Increasing arsenic sorption on red mud by phosphogypsum addition

Enhanced attenuation of arsenic by Quaternary agricultural soils of Eastern Punjab, India upon anionic clays and gypsum amendment

Agricultural soil of the Sutlej River basin was evaluated for its natural attenuation efficacy for arsenic (As) under the field variables of pH, competitive anions, contact time and varied As contents. The role of layered double hydroxides (HTLDH) and gypsum on uptake efficiency and long-term stability of entrapped As demonstrates rapid As uptake by both geosorbents without mineral structure altering. Arsenic retention by gypsum is poorer than that by HTLDH and greater uptake (∼100% within 2 h) was achieved in the co-precipitation process than adsorption on HTLDH. Freundlich isotherm and pseudo-second-order kinetic model fits of the data demonstrate the multilayer rate-limiting sorption process. NO3- and PO43- hardly affected As retention capacity of HTLDH and gypsum with greater retention at pH 6 and high sorbate concentrations. Studied soil shows a strong potential for As (0.68 g kg-1) which enhanced upon adding HTLDH, while gypsum lowered As retention efficiency of soil except at pH 6.0. Gypsum exhibited relatively greater desorption than HTLDH where almost no As was desorbed in the latter case within seven days of exposure, but ∼30% sorbed As gets desorbed from gypsum which was further enhanced by NO3-+PO43- and soil mixing. Identical behaviour was observed from the soil and HTLDH/gypsum mixture at variable ratios as well. This study shows that MgFe-based HTLDH can efficiently retard arsenic mobilization from the soil with competitive anions and wide pH ultimately limiting As bioavailability in the environment and can be successfully used as a potential scavenger for As remediation purposes.

Exploring the potential reuse of phosphogypsum: A waste or a resource?

Phosphogypsum (PG), the main industrial by-product of phosphate fertilizer industry, primarily consists of calcium sulfate dihydrate. However, it contains various impurities with variable quantities depending on the origin of the phosphate rock. These impurities can restrict the reuse of phosphogypsum as a secondary primary resource. Consequently, large quantities of produced PG are stored in surface stockpiles that occupy extensive land areas and may pose a significant risk of ecological contamination to the surroundings. Researchers have shown growing interest in addressing the worldwide accumulation of this waste material. To gain a comprehensive understanding of the environmental impact of phosphogypsum, it is crucial to explore its properties (e.g., chemistry, mineralogy, radioactivity), and how it interacts with the surrounding environment, enabling well-informed decisions decision regarding its management and its valorization. In this review, we will i) explore the chemical, radiological and mineralogical characteristics of PG; ii) discuss the environmental concerns related to land discharge and sea disposal; and iii) examine the latest advancements in various valorization techniques developed including agriculture, REE extraction, environmental application, chemical and thermal transformation, and also construction sector. Outlining their limitations and challenges restrict in the global variability of phosphogypsum (PG), technical and economic limitations, and the potential for secondary pollution in select valorization approaches. This requires a thorough assessment and comparison with conventional disposal alternatives.

Soil amendments affect the potential of Gomphrena claussenii for phytoremediation of a Zn- and Cd-contaminated soil

This study assessed the impact of inorganic and organic amendments upon zinc (Zn) and cadmium (Cd) availabilities in leachates collected from a Cd- and Zn-contaminated soil, while also evaluating the beneficial use of the tested amendments for decreasing metal availability, hence improving the phytoremediation potential of Gomphrena claussenii Moq. Plants were grown for 60 days in a Zn-smelting-affected soil containing 45,000 and 621 mg kg^-1 of Zn and Cd, respectively (pseudo-total concentrations), after application of the following amendments: limestone, calcium silicate, sewage sludge, triple superphosphate, and red mud. Zinc and Cd availabilities in the soil decreased following the addition of limestone, calcium silicate, and red mud. These amendments were effective in reducing metal mobility and availability, positively affecting plant growth. Plants grown in the soil amended with limestone and calcium silicate accumulated Zn mainly in the roots, while Cd was translocated to plant shoots, with smaller amounts being detected in the roots. Reductions of Zn and Cd concentrations in the leachate were found by adding red mud, with this decrease for Zn being less pronounced compared to what was verified after the application of limestone and calcium silicate. Moreover, the use of red mud resulted in a higher Zn:Cd ratio in the leachate, which favored a greater absorption and transport of Zn from root to shoot. In conclusion, the tested soil amendments reduced the availability of excessive concentrations of Cd and Zn in naturally contaminated soil, which resulted in improved growth and survival of Zn- and Cd-tolerant G. claussenii plants, with the application of limestone, calcium silicate, and red mud - i.e., alkaline amendments - standing out as the best combinations with G. Claussenii when designing a strategy to achieve optimal phytoremediation.

