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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, K0.7Al2(Si,Al)4O10(OH)2, was present in it. The complete chemical composition of the material was 74.4% SiO2, 14.55% Al2O3, 3.62% Fe2O3, 1.55% CaO, 1.37% MgO, 2.44% K2O and 0.72%Na2O. 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.

treatment in HCl acidic solutions. 1 0 There are several important studies in the literature on aspects of diatomite T he eVects of sintering and puri cation processes on including its puri cation, sintering, and processing. 6 ,1 1 -1 4 the porosity and speci c surface area of diatomaceousThe Turkish material was found to be essentially earth, mined in the A nkara region of T urkey, were amorphous but also contained crystalline illite, investigated. T he material was studied in three forms,and a small amount of feldspar. as received, calcined, and puri ed. Changes in surface As is the case for most deposits in Turkey, it did not area occurred, with large diVerences between as consist only of diatom skeletons, and so is classi ed as a received, calcined, and puri ed materials. A s received low grade diatomite. The chemical composition (wt-%) material had very high pore volume, with a speci c was 74•4%SiO 2 , 14•55%Al 2 O 3 , 3•62%Fe 2 O 3 , 1•55%CaO, surface area of 204 m2 g -1. For puri cation, the raw 1•37%MgO, 2•44%K 2 O, and 0•72%Na 2 O. material was treated in H Cl solutions varying in concentration f rom 1 to 5N for several hours, with and without heating. T he puri cation treatment caused EXPERIMENTAL PROCEDURES reductions in BET surface areas, with minimum area Materials preparationafter treatment being 136 m2 g -1. A s received andThe material was studied in three forms, as received, puri ed samples were calcined at various temperatures.calcined, and puri ed. The as received material had an T he eVects of puri cation treatment and sintering on average particle size of 12 mm with a broad size distribution surface area and on the contents of undesirable aluminvarying from <0•2 to 140 mm, and with a BET area of ium, calcium, magnesium, iron, and alkaline impurities 204 m 2 g -1 . This material was calcined without ux at in the materials were characterised.BCT /501 several temperatures, selected with reference to the temperatures for maximum weight loss (700°C), decomposition of Dr Goren

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