sodium polyacrylate 0 25 grams sodium hexametaphosphate and 0 17 grams sodium carbonate under optimum conditions to form 60 65 solids suspension the dispersed clay suspension was then fractionated on a centrifuge to give a product suspension having a particle size of 92 95 finer than 2 microns after fractionation the solids content was adjusted to 55 and 0 3 grams of sodium dithionite dissolved in 5 milliliters of water was added to 100 grams on a dry basis of the clay suspension to simulate leaching at a treatment level of six pounds of reducing agent per ton of clay on a dry basis the fractionated clay suspension was also acidified with sulfuric acid to a ph of 3 0 3 5 the leached clay suspension was then subjected to post leaching oxidation by adding 0 225 grams of sodium perborate per 100 grams of dry clay the post leaching treated clay suspension was then filtered via high pressure filtration on a baroid filter press to form a filter cake at 74 solids this filter cake was then redispersed to form a 70 solids slurry the post leaching treated clay had a predispersed brightness of 84 6 and a brookfield viscosity of.