Fast and effective arsenic removal from aqueous solutions by a novel low-cost eggshell byproduct

Developing alternative green solutions for local and correct recycling of eggshells waste (ES) are needed by the egg-processing industries. In this study, we proposed transforming ES into a novel low-cost chemical compound named hydroxyl-eggshell (ES-OH) and investigated its capacity for arsenic (As) removal from aqueous solutions. Laboratory experiments were conducted to investigate the effects of ES-OH doses, pH, kinetics, and isotherms on As removal efficiency. The kinetics study showed that ES-OH removed nearly all As from solution in less than 15 min. The pseudo-second-order model described the process, and the maximum As removal capacity predicted by the Langmuir isotherm model was 529 mg g^-1. Using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray detector (SEM-EDS), and X-ray diffraction (XRD), we found that the As removal mechanism by ES-OH was due to vladimirite precipitation, followed by weak electrostatic interactions between the precipitate and arsenate ions. Finally, after an economic analysis, we conclude that besides being a novel and economical income source, egg-producing companies might implement the ES-OH production process as a local environmentally-friendly way of recycling eggshells and reducing water As contamination.

A two-step approach for arsenic removal by exploiting an autochthonous Delftia sp. BAs29 and neutralized red mud

Groundwater arsenic contamination represents a global threat to human health. Among the proposed bioremediation applications, microbial transformation of arsenite (As (III)) seems to be the most favorable approach as it can be easily coupled with several adsorption techniques, without producing lethal by-products or demanding chemical addition. This study highlights the potential contribution of a highly efficient As (III) transforming bacteria Delftia sp. BAs29 followed by the adsorption of transformed arsenate (As (V)) using neutralized red mud under suitable treatment conditions. Diverse experimental conditions elucidated (inflow As (III) concentrations, flow rate) the rate and oxidation efficiency to mediate the process. Red mud is a waste by-product from the Bayer's process of the alumina industry, which when neutralized aids the removal of As (V). The neutralized red mud was characterized using X-ray diffraction (XRD) microanalysis, Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy (FTIR). Arsenate adsorption using neutralized red mud was also studied as a function of pH and time, adsorbent dosage, and initial As (V) concentration. The adsorption process was significantly affected by the solution pH, which on decreasing gradually increased the adsorption efficiency. The maximum monolayer capacity for adsorption of 274.1 mg/g As (V) was found at optimum conditions of pH 4.0 and a contact time of 30 min at a temperature of 30 °C, respectively. Furthermore, this process significantly contributed in fabricating a two-step bio-filter column for the removal of total arsenic from groundwater. Graphical abstract.

Arsenic removal in aqueous solutions using FeS2

This study tested the technical feasibility of pyrite and/or persulfate oxidation system for arsenic (As) removal from aqueous solutions. The effects of persulfate on As removal by the pyrite in the integrated treatment were also investigated. Prior to the persulfate addition into the reaction system, the physico-chemical interactions between As and the pyrite alone in aqueous solutions were explored in batch studies. The adsorption mechanisms of As by the adsorbent were also presented. At the same As concentration of 5 mg/L, it was found that As(III) attained a longer equilibrium time (8 h) than As(V) (2 h), while the pyrite worked effectively at pH ranging from 6 to 11. At optimum conditions (0.25 g/L of pyrite, pH 8.0 and 5 mg/L of As(III) concentration), the addition of persulfate (0.5 mM) into the reaction promoted a complete removal of arsenic from the solutions. Consequently, this enabled the treated effluents to meet the arsenic maximum contaminant limit (MCL) of <10 μg/L according to the World Health Organization (WHO)'s requirements. The redox mechanisms, which involved electron transfer from the S₂^2- of the pyrite to Fe³⁺, supply Fe²⁺ for persulfate decomposition, oxidizing As(III) to As(V). The sulfur species played roles in the redox cycle of the Fe³⁺/Fe²⁺ of the pyrite by giving its electrons, while the As(III) oxidation to As(V) was attributed to the pyrite. Overall, this work reveals the applicability of the pyrite as an adsorbent for water treatment and the importance of persulfate addition to promote a complete As removal from aqueous solutions.

