Study of a tropical soil in order to use it to retain aluminum, iron, manganese and fluoride from acid mine drainage

• Published in: Journal of environmental management 2017-12, Vol.204 (Pt 1), p.563-570
• Main Authors: Miguel, Miriam Gonçalves, Barreto, Rodrigo Paiva, Pereira, Sueli Yoshinaga
• Format: Article
• Language: English
• Subjects: Acid mine drainage; Acids - chemistry; Aluminum - chemistry; Brazil; Column test; Contaminant transport; Fluorides - chemistry; Iron - chemistry; Liner; Manganese; Mining; Soil - chemistry; Tropical soils; Uranium - analysis; Uranium - chemistry; Waste rock pile; Water
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2017.09.024

The Ore Treatment Unit (UTM-Caldas), in the city of Caldas, Minas Gerais, Brazil, nowadays in decommissioning stage, was the first uranium extraction mine in Brazil. Several negative environmental impacts in the area have occurred, because of mining, treatment and beneficiation processes. Waste rock pile 4 (WRP-4) generates acid mine drainage (AMD), which is discharged in the Nestor Figueiredo retention pond (NFP). However, leakage of acid water by the NFP dam foundation has been constantly observed. Therefore, this research aimed to investigate a typical tropical soil, in order to use it as mineral liner for the NFP to minimize the leakage of acid water through the dam foundation and to retain predominant chemical species. Geotechnical, chemical and mineralogical tests were performed to characterize the soil and a column test was carried out using the acid mine drainage as contaminant, which contained aluminum (Al), manganese (Mn), iron (Fe) and fluoride (F−). The soil presented micro aggregation, acid pH, and low values of organic matter content and cation exchange capacity, which are characteristics of highly weathered soils. Diffusion was the predominant transport mechanism in the column test. Effluent solutions with pH less than 6.0 indicated the formation of insoluble Al-F complexes in the soil and desorption of iron and manganese at concentrations above those allowed by the Brazilian legislation. At pH greater than 6.0, the desorption of iron and manganese and release of aluminum and fluoride in the free form occurred, with concentrations also higher than the allowed by the Brazilian legislation. •Column test was performed using a tropical soil and acid water as contaminant.•Soil was subjected to geotechnical, chemical and mineralogical tests.•Formation of insoluble Al-F complexes in the soil occurred at pH below 6.0.•Release of aluminum and fluoride in free form occurred at pH greater than 6.0.•Mn and Fe concentrations were higher than the allowed by the Brazilian legislation.