Effects of pollution and bioleaching process on the mineral composition and texture of contaminated sediments of the Reconquista River, Argentina

Abstract

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.

Contamination Alters the Physicochemical and Textural Characteristics of Clays in the Sediments of the Peri Urban Reconquista River, Affecting the Associated Indigenous Microorganisms

“…N 2 adsorption-desorption isotherms at 77 K for DR and SF sediments are shown in Figure S5. In all cases, a type IV shape, and a type H3 hysteresis loop according to the International Union of Pure and Applied Chemistry (IUPAC) classification were found [46,48], in agreement with the adsorption-desorption curve previously reported for sediments from nearby sites on the same riverbed [6,7,32]. These features are typical of mesoporous materials and indicate that the particles are, in general, agglomerated and with pores between parallel plates (slit-shaped) [46,48,53].…”

“…SEM micrographs of bulk sediment samples for sections DR1 (0-5 cm) and DR4 (15-20 cm) (Figure 7a,b) showed a multitude of shapes and sizes. However, the basic morphology is essentially given by clay plates, as was previously reported at nearby sites [7]. On the other hand, SEM micrographs taken from SF sediments at different depths revealed a greater heterogeneity (Figure 7d,e).…”

“…The presence of these mineral compounds was not confirmed here, but gave the SF sediments a black color and the appearance of a very thick plastic sludge that differed significantly from that of DR, which had a brownish color and a granular appearance, as seen in Figure S12. The main crystalline components here identified in both DR and SF sediments were quartz, feldspar, albite, and clay minerals, common in the outcrops of the riverbanks and found to also be present at other sites of the same river [6,7,32]. This evidenced a substantial similarity in the mineral composition of the pristine and contaminated sediments regardless of depth or contamination, with no major differences found between their clay fractions either.…”

“…These pollutants (i.e., heavy metals, polycyclic aromatic hydrocarbons (PAHs), organic chlorine pesticides, phenols, inorganic N compounds) are composed of untreated domestic and industrial effluents [1][2][3][4][5][6]. The understanding of such dynamics is essential for the design of processes in bioreactors that are efficient for the on site remediation of the contaminated sediments [7]. In this sense, it is important to know how contamination affects the textural properties of the sediment, especially clays, and how this modifies the adherence of microorganisms, especially bacteria, for the initial formation of biofilms, which are relevant to the riverine biogeochemical cycles.…”

“…Clay minerals influence the physical environment where microorganisms thrive, as certain characteristics of clay minerals such as a small particle size, large surface area, and combined hydrophilic and hydrophobic properties are necessary for the formation of organo-mineral aggregates and biofilm-mineral structures [12]. Several reports have described the idea that, in contaminated environments where the concentration of OM is very much higher than in other natural systems and the activity of iron reducing bacteria increases markedly, mineral transformations could be dramatically accelerated [7,[13][14][15][16][17]. Furthermore, it is well documented that OM influences the structure of the minerals present in sediments [18][19][20][21][22][23][24] and the clay-microorganism interactions [25][26][27][28][29][30], but only few studies have been carried out to gain insights into the modifications that occur in the structure of natural clays under conditions of strong organic contamination [5,7].…”