Increasing phosphate sorption on barium slag by adding phosphogypsum for non-hazardous treatment

Barium slag (BS) is a waste residue in the barium salt industrial procedure. Due to its high leaching concentration of Ba²⁺, BS is classified as a kind of hazardous waste. Industrial waste phosphogypsum (PG) is effective to immobilize barium ion in BS owing to the slightly soluble sulfate included. In this study, two different proportions of PG were selected for mixing with BS to solidify soluble barium ion. The non-hazardous BS samples treated with the proportions of PG (BS-PG1, BS-PG3) were then functionally used for phosphate removal in solution. Batch experiments for removal of phosphate were performed to evaluate the adsorption efficiency of BS-PG1 and BS-PG3. The effect of various factors such as contact time, initial pH, and reaction temperature on sorption performance was investigated. BS-PG1 and BS-PG3 reached adsorption equilibrium in approximately 3h at the initial concentration of 15 mg/L, and BS-PG1 exhibited adsorption capacity of 12.47 mg P/g, higher than that of BS (11.49 mg P/g) under the condition of solid:liquid, 1g:1L, 25 °C, natural pH. The results show that the adsorption processes of phosphates ions onto both BS-PG1 and BS-PG3 fitted well with the pseudo-second-order kinetic model. The Langmuir isothermal model was considered as the appropriate equation for experimental data, showing a maximum adsorption capacity for phosphate up to 13.67 mg P/g and 11.59 mg P/g for BS-PG1 and BS-PG3. In comparison with other adsorbents, BS-PG1 and BS-PG3 could be considered as efficient materials for the removal of phosphate.

Emerging technologies for arsenic removal from drinking water in rural and peri-urban areas: Methods, experience from, and options for Latin America

Providing drinking water with safe arsenic levels in Latin American (LA) countries (a total of 22 countries) is a major current challenge. Arsenic's presence in water has been neglected for many decades since it was first reported ~100 years ago in Argentina. The major arsenic source in this region is geogenic. So far, arsenic has been reported in 15 LA countries. Arsenic concentrations in drinking water have been reported up to >200 fold (2000 μg/L) the WHO limit of 10 μg/L. About 14 million people in the arsenic affected LA countries depend on contaminated water characterized by >10 μg/L of arsenic. Low-cost, easy to use, efficient, and sustainable solutions are needed to supply arsenic safe water to the rural and peri-urban population in the affected areas. In the present study, >250 research articles published on various emerging technologies used for arsenic remediation in rural and peri-urban areas of LA countries are critically reviewed. Special attention has been given to arsenic adsorption methods. The manuscript focuses on providing insights into low cost emergent adsorbents with an implementation potential in Latin America. Natural, modified and synthetic adsorbents used for arsenic decontamination were reviewed and compared. Advantages and disadvantages of treatment methods are summarized. Adsorbent selection criteria are developed. Recommendations concerning emerging adsorbents for aqueous arsenic removal in LA countries have also been made.

Effects of acid and phosphate on arsenic solidification in a phosphogypsum-based cement backfill process

Phosphogypsum (PG) produced during phosphoric acid production contains significant amounts of arsenic and can potentially cause adverse environmental and health effects. Cement backfill technology is an effective management technique that is used to store PG to prevent such problems. The goal of this paper is to study the influencing factors and mechanism of arsenic stabilization in a PG-based cement backfill process. First, a leaching toxicity test was conducted, which showed that the arsenic concentration in PG batches ranged from 129.1 μg L⁻¹ to 407.1 μg L⁻¹, which were all far above the standard limit (10 μg L⁻¹) set by GB/T 14848-93. In addition, the arsenic content was higher in samples with larger PG particles. Secondly, hydrogen and phosphate ions were added to the backfill to investigate how they influenced arsenic solidification, and the results indicated that phosphate ions, rather than hydrogen ions, delayed the arsenic solidification process. This suggests that controlling the soluble phosphate in PG will help reduce arsenic pollution during backfilling. A toxicity leaching test was carried out after backfill samples were cured for 28 d. All arsenic concentrations were below the standard limit, indicating that the cement backfill technology ensured the long-term solidification and stabilization of arsenic.

