Sulfidic Waste Research Articles

Sulfide Removal by Catalitic Oxidation From Rayon Waste

Catalytic oxidation of spent sulfidic caustic consist of SH- ion or NaHS compound by H 2 O2 in neutral or acidic solution to elemental sulphur may provide a convenient and economical method for the control of sulphide wastes and their associated odors at pulp, paper and textile industry. Oxidation of sulfide in rayon waste by hydrogen peroxide was investigated in the presence of ferric sulfate catalyst. Kinetic equations and activation energies of H 2 O2 and SH- ion to total sulphur and sulphate in rayon waste for catalytic oxidation reaction were calculated based on the experimental results. For the removal of sulfide from sulfide solution the most common process involves its catalytic oxidation to a more benign form sulfate. The rate of sulfidic catalytic oxidation was found higher at lower initial sulphide concentration and the rate of sulphide catalytic oxidation was found directly proportional to loading and hydrogen peroxide addition. Optimum total sulphide concentration was achieved when sulphide solutions in the presence of H 2 O 2 in the ratios SH-/H 2 O 2 1:4.2. The potential user of H 2 O 2 determine the optimal conditions for control of odor, corrosion and waste treatment cost due to sulfide consisting of sulphur ion, sulphate ion, etc. The catalytic oxidation of sulphides into sulphates by H 2 O 2 may be applied directly to aqueous wastes containing these odorants

Weathering of stannite–kësterite [Cu2(Fe,Zn)SnS4] and the environmental mobility of the released elements

Abstract. The sulfidic waste dumps of the historical mining sites Giftkies and Kaňk (Czech Republic) have been exposed to a temperate climate over decades. This exposure generated low-pH conditions caused by metal sulfide decomposition. Tin sulfides of the stannite–kësterite series [Cu2(Fe,Zn)SnS4] are common Sn minerals in the ores at the investigated sites. They decompose under acidic and oxidizing conditions and form in situ secondary precipitates. Compositional analyses of primary and secondary minerals were collected by electron microprobe to track the environmental mobility of the released elements during weathering. Transmission electron microscopy revealed a diffusion-driven alteration of stannite to Sn-rich chalcopyrite and the precipitation of native copper and silver from stannite. In assemblages containing arsenopyrite, an in situ and amorphous Sn–Fe–As (SFA)-rich phase precipitated close to the Sn sulfide. The SFA precipitate contains very little sulfur, which was probably released to the aqueous phase as oxidized species, whereas small amounts of Cu and Zn were captured by the SFA. This precipitate is metastable and acts as a temporaneous sink for mobile elements (Cu, Zn) and elements derived from acid-soluble silicates and phosphates (Ca, Si, Al, and P). With advanced weathering, complex redox reactions result in the precipitation of magnetite as an oxidation product of the sulfidic material under oxidative conditions. The stable minerals goethite and cassiterite mark the end of the weathering sequence and crystallized from the amorphous SFA precipitate.

Heavy metal release and acid generation during the oxidation of sulfide waste rock induced by ferric iron

As aby-product of waste rock from sulfide ore, Fe3+ is one of the important factors that promote acid production and heavy metals release from waste rock pile fields. In this paper, the dynamic leaching tests were conducted to investigate the behavior of acid generation and heavy metal release from the sulfide waste rock of Dexing copper mine under different Fe3+ concentrations. The Sulphur content in the waste rock samples was 3.56 % and the net acid production potential (NAPP) reached 47.95 kg·t−1 H2SO4. Under the oxidation of 600 mg·L-1 Fe3+, the pH value of the leaching system decreased to 5.53, which is 1.85 units lower than that of the control check group (CK). However, the quantity of SO42- in the leachate was reduced by 41.81 % compared to the CK group, as the jarosite precipitation was more likely to form under high Fe3+ conditions. The oxidation of Fe3+ effectively accelerated the release of heavy metals from the waste rock. In addition, the heavy metals release quantity gradually increased with the increase of the Fe3+ concentration, with the maximum release quantities of Cu, Pb, Zn, and As of 569.69, 333.75, 222.69, and 31.11 μg·kg−1, respectively, which increased by 27.66 %-129.60 % compared to the CK group. The release of SO42-, Cu, Pb, and Zn was controlled by the combined internal diffusion and the chemical reaction, while the release of As was best fitted to the interfacial chemical reaction-controlled model. The SEM analysis showed that the waste rock near the top of the column was strongly corroded, resulting in the increase of the specific surface area of the waste stone by 24.48 %. The re-precipitation reaction of heavy metals mainly occurred near the bottom of the leaching column. Leaching under Fe3+ oxidation caused a decrease in the proportion of residual heavy metals in the waste rock, which will lead to the easier release of heavy metals.

