Patent ID: 7875189

Claim:
A method for separating suspended solid materials from an aqueous medium comprising mixing the aqueous medium with a flocculant made of a polymer colloidal particles with cationic surface charge to obtain a flocculated material and subsequently separating the flocculated material from the aqueous medium, wherein the colloidal particles are formed by emulsion copolymerisation of one or more hydrophobic vinyl monomers with one or more cationic vinyl monomers, wherein the emulsion copolymerisation is implemented in a feed method wherein the one or more cationic vinyl monomers are fed in a continuous manner, wherein the charge density of the colloidal particles is from 5 μC/cm 2 to 35 μC/cm 2 and the size of the colloidal particles is from 50 nm to 1,000 nm, and wherein the one or more hydrophobic vinyl monomers are styrene and/or a homologue thereof, the one or more cationic vinyl monomers are N-methacryloyloxyethyl-N,N,N-trimethylammonium chloride, N-methacryloyloxyethyl-N,N-dimethyl-N-benzylammonium chloride and/or 4-vinylpyridine, and the cationic surface charge is bonded to the particle surface directly or via a spacer.