Bioleaching of copper in smelter dust

The Sarcheshmeh copper smelter is operated by two reverberatory furnaces and three converters. The gases and soot generated by these furnaces are purified by a balloon-shaped flue (recycling coarse dust) and an electrostatic precipitator (recycling fine dust). These smelting furnaces produce about 50 tons of soot per day and contain about 36% of copper. At present, these soots are returned to the smelting furnace, which reduces the efficiency of the furnace and increases the energy required for smelting. In addition, it also damages the refractory bricks and increases the circulation load of the furnace.

Previous studies have shown that the copper soot of the Sarcheshmeh plant is mainly composed of secondary copper sulfide minerals, which is much more reactive than chalcopyrite in bioleaching. The leaching rate of chalcopyrite is about five times that of chalcopyrite.

Most secondary copper sulfides can be leached with medium temperature bacteria cultures. The optimum conditions for growth of these bacteria are: temperature 32-35 ° C, pH = 1.5-2.5.

A series of continuous experiments in this study were performed in two-stage airlift bioreactors using acidophilic iron and sulfur oxidizing bacteria. Bioleaching and biooxidation are preferably accomplished in a continuous operation in which the productivity per unit volume per unit volume is high and the reactor volume is small. Types of reactors that have been studied include: a stirred tank percolation column, a Pachuca tank, an air lift column, and some specially designed reactors, such as a rotary reactor. Air agitated bioreactors are expensive to construct and operate, and their application is limited to the treatment of high value ores and concentrates. Airlift reactors are used in many chemical, petrochemical , mineral processing and biotechnology industries because of their simple design and construction, low power consumption, low shear, good mixing characteristics, and good heat transfer and mass transfer. In an airlift reactor, the volume of gas held in the riser and the downcomer is different, creating a pressure differential that forces liquid from the bottom of the downcomer to the riser, causing flow and mixing of the liquid.

The purpose of this study was to evaluate the bioleaching of copper on a laboratory scale. The composition of the mixed soot in the smelter is shown in Table 1.

Table 1 Chemical and mineral composition of mixed soot

Note: a-acid soluble copper.

As shown in Table 1, the main copper sulfide minerals in soot are 19% of chalcopyrite, 2% of chalcopyrite, 2% of azurite, and 3% of bauxite. Since a large amount (13%) of acid-soluble copper oxide was present, it was pre-soaked with dilute sulfuric acid, and at a pH of 1.5 and a slurry concentration of 10%, acid-soluble copper was leached 80% after 120 minutes.

The pre-impregnated soot (chemical and mineral composition is shown in Table 2) is leached with medium-temperature bacteria. This medium-temperature mixed culture of iron and sulfur-oxidizing bacteria is separated from the acid mine effluent of natural sulfide ore.

Table 2 Chemical and mineral composition of mixed soot after pretreatment

Note: a-acid soluble copper.

The effects of various parameters such as slurry concentration, residence time and temperature on the bioleaching behavior of copper sulfide fumes after pre-impregnation were evaluated. The results showed that increasing the bioleaching strength (ie shortening the residence time and increasing the slurry concentration) was not conducive to the recovery of copper. The redox potential in the reactor decreases with increasing pulp concentration and increases with increasing temperature. The average leaching concentrations were 2%, 4%, and 7%, respectively. Under the conditions of an average residence time of 2.7 days, 4 days, and 5 days at 32 ° C, the copper leaching rates were 90%, 89%, and 86%, respectively. At 38 ° C, copper was leached from a slurry of 7% concentration with a leaching rate of 91%. From these results, it is hopeful that the leaching of copper from soot with mixed moderate temperature bacteria in an airlift bioreactor is worthy of further study.