James A. Brierley

THE USE OF LARGE-SCALE TEST FACILITIES IN STUDIES OF THE ROLE OF MICROORGANISMS IN COMMERCIAL LEACHING OPERATIONS

Although temperature profiles have been identified in a few commercial leach dumps (such as Kennecott Copper Corporations Midas test dump at Bingham Canyon, Utah), there is no correlation on this large scale with bacterial activity (defined quantitatively as the most probable number, MPN, or number of Thiobacillus ferrooxidans per gram or cc of sample) or oxygen consumption. Recent experiments on unitized copper-bearing waste bodies weighing approximately 1.7 × 10 5 kg in insulated stainless steel (dewartype) containers 3.07 m in diameter and 12.3 m in height have allowed vertical temperature profiles in these ore bodies to be correlated with bacterial population (T. ferrooxidans most probably number, MPN) in the ore body, and oxygen distribution and consumption. It is suggested from these experiments that bacterial catalysis is somewhat critical within a range above about 10 5 organisms/g sample in the waste body. Oxygen consumption initially occurs when MPN reaches approximately 10 7 cells/g; independent of marked temperature influence. While the temperature profiles observed for two different waste bodies show varying degrees of correspondence with the mean ambient temperature, there is overwhelming evidence that the reaction kinetics (mainly exothermic pyrite oxidation) develop intrinsic temperatures within the ore body since temperatures have been observed as high as 59°C. This high temperature seems to be correlated with a marked decline in the Thiobacillus ferrooxidans population, and a concomitant indication that a high-temperature microorganism exists. One waste body (containing Kenneoott Corp. Chino Mines type 1 waste) has been stabilized at temperatures above 52°C. That is, a temperature plateau has been established between 50 and 60°C, and this is suggestive of bacterial control of the temperature of the waste body. The implications of bacterial control of the waste-body temperature and the use of high-temperature microorganisms to establish higher temperature plateaus and enhanced reaction kinetics is discussed in relation to commercial leaching operations.

MICROBIAL LEACHING OF COPPER AT AMBIENT AND ELEVATED TEMPERATURES

This report compares the leaching ability of Thiobacillus ferrooxidans, a microbe commonly associated with copper leaching operations at ambient temperature, and a high-temperature Sulfolobus- like microbe, an organism recently determined to be associated with metals extraction at 60°C. The mineral substrates used for leaching included mine waste and concentrate from the Kennecott Copper Corporation, Chino Mines Division, NM, ore from the Phelps-Dodge Corporation, Tyrone Division, AZ, and concentrate from the Phelps-Dodge Corporation, Ajo Division, AZ. The bio-leaching experiments were run in stationary batch reactors. Four nutrient conditions were evaluated for their effect on bio-leaching of copper minerals at room temperature and 60°C: 1) basic leach solution only; 2) basic leach solution supplemented with 0.02% yeast extract; 3) basic leach solution with 36 mM ferrous iron; and 4) a combination of basic leach solution, 0.02% yeast extract and 36 mM ferrous iron. Soluble copper concentration was monitored after 30 and 60-days leaching. The yeast extract did not greatly affect copper leaching by either T. ferrooxidans or the Sulfolobus- like microbe except with the Ajo concentrate which was leached more effectively. The addition of ferrous iron enhanced the bio-leaching of copper. Apparent increased bio-leaching at 60°C was attributed to temperature affect rather than enhanced bio-activity by the thermophile except with the Ajo concentrate, indicating greater ability by the Sulfolobus- like microbe for extracting copper from a mineral substrate rich in chalcopyrite.

Anaerobic Reduction of Molybdenum by Sulfolobus Species

Summary The acidothermophilic Archaebacteria, Sulfolobus acidocaldarius and S. brierleyi, oxidized elemental sulfur anaerobically producing sulfuric acid by using Mo (VI) as an apparent electron acceptor. Molybdenum reduction resulted in the formation of a blue color which was intensified in the presence of aluminum at concentrations of 20–50 mM. Molybdenum was not reduced when S. brierleyi was grown anaerobically on yeast extract as an energy source, suggesting that the organic substrate was utilized in a fermentative metabolism mode.

Microbiological leaching of a chalcopyrite concentrate and the influence of hydrostatic pressure on the activity of Thiobacillus ferrooxidans

SummaryThe effect of hydrostatic pressure on the activity of Thiobacillus ferrooxidans grown on chalcopyrite concentrate has been investigated. It was found that bacterial activity, measured by conventional respirometry, was little affected by subjecting these microorganisms to a pressure of 100 lbs/in2 (690 kPa). The total cooper concentration was as high as 18 g/l in 28 days of leaching at atmospheric pressure.