Patent ID: 7473409

Claim:
A method of treating a spent acid solution contaminated with inorganic and organic impurities comprising, in combination, a) providing a spent waste acid containing compounds selected from the group consisting of sulfuric acid, copper sulfate, iron sulfate, acetic acid, phosphoric acid, methyl sulfonic acid and combinations thereof, and also containing contaminants selected from the group consisting of arsenic, antimony, chromium, germanium, gallium, copper, at least one organic compound, and mixtures thereof; b) forming an admixture initially having a pH of less than 5 by contacting the spent waste acid with a Mg compound containing aluminum and iron; c) measuring and monitoring the pH of the admixture; d) agitating and maintaining the admixture at a temperature in the range from about ambient to about 97° C.; e) complexing the contaminants contained in the spent waste acid through flocculation by forming flocs selected from the group consisting of iron oxyhydroxide, aluminum oxyhydroxide, copper oxyhydroxide and mixtures thereof; f) increasing the pH of the admixture by continued addition of the Mg compound to the admixture until a pH of 5 or higher is obtained; and g) isolating a solution containing magnesium sulfate by separating the flocs containing the contaminants from the admixture using a filtration process.