Mineralogy, geochemistry and possible industrial applications of illite-smectite rich clays from Karak, northwestern Pakistan.

The Karak mudstone, cropping out in the vicinity of Karak town, NW Pakistan, is contained within an Eocene evaporitic sequence deposited in the rapidly sinking Kohat foreland basin. It was buried beneath 5 Km of younger sedimentary rocks. Illite-smectite with 20 to 30% expandable component is the most dominant clay mineral, which has converted from detrital smectite or highly expandable illite-smectite in a diagenetic environment at ~ 100 C. Time does not seem to be have played any significant role in the conversion of smectite layers to illite layers. The A1 and K necessary for the conversion reaction was provided by the breakdown of detrital K-feldspar. Muscovite does not seem to have contributed to this process as suggested by previous studies. Direct lattice images of illite-smectite revealed that conversion of smectite layers to illite layers took place through dissolution of smectite layers and precipitation of illite layers as well as by solid state mechanism. Whole rock chemical analysis suggests that the mudstone is a product of severe weathering of the source area which was mainly composed of acidic rocks. Depleted ions like Ba, Rb, Ca and Mn were probably flushed out from the restricted basin by influx of fresh water. The swelling properties of Karak mudstone are low and even Na activation does not enhance these properties. The smectite layers may already have undergone natural Na activation due to original sea water and pore water hypersalinity. Cation exchange capacity and total surface area values are also low, which suggests this material is unsuitable for most major bentonite related uses. Owing to the higher concentration of Mg and Fe ions in the octahedral site of illite-smectite these clays were easily activated with HCl. Acid activation also increased surface area as measured by BET method. Bleaching performance of activated material measured on rapeseed oil showed optimum bleaching capacity of 90% following treatment with 2N HCl for three hours or 3N HCl for two hours. The maximum bleaching capacity was not associated with maximum surface area. Pilot plant scale tests should be carried out to investigate the potential for industrial applications of this material.