Phosphate fluid fertilizers

Removing Heavy Metals from Phosphoric Acid and Phosphate Fluid Fertilizers... 

Heavy metals in wet-process phosphoric acid (WPA) and phosphate fluid fertilizers are an environmental concern in the United States and Europe. 

Sulffde Precipitants. The removal of heavy metals from waste waters using soluble sulfides has been studied extensively. Peters and Ku (13) showed that pH strongly affects the removal of heavy metal sulfides from waste water. Their data showed that the solubilities of most heavy metal sulfides, other than arsenic (HI) sulfide, decreases up to about pH 9. Since most phosphate fluid fertilizers, such as 10-34-0 and 11-37-0, have a pH in the range of 6 to 7, these data indicate that concentrations of several heavy metals in phosphate fluid fertilizers could be reduced to very low levels by precipitation with inorganic sulfide reagents. The use of soluble sulfides to precipitate heavy metals from WPA has also been reported. Both Maruyama (14) and Berglund (15) have... 

Ferrocyanide. The reaction of Fe(II) and Fe(III) with the ferrocyanide ion Fe(CN)6 to form highly insoluble compounds is well known. However, cadmium, lead, and probably other heavy metals also form ferrocyanide precipitates which may allow their removal from WPA and phosphate fluid fertilizers. 

Cyanuric Acid. Organic cyanurates and isocyanurates have been prepared as pure materials and their use as metal precipitants has been reported in the literature (25-25). Diallylisocyanurate salts of cadmium, copper, and lead have been described and polyisocyanurates have been cited as precipitants for monovalent and divalent metal ions — including Cd, Hg and Pb —from waste streams (26). Initial tests with 10-34-0 (pH 6.8) indicated that ammonium cyanurate was soluble in the media however, no measurement of the solubility was made and no precipitate was observed. Addition of ammonium cyanurate to a 10-30-0 (pH 6.0) grade phosphate fluid fertilizer containing 40 ppm cadmium indicated low solubility of the reactant in the media and resulted in no cadmium removal at stoichiometries ranging from 25 to 480%. Confirmatory tests... 

Inorganic Reagents. The removal of arsenic, cadmium, and lead from 10-34-0 using polysulfide was almost twice that obtained with sulfide. The polysulfides appear to be promising for removal of several heavy metals from phosphate fluid fertilizers but are not satisfactory for use with WPA. However, ferrocyanide was shown to be highly effective for use with WPA. Ferrocyanide precipitated iron, cadmium, and nickel from WPA to below the detectable limits of the analytical method. The possible formation of hydrocyanic acid and the extreme fineness and bulk of the metal-ferrocyanide precipitate are disadvantages of this method. 

The routes by which mineral phosphates are processed into finished fertilizers are outlined in Eigure 7. World and U.S. trends in the types of products produced are shown in Eigures 8 and 9, respectively. Most notable in both instances is the large, steady increase in the importance of monoammonium and diammonium phosphates as finished phosphate fertilizers at the expense of ordinary superphosphate, and to some extent at the expense of triple superphosphate. In the United States, about 65% of the total phosphate appHed is now in the form of granular ammonium phosphates, and additional amounts of ammonium phosphates are appHed as integral parts of granulated mixtures and fluid fertilizers. 

Clarity - Fluid fertilizers that are produced from wet-process phosphoric acids derived from uncalcined phosphate ores are black in color due to the presence of finely divided carbonaceous material. The black color has no effect on the nutrient value of the fertilizers, but it does restrict the sight identification of solid material in solution fertilizers that could clog the... 

Nitrogen in Multinutrient Fertilizers. Single-nutrient nitrogen materials suppHed over 85% of the fertilizer nitrogen used in the United States during the year ended June 30, 1990. The remaining 15% was suppHed as multinutrient materials (Fig. 3). This included 9% as ammonium phosphate, 2% as cogranulated mixtures, and 3% as fluid mixtures. 

Fig. 9. U.S. trends in types of phosphate fertilizers consumed, where (—) represents ammonium phosphates, cogranulated mixtures, and fluids (-)...

Scotts technology (17) uses fluid-bed (Wurster column) technology to apply polymeric coatings to a number of fertilizer substrates including urea, potassium nitrate, potassium sulfate, and monoammonium phosphate (MAP). The coating material is appHed as a water-borne latex onto the fluidized substrate. As the substrate is fluidized with warm air (40—50°C), water is driven off and the latex coalesces into a continuous film around the fertilizer particle. The particular latex compositions used have selected glass-transition and blocking temperatures, which enable quick removal of the water before the soluble fertilizer core dissolves. This obviates the need to use precoats prior to the latex appHcation. 

Tricresyl phosphate (a complex mixture containing tri-o, Xn-m-, and tri-para-cresyl phosphate that is used in certain hydraulic fluids) and TOCP are demonstrated testicular toxicants in rodents (Carlton et al. 1987 Somkuti et al. 1987a, 1987b). Tricresyl phosphate also has been shown to impair in vivo fertility in rats and mice (Carlton et al. 1987 Chapin et al. 1988a). In addition, tricresyl phosphate-treated female rats displayed vacuolar cytoplasmic alteration of ovarian interstitial cells (Carlton et al. 1987 NTP 1994). Reproductive effects have also been seen after oral exposure to butylated triphenyl phosphate (Latendresse et al. 1994b). 

The only element that was discovered in body fluids (urine). This is plausible, as P plays a main role in all life processes. It is one of the five elements that make up DNA (besides C, H, N, and 0 evolution did not require anything else to code all life). The P-O-P bond, phosphoric acid anhydride, is the universal energy currency in cells. The skeletons of mammals consists of Ca phosphate (hydroxylapatite). The element is encountered in several allotropic modifications white phosphorus (soft, pyrophoric P4, very toxic), red phosphorus (nontoxic, used to make the striking surface of matchboxes), black phosphorus (formed under high pressures). Phosphates are indispensable as fertilizer, but less desirable in washing agents as the waste water is too concentrated with this substance (eutrophication). It has a rich chemistry, is the basis for powerful insecticides, but also for warfare agents. A versatile element. 

Fig. 24.15. Estimated world production of fertilizers by product type. 1. Steam/water, chemical (including ammonium phosphate), and compacted granular products. 2. Single- and multiple-nutrient fluids, including anhydrous ammonia. 3. As reported by IFA, nutrient production (2002/03 reporting year) amounted to 152.2 million mt (N + P2Os + K20). Product mt were calculated by multiplying 2.35 times the nutrient mt.

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