Microbial jarosite and gypsum from corrosion of portland cement concrete

Abstract

Jarosite KFe3(SO/2(OH)6 and gypsum CaSO4.2H2O have been found in a corroded concrete sewer pipe' The rate of corrosion oftne concrete is calculated to be 4.3 {o 4.7 mm/year along the inner surface of the pipe' at 25-30C and H2S concentrations up to 400 ppm in the atmospheJe, under low-pH conditions. The number of Thiobacillus thiooidons on the corroded surface was foun'rl to be 103-104 g-1, and the C/N ratio after treatment with HCI was found to be 7-10, indicative of a high content of organic matter. TEM, SEM and EDAX studies reveal the mechanisms of crystal growth ofjarosite and gypsum grown from rod or granule. TEM photographs show that embryonic matter coadd with hydrated films is esseniially crystalline, having layer spacings characteristic of jarosite and gypsum. There appears to bcno morphological difference between jarosite and gypsum at the embryonic stage, but they have their own characteristic d-values. The amplitude of these phenomena depends upon the low pH of solution and the breakdown of cement concrete aided by the activity of T. thiooxidans. The deposition of jarosite and gypsum is