BACTERIAL LEACHING OF A LOW-GRADE CHALCOPYRITE ORE WITH DIFFERENT LIXIVIANTS

Abstract

A chalcopyrite-containing ore was shown to be able to retain measurable amounts of Cu2* ions from a 9 mM copper sulfate solution at pH values of 1.5 or above, which was percolated through it. The ore also exhibited significant buffering capacity when titrated with 0.01 N H,S0, or 0.01 N NaOH. Thiobacillus ferrooxidans strain Cu,S-2 accelerated leaching of the ore when using iron-free 1lixiviant at pH 1.5 or ferrous iron-containing lixiviant at pH 1.5. The total copper recovered in 20 weeks from inoculated percolation columns fed with ferrous lixiviant was the same as that recovered from inoculated columns fed with iron-free lixiviant, namely about 20% of the total copper in the ore, but the amount of copper recovered from uninoculated, sterile columns when using ferrous lixiviant was only about a third (3.2%) of that obtained with iron-free lixiviant fed to uninoculated, sterile columns in the same length of time (10.2%). When the ore was fed ferric lixiviant at pH 1.5, the bacteria exerted a strong retarding effect on the leaching process. In their absence, about 2.5 times as much copper (about 52% of the total copper in the ore) was recovered in 20 weeks than in their presence. The amount of copper recovered with bacteria in this case equalled approximately the amount recovered with bacteria using iron-free or ferrous ironcontaining lixiviants.