METHOD FOR TREATING A FERROUS METAL SUBSTRATE Russian patent published in 2018 - IPC C23C22/86 C23C22/36 C23C22/34 

FIELD: chemistry.

SUBSTANCE: invention relates to the removal of iron from a pretreatment bath withdrawn from operation. Variants of a method for removing iron from a pretreatment bath are proposed, substantially free of phosphate ions during its functioning, which are carried out in the absence of an article, which is to be coated with said pre-treatment composition. In a first variant of the method for removing iron from a pretreatment bath, containing composition for pretreatment, containing Group IIIB metal and / or Group IVB, (a) reducing the pH of said pretreatment bath to at least 0.2; (b) adding phosphate ions to said pretreatment bath from step (a); (c) increasing the pH of said pretreatment bath from step (b) to at least 0.2; and (d) removing the insoluble precipitate that is formed in the bath of step (c). In a second variant of the process, an acid is added to said pretreatment bath (a) to reduce the pH of said pre-treatment composition to less than 4.0; (b) adding phosphate ions to said pretreatment bath from step (a); (c) increasing the pH of said pre-treatment bath from step (b) to 4-5.5; and (d) removing the insoluble precipitate.

EFFECT: removal of iron.

19 cl, 5 dwg, 4 tbl, 8 ex