A large number of heavy metals are generated in tailings of precious metal extractive operations, which could cause high levels of water contamination. Because of the environmental and health concerns, many conventional technologies have been applied to capture heavy metals from mining-polluted streams with limited performance in terms of effectiveness and immobilization efficiency. In this context, this study evaluates the retention of mine-generated heavy metals using Technosols prepared with iron-rich soils and multicomponent nanoparticles of Fe/FeS (MCNPs). Firstly, nanoparticles were synthesized using orange-peel extract and sodium borohydride (NaBH4) as reductant agents and FeCl3.6H2O and Na2SO4 as metal precursors. The TEM and SEM images showed nanoparticles with roughly spherical morphology with a size in the range of 35.9 ± 11.7 nm arranged in a kind of filamentous structure. Secondly, Soils were dosed with 1% and 3% (w/w) of multicomponent nanoparticles and then used to capture heavy metals present in mine tailings using batch and fixed-bed column tests. The Technosol prepared with 97% soil, and 3% MCNPs reached on average 70% retention of heavy metals for fixed-bed setups. While, in batch experiments using the same Technosol, the capture of heavy metals was 80% after 6 min of treatment, and upon reaching 30 min, 90% removal was attained. This suggests that tailored Technosols might be part of a promising technology to treat contaminated mine tailings with reasonable spending.

This study evaluates the pollution of the Machángara River basin in Ecuador. For the assessment, water samples were pumped from the river for 1 to 4 h, with a representative water sample of 4 L collected. In the site and laboratory, the physicochemical parameters, carbamazepine (CBZ), and diclofenac (DIC) concentrations were measured using standardized analytical methods. On average, a temperature of 17.02 °C, pH of 7.06, electrical conductivity of 760.96 µS/cm, and turbidity of 83.43 NTU were found. Furthermore, the average solids content was 72.88, 495.47, and 568.35 mg/L for total suspended solids (TSS), total dissolved solids (TDS), and total solids (TS) in that order. The highest chloride concentration (Cl⁻ = 87.97 mg/L) was below the maximum permissible limit (MPL) based on the Ecuadorian regulations for surface and underground water for human consumption and domestic use, which only require conventional treatment. In contrast, levels of nitrate (NO₃⁻ = 27.75–288.25 mg/L) and nitrite in five points (NO₂⁻ = 2.02–5.42 mg/L) were higher than the MPLs. Moreover, sulfate (SO₄²⁻ = 34.75–110 mg/L) and phosphate (PO₄−P = 4.15–16.58 mg/L) contents caused turbidity and eutrophication in the river water., Additionally, concentrations of copper (Cu²⁺ = 0.002–0.071 mg/L), zinc (Zn²⁺ = 0.001–0.011 mg/L) and iron (Fe³⁺ = 0.000–0.287 mg/L) were within the permissible limits. On the other hand, carbamazepine concentrations in the Machángara River basin were below the limit of detection (LOD) up to a value of 0.121 mg/L. At the same time, diclofenac levels ranged from 9.32 to 48.05 mg/L. The concentration discrepancy for both pharmaceuticals is linked with the trend of drug consumption by Quito’s inhabitants. As measured in this investigation, meaningful amounts of CBZ and DIC are released to the Machángara River. Accordingly, the two pharmaceuticals in the river water may be dangerous for aquatic species.

A large number of heavy metals are usually contained in mine-derived liquids, which could cause contamination of surrounding water sources. Due to the detrimental effects on the environment and health, conventional treatments have been employed to capture heavy metals in mining-polluted streams. This study shows the results of the operation of a built prototype for the retention of arsenic contained in waters contaminated by mining activities using Technosols (mixtures of local soil with nanoparticles). Our team previously run laboratory tests using fixed-bed columns to find out the best dose of the Technosol (97% soil + 3% nanoparticles). Based on these results, the sizing and building of a scale model were conducted, which in turn was used to evaluate the performance of the treatment in a concrete channel packed with reactive barriers. Variations in water volume, barrier separation and gate opening were tested to analyze the behavior of the proposed system and to obtain the most optimal hydraulic retention time that allowed the prototype to reach an arsenic retention level of a minimum of 70%. Moreover, to analyze the procedure under conditions of high arsenic contamination, samples of mine tailings were enriched with the toxic metalloid. It was found that the content of Fe in the local soil allowed adsorption of the contaminant, which was subsequently compared with the increase in the uptake of As due to the Fe/FeS multicomponent nanoparticles (NPs), dosed in the Technosol in a proportion of 97% soil + 3% NPs. The best treatment achieved 70.5% of As removal in ten cycles with a volume of 44 L. Tests were run at a maximum input flow rate of 43.8 L·min⁻¹, an output flow rate of 13.2 L·min⁻¹, a speed of 6.0 m·min⁻¹ and a hydraulic retention time of 3.4 min per cycle. Results of arsenic retention using this prototype suggest that this simple and inexpensive technological setup could be scaled up to a functional field application to effectively capture the toxic metalloid.