The behavior of heavy metal release from sulfide waste rock under microbial action and different environmental factors.

The dissolution of heavy metals from the waste rock is controlled by many factors. Herein, we investigated the release behavior of iron (Fe), chromium (Cr), copper (Cu), and zinc (Zn) from sulfide waste rock under the actions of microorganisms and different environmental factors (solution pH value, particle size of waste rock, temperature, Fe3+ concentration). The release quantity of heavy metals was negatively correlated with pH and particle size and positively correlated with ambient temperature and Fe3+ concentration. Under the experimental conditions of pH value of 3.0, temperature of 35°C, and waste stone particle size of less than 0.075 mm,, the release quantity of Fe, Cr, Cu, and Zn reached 3680, 18.32, 132.20, 26.60 mg·kg-1 after 20 days of leaching, respectively. Rising the temperature to 45 °C, Fe, Cr, Cu, and Zn release quantities increased to 89.30, 5.81, 105.08, and 28.00 mg·kg-1. Six hundred milligrams per liter Fe3+ increased the release of heavy metals considerably (2.63-65.48 folds). The presence of microorganisms can significantly facilitate the release of heavy metals. Compared to the control group, the release quantities of Fe, Cr, Cu, and Zn increased 4.29, 3.17, 1.54, and 2.39 times, respectively. In addition, the waste rock under microbial action was more seriously corroded than that under chemical factors. The release behavior of these four heavy metals was consistent with the interfacial chemical reaction control model, indicating that the reactions mainly occurred on the surface of the waste rock. This study provides an essential reference for the study of heavy metal leaching behavior.

Soil Acidification, Mineral Neoformation and Heavy Metal Contamination Driven by Weathering of Sulphide Wastes in a Ramsar Wetland

Past waste disposal practices have left large volumes of sulphidic material stockpiled in a Ramsar wetland site on the Atlantic coast of southwestern Spain, leading to severe land degradation. With the aim of addressing this legacy issue, soil core samples were collected along two transects extending from the abandoned stockpiles to the adjacent marshland and subjected to XRD, SEM-EDS, ICP-OES and ICP-MS analyses. Sulphide oxidation has been shown to be a major driver of acid generation and metal leaching into the environment. The marsh soil receiving acid discharges from the sulphide wastes contains elevated levels (in mg kg−1) of Pb (up to 9838), As (up to 1538), Zn (up to 1486), Cu (up to 705), Sb (up to 225) and Tl (up to 13), which are retained both in relatively insoluble secondary minerals (mainly metal sulphates and oxides) and in easily soluble hydrated salts that serve as a transitory pool of acidity and available metals. By using a number of enrichment calculation methods that relate the metal concentrations in soil and their baseline concentrations and regulatory thresholds, there is enough evidence to conclude that these pollutants may pose an unacceptable risk to human and ecological receptors.

Potential of Mechanochemically Activated Sulfidic Mining Waste Rock for Alkali Activation

Sulfidic mining waste rock is a side stream from the mining industry with a potential environmental burden. Alkali activation is a promising method for transforming mining waste into construction materials. However, the low reactivity of minerals can be a sizeable challenge in alkali activation. In the present study, the reactivity of waste rock was enhanced by mechanochemical treatment with a LiCl-containing grinding aid. X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform (DRIFT) analysis were utilized to display the structural alteration of individual minerals. A schematic implication of the grinding mechanism of mica was provided according to the results of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The alkaline solubility displayed the enhanced chemical reactivity of the waste rock, in which Si and Al solubility increased by roughly 10 times and 40 times, respectively. The amorphization of aluminosilicate is achieved through chemical assisted mechanochemical activation. Sulfidic waste rock, as the sole precursor in alkali activation, achieved a 28-day compressive strength exceeding 10 MPa under ambient curing conditions. The simulation of the upscaled grinding process was conducted via the HSC Chemistry® software with a life-cycle assessment. The results showed that mining waste rock can be a promising candidate for geopolymer production with a lower carbon footprint, compared to traditional Portland cement.Graphical

Application of Silicate-Based Coating on Pyrite and Arsenopyrite to Inhibit Acid Mine Drainage.

