On the Coral Limestone from Tokunoshima and Okierabushima

Abstract

Coral limestone resourses are very aboundant in Amami Islands, but a slight amount of the ore has been only used for chemical industrial materials.The object of this paper is to describe the results of the writers' work on the fundamental properties of the coral limestone from Tokunoshima and Okierabushima, Kagoshima Prefecture.Several samples of coral limestones were collected from the each terrace in Tokunoshima (8 terraces), and in Okierabushima (6 terraces).Chemical analysis, X-ray analysis, determination of specific gravity, and various thermal tests etc. were conducted on these samples.Slaking test and sedimentation test were also made on these coral limestones calcined at 950°-1100°C. Following results were obtained.(1) Main mineral component in the coral limestone is calcite, often contains dolomite or quartz.(2) Coral limestones of 32 samples have the following physical properties and chemical composition: apparent specific gravity 1.67-3.05, bulk density 1.64-3.38, apparent porosity 2.22-18.34%, moisture content 1.11-9.97%, and CaO 47.65-55.41%, MgO 0.10-3.52%, SiO2 0.11-10.52%, Fe2O3+Al2O3 0.42-4.48%. The average value of CaCO3 content of Okierabushima are is 94.73%, but the coral limestone from Tokunoshima is of poor quality with a purity of CaCO3 89.50%.(3) It seems that the coral limestones located at higher terraces in Tokunoshima and Okierabushima have larger crystal size, larger thermal expansivity and more rapid thermal decomposition velocity than those of the coral limestones located at lower terraces, respectively.(4) The effect of calcining temperature on the slaking velocity of calcined ore is governed by the chemical and physical properties of the original rocks. The stiff coral limestone including a slight amount of impurities calcined at 950°C is of good results, but the porous coral limestone including a large amount of impurities, i.e. SiO2, Al2O3, Fe2O3 and MgO, has a slow slaking velocity at this calcination temperature.