Phosphate fertilizers from mineral phosphates

Eig. 7. Routes for making finished fertilizer from mineral phosphate. Consumption data are for year ending June 30, 1990 (5). includes quantities appHed... 

Small amounts of cadmium enter the environment from the natural weathering of minerals, but most is released as a result of human activities such as mining, smelting, fuel combustion, disposal of metal-containing products, and application of phosphate fertilizers or sewage sludges (USPHS 1993). In 1988, an estimated 306,000 kg of cadmium entered the domestic environment as a result... 

As discussed earlier in Section 3.17, the excessive application of arsenic-bearing pesticides and phosphate fertilizers on agricultural lands, golf courses, and lawns may locally contaminate surface waters and ground-waters (Welch et al., 2000), (Lewis et al., 2002), 590. Phosphates desorb arsenic from mineral surfaces and readily interfere with the sorption and coprecipitation of arsenic onto iron (oxy)(hydr)oxides (Campos, 2002). Commercial phosphate fertilizers also frequently contain >13 mg kg-1 of arsenic impurities (Campos, 2002), which may further contribute to groundwater contamination. 

Because of the low P content (usually < 0.2 %) of forage plants, P supplementation is commonly practiced in most ranches throughout the Amazon basin, particularly in Brazilian Amazonia. Assuming a stocking rate of 0.8 animal units per hectare per year, the annual input of P to the system through animal consumption of mineral supplementation would be around 2.0 kg, which is close to the amount expected to be exported annually by animal products (2.5 kg). The amount thus needed to balance the cycle would be only 0.5 kg. In the absence of phosphate fertilizer inputs, this P must come from the soil pool reserves, through forage consumption. 

For many of the more abundant elements, such as Al, Fe, and Mn, precipitation of mineral forms is common and may greatly influence or even control their solubility. For most trace elements, direct precipitation from solution through homogeneous nucleation appears to be less likely than adsorption-desorption, by virtue of the low concentration of these metals and metalloids in soil solutions in well-aerated dryland soils. When soils become heavily polluted, metal solubility may reach a level to satisfy the solubility product to cause precipitation. Precipitation may also occur in the immediate vicinity of the phosphate fertilizer zone, where the concentration of heavy metals and metalloids present as impurities may be sufficiently high. Precipitation of trace metals as sulfides may have a significant role in metal transformation in reduced environments where the solution sulfide concentration is sufficiently high to satisfy the solubility product constants of metal sulfides (Robert and Berthelin, 1986). 

Naturally occurring F associated with hydrous minerals has low mobility because it is occluded in structures. Airborne fluoride pollutants (from smelters, rock phosphate fertilizer factories, etc.) are, in contrast, easily dissolved on contact with the soil. These forms of fluoride can be bioaccumulated by plants before leaching, sorption, or precipitation processes have a chance to lower solubility. 

Rock phosphate is used as fertilizer only for acid and humus-rich soils. Generally, phosphates are fertilized in the form of water- or acid-soluble compounds, derived from rock phosphate (processed mineral phosphate fertilizers). An example is superphosphate, a mixture of monobasic calcium phosphate and calcium sulfate (7-9% P). In double or triple superphosphate the P-con-tent rises to about 20%. Manures contain... 

Sodium fluoride occurs naturally as the mineral villiau-mite, although the compound is not produced commercially from that source. Some sodium fluoride is obtained as a byproduct of the manufacture of phosphate fertilizers. In that process, apatite (a form of calcium phosphate that also contains fluorides and/or chlorides) is crushed and treated with sulfuric acid (H2S04). The products of that reaction include phosphoric acid (H3P04), calcium sulfate (CaS04),... 

Location, soii type, texture, sampiing depth and totai phosphorus concentration of controi sites in these studies are given in Table 11.1. Mineral phosphate fertilizer (with single superphosphate, triple super phosphate, calcium apatite, or rock phosphate) unless stated otherwise. Carbon concentrations from Lehmann etal. (2001a). 

Production of animal glue is considered as environmentally friendly , since it involves conversion of unpleasant waste into useful products, but economic operation depends on satisfactory disposal of residues some of these are used as slow-release nitrogenous fertilizers. The mineral residue from bone glue production ( bone meal ) by thermal methods is used as a phosphate supplement in animal feed and fertilizers it is also calcined at 1000-1200 °C to produce calcined bone, used in the manufacture of bone china to provide strength and translucency. Animal glues and technical gelatins contain added preservatives and a proportion of non-protein materials, usually mucopolysaccharides and soluble inorganic salts. These impurities differ with the source of raw material. 

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