Analysis of Aluminum, Manganese, and Iron Adsorption for the Design of a Liner for Retention of the Acid Mining Drainage

The first uranium extraction mine of Brazil, nowadays found in decommissioning phase, has caused several negative environmental impacts in its area, as a result of mining, treatment, and beneficiation processes. The generation of acid mine drainage in waste rock pile 4 (WR-4) is one of the negative impacts with the most critical situation. The acidic water, product of this drainage, presents heavy metals and radioactive elements and it may be infiltrated by the basis of the impoundment basin, where this water is collected for treatment. The objective of this study was to investigate a typical tropical soil, located in the area of Ores Treatment Unit of Caldas in the southwestern state of Minas Gerais, Brazil, in order to use it as a mineral liner for a retention basin to minimize leakage of acidic water through the foundation of a containment dam. In this way, geotechnical, chemical, and mineralogical tests were performed in order to characterize a soil sample collected in the area. In addition, adsorption tests were conducted with solutions of aluminum (Al), manganese (Mn), and iron (Fe), and with and without adjustment of the initial pH (pHₜₒ) of the solutions. The results indicated a well-weathered soil composed of kaolinite, gibbsite, and iron oxides. The adsorption tests showed different behaviors for Al, Mn, and Fe considering or not the adjustment of the pHₜₒ. Aluminum showed low adsorption by soil; because of this, only the adsorption isotherms of Mn and Fe for test with adjustment of the pHₜ₀were determinate. The coefficient of distribution (KD) of Mn was 0.0364 L g⁻¹and Fe 0.0281 L g⁻¹. As for the retardation factor (Rd), its values ranged from 81 to 91 for Mn and from 61 to 79 for Fe, considering different behaviors of the adsorption isotherm models.