PROCESS AND APPARATUS FOR PRECIPITATING CATIONIC METAL HYDROXIDES AND THE RECOVERY OF SULFURIC ACID FROM ACIDIC SOLUTIONS

摘要

An electric current is passed through an acidic solution containing one or more soluble metal salts in an electrolytic cell divided by an anion exchange membrane. The acidic solution is fed into the cathode compartment whereby the passage of electric current at sufficient voltage causes the generation of hydrogen at the cathode. This gives rise to a localized very highly polarized region at the cathode resulting in a localized effective high relative pH. This causes the metal cation species to precipitate as a hydroxide (or oxide) species and electroadsorption/electrocoagulation causes the finely precipitated hydroxide (or oxide) species to adhere to the cathode. Electrodialytic transport of the liberated acid anions across the anion exchange membrane selectively removes the acid anions. Oxygen and hydrogen ions are formed by hydrolysis as the counter-reaction at the anode. Hydrogen ions combine with the anions to regenerate sulfuric acid. This enables the recovery of cationic metal species within a solution in which the bulk pH would not ordinarily allow hydroxide formation, while simultaneously regenerating sulfuric acid. The anion exchange membrane keeps the acid anion separate from the metal and acid solution so as to enable the concentration and recovery of sulfuric acid.