Phosphogypsum (PG) produced during phosphoric acid production contains significant amounts of arsenic and can potentially cause adverse environmental and health effects.

A review on the potential uses of red mud as amendment for pollution control in environmental media

Red mud is a solid waste of bauxite processing by Bayer process which involves caustic digestion of Al-containing mineral for alumina production. The global inventory of red mud waste reached an estimated amount of 4 billion tons in 2015, increasing at an approximate rate of 120 million tons per year. Therefore, its management is becoming a global environmental issue for the protection of environment, and the need for awareness in this regard is becoming crucial. Although red mud is not considered as a hazardous material in many countries, its high alkalinity and fine particle size may pose significant environmental threat, and it is found to be an interesting material for environmental remediation purposes due to rich iron content. This paper provides a review of possible remedial applications of red mud in various environmental compartments. Modification of red mud creates novel opportunities for cost-effective and efficient removal of metal ions, inorganic anions, dyes, and phenols from wastewater and acid mine drainage. Re-vegetation of red mud disposal sites, treatment of metal-contaminated acidic soils presents the usefulness of this material but less research has been done so far to investigate its use in the stabilization of polluted sediments. On the other hand, leaching and eco-toxicological tests have also revealed that red mud does not pose high toxicity to the environment making it suitable for the treatment of contaminated media. Nevertheless, neutralization of red mud is recommended for its safe disposal and secure application in any environmental media.

Use of (modified) natural adsorbents for arsenic remediation: A review

Arsenic (As) is a ubiquitous element found in the atmosphere, soils and rocks, natural waters and organisms. It is one of the most toxic elements and has been classified as a human carcinogen (group I). Arsenic contamination in the groundwater has been observed in >70 countries, like Bangladesh, India, West Bengal, Myanmar, Pakistan, Vietnam, Nepal, Cambodia, United States and China. About 200 million people are being exposed to excessive As through consumption of contaminated drinking water. Therefore, developing affordable and efficient techniques to remove As from drinking water is critical to protect human health. The currently available technologies include coagulation-flocculation, adsorption, ion exchange, electrochemical conversion and membrane technologies. However, most of the aforementioned treatment techniques require high initial and maintenance costs, and skilled manpower on top of that. Nowadays, adsorption has been accepted as a suitable removal technology, particularly for developing regions, because of its simple operation, potential for regeneration, and little toxic sludge generation. Processes based on the use of natural, locally available adsorbents are considered to be more accessible for developing countries, have a lower investment cost and a lower environmental impact (CO₂ emission). To increase their performance, these materials may be chemically modified. Hence, this review paper presents progress of adsorption technologies for remediation of As contaminated water using chemically modified natural materials.

Increased As Adsorption on Maghemite-Containing Red Mud Prepared by the Alkali Fusion-Leaching Method

This study investigates the use of red muds as adsorbents for As (V) removal. Red mud is a waste that contains a large amount of iron oxides and hydroxides, which are excellent adsorbents of arsenic, especially those possessing magnetic properties and a large specific surface area. The purpose of the experiments was to study the possibility of obtaining an effective adsorbent by the direct extraction of alumina from bauxite using the caustic alkali fusion method and to compare the arsenic removal effectiveness and other properties of these red muds with industrial samples. Red muds were described using methods such as X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), SEM, vibrating sample magnetometry (VSM), and the Brunauer–Emmett–Teller (BET) method. The main iron-containing phase of the red muds obtained by fusing bauxite with caustic alkali is maghemite, which has a large specific surface area. The specific surface area of the obtained samples varied in the range of 6.1–54.9 m2/g. Arsenic adsorption experiments were carried out using five different types of red muds: industrial Bayer, industrial sintering, and red mud obtained through bauxite alkali fusion at 300, 500, and 700 °C. The red muds obtained by fusing bauxite with caustic alkali at 300 and 500 °C had the highest effectiveness removing arsenic; their As(V) uptake capacity was over 30 mg/g.