The prevention of acid generation from sulfidic mine wastes is a problem that challenges the global scientific community for decades. A promising strategy is related to the formation of coating layer around sulfides for inhibiting surface oxidation. In the current research, the conditions favoring the formation of an efficient silicate-based coating around pyrite and arsenopyrite were studied, using batch tests. The coating solutions contained silicate-oxyanions, an oxidant (H2O2) and buffered at pH 6. The effect of Si concentration (0.1-50mM), liquid/solid ratio (5-100mL/g) and contact time (up to 24h) was investigated. Pyrite tailings treated with a solution of 1mM Si/0.1M H2O2 at L/S:100mL/g for 24h resulted in the optimum formation of a coating, which reduced the amount of SO4-2-released by 72%, compared to the sample treated in the absence of Si. However, silicate treatment had a negative effect on arsenopyrite tailings inducing As mobilization.

A new recycling strategy for preparing flame retardants from polyphenylene sulfide waste textiles

In this paper, the waste polyphenylene sulfide (PPS) filter bag was converted to waste PPS powder through thermal aging, ball milling and screening, and firstly used as flame retardant to improve the flame retardance of epoxy resin (EP). TG results presented that, it started to decompose at 510.6 °C with 62.08% of residue mass at 800 °C, which showed good charring ability. The UL-94 and cone calorimeter tests showed that waste PPS not only improved the flame retardance of EP but also largely decreased heat and smoke/toxic gases release. Adding 15 wt% waste PPS made EP composites acquire a UL-94 V-1 rating and resulted in a 42.24% reduction in the peak of heat release rate (PHRR). What’ more, the peak of smoke production rate (PSPR) and peak of CO production (PCOP) declined by 27.27% and 45.16%. The morphology of char residue was also observed by scanning electron microscope (SEM), and it was concluded that, introduction of waste PPS indeed improved the compact of char layer, which was be responsible for enhancement in flame retardance. This work provided a new way and theoretical basis for realizing high value recycling of PPS solid waste.

Oxidative Dissolution of Sulfide Minerals in Single and Mixed Sulfide Systems under Simulated Acid and Metalliferous Drainage Conditions.

Chalcopyrite, galena, and sphalerite commonly coexist with pyrite in sulfidic waste rocks. The aim of this work was to investigate their impact, potentially by galvanic interaction, on pyrite oxidation and acid generation rates under simulated acid and metalliferous drainage conditions. Kinetic leach column experiments using single-minerals and pyrite with one or two of the other sulfide minerals were carried out at realistic sulfide contents (total sulfide <5.2 wt % for mixed sulfide experiments), mimicking sulfidic waste rock conditions. Chalcopyrite was found to be most effective in limiting pyrite oxidation and acid generation with 77-95% reduction in pyrite oxidation over 72 weeks, delaying decrease in leachate pH. Sphalerite had the least impact with reduction of pyrite dissolution by 26% over 72 weeks, likely because of the large band gap and poor conductivity of sphalerite. Galena had a smaller impact than chalcopyrite on pyrite oxidation, despite their similar band gaps, possibly because of the greater extent of oxidation and the significantly reduced surface areas of galena (area reductions of >47% for galena vs <1.5% for chalcopyrite) over 72 weeks. The results are directly relevant to mine waste storage and confirm that the galvanic interaction plays a role in controlling acid generation in multisulfide waste even at low sulfide contents (several wt %) with small probabilities (≤0.23%) of direct contact between sulfide minerals in mixed sulfide experiments.

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Heavy metal enrichment and potential ecological risks from different solid mine wastes at a mine site in Ghana

Solid mine wastes characterization is important for understanding their chemical composition, as well as potential ecological and health risks, although limited empirical data exist on this, particularly in developing countries. In this field study, quantitative contamination indices like geoaccumulation index, enrichment factor, contamination factor, Hazard quotient and ecological risk were used to characterize and compare solid mine wastes from three different sites (i.e., sulphide waste dump, oxide waste dump and mine tailings) and soil from a farmland (reference site). Fifteen plots (each measuring 20 m × 100 m) were randomly demarcated on each of the study sites. A composite sample was obtained from each plot and analyzed for heavy metals (Fe, Cu, Cd, As, Pb), following which the various contamination parameters were determined. Results showed high enrichment of the solid mine wastes with the studied heavy metals compared to the local background values, with non-essential metals (As, Cd, Pb) displaying higher accumulation potential than the essential metals (Fe, Cu). The heavy metal enrichment of the three waste types were high enough to exert significant health risks (HQ>1) and ecological risk (IER>600) compared to the reference site (HQ<1, IER<150). However, the magnitude of the health and ecological effects varied with waste type in the order: oxides<sulphides<tailings. These results highlight the need for proper solid mine wastes characterization to drive management decisions aimed at reducing heavy metal contamination of surrounding soils and the associated potential environmental and human health risks.

