Cinta Barba-Brioso

This study investigates the hydrometallurgical recovery of valuable metals from copper shaft furnace dust (SFD), a complex industrial waste containing approximately 40 wt.% Zn, 16 wt.% Pb, and 1 wt.% Cu. In contrast to conventional inorganic leaching processes that rely on aggressive acids and bases, this research explores the use of deep eutectic solvents (DESs) as eco-friendly and selective lixiviants. Deep eutectic solvents based on choline chloride combined with citric acid and lactic acid were evaluated as leaching media for metal recovery from SFD. The effects of temperature, leaching time, stirring intensity, and the DES:SFD ratio on metal extraction were systematically investigated. Analytical characterization of the raw material, leaching residues, and pregnant leach solutions was performed using Atomic Absorption Spectroscopy (AAS), X-ray Fluorescence Spectrometry (XRF), and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM–EDS). The experimental results demonstrated efficient recovery of Zn, Pb, Cu, and Sn under mild leaching conditions. For the citric acid–choline chloride system, the highest extraction efficiency was obtained at 60 °C using a DES:SFD ratio of 30, whereas increasing the temperature to 70–80 °C did not significantly improve metal extraction. The lactic acid–choline chloride system exhibited different leaching behaviour, with the highest recoveries achieved after short leaching times. These findings indicate that DES-based systems represent a promising, sustainable alternative for the selective leaching of heavy metals such as Zn, Pb, Cu, and Sn, from metallurgical secondary raw materials, contributing to the development of greener circular economy practices.

This research represents the first step at a pilot field scale following the success of a previous laboratory study that demonstrated the favourable performance of a bed of recycled concrete aggregates, reducing the pollutant load of acid drainage generated by polymetallic sulfidic mining residues.Mobility studies of trace metals in water and calcium chloride were conducted to evaluate the evolution of potential availability of an amended minesoil over three months, and to test the effect of each rainfall episode on it. Analysis of the solutions extracted were performed by ICP-OES.Mobil fraction of the main elements in surface was dominated by Ca, Mg and S, demonstrating that reactivity of the recycled concrete aggregates played a key role on the neutralization of minesoil surface, by dissolution of carbonates in reaction with the acid environment during rainfall.Trace elements reduced their mobility respect to the original soils while main elements increased. On the other hand, the mobility in calcium chloride showed no significant differences. Depth profiles indicate that particularly the concentration of Zn increases in the deeper levels, while As and Pb exhibit greater mobility at intermediate levels of the profile. Finally, Cu is the element that seems to have a more stable behaviour in depth. The potentially more hazardous elements have reduced their mobility compared to the initial conditions before the application of the amendment. However, the data suggest a higher efficiency of the treatment in the first centimetres of the profile, indicating a need for a readjustment of the proportions of reactive material in the amendment.

This investigation focused on the response of minesoils to which an upper substrate of recycled aggregates was added. The experience consisted in a first characterization of the minesoils (February’23) and two sampling after rainfall events, occurred in consecutive months (March and April’23). Soil sample reaction (pH-Eh and electrical conductivity) was studied with a portable multiparametric, chemical composition was analysed by X-Ray fluorescence and mineralogy was assessed by X-Ray diffraction and electron microscopy SEM.Results showed that soil surface became less acidic, changing from 3.6 to up 6 units of pH. It was probed that the alkalinizing lost reactivity at depth, since level b and c were progressively more acid, but also that it was being depleted in time. Redox conditions, nevertheless, behaved in distinct way, increasing at the three levels in time, that could affect the distribution of elements. In fact, content of Al, Fe and S slightly decreased in surface with time, but specially Al increased in depth, suggesting any mobilization to leader elements. On the other side, trace elements, specially As, trended to concentrate at the intermediate level, marking the importance of redox conditions in their distribution.Initial mineralogy hardly varied along time, maintaining the presence of the main minerals (quartz, mica and jarosite from the soil and calcite and dolomite from the amendment). Anyway, bassanite appeared during treatment, at the time than calcite and dolomite were depleted, showing the interaction of those with sulphur liberated from the oxidized pyrite observed by SEM.

