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This study focused on determining the optimal conditions for lead removal in aqueous solution models, by the spherical agglomeration technique (SAT), modifying the dose of Agave lechuguilla Torr. (lechuguilla) extract, used as biosurfactant. The SAT operating conditions at room temperature were: Initial pH 9, and constant agitation ω = 600 rpm. Experiments were performed under a 5x3 factorial design with five lechuguilla extract doses (0.3 - 2.0 g extract/g of pollutant), three different lead concentrations (1, 5 and 10 mg/L) and, for the SAT last stage, two different dosage ratio of CaCl2 (10:1 and 20:1 parts of Ca2+ by part of pollutant). Residual lead, sodium and calcium were determined by atomic absorption spectroscopy. According to statistical analysis, significant effects were observed for calcium dosages, initial lead concentration, extract dose and their interaction. The lead removal efficiency obtained by SAT reached 99.8%.

The aim of this research was to evaluate bioleaching of Mn, As, Pb and Zn from mining tailings using two different sets of variable processing conditions. In the first set pH (2.0, 4.0 and 6.0), tailings concentrations (10, 20 y 30 %, w/v [111.11, 250.00 and 428.57 g/L, respectively]), and two types of culture medium (9K [with nitrogen source] and nonN (nitrogen-free medium) were evaluated; in the second set the evaluation focused on continuous supplementation of biogenic H 2 SO 4 oxidized with two types of culture medium (9K and nonN) at different tailings concentrations (10, 20 y 30 %, w/v [111.11, 250.00 and 428.57 g/L, respectively]), with continuous supplementation of the media previously described (9K and nonN) oxidized by the native strains Leptospirillum ferriphilum and Leptospirillum ferrooxidans . In the first set, the highest removal of Mn (93.49 %), As (13.92 %) and Pb (> 99 %) was observed in both media at 10 % of tailings and initial pH of 2.0. In the second experimental set, the highest removal of Mn (99 %), As (> 85 %), Pb (> 99 %) and Zn (67 %) was found with both media at 10 % of tailings and initial pH 6.0. Continuous supplementation of biologically acidified and oxidized culture media enhanced the metals removal from solid waste or tailings. Similar metals removal in media without nitrogen compared to medium with nitrogen was observed in this research.