Methodand plant to recover chromium salts from tannery reflux water

摘要

The present invention refers to a method to recover trivalent chromium salts from reflux water originating from a hide tanning process, via the so-called "chromium" system, including the following steps in succession:PPflocculating all the trivalent chromium salts in the form of chromic hydroxide by treatment with an aqueous solution containing from 15 to 30%, by weight, of a salt made from a weak acid and a strong base, having a pH value lying between 6.9 and 7.2 and at a temperature lying betwen 22° and 26° C.;P P separating chromic hydrate, obtained in this way, from the aqueous dispersion by concentration in a clarifier-flocculating device and successive filtration of the concentrate until a precipitate, is obtained preferably containing approximately 20% dry residue, by weight and dissolving precipitate, thus obtained in sulphuric acid, at a pH value lying between 1.8 and 2 and at a temperature higher than 50° C., preferably at 70° C.PPThe present invention also illustrates the plant for carrying out this method.