Stabilization of Cd-, Pb-, Cu- and Zn-contaminated calcareous agricultural soil using red mud: a field experiment

Red mud (RM) was used to remediate heavy metal-contaminated soils. Experiments with two different dosages of RM added to soils were carried out in this study. It was found that soil pH increased 0.3 and 0.5 unit with the dosage of 3 and 5% (wt%), respectively. At the dosage of 5%, the highest stabilization efficiencies for Cd, Pb, Cu and Zn reached 67.95, 64.21, 43.73 and 63.73%, respectively. The addition of RM obviously transferred Cd from the exchangeable fraction to the residual fraction. Meanwhile, in comparison with the control (no RM added), it reduced 24.38, 49.20, 19.42 and 8.89% of Cd, Pb, Cu and Zn in wheat grains at the RM addition dosage of 5%, respectively. At the same time, the yield of wheat grains increased 17.81 and 24.66% at the RM addition dosage of 3 and 5%, respectively. Finally, the addition of RM did not change the soil bacterial community. These results indicate that RM has a great potential in stabilizing heavy metals in calcareous agricultural soils.

Accelerated crystallization of magnetic 4A-zeolite synthesized from red mud for application in removal of mixed heavy metal ions

To cope with the increasing environmental issues of red mud, an integrated technological route for its comprehensive utilization was developed through the extraction of valuable components and the synthesis of magnetic 4A-zeolite. To accelerate the crystallization process of the synthesized 4A-zeolite, sodium chloride (NaCl) was innovatively employed under hydrothermal treatment. The effects of various parameters, including mass ratio of red mud/NaOH, alkali fusion temperature, alkali fusion time and molar ratio of NaCl/Al₂O₃, were systematically investigated. The results showed that approximately 81.0% Al, 76.1% Si and 95.8% Fe were utilized from red mud using alkali fusion and acid leaching methods. The optimal conditions of the alkali fusion process were determined as: mass ratio of red mud/NaOH = 1/2, alkali fusion temperature of 800 °C, and time of 90 min. Furthermore, when the molar ratio of NaCl/Al₂O₃ was kept at 1.5, the crystallization time reduced from 240 min to 150 min, and particle size distributions narrowed from 20-100 μm to 1-10 μm. The practical applications in removal of mixed heavy metal ions (Zn²⁺, Cu²⁺, Cd²⁺, Ni²⁺, and Pb²⁺) from wastewater indicated that the as-synthesized magnetic 4A-zeolite is a promising candidate for heavy metals adsorption.

Reduced arsenic availability and plant uptake and improved soil microbial diversity through combined addition of ferrihydrite and Trichoderma asperellum SM-12F1

Arsenic (As) accumulation in agricultural soils is prone to crop uptake, posing risk to human health. Passivation shows potential to inactivate soil labile As and lower crop As uptake but often contributes little to improving the microbiota in As-contaminated soils. Here, the combined addition of ferrihydrite and Trichoderma asperellum SM-12F1 as a potential future application for remediation of As-contaminated soil was studied via pot experiments. The results indicated that, compared with the control treatment, the combined addition of ferrihydrite and T. asperellum SM-12F1 significantly increased water spinach shoot and root biomass by 134 and 138%, respectively, and lowered As content in shoot and root by 37 and 34%, respectively. Soil available As decreased by 40% after the combined addition. The variances in soil pH and As fractionation and speciation were responsible for the changes in soil As availability. Importantly, the combined addition greatly increased the total phospholipid fatty acids (PLFAs) and gram-positive (G+), gram-negative (G-), actinobacterial, bacterial, fungal PLFAs by 114, 68, 276, 292, 133, and 626%, respectively, compared with the control treatment. Correspondingly, the soil enzyme activities closely associated with carbon, nitrogen, and phosphorus mineralization and antioxidant activity were improved. The combination of ferrihydrite and T. asperellum SM-12F1 in soils did not reduce their independent effects.

Utilization of sludge based adsorbents for the removal of various pollutants: A review

Sludge based adsorbents are widely used for the removal of various pollutants from water and wastewater systems and the available data is much diversified. The purpose of this review is to organize and critically review the scattered available information on the potential of use of sludge based adsorbents for the removal of various pollutants. It was observed that performance of the sludge based adsorbents varies depending on the type of pollutants, type of precursor sludge, carbonization time-temperature profile and the type of activation conditions used. The variation in pyrolysis and activation conditions found to directly affect the adsorbent properties, adsorption capacity and the mechanism of pollutant removal by sludge based adsorbents. The interaction mechanisms of pollutants with adsorbent surface found to have a detrimental effect on desorption and regeneration of the adsorbents and its recycling potential. Therefore, desorption and regeneration technique used for recycle of the adsorbents is also discussed in detail. Moreover, life cycle and cost analysis of sludge based adsorbents is assessed to ensure the cost effectiveness of their application in water treatment operations.

