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I.

INTRODUCTION

BORONis a rare but very widely distributed element only found in a concentrated form in a few places. Ilj Boron compounds are very widely used in many branches of industry, f2) The production of boron compounds from borate ores (3-6~ and dissolution kinetics of borate ores in several acid solutions have been investigated, t7-1~ Colemanite is a boron-containing mineral with a composition 2 C a O . 3B203" 5H20 that has a density of 2400 kg m -3. The solubility and dissolution kinetics of colemanite in CO2-saturated water tl~,n~ and in SO2saturated water I~3~have been studied. It is well known that many amino polycarboxylic acids form stable complexes when they react with metal cations. Among these, the EDTA is the most commonly used. The E D T A leaching process has advantages in that it can be accomplished even under mild operating conditions, and furthermore, the E D T A can be recovered for r e u s e . I~4~ The leaching kinetics of pure and low-grade scheelite I14'151 in EDTA solutions have been studied by Konishi et al. Dissolution kinetics of azurite, malachite, and ehlite in E D T A solutions have also been studied, tt6~ In this study, the dissolution kinetics of colemanite in aqueous disodium EDTA solutions have been investigated. The reaction can be written as 2 C a O . 3B203" 5H~O + 2HaY z+ 2H~O --~ 2CaY e- + 6H3BO3 [ 1] where H2Y2 represents the ion of EDTA. The effects of concentration and pH of the EDTA solution, particle size of the mineral, and reaction temperature have been evaluated, and some kinetic data are reported.

II.

EXPERIMENTAL PROCEDURES

A. Preparation of Materials The colemanite sample used in the study was hand picked from Espey Mine, Turkey. After cleaning, it was ZAFER KARAGOLGE, Research Assistant, Department of Chemistry, Kazim Karabekir Faculty of Education, and M. MUHTAR KOCAKERIM, Professor, Head of Department of Chemical Engineering, Faculty of Engineering, are with Atatiirk University, Erzurum, Turkey. MAHIR ALKAN, Assistant Professor, formerly with Atattirk University, Kazim Karabekir Faculty of Education, is with the Department of Chemistry, Necatibey Faculty of Education, Uluda~ University, Balikesir, Turkey. Manuscript submitted February 25, 1991. METALLURGICAL TRANSACTIONS B

sieved to give - 1 7 0 0 + 850, - 8 5 0 + 425, - 4 2 5 + 250, - 2 5 0 + 150, and - 150/xm size fractions by using ASTM standard sieves. Analysis of the sample gave a composition of 27.23 pct CaO, 50.47 pct B 2 0 3 , and 22.30 pct H20. Other chemicals were made by Merck, Darmstadt, Federal Republic of Germany.

B. Method Dissolution experiments were carried out in a 100 ml glass vessel. Fifty milliliters of disodium EDTA solution which had been previously heated to the experiment temperature was added into the reaction vessel containing 0.5 g of colemanite. The reaction mixture was stirred by a magnetic stirrer and kept at the required temperature by a constant temperature circulator. At the end of the desired period of time, the reaction mixture was filtered, and the amount of CaO react