Mining activities in general, and quarrying processes in particular, generate huge amounts of tailings with a considerable presence of fine particles and with a variable composition of minerals, ...which could limit the direct application of those wastes. Under the paradigm of a circular economy, more effort has to be made to find adequate applications for those secondary raw materials. In this study, a process was proposed and tests were performed to valorise fine particle product as a raw material for the building and construction industry. Samples were taken from wastes in several aggregate production plants, being characterized and processed to remove the clayey components to obtain the cleanest quartz fraction. Then, different characterization and validation tests were carried out to analyse the application of these products as raw materials in the building and construction industry (cement and ceramics). Results showed that with no complex technologies, the tailings can be considered as a mineral raw material in different applications.
•Complex legacy of contamination afflicts As–Hg brownfields.•As- and Hg-rich waste analyzed in a paradigmatic study site.•Co-ocurrence of a complex speciation of As and Hg, and organic pollution ...(PAHs).•Arsenolite was determined to be the main source of risk at the site.•Unexpected Hg organo-compounds found.
The abandonment of Hg–As mining and metallurgy sites, together with long-term weathering, can dramatically degrade the environment. In this work it is exemplified the complex legacy of contamination that afflicts Hg–As brownfields through the detailed study of a paradigmatic site. Firstly, an in-depth study of the former industrial process was performed to identify sources of different types of waste. Subsequently, the composition and reactivity of As- and Hg-rich wastes (calcines, As-rich soot, stupp, and flue dust) was analyzed by means of multielemental analysis, mineralogical characterization (X-ray diffraction, electronic, and optical microscopy, microbrobe), chemical speciation, and sequential extractions.
As-rich soot in the form of arsenolite, a relatively mobile by-product of the pyrometallurgical process, and stupp, a residue originated in the former condensing system, were determined to be the main risk at the site. In addition, the screening of organic pollution was also aimed, as shown by the outcome of benzo(a) pyrene and other PAHs, and by the identification of unexpected Hg organo-compounds (phenylmercury propionate).
The approach followed unravels evidence from waste from the mining and metallurgy industry that may be present in other similar sites, and identifies unexpected contaminants overlooked by conventional analyses.
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•Soil washing performance after nZVI addition was examined.•Dilution effect caused by nZVI was considered for metallurgical accounting purposes.•Nanoparticle addition improved PTE ...removal.•nZVIs were selective for Cu, Pb and Sb.
The present study focuses on soil washing enhancement via soil pretreatment with nanoscale zero-valent iron (nZVI) for the remediation of potentially toxic elements. To this end, soil polluted with As, Cu, Hg, Pb and Sb was partitioned into various grain sizes (500–2000, 125–500 and <125 μm). The fractions were pretreated with nZVI and subsequently subjected, according to grain size, to Wet-High Intensity Magnetic Separation (WHIMS) or hydrocycloning. The results were compared with those obtained in the absence of nanoparticles.
An exhaustive characterization of the magnetic signal of the nanoparticles was done. This provided valuable information regarding potentially toxic elements (PTEs) fate, and allowed a metallurgical accounting correction considering the dilution effects caused by nanoparticle addition.
As a result, remarkable recovery yields were obtained for Cu, Pb and Sb, which concentrated with the nZVI in the magnetically separated fraction (WHIMS tests) and underflow (hydrocyclone tests). In contrast, Hg, concentrated in the non-magnetic fraction and overflow respectively, while the behavior of As was unaltered by the nZVI pretreatment. All things considered, the addition of nZVI enhanced the efficiency of soil washing, particularly for larger fractions (125–2000 μm). The proposed methodology lays the foundations for nanoparticle utilization in soil washing operations.
The use of quebracho extract as a pyrite depressing agent to improve Cu/Fe ratio in copper minerals flotation was studied. The depressing effect in the case of pure pyrite, pure chalcopyrite and a ...sample of disseminated copper ore was tested considering different pH values and modifiers, and different levels of tannin addition. Results show that quebracho extract can be considered a cleaner option in these processes.
