Leaching of low grade zinc oxide ores in NH4Cl–NH3 solutions with nitrilotriacetic acid as complexing agents

• The efficient and selective leaching process is obtained in NH4Cl–NH3–NTA solutions.
• The addition of NTA plays a positive role in the leaching process.
• The zinc extraction mainly depends on the zinc complexes stability constant.

A novel method for leaching of low grade zinc oxide ores in NH4Cl–NH3 solutions containing nitrilotriacetic acid (NTA) as complexing agents is proposed in this paper. The influences of NTA concentration, leaching temperature, stirring speed, particle size and liquid–solid ratio on the zinc extraction are discussed. It is found that the addition of NTA facilitates the zinc extraction. Under the condition that particle size is 64–71 μm, NTA concentration is 0.1 mol/L, liquid–solid ratio is 20 mL/g, leaching temperature is 40 °C and stirring speed is 400 rpm, the zinc extraction reaches 90.3%. The result of leaching kinetic study indicates that the leaching process is controlled by the interface transfer and diffusion through the product layer and the corresponding activation energy is 22.3 kJ/mol.