International Journal of Mineral Processing, 7 (1980) 255--262 255 Elsevier Scientific Publishing Company, Amsterdam --Printed in The Netherlands A PROPOSED REFERENCE FOR MEASURING THE CITRIC ACID SOLUBILITY OF CALCAREOUS PHOSPHATES A.-Z.M. ABOUZEID 1 and I.S. EL-JALLAD 2 Cairo University, Faculty of Engineering, Department of Mining, Giza (Egypt) (Received May 5, 1980; revised version accepted May 28, 1980) ABSTRACT Abouzeid, A.-Z.M. and E1-Jallad, I.S., 1980. A proposed reference for measuring the citric acid solubility of calcareous phosphates. Int. J. Miner. Process., 7: 255--262. The quality of calcareous phosphate rocks is normally assessed by both their grades and their chemical reactivity. Chemical reactivity is measured directly on the run-of-mine samples or their calcined products. Since chemical reactivity was found to be a function of the calcareous compounds in the sample (CaCO 3 and CaO) it was necessary to propose a standard reference that makes the reactivity parameter independent of the ore grade. A calcareous sample treated with triammonium citrate solution before reactivity measurement is proposed as a standard reference for chemical reactivity of phosphate minerals in phos- phate rocks. This will make the chemical reactivity an independent parameter for evaluating the phosphate quality in addition to the grade of the ore. 4% citric acid solution was used in this research work for measuring the relative solubility of the phos- phate samples. INTRODUCTION It has been a long time since it was realized that a reliable measure for the suitability of phosphate rocks as a fertilizer was needed. The chemical reactivity of the rock was found to be a good measure of the suitability of the phosphates for fertilizer purposes or for direct application to the soil. The solubility behavior of phosphate rocks in mild solvents such as citric acid, neutral ammonium citrate and alkaline citrate solutions provides an indication of relative reactivity. The Association of Official Agricultural Chemists (A.O.A.C.) adopted the citrate method !n 1884 (A.O.A.C., 1950) for determining the relative solubility of calcium phosphates. The method used a neutral solution of ammonium citrate as extractant. There are, how- Present addresses: 1 Department of Materials Science and Mineral Engineering. University of California, Hearst Mining Building, Berkeley; Calif. 94720, U.S.A. 2 Jordan Phosphate Company, Amman. Jordan. 0301-7516/80/0000--0000/$ 02.25 ©1980 Elsevier Scientific Publishing Company