Pit Lake and Drinking Water Intake: Example of Coexistence (Middle Urals, Russia)

The dewatering system of the Lipovsky nickel mining pit (Middle Urals, Russia) has performed a dual role. From 1961 to 1991, while nickel was being mined there, it protected the pit from flooding with groundwater; since 1989, it has been the principal source of drinking water for the town of Rezh (≈ 50,000 residents). After mining ceased, water withdrawal from the drainage wells decreased 2.5 times (to 100 L/s), resulting in a 120 m deep pit lake. A mass balance analysis has shown that water from the pit lake has become the leading source of water intake. However, the concentrations of the water’s basic constituents at the eastern edge of the pit are several times higher than at the western edge. The reason for the significant increase in the water withdrawn by the wells of the western intake is the fact, that during the working of the main ore body, the eastern part of the pit was filled with overburden rock and substandard ore with dispersed sulfide mineralization. Flooding of the pit created a single aquifer between the pit lake and the eastern water intake facility, including an artificial aquifer within the refilled part of the pit. The rise of the groundwater level in the artificial aquifer to an elevation above 150 m (after 1994) led to active chemical weathering of sulfide-containing minerals and dissolution of secondary sulfates, which accounts for the increasing levels of constituents in the eastern part of the pit. The artificial aquifer has become a generator of salts. The dumping of sulfidic wastes and subsequent recovery of the water table have led to the release of sulfate, calcium, and metals into the local groundwater. To prevent the formation of an artificial aquifer, it is necessary to either completely remediate the unflooded portion using non-acid generating material or completely inundate the pit. Partial remediation would be the worst scenario as it could destabilize the hydrogeochemical processes and render long-term coexistence of the drinking water intake and the flooded pit problematic.

Kinetic Testing for Oxidation Acceleration and Passivation of Sulfides in Waste Rock Piles to Reduce Contaminated Neutral Drainage Generation Potential

Contaminated neutral drainage (CND), generated when metals are leached and enough neutralizing minerals are present to keep a near-neutral pH, is a growing environmental concern related to mine waste management. There is a need to find ways to reduce CND generation from mine waste to avoid perpetual effluent treatment. Nickel concentrations at the Lac Tio mine effluent have been sporadically higher than provincial environmental standards. In this project, three different treatment solutions were applied to Lac Tio mine waste rock samples in 70 kg waste rock columns in an attempt to reduce nickel CND generation potential by forcing sulfide oxidation and/or passivation. Following the applications, kinetic tests were used to determine any reduction in sulfide oxidation and nickel leaching. Hydrogen peroxide and sodium silicate were the main products tested, alone and in combination with a sodium bicarbonate buffer. Buffered hydrogen peroxide showed the best potential to reduce CND generation, with nickel release reduced from 1.4 × 10–3 mg/kg/day (untreated) to 4.0 × 10–5 mg/kg/day (treated) and near-neutral pH values. This passivation treatment also reduced the sulfur release rate by more than 50%. Optical and scanning electron microscopy observations supported the laboratory results. To conclude, this research project proposes a new way to reduce the CND generation potential of low sulfide waste rock.

Competitive Growth of Sulfate-Reducing Bacteria with Bioleaching Acidophiles for Bioremediation of Heap Bioleaching Residue.

sMining waste rocks containing sulfide minerals naturally provide the habitat for iron- and sulfur-oxidizing microbes, and they accelerate the generation of acid mine drainage (AMD) by promoting the oxidation of sulfide minerals. Sulfate-reducing bacteria (SRB) are sometimes employed to treat the AMD solution by microbial-induced metal sulfide precipitation. It was attempted for the first time to grow SRB directly in the pyritic heap bioleaching residue to compete with the local iron- and sulfur-oxidizing microbes. The acidic SRB and iron-reducing microbes were cultured at pH 2.0 and 3.0. After it was applied to the acidic heap bioleaching residue, it showed that the elevated pH and the organic matter was important for them to compete with the local bioleaching acidophiles. The incubation with the addition of organic matter promoted the growth of SRB and iron-reducing microbes to inhibit the iron- and sulfur-oxidizing microbes, especially organic matter together with some lime. Under the growth of the SRB and iron-reducing microbes, pH increased from acidic to nearly neutral, the Eh also decreased, and the metal, precipitated together with the microbial-generated sulfide, resulted in very low Cu in the residue pore solution. These results prove the inhibition of acid mine drainage directly in situ of the pyritic waste rocks by the promotion of the growth of SRB and iron-reducing microbes to compete with local iron and sulfur-oxidizing microbes, which can be used for the source control of AMD from the sulfidic waste rocks and the final remediation.

