Pressure leaching of high silica Pb–Zn oxide ore in sulfuric acid medium

The pressure leaching of high silica Pb–Zn oxide ore using air as pressurized gas in sulfuric acid medium is studied systematically in the present paper. Study parameters include the concentration of sulfuric acid, partial air pressure, leaching temperature, leaching time, and liquid-to-solid ratio. The experimental results obtained show that under optimum conditions, the extraction percentage of Zn is up to 96% and the extent of dissolution of Si, Pb, and Fe are as low as 1%, 2%, and 6%, respectively. Leaching pulp had good filter performance, and the silicic acid formed during sulfuric acid leaching was transformed into easily filterable dehydrated SiO2 particles that can enter the slag. The filtration rate can be as high as 893 L/m2 h.

Research highlights
► The pressure leaching of high silica Pb–Zn oxide ore using air as pressurized gas in sulfuric acid medium is studied systematically in the present paper. Study parameters include the concentration of sulfuric acid, partial air pressure, leaching temperature, leaching time, and liquid-to-solid ratio.
► Conclusions
► (1) The pressure leaching of Pb–Zn silicate oxide ores with air as pressurized gas in a sulfuric acid medium was studied. Optimum operating parameters were established as follows: sulfuric acid concentration of 120g/L, partial air pressure of 0.6MPa, leaching temperature of 120 °C, leaching time of 2h, L/S of 5:1, ore size of 75–80 μm, and stirring rate of 700rpm. Under these conditions, the extraction of Zn is greater than 96%, the leaching rate of Si is less than 1%, the concentration of Fe in solution is less than 0.5 g/L, and almost all of the Pb is recovered from the leaching residues. Si in the form of easily filterable dehydrated SiO2 and muscovite, rather than silica gel, forms. Leaching pulp had good filter performance. The acid pressure leaching of Pb–Zn silicate oxide ores is technologically feasible.
► (2) Experimental results show that leaching temperature, liquid-to-solid ratio, air partial pressure, and sulfuric acid concentration have significant effects in the process, but leaching time has a relatively small impact. Partial air pressure was primarily used to maintain the higher temperature necessary for the reaction and oxidization of the ferrous ion. To obtain leaching pulps with good filter performance, the leaching temperature must be higher than 120 °C and the liquid-to-solid ratio must be no higher than 6:1.
► (3) In a variety of single factor experiments, the filtration rate increased with decreasing Si leaching rate.
► (4) When the pH at the end of the pressure leaching process was 4.8–5.0, electropositive Fe(OH)3 colloids and electronegative silica gel aggregate and coprecipitate because of electrostatic attraction.