The reddish brown flint clay alias Akabannendo which mainly consists of kaolinite exists enormously in Iwaizumi-cho, Iwate Prefecture.In spite of its high alumina content, the utilization of the clay has not been achieved because of its high iron content.In this paper, the acid treatment has been investigated for the purpose of iron removal from the clay.The clay specimen was crushed into different size fractions, and treated with 0.1-10N hydrochloric acid, sulfuric acid and nitric acid under the temperature condition between 20°C and boiling point.The results are summarized as follows.
(1) The specimen almost consists of fine grains of kaolinite under 1μ size and its iron content is 5.63wt% as ΣFe2O3. Some iron minerals, such as hematite, siderite and magnetite were ascertained in the specimen and the amount of hematite consist of fine particle was much larger than that of the other iron minerals.
(2) The extent of iron leaching is mainly affected by the sort of acid solution, acid concentration and treating temperature. Under the same treating condition, the amount of iron leached by each acid solution decreases in the order of hydrochloric acid, sulfuric acid and nitric acid, but alumina is leached in the reverse order.
(3) The iron content of the specimen decreased to 0.56wt% by hydrochloric acid treatment and the yield of purified product obtained was about 90% in weight.But about 10% portion of iron constituent in the specimen could not be removed by the acid treatment.
(4) According to the autoclaving tests, it is considered that the decomposition of kaolinite structure by the acid treatment arises at the lower crystalline part and gradually goes on to the higher one with proceeding the reaction.
(5) The most suitable acid for the iron removal from “Akabannendo” is concluded to be hydrochloric one for the reasons of its difficulty to destroy the structure of kaolinite and its high iron extractability.In this case, the treatment was effectively carried out under the condition in which the acid concentration and temperature of the solution were 6N and 60°C, respective.
