SOME FACTORS AFFECTING DESORPTION OF SILICATE IN THE WHITE WATER-SYSTEM OF A PAPER-MACHINE

Soluble silicates, released during the production of peroxide bleached mechanical pulp, potentially detrimental to papermaking, were studied on a laboratory scale. Pressurised groundwood pulp samples were bleac hed in a water bath whereupon kaolin, calcium salt or aluminium salt w as introduced in conjunction with dilutions of the bleached pulp to pa permaking consistency. Kaolin and calcium ions clearly gave rise to de sorption of the silicate whereas the addition of aluminium resulted in coagulation of silicate onto the fibre surface. Increased temperature together with kaolin or calcium increased the desorption further High er temperature could not alone, however desorb silicate. Shear forces did not cause the desorption of silicate even under very drastic condi tions.