Application of Fly Ash and Organic Material as Dry Cover System in Prevention of Acid Mine Drainage Generation

The common practice in AMD prevention is a dry cover technique. In this technique, rock that is potential in producing acidity (PAF) will be placed below non-acid producing rock (NAF). Depends on NAF availability in the mine site situation, organic covers can be used to prevent diffusion of oxygen into reactive sulphide wastes and subsequently to eliminate sulphide compounds oxidation and generation of acidic waters. The utilization of additional material cover layer is proposed, by using fly ash and organic material combination. To investigate the possibility of using these materials, a column leaching test in the laboratory scale was conducted with several scenarios of simulation. By comparing between column with different thickness of fly ash and organic material, the leachate water behavior is observed in the experiment, including the measurement of water quality (pH and EC), major cations-anions. The result suggests the possible thickness of fly ash (FA) and organic material (OM) as cover layer material, especially in the case of mine with domination of PAF rock material.

Characterization of phosphate coating formed on pyrite surface to prevent oxidation

The sulfidic wastes produced from mining activities when exposed to atmospheric oxidizing conditions during disposal and in the absence of sufficient alkaline minerals can result in the generation of acidity as well as the release of toxic metals and metalloids. An emerging technique to prevent acid generation is the formation of protective coating layers on the surface of sulfide grains (mainly pyrite) in order to inhibit the oxidation process. The composition of phosphate coating and its effectiveness in inhibiting pyrite oxidation under oxidizing conditions is investigated in the present study. A combination of wet-chemical, microscopic (SEM/EDS) and spectroscopic techniques (FTIR, XPS) was used. The experiments involved treatment of pyritic tailings with solutions containing PO43− and H2O2 at pH 5.5. Based on the results, the protective coating layer around pyrite particles is composed mainly of Fe(II)-phosphates followed by Fe(III)-phosphate, iron (hydr)oxides and iron oxyhydroxysulfate phases. The optimum conditions for the development of an efficient protective layer on pyrite particles correspond to treatment with 0.01 M PO43− for 48 h. In this case, the oxidative dissolution of sulfur was reduced by 66%, as compared to the non-treated pyrite sample.

Technical and economic evaluation of separation of dimethyl disulfide from disulfide oil at liquefied petroleum gas treatment facilities of Assaluyeh gas refinery

AbstractDisulfide oil (DSO) is produced as a hydrocarbon sulfide waste stream in liquefied petroleum gas and condensate sweetening units in refineries and can cause acute environmental pollutions. In this article, a simple process composed of two units including a distillation unit and a hydrodesulfurization (HDS) unit is proposed to overcome the disulfide oil problem in refineries. The commercial HDS catalyst is CoMo type that is applicable for hydrotreating of DSO. This catalyst is developed by different licensors such as Axens. The high sulfur content in DSO feed causes an increase in heat of reaction and partial pressure of H2S in HDS reactor. By using special design techniques such as reactor quenching or increase H2/oil ratio, the reactor can be designed properly for DSO feed. The waste stream DSO is converted to valuable products including: dimethyl disulfide (DMDS), sweet gas and condensate. A process flow diagram consisting of distillation and HDS units together with amine treating and hydrogen compression system is proposed and simulation of the process is carried out by Aspen plus: The distillation unit separates DMDS and the HDS unit removes sulfur from remainder DSO. Capital cost estimation methodology is based on bare module factor. The capital and operating cost of the process are estimated for a real capacity of DSO just produced in south pars of Iran. Financial parameters and sensitivity analysis show that the process is feasible both technically and economically with an internal rate of return of 73.6%. The proposed process is accepted environmentally by converting a harmful waste to saleable products.

