Assessing the role of bed sediments in the persistence of red mud pollution in a shallow lake (Kinghorn Loch, UK)

Red mud is a by-product of alumina production. Little is known about the long-term fate of red mud constituents in fresh waters or of the processes regulating recovery of fresh waters following pollution control. In 1983, red mud leachate was diverted away from Kinghorn Loch, UK, after many years of polluting this shallow and monomictic lake. We hypothesised that the redox-sensitive constituents of red mud leachate, phosphorus (P), arsenic (As) and vanadium (V), would persist in the Kinghorn Loch for many years following pollution control as a result of cycling between the lake bed sediment and the overlying water column. To test this hypothesis, we conducted a 12-month field campaign in Kinghorn Loch between May 2012 and April 2013 to quantify the seasonal cycling of P, As, and V in relation to environmental conditions (e.g., dissolved oxygen (DO) concentration, pH, redox chemistry and temperature) in the lake surface and bottom waters. To confirm the mechanisms for P, As and V release, a sediment core incubation experiment was conducted using lake sediment sampled in July 2012, in which DO concentrations were manipulated to create either oxic or anoxic conditions similar to the bed conditions found in the lake. The effects on P, As, and V concentrations and species in the water column were measured daily over an eight-day incubation period. Phosphate (PO4-P) and dissolved As concentrations were significantly higher in the bottom waters (75.9 ± 30.2 μg L−1 and 23.5 ± 1.83 μg L−1, respectively) than in the surface waters (12.9 ± 1.50 μg L−1 and 14.1 ± 2.20 μg L−1, respectively) in Kinghorn Loch. Sediment release of As and P under anoxic conditions was confirmed by the incubation experiment and by the significant negative correlations between DO and P and As concentrations in the bottom waters of the lake. In contrast, the highest dissolved V concentrations occurred in the bottom waters of Kinghorn Loch under oxic conditions (15.0 ± 3.35 μg L−1), with the release from the bed sediment apparently being controlled by a combination of competitive ion concentrations, pH and redox conditions

The use of pHstat leaching tests to assess chemical speciation and potential mobilisation of trace metals from soils, sediments and waste materials: A state of the art

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Environmental impact and potential remedation of contaminated land affected by Zn-Pb mining

International Workshop Current developments in remediation of contaminated lands 27 - 29 October 2005, Pulawy, Poland Environmental impact and potential remediation of contaminated land affected by Zn-Pb mining Valérie Cappuyns*1, Rudy Swennen1, Patrick Ganne1,2 and Marjan Niclaes1 1Katholieke Universiteit Leuven, Fysico-chemische Geologie, Celestijnenlaan 200C, B-3001 Heverlee, Belgium 2 Katholieke Universiteit Leuven, Mijnbouw, Kasteelpark Arenberg 40, B-3001 Heverlee, Belgium 1. Introduction From the Middle Ages until the beginning of the 20th century, extensive Zn-Pb mining and smelting was carried out in East-Belgium. By lack of waste treatment techniques and of sustainable management practices, metal-bearing slags and unprocessed waste were dumped. Besides the important amount of waste that is stored in huge mine tailings, the surroundings of the tailings are often contaminated as a consequence of the dispersal of contaminants by wind erosion, runoff or fluvial transport. In the present study, the distribution pattern, the actual and potential mobilisation and (natural) attenuation of Pb, Zn and Cd in the mine tailings of La Calamine and Angleur (East-Belgium) was investigated. 2. Methodology In La Calamine and Angleur (East-Belgium), vertical profiles were sampled in detail within tailings consisting of respectively dredged mine tailing pond sediments and waste from the metallurgical process of Zn-production. Samples were also taken from overbank sediments along the Geul 7, 9 and 12 km downstream from the mine tailing pond of La Calamine and in the neighbourhood (300 m) of the dump site of Angleur. Total metal concentrations, pH and grainsize were determined for all the samples and a mineralogical (petrography, XRD, SEM-EDX) investigation of tailing material from La Calamine and Angleur was carried out. Porewater extractions and the DIN 38414-S4 leaching test (extraction with water at a liquid/solid ratio of 10/1) were used to evaluate heavy metal leaching from the tailing material. pHstat leaching tests and geochemical modelling of the pH-dependent leaching behaviour were performed on a selection of samples from both mine tailings. The feasibility of the addition of phosphates as a measure to reduce the release of Pb, Zn and Cd into the environment was also investigated. 3. Results and discussion 3. 1. Mineralogical and physico-chemical characterisation At both locations, mine tailings and soils in the surrounding of the tailings were contaminated with Zn, Pb, Cd and As (Table 1). The mine tailing in La Calamine is located in a rural area with a low population density. The nearby Geul river flows through the mine tailing, resulting in a severe contamination of alluvial soils downstream from the tailing. The area around the mine tailing in Angleur has been urbanised. The main minerals in the La Calamine mine tailing were sfalerite (ZnS), smithsonite (ZnCO3), anglesite (PbSO4), cerrusite (PbCO3), galena (PbS), pyrite (FeS2) and marcasite (FeS2). Whereas more acid pH values (between 3 and 4.9) were encountered in the deeper part of the tailing (between 2.6 and 4 m depth), a lower mobility of Zn, Pb and Cd was found compared to the upper part of the tailing, where pH was in the range 5-7. The oxidation of sulphide minerals within the mine tailing releases H+, SO42-, Fe2+, and trace metals into the porewater. Subsequent pH-buffering in carbonate-rich layers results in the precipitation of secondary minerals such as ZnCO3, FeCO3 and CaSO4.2H2O. These precipitation processes result in the formation of cemented layers, which show an enrichment in Cd and Zn. Whereas the carbonate-rich layers provide some natural attenuation of contaminants, elevated Zn-, Pb- and Cd concentrations are found in the porewater in the surface layers of the tailing (0-2.6 m depth). In the mine tailing of Angleur, XRD analysis revealed the presence of several oxides and silicates such as franklinite (ZnFe2O4), willemite (Zn2SiO4), wollastonite (CaSiO3), and traces of sulphates, sulphides and carbonates. pH was neutral to slightly alkaline for al the samples investigated. The upper part of the tailing (0-0.7 m depth) was less contaminated than the lower part (0.7- 4 m depth). Contrary to the tailing material in La Calamine and despite the elevated total heavy metal and arsenic concentrations on the site, the DIN 38414-S4 leaching test indicates that heavy metal release is very limited and far below European limit values for slag material on dumps (category 1). Table 1: Total Pb-, Zn-, Cd- and As-concentrations in the mine tailings and the surrounding of the mine tailings of La Calamine and Angleur. Zn and Pb in g/kg, Cd and As in mg/kg; n = number of samples La Calamine mine tailing (n = 20) alluvial soils downstream (n = 100) Zn Pb Cd As Zn Pb Cd As average 38 19 146 679 3.9 1.3 7 23 stdv 36 13 138 444 3.4 1.7 8 25 min 1 2.4 3 31 0.3 0.04 0.1 4 max 108 40 307 2294 13 6.5 37 121 Angleur mine tailing (n = 91) surrounding of the tailing (n = 16) Zn Pb Cd As Zn Pb Cd As average 52 8 100 231 1.6 0.6 30 266 stdv 30 6 74 159 1.4 0.5 20 280 min 12 1.0 3 18 0.2 0.4 4 32 max 162 31 403 1928 4.5 2.3 68 942 3.2. pH-dependent leaching behaviour and potential remediation A multidisciplinary approach, combining pHstat leaching tests, solid-phase characterization (XRD, SEM-EDX) and thermodynamical modelling (MINTEQA2) confirmed that the solubility of Zn, Pb and Cd in the mine pond tailing of La Calamine is mainly controlled by Pb-Zn minerals. In Angleur, vitreous phases seem very important in controlling heavy metal mobility since metals that are locked up in a silicate matrix are protected against leaching. Liming will not be an effective remediation option for the tailing in Angleur, since As and Pb will be mobilised when pH increases (Fig. 1). However, for the La Calamine dredged mine tailing pond sediments, a pH-increase significantly decreases the leachability of Zn, Cd and Pb, whereas the solubility of As is not affected and remains very low. The addition of phosphates in combination with liming results in an additional decrease of heavy metal solubility and contributes to a reduction of the release of Pb, Zn and Cd into the environment. Fig. 1: pH-dependent leaching behaviuor of Pb, Cd and As in a sample from the tailing of La Calamine (a) and Angleur (b). Total Pb-, Cd- and As-concentrations and pH of the samples are also indicated. 4. Conclusion In La Calamine, liming and the addition of phosphates can effectively reduce heavy metal leaching from the tailing. However, at both locations, wind erosion and runoff can cause the spreading of fine-grained dust, especially since the waste material is not covered. For a sustainable development of the mining areas of La Calamine and Angleur surface stabilisation is also necessary.status: publishe