Traditional mining activities in Zaruma-Portovelo (SE Ecuador) have led to high concentrations of pollutants in the Puyango River due to acid mine drainage (AMD) from abandoned waste. Dispersed alkaline substrate (DAS) passive treatment systems have shown efficacy in neutralizing acidity and retaining metals and sulfates in acidic waters, achieving near a 100% retention for Fe, Al, and Cu, over 70% for trace elements, and 25% for SO₄²⁻. However, significant solid residues are generated, requiring proper geochemical and mineralogical understanding for management. This study investigates the fractionation of elements in AMD precipitates. Results indicate that Fe³⁺ and Al³⁺ predominantly precipitate as low-crystallinity oxyhydroxysulfate minerals such as schwertmannite [Fe³⁺₁₆(OHSO₄)_12–13O₁₆·10–12H₂O] and jarosite [KFe³⁺₃(SO₄)₂(OH)₆], which retain elements like As, Cr, Cu, Pb, and Zn through adsorption and co-precipitation processes. Sulfate removal occurs via salts like coquimbite [AlFe₃(SO₄)₆(H₂O)₁₂·6H₂O] and gypsum [CaSO₄·2H₂O]. Divalent metals are primarily removed through carbonate and bicarbonate phases, with minerals such as azurite [Cu(OH)₂·2CuCO₃], malachite [Cu₂(CO₃)(OH)₂], rhodochrosite [MnCO₃], and calcite [CaCO₃]. Despite the effectiveness of DAS, leachates from the precipitates exceed regulatory thresholds for aquatic life protection, classifying them as hazardous and posing environmental risks. However, these residues offer opportunities for the recovery of valuable metals.

Traditional mining activities in Zaruma-Portovelo (SE Ecuador) have led to high concentrations of pollutants in the Puyango River due to acid mine drainage (AMD) from abandoned waste. Dispersed Alkaline Substrate (DAS) passive treatment systems have shown efficacy in neutralizing acidity and retaining metals and sulfates in acidic waters, achieving near 100% retention for Fe, Al, and Cu, over 70% for trace elements, and 25% for SO₄²⁻. However, significant solid residues are generated, requiring proper geochemical and mineralogical understanding for management. This study investigates the fractionation of elements in AMD precipitates. Results indicate that trivalent metals (Fe, Al) form low-crystallinity oxyhydroxysulfate minerals such as schwertmannite and jarosite, which retain elements like As, Cr, Cu, Pb, and Zn through adsorption-coprecipitation. Sulfate removal occurs via salts like coquimbite and gypsum. Divalent metals are primarily removed through carbonate and bicarbonate phases, with minerals such as azurite, malachite, rhodochrosite, and calcite. Despite the effectiveness of DAS, leachates from the precipitates exceed regulatory thresholds for aquatic life protection, classifying them as hazardous and posing environmental risks. However, these residues offer opportunities for the recovery of valuable metals.