Beneficial use of industrial by-products for phytoremediation of an arsenic-rich soil from a gold mining area

This study investigated two industrial by-products - red mud (RM) and its mixture with phosphogypsum (RMG), as amendments in an As((5+))-contaminated soil from a gold mining area in Brazil in order to grow three plant species: Brachiaria decumbens, Crotalaria spectabilis, and Stylosanthes cv. Campo Grande. These amendments were applied to reach a soil pH of 6.0. Using RM and RMG increased shoot dry matter (SDM) and root dry matter (RDM) of most plants, with RMG being more effective. Adding RMG increased the SDM of Brachiaria and Crotalaria by 18 and 25% and the RDM by 25 and 12%, respectively. Stylosanthes was sensitive to As toxicity and grew poorly in all treatments. Arsenic concentration in shoots of Brachiaria and Crotalaria decreased by 26% with the use of RMG while As in roots reduced by 11 and 30%, respectively. Also, the activities of the plant oxidative stress enzymes varied following treatments with the by-products. The plants grew in the As-contaminated soil from the gold mining area. Thus, they might be employed for phytoremediation purposes, especially with the use of RMG due to its potential advantage in terms of nutrient supply (Ca(2+) and SO4(2-) from phosphogypsum).

Iron and aluminium oxides containing industrial wastes as adsorbents of heavy metals: Application possibilities and limitations

Industrial wastes with a high iron or aluminium oxide content are produced in huge quantities as by-products of water treatment (water treatment residuals), bauxite processing (red mud) and hard and brown coal burning in power plants (fly ash). Although they vary in their composition, the wastes have one thing in common--a high content of amorphous iron and/or aluminium oxides with a large specific surface area, whereby this group of wastes shows very good adsorbability towards heavy metals, arsenates, selenates, etc. But their physical form makes their utilisation quite difficult, since it is not easy to separate the spent sorbent from the solution and high bed hydraulic resistances occur in dynamic regime processes. Nevertheless, because of the potential benefits of utilising the wastes in industrial effluent treatment, this issue attracts much attention today. This study describes in detail the waste generation processes, the chemical structure of the wastes, their physicochemical properties, and the mechanisms of fixing heavy metals and semimetals on the surface of iron and aluminium oxides. Typical compositions of wastes generated in selected industrial plants are given. A detailed survey of the literature on the adsorption applications of the wastes, including methods of their thermal and chemical activation, as well as regeneration of the spent sorbents, is presented. The existing and potential ways of modifying the physical form of the discussed group of wastes, making it possible to overcome the basic limitation on their practical use, are discussed.

Chemical stabilization of metals in mine wastes by transformed red mud and other iron compounds: laboratory tests

A series of static and kinetic laboratory-scale tests were designed in order to evaluate the efficacy of transformed red mud (TRM) from bauxite refining residues, commercial zero-valent iron, and synthetic iron (III) hydroxides as sorbents/reagents to minimize the generation of acid drainage and the release of toxic elements from multi-contaminant-laden mine wastes. In particular, in some column experiments the percolation of meteoric water through a waste pile, alternated with periods of dryness, was simulated. Wastes were placed in columns together with sorbents/reagents in three different set-ups: as blended amendment (mixing method), as a bed at the bottom of the column (filtration method), or as a combination of the two previous methods. The filtration methods, which simulate the creation of a permeable reactive barrier downstream of a waste pile, are the most effective, while the use of sorbents/reagents as amendments leads to unsatisfactory results, because of the selective removal of only some contaminants. The efficacy of the filtration method is not significantly affected by the periods of dryness, except for a temporary rise of metal contents in the leachates due to dissolution of soluble salts formed upon evaporation in the dry periods. These results offer original information on advantages/limits in the use of TRM for the treatment of multi-contaminant-laden mine wastes, and represent the starting point for experimentation at larger scale.