Geochemistry and pH control of seepage from Ni-Cu rich mine tailings at Selebi Phikwe, Botswana

Abstract

Acid mine drainage from mine tailings at Selebi Phikwe, eastern Botswana, has been investigated using a combination of total decomposition, sequential extraction, X-ray diffraction, Mössbauer spectroscopy, and SEM analyses of solid phase samples, water analyses, isotopic analyses, and geochemical modeling. The principal ferric phases in the seepage stream sediments are jarosite and goethite, which incorporate Ni and Cu. The Mössbauer spectroscopy (MS) indicated exclusively 3+ oxidation state of iron with typical features of ferric hydroxides/sulfates. A fraction of dissolved sulfate is also sequestered in gypsum which precipitates further downstream. Significant portions of Fe, Ni, and Cu are transported in suspension. Values of pH decreased downstream due to H generated by the precipitation of jarosite. Values of δH and δO indicate evaporation of pore water in the mine tailings before seepage. Values of δS(SO) are consistent with the oxidation of sulfides, but sample from the seepage face is affected by dissolution of gypsum. No minerals of Ni and Cu were detected and the principal attenuation processes seem to be adsorption and co-precipitation with jarosite. Higher contents of Cu are sequestered in solid phases compared to Ni, in spite of much higher dissolved Ni concentrations. Based on the speciation calculations, seepage water is undersaturated with respect to all Ni and Cu phases and adsorption and co-precipitation with jarosite seems to be the principal attenuation processes. Direct geochemical modeling was able to reproduce downstream pH trends, thus confirming the precipitation of jarosite as the principal pH-controlling process.

Contaminant Binding and Bioaccessibility in the Dust From the Ni‐Cu Mining/Smelting District of Selebi‐Phikwe (Botswana)

“…In addition, the occurrence of Fe oxyhydroxides (goethite) and Fe oxysulfates (jarosite), which also contain some of these contaminants, is reported in our soils (Figure 2; Table S6 in Supporting Information ). The presence of jarosite, a typical phase for the acidic environments of the Selebi‐Phikwe tailings (Sracek et al., 2018), agrees with the high soil acidity (pH = 3.2) and high sulfur content (up to 0.45 wt%) (unpublished results). In contrast, goethite (Figure 2i) preferentially precipitates under slightly acidic‐to‐circumneutral conditions (Majzlan & Myneni, 2005), but there are indications that goethite can also form under acidic conditions with a pH around three in many mining‐affected environments (Murad & Rojík, 2005; Sracek et al., 2018).…”

“…Also, precipitated jarosite can be transformed to goethite during the process of aging and release co‐precipitated and adsorbed contaminants (Baleeiro et al., 2018 ; Fukushi et al., 2003 ) relatively weakly bound as bidentate surface complexes (Gräfe et al., 2008 ). At Selebi Phikwe, large contents of Ni (up to 2,681.5 mg/kg) and especially Cu (up to 8,101 mg/kg) were found in jarosite in the sediments of the stream flowing from the base of the mine tailings (Sracek et al., 2018 ).…”

“…This study deals with dust fractions of waste materials and soil collected in and near the mining district of Selebi‐Phikwe, located in the semi‐arid east of Botswana, where Ni‐Cu ores were mined and processed by a pyrometallurgical operation. Previous studies in this area were focused on the distribution of the metals in the soils and vegetation (Ekosse, 2005; Ekosse et al., 2003; Manyiwa et al., 2022; Motswaiso et al., 2019; Ultra & Manyiwa, 2021), and on the geochemistry, environmental impacts, and potential rehabilitation of the contaminated mine tailing sites (Schippers et al., 2007; Schwartz & kgomanyane, 2008; Sracek et al., 2018; Ultra, 2020; Ultra & Manyiwa, 2021). The human health issues in the Selebi‐Phikwe area were only evaluated using the old statistical data from the 1990 s and the statistical processing of questionnaires acquired during the early 2000 s, when the mine and smelter were still in operation, and indicated that mine workers suffered from different symptoms and illnesses such as influenza, headaches, chest pain, and coughing (Asare & Darkoh, 2001; Ekosse, 2008).…”

Successful Conversion of Pb-Contaminated Soils to Low-Bioaccessibility Plumbojarosite Using Potassium-Jarosite at Ambient Temperature

“…The mineral was allowed to hydrate for 1 h. Pb stock solution (5 mL, 0.03 M) was then applied to each reactor vessel. pH was then measured (Cole-Parmer P200) and adjusted using HCl to pH 2.5 to facilitate suitable PLJ formation conditions as more basic pH may facilitate unwanted anglesite formation. ,,, The vessels were then placed on a rotary mixer at 30 rpm and allowed to react for 8, 24 h, 1 week, and 1 month, with each vessel being sacrificed for every timepoint. Postreaction solid phases were collected, washed with DI water twice, and freeze-dried in preparation for solid phase characterization and X-ray absorption spectroscopy analyses.…”

Pollution Assessment of Potentially Toxic Elements (PTEs) in Soils around the Yanzhuang Gold Mine Tailings Pond, Pinggu County, Beijing, China

“…As a result of high PTE concentration, the nearby residents got various health problems [ 9 , 10 ]. Worse still, a large number of PTEs from mining activities and tailings have been transferred to agricultural soil, which may pollute agricultural products [ 11 , 12 , 13 ]. Due to the above facts, soil environmental sampling has become a crucial means to evaluate the anthropogenic pollution with PTEs.…”