La Preciosa II is an abandoned copper-pyrite and chalcopyrite mine site located in the eastern part of Seville Province (South of Spain), close to Neogene materials of the Guadalquivir Basin (calcarenite and marl). Recently, a part of the mine wastes were covered with such carbonated rocks and building materials, as a reclamation purpose for agricultural activities such as growing citric trees. However, acid mine drainage is still leaching from the subsoil, discharging into a natural stream (neutral pH) and then into the Guadalquivir river. A mineralogical and geochemical study of mine wastes and cultivated soils was carried out to assess the environmental impact and the potential health risk.Several samples from the mine wastes and the cultivated soils were collected. Major and potentially toxic elements (PTE) were determined by X-ray fluorescence and the mineralogy by X-ray diffraction. Some samples were examined by scanning electron microscopy and one mine waste, and one soil samples were selected for sequential extractions and oral bioaccesibility (BARGE method).The cultivated soils were composed of quartz, calcite, feldspar, illite and traces of gypsum. The mine waste showed pyrite, quartz, magnetite, mica, amphibole, and secondary minerals such as jarosite and gypsum. The lack of calcite in mine wastes and some of the soil samples suggests that carbonate materials were completely dissolved to form gypsum, but no more neutralizing potential is present in the mine wastes.Very high concentrations of PTE were found in the mine wastes and soil samples. Some of them, such as Cu (up to 0.7 %), Zn (up to 0.2 %) and Ag (up to 50 mg/kg) could even be recovered, contributing to the circular economy. The high content in Pb (up to 0,8 %) occurred in samples with jarosite, highlighting the role of this mineral in the retention of Pb. Other very toxic elements such as As and Cd were also present.Sequential extractions showed a high mobility of Cd and Zn, and important fraction of Cu associated to sulphides, as well as Pb associated to crystalline iron oxy-hydroxides, mainly jarosite. The mobility of PTE in the soil sample was lower than in the mine wastes, showing that the amendment of carbonate rocks decreased the mobility of PTE. The oral bioaccesibility was also higher in mine wastes, but a fraction of Zn, Cu, Co and, partially, Pb is still bioaccessible in the soil sample studied.The addition of carbonates promotes the precipitation of secondary minerals and decrease the mobility and bioaccesibility of PTE. However, more efforts are necessary to remediate the mine waste dumps in la Preciosa II, focused to preserve the environment, avoid the transfer soil-plants, and consequently reduce the human health risks.

The use of aluminum-rich clays and bauxites as refractory materials is common. Upon firing, these materials form mullite crystals in the shape of needles embedded in a siliceous and vitreous matrix, with mullite being responsible for the refractory properties. In this study, bauxite samples for use in refractory applications have been characterized. Chemical analysis revealed that the alumina content varied between 34 and 40%, with silica values generally being high (around 40%), except for one sample (26%). Two samples were found to be the most suitable for use as “refractory clay” refractories. However, high silica or Fe oxide contents can affect mineralogical transformations at high temperatures. Mineralogical analysis confirmed the presence of several minerals in the bauxite materials, including kaolinite, halloysite, anatase, rutile, gibbsite and boehmite. Differential thermal analysis (DTA) showed the decomposition of gibbsite and its partial transformation to boehmite and alumina, and the dehydroxylation of kaolinite, with primary mullite crystallization observed at a high temperature. These findings provide valuable information for the selection and optimization of bauxite materials for refractory applications, considering their chemical composition and mineralogical characteristics.

Currently, only 50% of concrete produced from construction and demolition waste is being recycled in Europe. This falls short of the European Union’s target of 70% by 2020. Moreover, this figure only considers coarse fractions (>4 mm), as technical issues arise when using fine fractions. In pursuit of a complete circular life for recycled concrete, this investigation explores the potential use of fine fractions to enhance the physicochemical conditions and reduce the element concentration of acid mine drainage. Two trickling sets were prepared using a filter holder, with acidic waters passing through a layer of recycled concrete aggregates. Results revealed an immediate increase in water pH to neutral levels, a reduction in solution oxidation, and the complete, or near-complete retention, of potentially toxic elements by the substrate (with retention percentages of over 99.9% for Al and Fe, between 43.1% and 61.1% for S, over 91.1% for Zn, and over 99.1% for Cu). The experiment also showed a significant increase in Ca levels (tripling the initial value) and some Mg in the water, which could promote the subsequent precipitation of carbonates and the retention of trace metals. In summary, this study demonstrates the effectiveness of using recycled concrete aggregates in a laboratory setting. Further investigation is necessary to evaluate the feasibility of implementing this technique at the pilot scale.

