Metal contents of phosphate rocks

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Abstract
Significant amounts of phosphate rocks (PRs) are mined around the world annually. The rocks are either applied directly to soils or manufactured to produce water‐soluble phosphorus (P) fertilizers. In this study, we analyzed 12 PRs obtained from various deposits in Africa, United States, and Peru for total P, ten trace metals [cadmium (Cd), cobalt (Co), copper (Cu), chromium (Cr), lithium (Li), manganese (Mn), nickel (Ni), lead (Pb), rubidium (Rb), and zinc (Zn)] and eight nontrace metals [aluminum (Al), barium (Ba), calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), sodium (Na), and strontium (Sr)]. The empirical formulae and the unit‐cell a dimension of the apatite contents were also determined. Results showed that the values of the unit‐cell a dimension ranged from 9.324 Å for North Carolina PR to 9.365 Å for Tahoua PR. The total P contents ranged from 109 g/kg for Kodjari PR to 176 g/kg for Parc W PR. The concentration of the trace metals in the PRs varied considerably. Expressed in mg/kg PR, the ranges and median values were: Cd (5–47, 10), Co (6–104, 22), Cu (5–41, 8), Cr (18–331, 46), Li (2–9, 2), Mn (11–6553, 263) , Ni (1–61, 10) , Pb (7–43, 14), Rb (3–18, 6), and Zn (54–576, 124). The corresponding values of the nontrace metals expressed in g/kg were: Al (1.7–20.0, 5.6), Ba (0–4.4, 0.4), Ca (211–330, 298), Fe (1.4–45.7, 6.8), K (0.3–10.9, 1.4), Mg (0.6–16.9, 2.2), Na (1.0‐ 22 .8, 10.4), and Sr (0.3–6.7, 1.0). At the detection limit of 5 ng/mL, no cesium (Cs) was found in the PR analyzed.