A study on the purification of diatomite in hydrochloric acid

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This paper describes the purification of diatomaceous earth mined in the Ankara region of Turkey. The diatomaceous earth was found to be essentially amorphous, but a small amount of crystalline illite, K 0.7 Al 2 (Si,Al) 4 O 10 (OH) 2 , was present in it. The complete chemical composition of the material was 74.4% SiO 2 , 14.55% Al 2 O 3 , 3.62% Fe 2 O 3 , 1.55% CaO, 1.37% MgO, 2.44% K 2 O and 0.72%Na 2 O. In connection with the purification of the diatomite, two different processing routes were planned: (i) leaching of the diatomaceous earth directly in cold acidic solutions of HCl; (ii) leaching of the diatomaceous earth directly by using hot 1 and 2 N HCl. It was found that all of the undesirable elements in the composition of the diatomaceous earth were dissolved when treated at about 100°C with acidic solutions prepared using 1 and 2 N HCl for various leaching times. Under several cold acid concentrations, varying from 1 N to 5 N HCl, however, only a small amount of silica is dissolved, while significantly reducing the contribution of undesirable aluminium, calcium, magnesium, iron and alkaline elements.