METAL CONTENTS OF PHOSPHATE ROCKS

Significant amounts of phosphate rocks (PRs) are mined around the worl d annually. The rocks are either applied directly to soils or manufact ured to produce water-soluble phosphorus (P) fertilizers. In this stud y, 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 met als [aluminum (Al), barium (Ba), calcium (Ca), iron (Fe), potassium (K ), magnesium (Mg), sodium (Na), and strontium (Sr)l. The empirical for mulae and the unit-cell a dimension of the apatite contents were also determined. Results showed that the values of the unit-cell a dimensio n ranged from 9.324 Angstrom for North Carolina PR to 9.365 Angstrom f or Tahoua PR. The total P contents ranged from 109 g/kg for Kodjari PR to 176 g/kg for Pare W PR. The concentration of the trace metals in t he PRs varied considerably. Expressed in mg/kg PR, the ranges and medi an values were: Cd (5-47, 10), Co (6-104, 22), Cu (5-41, 8), Cr (18-33 1, 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 no ntrace metals expressed in g/kg were: Al (1.7-20.0, 5.6), Pa (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 detec tion limit of 5 ng/mL, no cesium (Cs) was found in the PR analyzed.