Ecuador is a signatory of the Stockholm Convention on chemical substances and hazardous waste and is responsible for complying with the guidelines for the environmentally adequate disposal of Polychlorinated Biphenyls (PCBs) in the country until 2025. The global management of PCBs begins with the sampling of transformers, analysis of dielectric oil, characterization and final disposal of transformers, oil and PCB material belonging to the electricity sector and private owners. The information on the characterization of PCBs is recorded and stored in a computer system called the National PCB Inventory and Monitoring System (SNIS-PCB), in which, the information of 216,632 transformers must be recorded for the present investigation. In the past 2018, the system registered 90,346 transformers, equivalent to 40% of the inventory, 3,494 of them were contaminated and are owned by electricity companies, and it was estimated that there are 1,063 contaminated transformers from private owners. The objective of the research is to analyze the economic and technical feasibility of the technologies available and allowed in the national regulations for the final disposal of these hazardous wastes. According to the technical characteristics of the technologies, logistical limitations and quantity of PCBs in the country, it has been determined that Dichlorination is a technological option that can be used for the treatment of PCBs, also offering the opportunity of decontamination, reuse of the material, and it is friendly with the environment.

Some areas of tropical soils where cocoa grows contain high cadmium (Cd) concentrations. The cocoa plant's need for nutrition causes the reticular system to uptake the toxic metal, translocate it, and accumulate it in roots, stems, and other edible parts such as cocoa beans and shells, threatening the health of cocoa consumers. To cope with this difficulty, different treatments have been applied to cadmium-contaminated soils, but they showed limited success. In this study, we prepared multicomponent nanoparticles (MCNPs) to treat cocoa soils in fixed-bed columns and field tests. Also, MCNPs were mixed with two varieties of cocoa beans, CNN51 and Fino de Aromain, during the fermentation, aiming to capture the cadmium. Our field investigations began by collecting soil samples from three Ecuadorian cocoa-producing farms to determine their physicochemical properties, cadmium, and iron contents. A few weeks later, a home-built prototype was installed in a cocoa plantation to fabricate the nanomaterials using commercial-grade chemicals and rainwater. Scanning Electron Microscope (SEM) images showed MCNPs with an average size of 65.21 nm and the formation of chain-like aggregates. In contrast, MCNPs size was 76.6 nm, measured with Dispersed Light Scattering (DLS). The chemical composition of MCNPs was 90.7 % Fe0 and 1.81 % sulfur (S), analyzed by energy dispersal X-ray (EDX) and confirmed by X-ray diffraction (XRD) spectrometer measurements. Regarding the treatments, for the fixed-bed column tests, 0.28–1.08 L/kg was dosed into the soil, while for field treatments, 250, 500, and 835 mL/min MCNPs were injected in soil areas of 5 m² surrounding each cocoa tree (0.5–4.5 mg MCNPs/kg soil) at depths between 0 and 5 cm. Test results revealed that the procedure applied in the field did not reproduce the metal's immobilization (∼22 %) as in the fixed-bed columns (∼80 %). Moreover, cadmium removal was ∼20 % and ∼75 % after treating CCN51 and Fino de Aroma cocoa beans with 0.112 kg MCNPs/kg in the fermentation on-site and 0.034 kg MCNPs/kg in the laboratory. In this study, the size and chain-like aggregates of MCNPs notably influenced the field treatments as they precluded the filtration of MCNPs downwards. However, immobilizing cadmium could be more effective in soils with higher concentrations of the metal and multicomponent nanoparticles of smaller size, expanding our research scope and offering a practical solution to pollution issues in cocoa-growing regions.

Mining activities generate a large amount of solid waste and acid drains that contain heavy metals in high concentrations. In wastewater of gold mines from Southern Ecuador (Portovelo), arsenic concentrations between 4.8 and 27.5 μg/L have been detected. In this context, the objective of this study is to prepare a technosol, which was used in the capture of arsenic dissolved in the acid drains. Technosol was elaborated using a clay-silty soil (iron-rich soil), collected in the mining area, and iron nanoparticles synthetized with the extract of orange peel. The technosol was experimentally characterized using adsorption isotherms and uptake kinetics. Besides, a mathematical model was developed using Vensim® to scale the process and predict the dynamic behavior of the adsorbent. Results indicate that adsorption behavior of technosol can be fitted to Langmuir isotherms (R² > 0.9), with 95% of adsorption of As from an input of 4.5 mg/L. The model will be useful to predict the time needed to remedy contaminated water and the duration of the adsorbent (until its saturation).