Mechanochemical leaching of refractory zinc silicate (hemimorphite) in alkaline solution

A process was developed for extracting zinc from refractory zinc silicate (hemimorphite) by mechano-chemical leaching in sodium hydroxide solution with calcium oxide added to inhibit the leaching of silica. The effects of mechanical activation, calcium oxide dosage, temperature, leaching time, liquid–solid ratio and sodium hydroxide concentration were investigated. The dissolution of silica was considerably inhibited by adding CaO, but zinc extraction was almost unchanged. Under optimum conditions in 4.5 mol/L NaOH and twice the stoichiometric CaO at 383 K, the dissolution of Zn and SiO2 were 93.6% and 7.3%, respectively, after 1 h using a liquid–solid ratio (L/S) of 10:1.