Study Of Purifying High Arsenic Contaminated Acid By Cyclone Electrowinning Technology

Contaminated acid is one of the common waste acid in nonferrous metals smelting process, which is characterized by complicated component, high acidity and difficulty to treat. Contaminated acid is also the main source of the acid heavy metal ion wastewater in smelting plant. Arsenic is the highest content and the most harmful element in contaminated acid which produced from non-ferrous metals smelting industry such as copper, nickel, lead, zinc, and gold. The traditional treatments of contaminated acid produce a large amount of hazardous waste and cost a lot. The electro deposition of copper and arsenic may produce a large amount of acid mist and AsH3 during the removing copper and impurity process.The toxic gases seriously threatened the environment and human health.Aiming at the above problems, the advanced and environmentally friendly cyclone electrowinning technology was used to purify contaminated acid. The effects of current density, temperature, circulating flow rate, concentration of copper ion and the fluorine chlorine ion on the removal rate of copper and arsenic were studied. And then a new process of purifying contaminated acid by four stage cyclone electrowinning technology was designed.Using 304 stainless steel as cathode, the best technological conditions of four section cyclone electrowinning were as follows: circulating flow rate 250 L/h, current density 500 A/m2. In the first section, the initial concentration of copper ion in the contaminated acid was adjusted to 3 g/L. In the second, third and fourth sections, the concentration of copper ions were adjusted to 1 g/L at the 6 h, 8h and 10 h,then cyclone electrowinning continued to the 14 h. The initial concentration of arsenic ion in the contaminated acid was 5.41 g/L,at the end the arsenic removal rate reached 89.08%.The optimal current density of copper and arsenic removal with cyclone electrowinning is 500 A/m2, which is much higher than that of the controlling cathodic potential electrowinning(200 A/m2) and that of the continuous parallel and cycle electrowinning(320 A/m2). The high utilization rate of electric energy and energy saving cyclone electrowinning technology can effectively remove the copper and arsenic at room temperature, while the solution temperature needed to be heated to more than 60℃ with the derivative method and the continuous parallel and cycle electrowinning.The analytical techniques, such as SEM, EDS and XRD, were used for the electrolytic slag of copper and arsenic removal by cyclone electrowinning. The main elements of electrolytic slag were As, Cu and oxygen, and the main compounds were Cu5As2 and As2O3. The reaction mechanism of copper and arsenic removal was confirmed by the test results.The average copper arsenic ratio in electrolytic slag was 0.875:1, basically the same to the theory copper arsenic ratio 0.886:1, indicating that there was no production of AsH3 in cyclone electrowinning process. The copper arsenic ratio in slag was much lower than the continuous parallel and cycle electrowinning(1.8~2.8): 1 and control cathodic potential electrowinning 6.6:1,thus reduced the content of copper in arsenic slag, and saved the copper resources. Electrolytic slag could be resource utilized as raw material for the production of copper arsenate.