Chemical and physical characteristics of phosphate rock materials of varying reactivity

Abstract

Several chemical and physical properties of 10 phosphate rock (PR) materials of varying reactivity were evaluated. These included North Carolina phosphate rock (NCPR), Sechura phosphate rock (SPR), Chatham Rise phosphorite (CRP), Arad phosphate rock (APR), Gafsa phosphate rock (GPR), North Florida phosphate rock (NFPR), Jordanian phosphate rock (JPR), Mexican phosphate rock (MPR), Nauru Island phosphate rock (NIPR), and Makatea Island phosphate rock (MIPR). Concentrations of As and Cd were highest in NCPR and U was higher in APR and CRP than in the other reactive PR materials. Because Cd and U can accumulate in biological systems, it may be necessary to direct more attention towards the likely implications of Cd and U concentrations when evaluating a PR for direct application. Three sequential extractions with 2% citric acid may be more useful for comparing the chemical solubility of PR materials, particularly for those containing appreciable CaC03. For each particle-size fraction from <63 to >500 pm, SPR was more soluble in 2% citric acid than was NCPR. The higher solubility of SPR than NCPR in 2% citric acid, 2% formic acid, and neutral ammonium citrate possibly results from a higher chemical reactivity rather than from any difference in the surface area presented for dissolution. The poor relationship obtained between surface area and the solubility of the PR materials in the three chemical extractants suggests that surface area plays a secondary role to chemical reactivity in controlling the solubility of a PR in a chemical extractant. A Promesh plot provided an effective method for describing the particle-size characteristics of those PR materials which occurred as sands. Fundamental characteristics, such as mean particle size and uniformity, can readily be determined from a Promesh plot.

Efeito de fosfatos naturais em plantas de melão cultivadas em vasos

“…O Fosbahia, mesmo apresentando granulometria mais fina que a do Gafsa (Quadro 2), por ser menos reativo que este, revelou menor eficiência que a do Gafsa, no PAe (Quadro 4). Syers et al (1986) mencionaram que a eficiência dos FN depende mais de sua solubilidade nos extratores químicos que da sua área de superfície específica. A solubilidade de fosfatos naturais em ácido cítrico 2 % tem sido um critério adequado para avaliação de sua eficiência agronômica, existindo correlação altamente significativa entre estas características (Oliveira et al, 1984).…”

Avaliação do fosfato natural de Gafsa para recuperação de pastagem degradada em latossolo vermelho-escuro

“…Os fosfatos de origem ígnea ou metamórfica, em cuja categoria se enquadram os fosfatos naturais brasileiros de importância comercial, são pouco reativos, em contraste com os fosfatos de origem sedimentar, como os de Gafsa e Carolina do Norte, classificados como altamente reativos (Syers et al,1986;León et al, 1986).…”

Cadmium status of soils, plants, and grazing animals in New Zealand

“…Australian superphosphate has been shown to contain, on average, 33 jig Cd/g (range 6-68 ng/g) (Hilliard et al 1988) whereas New Zealand superphosphate contained, on average, 48 ug Cd/g (range 34-69 ug/g) (Rothbaum et al 1986). The Cd in superphosphate arises primarily from the phosphorite used as the raw material, although Cd content varies considerably with origin of the phosphorite (Syers et al 1986). …”

“…While there is much overseas work published on Cd in the agricultural environment, few studies published are relevant to New Zealand soils and pastoral agricultural systems (Roberts 1981;Solly et al 1981;Rothbaum et al 1986;Syers et al 1986;Bramley 1990).…”