In situ production of prebiotic AXOS by the hyperthermophilic xylanase B from Thermotoga maritima in high quality bread

In situ enrichment of bread with arabinoxylan-oligosaccharides (AXOS) through enzymic degradation of wheat flour arabinoxylan (AX) by the hyperthermophilic xylanase B from Thermotoga maritima (rXTMB) was studied. The xylanolytic activity of rXTMB during breadmaking was essentially restricted to the baking phase. This prevented problems with dough processability and bread quality that generally are associated with thorough hydrolysis of the flour AX during dough mixing and fermentation. rXTMB action did not affect loaf volume. Bread with a dry matter AXOS content of 1.5% was obtained. Further increase in bread AXOS levels was achieved by combining rXTMB with xylanases from Pseudoalteromonas haloplanktis or Bacillus subtilis. Remarkably, such a combination synergistically increased the specific bread loaf volume. Assuming an average daily consumption of 180 g of fresh bread, the bread AXOS levels suffice to provide a substantial part of the AXOS intake leading to desired physiological effects in humans.status: publishe

Incorporation of bioleached sulfidic mine tailings in one-part alkali-activated blast furnace slag mortar

Abstract Sulfidic mine tailings are potential waste materials from mining and mineral processing, and they can contain a high content of sulfur and metal(loid)s, even after bioleaching. Due to the large amount of tailings waste from historical mining, it is crucial to find alternative methods for utilizing such waste rather than permanent storage in tailings impoundments. One-part alkali-activated slag mortars are promising co-binder systems for the recycling of sulfidic mine tailings thanks to their practicability, easy transportation, and user-friendly production. In this work, up to 50 wt% mine tailings were incorporated into alkali-activated blast furnace slag mortars. C-(N)-A-S-H gels were formed in all final samples with hydrotalcite zeolites. Tailings hardly participate in alkali activation, but they do have a considerable influence on physical and chemical properties. The 20 wt% tailings-containing sample showed the highest compressive strength of 91.1 MPa after 90 days of curing. The results of isothermal calorimetry indicate that incrementally increasing the percentage of tailings promotes the pre-induction reaction but hinders the slag hydration process. In addition, the results of X-ray microcomputed tomography showed higher porosity when the mortar contains more tailings; thus, the sample with 10 wt% mine tailings showed the lowest porosity. According to the European Union batch leaching test, up to 20 wt% bioleached sulfidic mine tailings can be valorized in a co-binder system while remaining below the nonhazardous waste thresholds