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

摘要

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.