Bioweathering of Zn-Pb-bearing rocks: Experimental exposure to water, microorganisms, and root exudates

摘要

Zn-Pb-bearing rocks from mining sites in Olkusz, southern Poland may continue to represent a risk to the environment through the mobilization of metals. This study experimentally simulated the exposure of calaminetype rocks and goethite crusts to various weathering conditions and then compared the behavior of these mineralogically diverse samples. Study conditions included sample exposures to and comparisons of native microorganisms (biostimulation of the soil solution favoring microbial growth) and sterile soil extracts, single bacterial strains (Acidithiobacillus thiooxidans bioaugmentation) and sterile acidic growth mediums, root exudates of various concentrations, and water. This study demonstrated that A. thiooxidans and root exudates had the largest influence on the mobilization of metallic elements (up to 44% for Zn, 29% for Pb, and 78% for Cd), whereas H2O was found to play a minor role (0.13% for Zn, 0.27% for Pb, and 1.23% for Cd). The sample composed of goethite crust with quartz was generally more susceptible to bioweathering than the calamine-type rock, a result that was likely caused by the presence of goethite and smithsonite, both undergoing severe dissolution. We conclude that bioweathering was an important driver affecting the stability of the sample rocks. The dissolution of minerals such as hemimorphite and smithsonite under experimental conditions proves that analogic dissolution can also occur under natural weathering conditions.