The interaction of mixed metal sulfides has been widely studied in the context of (bio)leaching and flotation of ore concentrates. Sulfides in ore concentrates, act as galvanic coupled systems as a result of the physical contact between grains. A galvanic contact leads to a uniform Fermi level (E_F) between the different complexities affecting pyrite oxidation metal sulfide particles. In this experiment, we use the combination of galena (PbS), pyrite (FeS₂), and sphalerite (ZnS), which are the most common metal sulfides, to determine their oxidation rate.

Because galena and sphalerite have lower rest potentials than pyrite, it is energetically more favorable to withdraw electrons from these base-metal sulfides than from pyrite, affecting negating the oxidation rate of pyrite. However, it is not clear if sulfides in mine waste are best described by the galvanic model. Formation of oxide coatings, as well as separation by non-conducting minerals or organic matter, may prevent the flow of electrons causing to become the sulfides as intermittently galvanic coupled or as entirely electrically isolated grains. Also, it is important to consider how metal sulfides may interact if they are not galvanic coupled.

The hypothesis is that isolated particles will ultimately equilibrate with the solution they share, rather than through a galvanic contact. The H₂O₂ formed by the water-pyrite reaction may very well be a key reactant in mixed slurries. Depending in how is the reaction, it will affect the oxidation rate of pyrite. Hence, this is important to study because the oxidation of pyrite generates acid drainage, in which it is metal-rich water that contains sulfur bearing-minerals and it forms red, yellow, and orange sediments. The problem is that the acid drainage contaminates drinking water, disrupted growth and reproduction of aquatic plants and animals, and creates acid rains.

To realize this study, we will conduct several different column experiments. The column experiments are used to evaluate if galvanic contact is necessary for metal sulfides to influence each other’s oxidation rate.

We will study the interaction between two different mixtures of sulfides: sphalerite/pyrite and galena/pyrite. In a series of column experiments we will determine the rate of oxidation of the endmembers as well as for the 50:50 mixtures. However, the mixtures will be studied with two different column-packing configurations. One is to pack the column with a well-randomized binary metal sulfide mixture. In the second packing, the same amount of sulfides is used but the two sulfides will be packed in mono-mineralic layers separated by a small amount of Teflon beads. Hence, in the second packing the two sulfides will share a solution but they will not be in direct contact.

The expectation is that by studying a range of model systems from fully galvanic-coupled systems to systems, helps evaluate the importance of galvanic coupling as well as if (and which) uncoupled systems exhibit synergistic or antagonistic interactions. These results will be of importance in developing more realistic oxidation rate models for complex metal sulfide waste.