Intensification of sulfuric acid leaching of copper from sulfide concentrates with the use of ozone and iron ions

The studies were carried out in order to establish the patterns of sulfuric acid dissolution of metal sulfides with the participation of environmentally friendly oxidizing agents – ozone and iron (III) ions, to determine the parameters and intensification modes of metal extraction into the solution, reduce oxidizing agent consumption. The purpose of the studies was to develop the least environmentally intense, cost-effective methods for extracting non-ferrous metals from sulfide ores, concentrates and industrial waste. For study, we used copper sulfide concentrate of flotation concentration of ore from the Udokan deposit with a grain size of 90 % –0.074 mm with a copper content of 24.5 %, ozone with a concentration of 80–180 mg/l in a gas mixture with oxygen, fed to the reactor at a speed of 1–5 ml/s. Patterns were studied in the range of sulfuric acid concentration of 20–100 g/l, Fe(III) ion concentration of 7.8–29.2 g/l, temperature of 18–60 °C in stirred reactors with the solid-to-liquid ratio of 1.1÷1.5. It was found that the use of Fe(III) ions and ozone can significantly intensify copper recovery from sulfides to the sulfuric acid solution. Copper extraction from sulfides increases in proportion to the 2.4-fold increase in the concentration of Fe(III) from 7.8 to 29.25 g/l. Ozone effectively oxidizes Fe(II) and regenerates Fe(III) ions. With the rising temperature and iron concentration, ozone consumption for oxidation increases:0.22 mol of O3 is consumed per 1 mol of Fe that is more than the theoretical value of 0.17. An increase in the rate of copper extraction from sulfides using ozone is achieved by increasing the temperature from 20 to 50 °C (1.4 times), ozone concentration from 85 to 180 mg/l (3 times), feed rate of ozone-oxygen mixture from 1 to 5 ml/s (2.7 times at 20 °C, 3.9 times at 50 °C), by adding Fe(III) ions (~1.5 times at 50 °C [Fe(III)] = 10 g/l). The highest oxidizing activity in a sulfuric acid solution is provided by ozone decomposition products at a temperature of 50 °C when its solubility decreases. Ozone utilization coefficient and specific ozone consumption for extracted copper decrease with an increase in the ozone-oxygen mixture supply rate with oxygen from 1 to 5 ml/s (1.42 times at 20 °C, 1.16 times at 50 °C) and increase with rising temperature and Fe(III) concentration due to the rapid ozone decomposition and unproductive use for iron oxidation.

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