Separation of Copper and Arsenic from Polluted Acid by Multi-stage Scorodite Precipitation

The production process of sulfuric acid produces a large amount of polluted acid containing high concentration of heavy metal ions such as copper, arsenic, and lead. The traditional sulfidation method or lime method cannot remove arsenic with high selectivity to realize the recovery of valuable metals. In this study, the multi-stage scorodite precipitation method was used to achieve the efficient separation of copper and arsenic in polluted acid. The arsenic precipitation rate from the polluted acid reached 97.1% with a copper loss rate of 9.1% at the conditions of airflow rate of 160 L/min, 1% addition of seed crystals (scorodite crystals), reaction temperature of 70 ℃, five-stage step-by-step precipitation removal of arsenic (24 min reaction time for each stage with an initial pH value of 1.1, 1.9, 2.4, 3.1 and 3.8 respectively for the five-stage). The multi-stage scorodite precipitation method could effectively shorten the reaction time (compared with the one-step scorodite precipitation method) reducing the comprehensive cost significantly which promised a strong application prospect.