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Anaerobic sediments of urban watercourses are subjected to industrial pollution and frequently tend to accumulate heavy metals. The biocatalyzed oxidation and reduction of sulphur compounds that occur within the sediment are key reactions that determine mobility of metals such as that occurred in mine acidic drainage reactions. The aim of this work was to study the application of these processes using heap leaching technology for the remediation of anaerobic contaminated sediments from Reconquista River basin. The bioleaching potentiality for remediation was demonstrated through batch tests in shake flasks with different pulp densities of anaerobic sediment containing 338 mg kg of Zn and 117 mg kg of Cu. Subsequently, bioleaching heap systems were compiled into columns of 12-cm height and 6-cm diameter, fitted with perlite to improve drainage. In order to assess the effect of elementary sulphur over the mobility of metals from the bioheap to the aqueous solution, increasing concentrations of elementary sulphur (1, 2, 5 % w/w) were added. After 3 months of acidification generated by periodic watering, the extraction of 70 % of the initial Zn and 43 % of the initial Cu was achieved. Polluted sediments from waterways as Reconquista River should not be indiscriminately manipulated if acid drainage is possible. Remediation by a simple and economically viable strategy like heap leaching is feasible.

In this work, we report on the structural and textural changes in fluvial sediments from Reconquista River´s basin, Argentina, due to processes of contamination with organic matter and remediation by bioleaching. The original uncontaminated matrix showed quartz and phyllosilicates as the main primary mineral constituents and phases of interstratified illite-montmorillonite as secondary minerals. It was found that in contaminated sediments, the presence of organic matter in high concentration causes changes in the specific surface area, particle size distribution, size and distribution of micro and meso, and the morphology of the particles with respect to the uncontaminated sediment. After the bioleaching process, there were even greater changes in these parameters at the level of secondary mineral formation and the appearance of nanoparticles, which were confirmed by SEM. Especially, we found the formation of cementing substances such as gypsum, promoting the formation of macroporous aggregates and the weathering of clay components. Our results indicate that the bioleaching not only decreases the content of metals but also favors the formation of a material with improved characteristics for potential future applications.