Several metals and metalloids (e.g., As, Cd, Cu, Pb, Zn) are toxic at low concentrations, thus their presence in sediments can raise environmental concern. However, these elements can be of economic ...interest, and several techniques have been used for their recovery and some of them have been widely applied to mining or to industrial soils, but not to sediments. In this work, wet high-intensity magnetic separation (WHIMS) was applied for As, Cd, Cu, Pb and Zn recovery from polluted sediments. A composite sample of 50 kg was taken in the Avilés estuary (Asturias, North Spain) with element concentrations above the legislation limits. Element distribution was assessed using wet-sieving and ICP-MS analysis, revealing that the 125–500 μm grain-size fraction accounts for the 62 w% of the material and that element concentration in this fraction is lower than in the other grain size fractions. Subsequently, WHIMS was applied at three different voltage intensities for the 125–500 μm and <125 μm fractions, revealing excellent recovery ratios, especially for the coarser material. Furthermore, magnetic property measurements coupled to microscopy analysis revealed that the success of the technique derives from concentrating metal-enriched iron oxides particles (ferro- and para-magnetic material) in a mixture of quartz and other minerals (diamagnetic particles). These results indicate the feasibility of the magnetic separation for metal and metalloid recovery from polluted sediments, and thus offer a double benefit of coastal area restoration and valuable material recovery in the context of a circular economy.
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•Magnetic separation is a useful technique for metal recovery from polluted sediments.•Metal-enriched particles (ferro/para-magnetic material) were separated from quartz.•Electron microprobe found As & metals associated to sphalerite and Fe oxides.•This approach leads to clean sediments and recovered elements.
► Abandoned mining-metallurgy sites are usually affected by As–Hg pollution. ► We examine soil washing alternatives for an As–Hg polluted site. ► We apply novel techniques (grindability and ...specific-gravity tests) for washing feasibility. ► Soil washing approach proposed includes grinding of particles above 125
μm and hydrocycloning.
Soils in abandoned mining sites generally present high concentrations of trace elements, such as As and Hg. Here we assessed the feasibility of washing procedures to physically separate these toxic elements from soils affected by a considerable amount of mining and metallurgical waste (“La Soterraña”, Asturias, NW Spain). After exhaustive soil sampling and subsequent particle-size separation via wet sieving, chemical and mineralogical analysis revealed that the finer fractions held very high concentrations of As (up to 32,500
ppm) and Hg (up to 1600
ppm). These elements were both associated mainly with Fe/Mn oxides and hydroxides. Textural and geochemical data were correlated with the geological substrate by means of a multivariate statistical analysis. In addition, the Hg liberation size (below 200
μm) was determined to be main factor conditioning the selection of suitable soil washing strategies. These studies were finally complemented with a specific-gravity study performed with a C800 Mozley separator together with a grindability test, both novel approaches in soil washing feasibility studies. The results highlighted the difficulties in treating “La Soterraña” soils. These difficulties are attributed to the presence of contaminants embedded in the soil and spoil heap aggregates, caused by the meteorization of gangue and ore minerals. As a result of these two characteristics, high concentrations of the contaminants accumulate in all grain-size fractions. Therefore, the soil washing approach proposed here includes the grinding of particles above 125
μm.
Soil in a brownfield contaminated by pyrite ashes showed remarkably high concentrations of several toxic elements (Hg, Pb, Zn, Cu, Cd, and As). Initially, we assessed various physical, chemical and ...mineralogical properties of this soil. The data obtained, and particularly multivariate statistics of geochemical results, were useful to establish the predominant role of the soil organic matter fraction (6%) and iron oxyhydroxides in the binding of heavy metals and arsenic. In addition, we studied the viability of soil washing techniques to reduce the volume of contaminated soil. Therefore, to concentrate most of the contaminants in a smaller volume of soil, the grain-size fraction below 125
μm was treated by hydrocycloning techniques. The operational parameters were optimized by means of a factorial design, and the results were evaluated by attributive analysis. This novel approach is practical for the global simultaneous evaluation of washing effectiveness for several contaminants. A concentration factor higher than 2.2 was achieved in a separated fraction that contained less than 20% of the initial weight. These good yields were obtained for all the contaminants and with only one cycle of hydrocycloning. Hence full-scale soil washing is a plausible remediation technique for the study site.
