Metal mobility and bioaccessibility from cyanide leaching heaps in a historical mine site

• Published in: Journal of hazardous materials 2023-04, Vol.448, p.130948-130948, Article 130948
• Main Authors: Cánovas, Carlos Ruiz, González, Raúl Moreno, Vieira, Bruno J.C., Waerenborgh, Joao Carlos, Marques, Rosa, Macías, Francisco, Basallote, María Dolores, Olias, Manuel, Prudencio, Maria Isabel
• Format: Article
• Language: English
• Subjects: Cyanide leaching; Hazardous wastes; Metal bioavailability; Sulfide mining
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2023.130948

Unlike acidic sulfide mine wastes, where metal/loid mobility and bioaccessibility has been widely studied, less attention has been paid to alkaline cyanide heap leaching wastes. Thus, the main goal of this study is to evaluate the mobility and bioaccessibility of metal/loids in Fe-rich (up to 55%) mine wastes resulting from historical cyanide leaching activities. Wastes are mainly composed of oxides/oxyhydroxides (i.e. goethite and hematite), oxyhydroxisulfates (i.e. jarosite), sulfates (i.e., gypsum, evaporitic sulfate salts), carbonates (i.e., calcite, siderite) and quartz, with noticeable concentrations of metal/loids (e.g., 1453–6943 mg/kg of As, 5216–15,672 mg/kg; of Pb, 308–1094 mg/kg of Sb, 181–1174 mg/kg of Cu, or 97–1517 mg/kg of Zn). The wastes displayed a high reactivity upon rainfall contact associated to the dissolution of secondary minerals such as carbonates, gypsum, and other sulfates, exceeding the threshold values for hazardous wastes in some heap levels for Se, Cu, Zn, As, and sulfate leading to potential significant risks for aquatic life. High concentrations of Fe, Pb, and Al were released during the simulation of digestive ingestion of waste particles, with average values of 4825 mg/kg of Fe, 1672 mg/kg of Pb, and 807 mg/kg of Al. Mineralogy may control the mobility and bioaccessibility of metal/loids under rainfall events. However, in the case of the bioaccessible fractions different associations may be observed: i) the dissolution of gypsum, jarosite and hematite would mainly release Fe, As, Pb, Cu, Se, Sb and Tl; ii) the dissolution of an un-identified mineral (e.g., aluminosilicate or Mn oxide) would lead to the release of Ni, Co, Al and Mn and iii) the acid attack of silicate materials and goethite would enhance the bioaccessibility of V and Cr. This study highlights the hazardousness of wastes from cyanide heap leaching, and the need to adopt restoration measures in historical mine sites. [Display omitted] •The high release of Se makes cyanide leaching wastes to be hazardous.•High release of Fe, Pb, and Al observed during the simulation of oral ingestion.•Mn and Zn exhibited a high relative bioaccessibility (52–72% of total content).•Silicates and goethite may release V and Cr during accidental oral ingestion.•Water-soluble secondary minerals host high amounts of Se, Pb, Tl, Mn, Co, Ni, or Zn.