Six different phosphate rocks from northeast Brazil were characterized chemically and mineralogically and were studied in relation to their decomposition with nitric acid, hydrochloric acid, and sulfuric acid. To measure the degree of decomposition, a specific procedure, called the technological aptitude test, was used. The results are represented in the form of graphs showing the reactivity of each rock against the time of decomposition. The results differ widely from one sample to another, and for this reason, a control rock (Morocco rock) was used. Rocks with similar geological origin present similar behavior toward acid attack. The rocks of sedimentary origin showed quite high values of reactivity even within the first 3 min of reaction (not less than 65% reactivity). On the other hand, the aluminum phosphates showed very low reactivity all over the tests (not more than 25% reactivity). Also, an average AP index (technological aptitude index) is proposed to compare directly one rock to another when submitted to some acid attack. © 1990, American Chemical Society. All rights reserved.
