US 5,562,828 A · Method and apparatus for recovering acid and metal salts from pricklining liquors

Abstract

Spent acid contaminated with metal salts in a hot solution removed from a metal pickling bath is directed to one side of an anionic membrane to separate acid ions from the metal salt solution by diffusion dialysis through the membrane. Most of the metal salts in the remaining low acidity mother liquor are crystallized by refrigerating the mother liquor. The crystals are dewatered (in a centrifuge, for example) to produce a commercially viable noncorrosive byproduct, and the substantially decontaminated mother liquor is directed to the opposite side of the diffusion membrane, where it receives the acid ions diffusing through the membrane, and is then recycled to the pickling bath. Heat interchange between the hot spent acid solution and the recycled acid lowers the temperature of the spent acid to an optimum value for dialysis while raising the temperature of the recycled acid to close to the bath temperature. Heat interchange between the contaminated mother liquor leaving dialysis and the refrigerated decrystallized mother liquor precools the contaminated liquor prior to refrigeration and concurrently warms the returning mother liquor to near optimum dialysis temperature.

Claims15

Dependent claims

A process for recovering acid from a metal pickling operation including the steps of treating metal products in an acid bath to remove metal oxides, withdrawing a first solution of metal salts in acid from the pickling operation, delivering the first solution to one side of an anion exchange membrane such that a portion of the acid permeates through the membrane to an opposite recovery side of the membrane, withdrawing a reduced strength acid solution of the metal salts from the one side of the membrane, and returning acid from the recovery side of the membrane to the pickling operation, wherein the improvement comprises:

chilling the reduced strength solution of metal salts which have been withdrawn from said one side of the membrane to a temperature at which a least a portion of the metal salts crystallize, whereby the remaining liquid constitutes a mother liquor of reduced strength acid depleted of metal salts;
extracting the mother liquor from the crystallized metal salts, the metal salt crystals having a low acidity corresponding to the reduced strength acid of the mother liquor;
delivering the mother liquor to mix with the acid on the recovery side of the membrane for return to the pickling operation;
and
discharging the crystallized metal salts.

2 more elements

An acid recovery system for a metal treating facility having an acid bath pickling tank, a diffusion dialysis unit having a waste acid inlet, a metal contaminants outlet, a water inlet, and a recovered acid outlet, means for transferring contaminated spent acid from the pickling tank to the waste acid inlet, and means for transferring purified acid from the recovered acid outlet to the pickling tank, wherein the improvement comprises:

a crystallizer tank;
a conduit connecting the metal contaminants outlet of the diffusion dialysis unit to the crystallizer tank for conveying a stream of dilute mother liquor containing metal contaminants to the crystallizer tank;
a refrigeration device for chilling the contents of the crystallizer tank to crystallize a substantial portion of the metal contaminants in the dilute mother liquor;
and
a conduit connecting the crystallizer tank to the water inlet of the diffusion dialysis unit for returning purified dilute mother liquor to the diffusion dialysis unit.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for recovering acid and metal salts from pricklining liquors

Life of this patent

Method and apparatus for recovering acid and metal salts from pricklining liquors

Life of this patent

Abstract

Claims15