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Deironation Treatment of Clays with Oxalic Acid and Their Plasticity

Deironation treatment of clays with oxalic acid were studied by the chemical analysis and plasticity measurement. Examined calys were three kinds of Japanese ball clays, i. e., Kibushi clay (K), Kibushi clay (S) and Gairome clay (G) from Aichi Prefecture, and a Chinese ball clay, i. e., Kokudei clay (B). These plastic clays were treated by 1% and 4% of oxalic acid for 1 to 5 days. Leached iron was evaluated from total chemical analysis andextracted iron ion in solution. The plasticity change before and after the treatment was measured by Pfefferkorn plasticity test. Following results were obtained. (1) The extractability of iron (deironation ratio) was in the order of B >> S > G K. In the case of Chinese ball clay (B) which contains large amount of iron hydroxide, one third of total iron were extracted by the treatment with 4% of oxalic acid for 5 days. (2) By the oxalic acid treatment the Pfefferkorn plasticityindex increased, and water retentivity and characteristic value of plasticity decreased. Some consideration are given for these changes of plasticity.