This paper describes a feasibility study of physical soil washing techniques to separate potentially toxic elements, such as As, Cu, Hg, Pb and Sb, in a brownfield affected by pyrite ash disposal. To ...this end, complete pedological and geochemical analyses were conducted in order to determine the properties of the soil. Afterwards exhaustive lab-scale soil washing tests were performed with the aim to concentrate most of the contaminants into a small fraction of treated soil. The procedures used included gravity separation–heavy liquid assays–, hydrocycloning and wet and dry magnetic separation.
Within this context, grain-size classification proved effective only for the treatment of the sizes below 63 μm. Better results were obtained by heavy liquid separation, which was optimal at most grain sizes, except fractions of the soil between 1000 and 2000 μm, and below 63 μm. As regards magnetic separation, dry high-intensity magnetic separation was suitable for the treatment of grain sizes above 500 μm and gave yields similar to those achieved by heavy liquid assays in most cases. The results of the experiments were compared through the novel approach of attributive analysis, and the findings indicated that the separation procedures for pollutants yielded repeatable results. Moreover, an intuitive method of evaluating the performance of the separation techniques by introducing a “success score” was developed. This procedure takes into account not only the various scenarios contemplated by legislation but also the performance of each washing method for each element.
All things considered, in feasibility studies for soil washing methods and also for mineral processing purposes, both attributive analysis and the “success score” may be useful for selecting optimal operating conditions, thus facilitating the scale-up of the results. Moreover, the method presented could be used in any operating plant that aims to reduce emissions while at the same time maximizing product outputs.
•A soil washing feasibility study was conducted.•Tests were evaluated by means of attributive analysis and a “success score”.•Gravity and magnetic separation offered repeatable results.•The attributive analysis and “success score” were effective at assessing treatment performance.
Background and aim
The use of amendments to immobilize metals in polluted soils is a widely accepted remediation approach, and in the framework of the circular economy, amendments produced from ...mining and/or biomass waste have gained relevance. However, the application of such amendments can also mobilize metalloids. Here we propose the combination of nanoscale zero-valent iron nanoparticles (nZVI) with dunite (mining waste) and compost for the remediation and restoration of soil affected by high concentrations of As and metals.
Methods
To this end, we treated pots containing the polluted soil with combinations of dunite, compost, and nZVI for 75 days. In addition,
Sinapis alba
was used to evaluate the effects of the amendments on pollutant accumulation in the plant. The mobility of the pollutants was monitored through TCLP extraction and by sampling pore water. Furthermore, pH, available P, and cation exchange capacity (CEC) were also determined.
Results
Dunite application led to the immobilization of metals, and supplied Mg, thus improving CEC. On the other hand, compost increased nutrient content, and also promoted plant growth. However, this amendment caused a dramatic increase in As accumulation in the plants. Finally, the application of nZVI in combination with the other two amendments was found to be the most appropriate strategy since it not only prevented As mobilization and accumulation but also added nutrients to the soil, thus promoting plant growth.
Conclusion
The combination of nZVI with dunite mining waste and compost proved effective for the remediation of soil simultaneously polluted by As and metals.
► We conducted a soil washing feasibility study at a Pb mining-metallurgy site. ► Soil contained heavy metals associated with lead slag fragments. ► Magnetic characterization of the slag shows a weak ...ferro/ferri magnetic response. ► Dry high intensity magnetic separation was successful for sands. ► Wet high intensity magnetic separation was effective for finer fractions.
The industrial history in the district of Linares (Spain) has had a severe impact on soil quality. Here we examined soil contaminated by lead and other heavy metals in “La Cruz” site, a brownfield affected by metallurgical residues. Initially, the presence of contaminants mainly associated with the presence of lead slag fragments mixed with the soil was evaluated. The subsequent analysis showed a quasi-uniform distribution of the pollution irrespective of the grain-size fractions. This study was accompanied by a characterization of the lead slag behavior under the presence of a magnetic field. Two main magnetic components were detected: first a ferromagnetic and/or ferrimagnetic contribution, second a paramagnetic and/or antiferromagnetic one. It was also established that the slag was composed mainly of lead spherules and iron oxides embedded in a silicate matrix. Under these conditions, the capacity of magnetic separation to remove pollutants was examined. Therefore, two high intensity magnetic separators (dry and wet devices, respectively) were used. Dry separation proved to be successful at decontaminating soil in the first stages of a soil washing plant. In contrast, wet separation was found effective as a post-process for the finer fractions.
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