Industrial Heap Bioleaching of Copper Sulfide Ore Started with Only Water Irrigation

Sulfuric acid solution containing ferric iron is the extractant for industrial heap bioleaching of copper sulfides. To start a heap bioleaching plant, sulfuric acid is usually added to the irrigation solution to maintain adequate acidity (pH 1.0–2.0) for copper dissolution. An industrial practice of heap bioleaching of secondary copper sulfide ore that began with only water irrigation without the addition of sulfuric acid was successfully implemented and introduced in this manuscript. The mineral composition and their behavior related to the production and consumption of sulfuric acid during the bioleaching in heaps was analyzed. This indicated the possibility of self-generating of sulfuric acid in heaps without exogenous addition. After proving by batches of laboratory tests, industrial measures were implemented to promote the sulfide mineral oxidation in heaps throughout the acidifying stages, from a pH of 7.0 to 1.0, thus sulfuric acid and iron was produced especially by pyrite oxidation. After acidifying of the heaps, adapted microbial consortium was inoculated and established in a leaching system. The launch of the bioleaching heap and finally the production expansion were realized without the addition of sulfuric acid, showing great efficiency under low operation costs.

Influence of jarosite precipitation on iron balance in heap bioleaching at Monywa copper mine

Ferric iron is an important oxidant in sulfide ore bioleaching. However, recirculating leach liquors leads to excess iron accumulation, which interferes with leaching kinetics and downstream metal recovery. We developed a method for controlling iron precipitation as jarosite to reduce excess iron in heap bioleaching at Monywa copper mine. Jarosite precipitation was first simulated and then confirmed using batch column tests. From the simulations, the minimum pH values for precipitation of potassium jarosite, hydronium jarosite, and natrojarosite at 25 °C are 1.4, 1.6, and 2.7, respectively; the minimum concentrations of potassium, sulfate, ferric, and sodium ions are 1 mM, 0.54, 1.1, and 3.2 M, respectively, at 25 °C and pH 1.23. Column tests indicate that potassium jarosite precipitation is preferential over natrojarosite. Moreover, decreased acidity (from 12 to 8 g/L), increased temperature (from 30 to 60 °C), and increased potassium ion concentration (from 0 to 5 g/L) increase jarosite precipitation efficiency by 10, 5, and 6 times, respectively. Jarosite precipitation is optimized by increasing the irrigating solution pH to 1.6. This approach is expected to reduce the operating cost of heap bioleaching by minimizing the chemicals needed for neutralization, avoiding the need for tailing pond construction, and increasing copper recovery.

Competitive Growth of Sulfate-Reducing Bacteria with Bioleaching Acidophiles for Bioremediation of Heap Bioleaching Residue

Mining waste rocks containing sulfide minerals naturally provide the habitat for iron- and sulfur-oxidizing microbes, and they accelerate the generation of acid mine drainage (AMD) by promoting the oxidation of sulfide minerals. Sulfate-reducing bacteria (SRB) are sometimes employed to treat the AMD solution by microbial-induced metal sulfide precipitation. It was attempted for the first time to grow SRB directly in the pyritic heap bioleaching residue to compete with the local iron- and sulfur-oxidizing microbes. The acidic SRB and iron-reducing microbes were cultured at pH 2.0 and 3.0. After it was applied to the acidic heap bioleaching residue, it showed that the elevated pH and the organic matter was important for them to compete with the local bioleaching acidophiles. The incubation with the addition of organic matter promoted the growth of SRB and iron-reducing microbes to inhibit the iron- and sulfur-oxidizing microbes, especially organic matter together with some lime. Under the growth of the SRB and iron-reducing microbes, pH increased from acidic to nearly neutral, the Eh also decreased, and the metal, precipitated together with the microbial-generated sulfide, resulted in very low Cu in the residue pore solution. These results prove the inhibition of acid mine drainage directly in situ of the pyritic waste rocks by the promotion of the growth of SRB and iron-reducing microbes to compete with local iron and sulfur-oxidizing microbes, which can be used for the source control of AMD from the sulfidic waste rocks and the final remediation.