Impact of declining oxygen conditions on metal(loid) release from partially oxidized waste rock

The best available technology for preventing the formation of acid drainage water from the sulfidic waste rock at mine closure aims to limit the oxygen access to the waste. There is, however, a concern that contaminants associated with secondary minerals become remobilized due to changing environmental conditions. Metal(loid) mobility from partially oxidized sulfidic waste rock under declining and limited oxygen conditions was studied in unsaturated column experiments. The concentrations of sulfate and metal(loid)s peaked coincidently with declining oxygen conditions from 100 to < 5 sat-% and to a lesser extent following a further decrease in the oxygen level during the experiment. However, the peak concentrations only lasted for a short time and were lower or in the similar concentration range as in the leachate from a reference column leached under atmospheric conditions. Despite the acid pH (~ 3), the overall quality of the leachate formed under limited oxygen conditions clearly improved compared with atmospheric conditions. In particular, the release of As was two orders of magnitude lower, while cationic metals such as Fe, Cu, Mn, and Zn also decreased, although to a lesser extent. Decreased sulfide oxidation is considered the primary reason for the improved water quality under limited oxygen conditions. Another reason may be the immobility of Fe with the incorporation of metal(loid)s in Fe(III) minerals, in contrast to the expected mobilization of Fe. The peaking metal(loid) concentrations are probably due to remobilization from solid Fe(III)-sulfate phases, while the relatively high concentrations of Al, Mn, and Zn under limited oxygen conditions were due to release from the adsorbed/exchangeable fraction. Despite the peaking metal(loid) concentrations during declining oxygen conditions, it is clear that the primary remediation goal is to prevent further sulfide oxidation.

Suitability study of secondary raw materials for prevention of acid rock drainage generation from waste rock

Prevention and mitigation of acid rock drainage (ARD) from mine wastes are crucial for limiting environmental impact. However, preventive measures are often too expensive, potentially harmful to the environment or not applied early enough. This study aimed to test the potential of different secondary raw materials for maintaining a circumneutral pH (6–7) in a sulfide oxidation environment, allowing secondary minerals to form on reactive sulfide surfaces to prevent release of acid, metals and metalloids, and thereby ARD generation. Five materials (blast furnace slag, granulated blast furnace slag, cement kiln dust, bark ash, lime kiln dust) were selected based on their alkaline properties, availability and yearly yield. High sulfidic (>50 wt%, sulfide) waste rock from an active Cu–Zn–Au–Ag open pit mine in northern Sweden was leached in small-scale laboratory test cells under ambient condition for 4–8 weeks before adding secondary raw materials on the surface in an attempt to prevent ARD generation. During 52 subsequent weeks of leaching, the pH and electrical conductivity in the leachate from the waste rock varied between 1.7-4.6 and 2.1–22.8 mS/cm, respectively. All secondary raw materials were able to increase the pH to circumneutral. However, blast furnace slag, granulated blast furnace slag and cement kiln dust were not able to maintain a circumneutral pH for an extended time due to self-cementation or carbonation, whereas bark ash (1 wt%) and lime kiln dust (5 wt%) prevented acidity, metal and metalloid leaching. Materials such as cement kiln dust and bark ash contained elevated concentrations of, e.g., Cd and Zn, but the release of metals and metalloids was generally low for most elements, except for Cl, K and Na, most likely due to salt dissolution.

Indium distribution in metalliferous mine wastes of the Iberian Pyrite Belt, Spain–Portugal

Indium is a rare, post-transition metal that is widely used in modern technological applications. However, despite its known toxicity the environmental processes of this element are poorly understood. This study reports on the abundance, mineralogical siting and mobility of indium in waste rock at six selected historic mine sites (Angostura, La Zarza, Rio Tinto, San Telmo, Sao Domingos, Tharsis) of the Iberian Pyrite Belt (IPB), Spain–Portugal. Sulfidic waste rock samples are invariably enriched in indium (mean 6 mg/kg In), with concentrations well above average crustal abundances (50 µg/kg In). Indium is largely present as cation substitutions in the crystal lattices of sulfide minerals, in particular kesterite (max. 0.5 wt% In), sphalerite (max. 0.27 wt% In) and chalcopyrite (max. 0.05 wt% In). The sulfidic wastes have undergone extensive oxidation prior to and after mining, with partially oxidized sulfidic waste rocks invariably enriched in indium (mean 1.5 mg/kg In). At the toe of waste dumps, oxygenation of acid rock drainage (ARD) waters leads to the development of abundant secondary metal and/or alkali (hydrous) sulfates and the formation of Fe-rich precipitates and evaporative salts (mean 1.5 mg/kg In). Consequently, indium is significantly enriched in sulfidic mine wastes of the IPB and displays mobility in ARD environments, with its mobility somewhat constrained by oxygenation of ARD waters and subsequent iron precipitation.