Abstract
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.
Highlights
A solution containing sulfuric acid, ferric iron, and acidophilic iron- and sulfur- oxidizing microbes is used as the irrigation solution to heaps [2,3]
Several combined operations for pyrite oxidation accelerating were applied to the industrial heaps to start the heap bioleaching, and to expand the production to a capacity of 30 million tonnes of ore per year, starting with only water irrigation
In order to obtain more convincing evidence regarding industrial application, especially in considering sulfuric acid balance, batches of laboratory column tests were carried out, simulating the heap bioleaching-solvent extraction process. These tests proved that it was possible to achieve the goal of starting the heap bioleaching only by water irrigation, but some critical points should still be followed to accelerate the process: (1) select the ore with higher pyrite content and lower alkali gangue mineral; (2) wet the ore earlier to guarantee more time for sulfide mineral oxidation; (3) inoculating the iron and sulfur oxidizing bacteria will greatly promote the pyrite oxidation and copper leaching; (4) adapt the microbes in a low nutrient and high pH environment to accustom them to the environment of the heap; (5) control the ore size to ensure the exposure of sulfide minerals, and ensure the permeability of the ore; (6) use intermittent irrigation to promote the pyrite
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Preparing the heap irrigation solution by adding sulfuric acid and ferric sulfate is costly [8], therefor their minimization, especially in the beginning of heap irrigation, is important to run a heap leaching plant Metal sulfides such as pyrite, are a source of sulfuric acid and ferric ion, commonly found in copper sulfide deposits [9,10]. Whether to buy huge amounts of sulfuric acid and to build sulfuric acid storage facilities in order to start and run the heap bioleaching was a tough decision for the company to make This project was based on the company’s actual demand, to assess the need for sulfuric acid, especially at the beginning of the process of heap bioleaching. Several combined operations for pyrite oxidation accelerating were applied to the industrial heaps to start the heap bioleaching, and to expand the production to a capacity of 30 million tonnes of ore per year, starting with only water irrigation
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