Biocorrosion in Underground Metal Sulfide Ore Mines

摘要

Microbially influenced corrosion (MIC) of metal and concrete supports in underground sulfide ore mines has been investigated in field and laboratory experiments. Coupons made of carbon steel (CS) and concrete specimens were placed in a mine at a spot where biofouling had been observed under water percolating from the upper horizon. Static laboratory experiments were conducted in the following media: natural mine water (medium Ia); sterilised natural mine water (medium Ib); sterilised natural mine water subsequently inoculated with mixed culture of micro-organisms by addition of natural water and immersion therein of microscopic glasses with colonies of micro-organisms formed in field conditions (medium Ic); synthetic sterile mine water (medium IIa); synthetic mine water sterilised and inoculated with mixed culture by addition of selective nutrient media with micro-organisms isolated and grown for one week (medium IIb); the same as IIb but with sterile nutrient media added (medium IIc). CS specimens were also exposed to continuously flowing (10 cm~3h~(-1)) synthetic inoculated mine water. Corrosion rate (V_(corr)) was determined by mass loss measurements. The following averaged corrosion rates were found in 30 days experiments: Ia - 0.1171, Ib - 0.0854, Ic - 0.1021, IIa - 0.0848, IIb - 0.0958, IIc - 0.1126 gm~(-2)h~(-1). Corrosion rates of 0.1742 and 0.2072 gm~(-2)h~(-1) were determined in laboratory dynamic and in field experiments respectively. Oscillations in open circuit potential (OCP) recorded in non-sterile media and nearly steady values for sterile media were consistent with localised corrosion observed in non-sterile media and nearly uniform corrosion for sterile media. A decrease in strength and in the calcium and magnesium content in the surface layer is the main result from microbial action on concrete. It has been found that biocorrosion is due to the mixed activity of consortia of bacteria (anaerobic, aerobic and micro-aerobic) and of fungi. Data obtained clearly revealed the role of micro-organisms in the corrosion of CS and concrete in underground sulfide ore mines. Results showed that probably the best way to investigate the mechanism of MIC in laboratory is to use continuously flowing media inoculated by addition of natural water or immerse metal or glass coupons with colonies of micro-organisms formed under field conditions. Results for V_(corr), OCP, as well as polarisation data suggest that in the case investigated the increase in V_(corr) is probably due to the increased number of cathodic sites formed as a result of microbial activity. Low alloyed copper-containing steel can be used for metal supports to delay initiation of MIC.