Phosphoms leaching

In the United States the analytical methods approved by most states are ones developed under the auspices of the Association of Official Analytical Chemists (AOAC) (3). Penalties for analytical deviation from guaranteed analyses vary, even from state to state within the United States (4). The legally accepted analytical procedures, in general, detect the solubiUty of nitrogen and potassium in water and the solubiUty of phosphoms in a specified citrate solution. Some very slowly soluble nutrient sources, particularly of nitrogen, are included in some specialty fertilizers such as turf fertilizers. The slow solubihty extends the period of effectiveness and reduces leaching losses. In these cases, the proportion and nature of the specialty source must be detailed on the labeling. 

The paper-impregnation drying oven exhausts contain high concentrations (10—20% LEL) of alcohols and some resin monomer. Vinyl resins and melamine resins, which sometimes also contain organic phosphate fire retardants, may be used for air filters. The organic phosphates could shorten catalyst life depending on the mechanism of reduction of catalyst activity. Mild acid leaching removes iron and phosphoms from partially deactivated catalyst and has restored activity in at least one known case. 

Like nitrates, phosphates are included in the indicative list of main pollutants (Water Framework Directive, 2000/60/EC) because of their contribution to eutrophication. Phosphorus is an essential nutrient for all plants and in modem agriculture this element has to be supplied to the crops as fertilizer. Wind erosion, surface mnoff and leaching constitute the main pathways for transport of phosphoms from terrestrial to aquatic ecosystems. The process is accelerated by agriculture, animal husbandry and anthropogenic discharges. 

During leaching, not only the rare-earths but also impurity elements such as calcium, sodium, phosphorus, chlorine, magnesium, antimony, manganese, iron, and aluminum were dissolved. In order to remove these impurities, hydroxide precipitation at pH 10 with ammonia and the subsequent hydrochloric acid leaching of the precipitate were studied. By the hydroxide precipitation, sodium, phosphoms, chlorine, calcium, and magnesium remained in the supernatant and rare earths formed a precipitate. After dissolving the precipitate with hydrochloric acid, rare earths were recovered by the oxalate... 

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