Métodos de extração para quantificação de cobre disponível em fertilizantes

Phytoavailability of Copper in Industrial by-Products and Mineral Fertilizers

“…At pH 2.3, the deprotonation of the three carboxyl groups from the molecules of citric acid, which is a condition for the release of oxygen as an electron donor group to the metal chelate, is more difficult (Alcarde and Ponchio, 1979), resulting in a complexing action of lower intensity in the 2 % CA solution than in NAC. Other authors also reported higher solubility of Cu sources in the NAC extractant compared to 2 % CA (Bastos et al, 2007a;Moura, 2010).…”

“…However, the low solubility of Cu was found in the scrap slag (Table 4), in which the element appears in the form of oxide (Table 3), as well as the metallic form. According to Bastos et al (2007a), metallic Cu in the crystalline phase is related to its difficult solubilization and could be better solubilized in stronger extractants derived from nitric acid, hydrochloric acid or their mixture. In addition to the presence of metallic Cu, the high concentration of Cu in this sample (35 dag kg -1 , Table 1) may have reduced the extraction capacity of NAC+water (1:1); and the presence of Zn and other minerals in Cu ore, shown by X-ray diffraction (Table 3), also decreased the solubilizing capacity of this extractant.…”

“…Interestingly, the granulated Cu fertilizer did not reach the required minimum solubility (Table 4), although it is registered and authorized by MAPA for the market. This fertilizer contains Cu in the form of alloy (urusovite), carbonate (malachite and azurita) and sulfide (chalcopyrite) (Table 3), which are chemical forms known for their lower solubility (Bastos et al, 2007a;Moura, 2010).…”

“…Possibly, the higher Cu availability in this source was due to its presence in oxide and sulfate rather than sulfide forms (Table 3), and this may also be related to the slow solubilization of this source in the soil. Bastos et al (2007a) stated that the availability of Cu to wheat plants by the application of some mineral sources to the soil resulted in lower uptake of the element when the source was chalcopyrite ore, followed by industrial copper oxide 40 %. The other Cu sources evaluated in this study were Cu sulfate, cupric oxide mixture+ground Cu metal, ground Cu metal, and cupric oxide.…”

“…This extractant was selected based on studies that showed its good performance in predicting Cu availability to rice plants Alcarde, 1999, 2003;Bastos et al, 2007a). However, for secondary materials and ores containing Cu, the law requires only a declaration of the levels determined in HCl (Brasil, 2007b).…”