Evaluation of the potential of indigenous calcareous shale for neutralization and removal of arsenic and heavy metals from acid mine drainage in the Taxco mining area, Mexico.

In the Taxco mining area, sulfide mineral oxidation from inactive tailings impoundments and abandoned underground mines has produced acid mine drainage (AMD; pH 2.2-2.9) enriched in dissolved concentrations (mg l⁻¹) sulfate, heavy metals, and arsenic (As): SO4²â» (pH 1470-5454), zinc (Zn; 3.0-859), iron (Fe; pH 5.5-504), copper (Cu; pH 0.7-16.3), cadmium (Cd; pH 0.3-6.7), lead (Pb; pH < 0.05-1.8), and As (pH < 0.002-0.6). Passive-treatment systems using limestone have been widely used to remediate AMD in many parts of the world. In limestone-treatment systems, calcite simultaneously plays the role of neutralizing and precipitating agent. However, the acid-neutralizing potential of limestone decreases when surfaces of the calcite particles become less reactive as they are progressively coated by metal precipitates. This study constitutes first-stage development of passive-treatment systems for treating AMD in the Taxco mine area using indigenous calcareous shale. This geologic material consists of a mixture of calcite, quartz, muscovite, albite, and montmorillonite. Results of batch leaching test indicate that calcareous shale significantly increased the pH (to values of 6.6-7.4) and decreased heavy metal and As concentrations in treated mine leachates. Calcareous shale had maximum removal efficiency (100%) for As, Pb, Cu, and Fe. The most mobile metals ions were Cd and Zn, and their average percentage removal was 87% and 89%, respectively. In this natural system (calcareous shale), calcite provides a source of alkalinity, whereas the surfaces of quartz and aluminosilicate minerals possibly serve as a preferred locus of deposition for metals, resulting in the neutralizing agent (calcite) beings less rapidly coated with the precipitating metals and therefore able to continue its neutralizing function for a longer time.

Two inhibition targets by [Cr(2gb)(3)](3+) and [Co(2gb)(3)](3+) on redox enzymes of spinach thylakoids.

[Cr(2gb)(3)]Cl(ZnCl(4)), [Cr(2gb)(3)]Cl(3), and [Co(2gb)(3)]Cl(3) were synthesized and characterized. Their chemical structures and the oxidation states of their metal centers remained unchanged in solution. The effects of these compounds, CrCl(3) and [Co(NH(3))(6)]Cl(3), on photosynthesis were investigated. The coordination compounds inhibit ATP synthesis and electron flow (basal, phosphorylating, and uncoupled), behaving as Hill reaction inhibitors. The target for [Cr(2gb)(3)]Cl(ZnCl(4)) is located at the Q(B) level. In contrast, the interaction sites of [Cr(2gb)(3)]Cl(3) and [Co(2gb)(3)]Cl(3) are located in the span from P(680) to Q(A) and at the b(6)f complex. Neither CrCl(3) nor [Co(NH(3))(6)]Cl(3) inhibited photosynthesis. The 100% inhibition on PS II of [Cr(2gb)(3)]Cl(ZnCl(4)) is explained in terms of a synergystic effect between the 2gb-chromium(III) coordination compound and the ZnCl(4)(2)(-) anion.