Mineralogy and heavy metal content of secondary mineral salts: A case study from the Witwatersrand Gold Basin, South Africa.

Secondary minerals associated with acid mine drainage play an important role in metal cycling and may pose a geochemical hazard. The occurrence of secondary minerals indicates prevailing and past geochemical conditions. Detecting and characterising secondary minerals is necessary to the planning of remediation programmes. This paper investigates the mineralogical and heavy metal contents of mineral salts associated with acid mine drainage in the East Rand area of the Witwatersrand Basin. Powdered X-ray diffraction was used to identify and quantify mineralogical phases and a scanning electron microscope was used to determine the morphology of the identified minerals. Major cations and anions were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Ion Chromatography (IC). Geochemical modelling was used to predict the saturation of the minerals. Efflorescent crusts contained high levels of trace metals. Enrichment of trace metals, electrical conductivity and sulphate were highest in white salts. A high metal content was associated with low pH values in mineral salts. The salts were dominated by quartz and clay minerals of the smectite group. Tamarugite, apjohnite and jarosite were the predominant sulphate minerals in the salts. These minerals are very acidic and will accelerate weathering in the surrounding soils. Geochemical modelling yielded precipitated hydrated sulphate, halite and goethite. The information gathered during this study will be useful in managing salinity and high metal contents in receiving waters and soils associated with gold mining activities

Floristic composition of gold and uranium tailings dams, and adja­cent polluted areas, on South Africa’s deep-level mines

Gold and uranium tailings (‘slimes’) dams and the adjacent polluted soils in the deep-level mining regions of South Africa (Carletonville, Klerksdorp and Welkom) were surveyed for the frequency of occurrence of naturally colonizing, actively introduced and persisting plant species. Fifty-six tailings dams with a combined area of 5864 ha. and a similar area o f tail- ings-polluted soils, were surveyed between July 1996 and March 1997. During the survey, 376 plant species and subspecies were recorded from the dams and adjacent polluted soils, with an additional  8 6  records obtained between 1998 and 2003 (i.e. a total of 462 taxa: species and infraspecific species). Overall, the most commonly represented families were the Poaceae (107 species and subspecies), Asteraceae (81). Fabaceae (55) and Anacardiaceae (16). with other families represented by just one to 14 species. Only 60 species were common to all three regions, and of these 24 had been introduced during rehabilitation attempts. Most of the species found on tailings were persisters or natural colonizers (53-88%, depending on substrate), with the vast majority being indigenous and perennial taxa (76% and 85% respectively), with semi-woody to woody growth forms (6 6% being resprouters, forbs, shrubs and trees). Less than 4% of the naturally-colonizing taxa found during the survey had also been introduced by vegetation practitioners. The majority of introduced plants were alien herbaceous taxa. The number and frequency of annuals was only high on recently vegetated sites, whereas annuals were rarely present on old-vegetated and never-vegetated dams. This list includes a wide range of indigenous plant species that may be suitable for phytoremediation of tailings dams and polluted soils due to their apparent tolerance of acid mine drainage and salinity

Effects of the mycorrhizal fungus ¤Glomus intraradices¤ on uranium uptake and accumulation by ¤Medicago truncatula¤ L. from uranium-contaminated soil

Phytostabilization strategies may be suitable to reduce the dispersion of uranium (U) and the overall environmental risks of U-contaminated soils. The role of Glomus intraradices, an arbuscular mycorrhizal (AM) fungus, in such phytostabilization of U was investigated with a compartmented plant cultivation system facilitating the specific measurement of U uptake by roots, AM roots and extraradical hyphae of AM fungi and the measurement of U partitioning between root and shoot. A soil-filled plastic pot constituted the main root compartment (C-A) which contained a plastic vial filled with U-contaminated soil amended with 0, 50 or 200 mg KH2PO4-P kg(-1) soil (C-B). The vial was sealed by coarse or fine nylon mesh, permitting the penetration of both roots and hyphae or of just hyphae. Medicago truncatula plants grown in C-A were inoculated with G. intraradices or remained uninoculated. Dry weight of shoots and roots in C-A was significantly increased by G. intraradices, but was unaffected by mesh size or by P application in C-B. The P amendments decreased root colonization in C-B, and increased P content and dry weight of those roots. Glomus intraradices increased root U concentration and content in C-A, but decreased shoot U concentrations. Root U concentrations and contents were significantly higher when only hyphae could access U inside C-B than when roots could also directly access this U pool. The proportion of plant U content partitioned to shoots was decreased by root exclusion from C-B and by mycorrhizas (M) in the order: no M, roots in C-B > no M, no roots in C-B > M, roots in C-B > M, no roots in C-B. Such mycorrhiza-induced retention of U in plant roots may contribute to the phytostabilization of U contaminated environments

Impact of arbuscular mycorrhizal fungi on uranium accumulation by plants

Contamination by uranium (U) occurs principally at U mining and processing sites. Uranium can have tremendous environmental consequences, as it is highly toxic to a broad range of organisms and can be dispersed in both terrestrial and aquatic environments. Remediation strategies of U-contaminated soils have included physical and chemical procedures, which may be beneficial, but are costly and can lead to further environmental damage. Phytoremediation has been proposed as a promising alternative, which relies on the capacity of plants and their associated microorganisms to stabilize or extract contaminants from soils. In this paper, we review the role of a group of plant symbiotic fungi, i.e. arbuscular mycorrhizal fungi, which constitute an essential link between the soil and the roots. These fungi participate in U immobilization in soils and within plant roots and they can reduce root-to-shoot translocation of U. However, there is a need to evaluate these observations in terms of their importance for phytostabilization strategies

Role and influence of mycorrhizal fungi on radiocesium accumulation by plants

This review summarizes current knowledge on the contribution of mycorrhizal fungi to radiocesium immobilization and plant accumulation. These root symbionts develop extended hyphae in soils and readily contribute to the soil-to-plant transfer of some nutrients. Available data show that ecto-mycorrhizal (ECM) fungi can accumulate high concentration of radiocesium in their extraradical phase while radiocesium uptake and accumulation by arbuscular mycorrhizal (AM) fungi is limited. Yet, both ECM and AM fungi can transport radiocesium to their host plants, but this transport is low. In addition, mycorrhizal fungi could thus either store radiocesium in their intraradical phase or limit its root-to-shoot translocation. The review discusses the impact of soil characteristics, and fungal and plant transporters on radiocesium uptake and accumulation in plants, as well as the potential role of mycorrhizal fungi in phytoremediation strategies