Abstract
The chemical and mineralogical characteristics of two major kinds of phosphate rock (PR) deposits identified in the Lau group, eastern Fiji, were investigated before and after acidulation and calcination. X-ray diffraction analyses of the Lau PRs showed the presence of Ca and Al rich phases of phosphate minerals. The oolitic material consisted of dominant amounts of fluorohydroxyapatite and only subordinate amounts of crandallite whilst the phosphatic clay consisted almost entirely of crandallite. Acidulation of the PRs caused a marked increase in water, citric and formic acid extractable-P. However the amounts extracted were almost 10–15 times less than that released by a reference North Carolina PR. Of the two types of PR found in Fiji, the apatite rich oolitic material released 8–10 times more extractable P than phosphatic clays following acidulation. Calcination of crandallite rich phosphatic clay at 800°C caused a small but significant increase in extractable P; but, the effect was less marked than that of acidulation, suggesting that the small amounts of apatite minerals present in the phosphatic clay have a greater influence following acidulation on available P than crandallite.
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