In this important paper, the authors, Soren Bellenberg, Margarete Kalin, and Wolfgang Sand, present for the first time, a description, including an enumeration of the microbial communities found associated with German lignite, in the presence and absence of NPR, and under sterile and microbe-inoculated conditions using a column experiment. Field and laboratory work to reduce sulfide oxidation in pyritic waste rock using various phosphate formulations including phosphate mining wastes (Natural Phosphate Rock, NPR) has been an intensive focus since the mid nineteen eighties. The noted reductions in sulfide oxidation were thought to be the result of the various iron-phosphate precipitates. However in 2003, Jones refuted the effectiveness of an iron phosphate coating confirming the presence of microbes underneath the coating on arsenopyrite. In 2005, Mudder et al. summarized 5-year laboratory and field tests using thiocyanate as biocide in combination with NPR and commercial fertilizers. They proposed a combined biotic abiotic effect on the initial reduction of acid generation.
However, this effect was short-lived. Testing local NPR and commercial fertilizer on sulfidic waste rock in Australia, Mauric and Lottermoser found that phosphate was ineffective in reducing sulfide oxidation. In 1991, long-term tests in various sulfidic wastes were set up in Canada using NPR by Boojum Research Ltd. Samples were recovered after a period of 3 to 5 years. After extensive exposure to oxidizing conditions, effluents with NPR produced low acidity. The surfaces of sulfidic waste rock from one of the experiments where NPR was added, were inspected with SEM/EDX. An organic biofilm was noted covering the mineral surface. Only traces of iron phosphate precipitates were found. Rock surfaces from the experiment after being stored outdoors in plastic containers for 11 years still showed the presence of the biofilms.
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