Abstract: A process for obtaining a plant extract containing condensed tannins, with astringent characteristics, and modified by copolymerization, produces a material suitable for the tanning and retanning of skins. The process includes adding water to a reactor, adding a copolymerization agent, adding thioglycolic acid and allowing to react, adjusting pH, mixing a powdered extract of a plant or tannin to a desired concentration, raising the temperature, adding sodium bisulfite, and keeping the reaction heated and at pressure for about 4 hours.

Abstract: The present invention refers to a process for preparing a coagulating/flocculating agent comprising the following steps: a) mixing an aldehyde, an ammonium salt, and a mineral acid catalyst in a reaction vat at a temperature below 45° C. in an aqueous medium; b) reacting said mixture by heating said mixture until a colorless liquid is obtained; c) reacting said obtained colorless liquid with an aqueous tannin solution by stirring and heating to obtain a viscous liquid; and d) optionally, atomizing said viscous liquid to obtain a uniformly grained powder.