A comparative assessment of the application of ammonium chloride and glycine as lixiviants in the heap leaching of chalcopyritic ores

A largely electrochemical investigation into the possible use of ammonium chloride or glycine as lixiviants in the heap leaching of chalcopyrite-rich ores has provided good comparative data with which to compare the reagents and also identified several important considerations that need to be taken into account when considering such processes. The high stability of the copper(II) glycinate complexes results in low reactivity (as measured electrochemically) for the oxidative dissolution of chalcopyrite except at high pH values. The lower stability of the copper(II) ammine complexes results in significantly greater (fifty-fold) rates in the ammonium chloride system under the same conditions. The rates are tenfold higher for the ammonium chloride system at pH 8 compared to glycine at pH 10. Agitated leaching testwork on a chalcopyrite concentrate and column leaching of a chalcopyrite ore have confirmed the electrochemically derived trends. Loss of copper(II) occurs by precipitation as a basic chloride in the ammonium chloride system at pH values below about 8 depending on the ammonium chloride concentration. The relatively high cost of glycine and even of ammonium chloride would probably preclude use of these reagents unless the rates of heap leaching can be shown to be significantly greater than those of alternative acidic lixiviant systems.