# US 9,873,070 B2 · Method for preparing a precoat on the surface of the filter medium of a polishing filter, polishing filter and use of a polishing filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,873,070 B2 - Document ID: US9873070B2 - Status: Granted - Kind: B2 - Application number: 14/351,207 - Filed: 2012-10-10 - Published: 2014-08-21 - Granted: 2018-01-23 - Earliest claimed: 2011-10-11 - Assignees: Outotec (Filters) Oy - Applicants: Outotec (Filters) Oy - Inventors: Leena Tanttu; Janne Kauppi; Yrjo Oinonen - Web page: https://patentgrep.com/patent/US9873070B2 ## CPC - B01D 37/02: Precoating the filter medium; Addition of filter aids to the liquid being filtered {(devices for feeding reagents C02F1/685 and sub-groups; filter aids)} - B01D 36/04: Combinations of filters with settling tanks - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) ## Abstract Methods and equipment for preparing a precoat on the surface of a filter medium of a polishing filter. A feature in the invention is that in the polishing filter, the precoat is formed either exclusively or jointly from the underflow created in the separation process. ## Claims ### Claim 1 A method comprising forming a precoat on the surface of a filter medium of a polishing filter, where the precoat is at least partially formed of the underflow of at least one of a thickener and a clarifier, where the precoat serves as a filter aid medium in polishing filtration of the overflow of said at least one of a thickener and a clarifier, where particles of the filter aid medium created by the precoat formed of the underflow serve as seed crystals, where particles contained in a supersaturated solution of the overflow are crystallized, and where the precoat is formed of essentially the same material as that to be filtered from the supersaturated solution of the overflow. ### Claim 2 (depends on 1) A method according to claim 1, where the precoat is a filter aid medium in pressurized polishing filtration, on the surface and/or in the structure of which there are separated nanoparticle-size solids from an overflow that has a smaller particle size than the underflow. ### Claim 3 (depends on 1) A method according to claim 1, where the underflow has a larger particle size and serves as a filter aid medium forming a porous precoat in which nanoparticle-size solids that are fed at a slow filtering rate and have a smaller particle size are at least one of filtered, precipitated, adsorbed and crystallized. ### Claim 4 (depends on 1) A method according to claim 1, where the size of the particles contained in the underflow and in the particles contained in the overflow is generally less than 1,000 nm, by average 40-400 nm. ### Claim 5 (depends on 1) A method according to claim 1, where the precoat is formed of essentially the same substance as the substance to be filtered. ### Claim 6 (depends on 1) A method according to claim 1, where the underflow and the overflow comprise those of a CaSO4 clarifier. ### Claim 7 (depends on 1) A method according claim 1, where the precoat is conducted back to polishing filtration, and reused as the filter aid medium creating the precoat. ### Claim 8 A polishing filter having a filter medium comprising a precoat, where the precoat is at least partially formed of the underflow of at least one of a thickener and a clarifier, and where the precoat serves as a filter aid medium in polishing filtration of an overflow of said at least one of a thickener and clarifier, where particles of the filter aid medium created by the precoat formed of the underflow serve as seed crystals, where particles contained in a supersaturated solution of the overflow are crystallized, and where the precoat is formed of essentially the same material as that to be filtered from the supersaturated solution of the overflow. ### Claim 9 (depends on 8) A polishing filter according to claim 8, where the precoat is a filter aid medium of a pressurized polishing filter, on the surface and/or in the structure of which there are separated nanoparticle-size solids from an overflow that has a smaller particle size than the underflow. ### Claim 10 (depends on 9) A polishing filter according to claim 9, where the solids from the underflow that has a larger particle size than the overflow are arranged as a filter aid medium comprising the precoat in connection with the filter medium of polishing filtration, and boost at least one of the filtering, precipitation, adsorption and crystallization of nanoparticle-size solids contained in the overflow that have a smaller particle size than the underflow. ### Claim 11 (depends on 8) A polishing filter according claim 8, where the filter aid medium arranged in the polishing filter enables the filtering of such nanoparticle-size solids from the process solution where the particle size is generally less than 1,000 nm, by average 40-400 nm. ### Claim 12 (depends on 8) A polishing filter according claim 8, including elements for conducting used precoat back to polishing filtration, to be reused to form the precoat serving as a filter aid medium.