Abandoned mine lands often have lost their natural resilience and adaptive capacity to retain potentially toxic trace elements (PTE) and, therefore, can act a secondary source areas of acidic effluents and harmful contaminants into surface and pore waters. To address this issue, a batch leaching test was conducted to assess the effects of tailored combinations of non-hazardous industrial wastes on the immobilization of PTE in three mine soils (MS2, MS3, MS4) of the historic Rio Tinto mining district (Spain). To do this, different Technosols (T) were prepared by mixing, at a ratio of 60:40 (w/w), organic (R2: sludge from the clear treated water) and inorganic waste materials with acid-neutralizing capability (R4 and R5: slags from the iron and steel making industry) and adsorbent properties (R6: red gypsum). The Technosols tested were made of: (T0) exclusively MS2, MS3 and MS4 (controls); (T1) 80%MS4+20%[R2+(R5+R6)]; (T2) 75%MS3+25%[R2+(R5+R6)]; (T3) 75%MS2+25%[R2+R4]; (T4) 75%MS2+25%[R2+R5]; (T5) 75%MS3+25%[R2+R5]; and (T6) 75%MS4+25%[R2+R5]. The leaching test was performed according to the standard EN-12457-4, at a liquid-to-solid ratio of 10 L kg-1 with constant agitation for 24 h. The leaching conditions were recorded in terms of pH and Eh values, and the PTE concentrations in the leachate solutions were analyzed by ICP-MS. Results showed that the leachates from untreated MS were ultra acid (pH 2.5-3.5) and had concentrations of Cu, Pb and Zn as high as 556 mg kg-1 (MS3), 90 mg kg-1 (MS4) and 28 mg kg-1 (MS3), respectively, while the released concentrations of Cr, Ni, As and Cd were below 1 mg kg-1. In relative terms, the most mobile PTE were Cd, Cu and Zn, which accounted for 12.6%, 10.3% and 5.4% of its total concentration, respectively. The Technosol application was able to buffer the soil pH to average values of 7.6, thus enhancing the attenuation of PTE by chemical fixation. The mobile fraction of PTE was drastically reduced or even rendered virtually negligible (<0.10%) except for Ni, which was leached from the T1 up to 0.79% of its total concentration, and for Cd (0.49% from the T2). In particular, T3 was the most effective for reducing the mobility of Cd, and T4 and T5 showed promise for assisting in the attenuation of Cu. Chemical speciation calculations predict that most of the PTE leached from untreated MS are in the form of sulfate complexes, comprising 62-77% of the dissolved fraction, and to a lesser extent as free ions. Upon treatment, the activity of such species decreased noticeably with increasing pH, while the contribution of hydroxyl complexes was shown to increase. In conclusion, the use of Technosols was effective in reducing the acid generation potential of the MS and for boosting the PTE stabilization processes.

Mineralogical analysis and laboratory-based leaching tests coupled with speciation modeling were undertaken to quantify the potential for short-term acid generation and the release of trace elements from soils heavily contaminated with mine waste at Rio Tinto. Three different waste materials were considered as case studies: roasted pyrite, copper slags, and leached sulfide ores. The results showed elevated values of net acid generation (up to 663 mmol H⁺/kg), the major pools being potential sulfidic acidity and acidity retained in jarosite. Remarkable contents of As and toxic heavy metals were found especially in the slag-contaminated soil. Copper, Zn, and Pb were the most abundant metals in the acid leach solutions resulting from mine soil-water interaction, with peak values of 55.6 mg L⁻¹, 2.77 mg L⁻¹, and 2.62 mg L⁻¹, respectively. Despite the high total contents of trace elements occurring in soil, the mobile fraction was limited to maximum release values of 12.60% for Cd and 10.27% for Cu, according to the test leaching. Speciation calculations indicated that free metal ions (M²⁺) and sulfate species (MSO₄⁰) accounted for most of the dissolved load. Acid soil drainage is a secondary source of acid and heavy metals in the mine site and, therefore, an effective land reclamation program should ensure that acidity and metal mobility are reduced to environmentally sustainable levels.