Partitioning and mobility of arsenic (As) and lead (Pb) in an ancient Pb–Zn mine in central Mexico: Role of amorphous ferric arsenate

• Published in: Applied geochemistry Vol. 136; p. 105172
• Main Authors: Aguilar-Carrillo, J., Velázquez, A., Gutiérrez, Emmanuel J., Reyes-Domínguez, Iván A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-2022
• Subjects: Adsorption; AFA; Anglesite; Mine wastes; Poorly-crystalline minerals; Sediments; Sequential extraction; Adsorption; Poorly-crystalline minerals; Sequential extraction; Anglesite; Mine wastes; Sediments; AFA
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2021.105172

This study delves into the interactions between Pb and As and poorly-crystalline minerals, particularly amorphous ferric arsenate (AFA), in an ancient mine characterized by highly-dispersed pollutants due to strongly acidic conditions (pH 2.2 to 2.6) originated from mine drainage (AMD). On-site observations accompanied by laboratory-based mineral formation and transformation experiments were undertaken to examine the reactions of mobile Pb and As from abandoned mine residues on the mineralogy of the impacted sediments, as well as to examine associated controls on their mobility. Natural attenuation of Pb and As mobility predominantly occurred via formation of lead arsenate (PbHAsO4), Pb–As-rich Fe(III) minerals, and AFA, resulting in solid-phase concentrations ranging from ∼1088 to ∼1545 and from ∼278 to ∼734 mg kg−1 for Pb and As, respectively. Subsequent sorption experiments with synthetic AFA revealed the retention of Pb by the formation of anglesite (PbSO4) due to an appreciable sulfur content (up to 4 wt%) in AFA chemical composition, whereas As was effectively retained by a non-exchangeable surface adsorption mechanism. The results of this study show the occurrence of metastable phases like AFA in AMD environments as well as its role in controlling Pb and As mobility under strongly acidic conditions.
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•Abandoned mine residues as a continuous source of potentially harmful elements.•A relationship between AFA and Pb–As-impacted sediments is established.•A sequential extraction procedure is carried out to assess Pb and As distribution.•Very high concentrations of Pb and As are associated with amorphous phases like AFA.•Appreciable S content in AFA chemical composition favored the formation of anglesite.