] Ca (P0 2F- Phosphate rock deposits contain an average concentration of 3.5 wt % fluorine. During phosphate processing these fluorine values are partially recovered as by-product fluorosihcic acid. The amount of fluorosiUcic acid recovered has grown steadily, in part because of environmental requirements (see Phosphoric acid and THE phosphates). 

The Zinc Phosphating Process. The zinc phosphating reaction involves acid attack on the substrate metal at microanodes and deposition of phosphate crystals at microcathodes (8). Liberation of hydrogen and the formation of phosphate sludge also occur. The equation for the dissolution of iron together with precipitation of dissolved iron as sludge in a nitrite accelerated system is as foUows ... 

The first successflil production method for the separation of Pu from U and its fission products was the bismuth phosphate process, based on the carrying of Pu by a precipitate of BiPO (126). That process has been superseded by Hquid-Hquid extraction (qv) and ion exchange (qv). In the Hquid-Hquid... 

The majority of phosphate processes in use today are accelerated to obtain shorter treatment times and lower processing temperatures. The most common mode of acceleration is by the addition of oxidising agents such as nitrate, nitrite, chlorate and hydrogen peroxide. By this means, a processing time of 1 to 5 min can be obtained at temperatures of 43-71 °C. The resultant coatings are much smoother and thinner than those from unaccelerated processes, and, while the corrosion resistance is lower, they cause less reduction of paint gloss and are more suited to mass-production requirements. 

In certain cases rinsing may be dispensed with after non-accelerated phosphate treatment, but blistering of paint due to local concentration of solution in seams and crevices may occur. Rinsing is generally applied, regardless of the type of phosphate process employed... 

Similarly in Japan there has been a strong move towards full dip treatment and over 50% of car body lines now employ this method. In Europe, while there are some dip-only plants, the majority of recent installations have presprays prior to the dip tank. In the USA spray-only plants still predominate. Zinc phosphate processes normally operate in the range 50-60°C. Low temperature processes operating at 25-35°C are widely used in the UK and Italy but have not been extensively adopted elsewhere. 

A Radiometric Study of the Iron Phosphating Process , US Dept, of Commerce, Office of Technical Services, Rep. No. PB 111, 400 (1953)... 

Electric storage hot water heaters and instantaneous water heaters are used for simple domestic applications and are not considered in this text. For many smaller HW and lower pressure steam generation applications (including bakery ovens and proofers, jacketed kettles, fish pots and other cooking equipment, wineries, breweries, textiles, laundries, phosphatizing processes, humidification, steam baths, clean rooms, and pharmaceuticals), electric boilers offer significant advantages over fossil-fuel boilers and are often the product of choice. 

The brominated phosphate is an efficient flame retardant for polycarbonate resin. UL-94 ratings of V-0 with oxygen index values of greater than 40 are obtained. Polycarbonate resin containing brominated phosphate processes with greater ease than resin containing brominated polycarbonate as measured by injection molding spiral flow measurements. The heat distortion temperature is reduced... 

Gough, L.P. and R.C. Severson. 1976. Impact of point source emissions from phosphate processing on the element content of plants and soils, Soda Springs, Idaho. Pages 225-233 in D.D. Hemphill (ed.). Trace Substances in Environmental Health. Vol. X, Univ. Missouri, Columbia. 

Depending upon the quality level desired, the type of paint and the application method used, and the metal mix treated, a number of different types of pretreatment processes are available. For use as a paint base, the phosphate processes are either of the "iron phosphate" or the "zinc phosphate" type. 

Figure 6 Sodium phosphate process from wet process (from Ref. 8).

Practically all phosphating processes involve patented proprietary solutions which produce superior coatings in shorter times and at lower temperatures than ure obtainable with phosphoric acid alone. Treating times have been reduced from die earlier I - 2-hour to I - 5-minute periods, while temperatures have been reduced from 98 to 2(l-30l C. 

The oldest, most well-established chemical separation technique is precipitation. Because the amount of the radionuclide present may be very small, carriers are frequently used. The carrier is added in macroscopic quantities and ensures the radioactive species will be part of a kinetic and thermodynamic equilibrium system. Recovery of the carrier also serves as a measure of the yield of the separation. It is important that there is an isotopic exchange between the carrier and the radionuclide. There is the related phenomenon of co-precipitation wherein the radionuclide is incorporated into or adsorbed on the surface of a precipitate that does not involve an isotope of the radionuclide or isomorphously replaces one of the elements in the precipitate. Examples of this behavior are the sorption of radionuclides by Fe(OH)3 or the co-precipitation of the actinides with LaF3. Separation by precipitation is largely restricted to laboratory procedures and apart from the bismuth phosphate process used in World War II to purify Pu, has little commercial application. 

Corrosion of a Carbon Steel Tank in a Phosphatizing Process... 

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