Neutralization Of Acid Mine Drainage Research Articles

Acid Mine Drainage Neutralization by Ultrabasic Rocks: A Chromite Mining Tailings Evaluation Case Study

Chromite is formed in nature in ophiolitic layers and ultrabasic rocks through fractional crystallization. The corresponding mining technologies separate the ore from these ultrabasic rocks, which are considered to be tailings for the process but may be valorized in other applications. The need to utilize this material is due to the large quantities of its production and the special management required to avoid possible secondary pollution. In the present work, the ultrabasic rocks of chromite mining were applied to acid mine drainage (AMD) neutralization. The aim was to increase the technological maturity of the method and promote circular economy principles and sustainability in the mining sector. Ultrabasic rocks were obtained from a chromite mining facility as reference material. Furthermore, an artificial AMD solution was synthesized and applied, aiming to simulate field conditions. According to the results, the sample was successfully utilized in AMD neutralization (pH 7), achieving rapid rates in the first 30 min and maximum efficiency (liquid to solid ratio equal to 8.3) at 24 h. However, the method presented a drawback since Mg was leached, even though the concentration of other typical metals contained in an AMD solution decreased.

Temporal dynamics of contaminants in an estuarine system affected by acid mine drainage discharges

The estuary of Huelva is constituted by the common mouth of the Odiel and Tinto rivers, which are extreme cases of acid mine drainage contamination due to the Iberian Pyrite Belt, the world's largest sulfide mineral province. The drained acidic waters are subjected to seawater mixing and thus, to dilution and precipitation processes that drive the load of contaminants entering the oceanic environment. This research reports the distribution of major metal(loid)s present in the highly acidic waters across the entire Tinto and Odiel estuarine systems as they are subjected to acid mine drainage neutralization, until reaching the ocean. The datasets presented are divided in low- and high-flow periods, corresponding to dry/warm and wet/cold seasons, respectively. Iron and Al were almost entirely removed from solution with pH increase at both periods due to their precipitation as schwertmannite and basaluminite, respectively. These mineral phases also, controlled the behavior of As, Cu and Pb, which were removed from solution, with >90 % of their concentration ending up in the particulate phase due to sorption processes. However, at pH >7, As returned entirely to the dissolved phase at both sampled seasons because of desorption, similarly to Cu at the low-flow period. On the other hand, concentrations of Zn, Cd, Mn, Co and Ni in solution decreased only by dilution with seawater, with null partitioning to any sorption processes during estuarine mixing until reaching the Atlantic Ocean.

Energy harvesting from acid mine drainage using a highly proton/ion-selective thin polyamide film

A huge chemical potential difference exists between the acid mine drainage (AMD) and the alkaline neutralization solution, which is wasted in the traditional AMD neutralization process. This study reports, for the first time, the harvest of this chemical potential energy through a controlled neutralization of AMD using H+-conductive films. Polyamide films with controllable thickness achieved much higher H+ conductance than a commercially available cation exchange membrane (CEM). Meanwhile, the optimal polyamide film had an excellent H+/Ca2+ selectivity of 63.7, over two orders of magnitude higher than that of the CEM (0.3). The combined advantages of fast proton transport and high proton/ion selectivity greatly enhanced the power generation of the AMD battery. The power density was 3.1 W m–2, which is over one order of magnitude higher than that of the commercial CEM (0.2 W m–2). Our study provides a new sustainable solution to address the environmental issues of AMD while simultaneously enabling clean energy production.

OPTIMASI PROSES PENETRALAN AIR ASAM TAMBANG PADA SETTLING POND PT DARMA HENWA TBK JOBSITE PT ARUTMIN INDONESIA SITE ASAM-ASAM

One of method which ussualy used in neutralizing Acid Mine Drainage using neutralizing agents is Settling Pond. This treatment process requires adding neutralizing agents to the waters or through a mixing system and allowing deposits to form in the pond. Many factors and process mechanisms can affect the effluent quality of an Acid Mine Drainage processing system. The purpose of this study is to evaluate the effectiveness and optimize the Acid Mine Drainage neutralization process carried out in Settling Pond 19. The research method used is to make theoretical simulations both modeling using PHREEQC and calculations to simulate various neutralization process options. The results showed that the neutralization process was affected by the quality of the neutralizing agent, the number of doses, the saturation index (precipitation) limit, the dissolution process of the neutralizing agent, the duration of dosing, and the duration of neutralization. According to modeling and theoretical calculations, the technical recommendations for optimizing the Acid Mine Drainage neutralization process to produce effluent quality that meets wastewater quality standards are the duration interval to inject neutralizer from every 60 minutes to every 13.6 minutes with a continuous dosing mechanism; The use of a maximum dose of limestone of 0.22 g/L to avoid oversaturated events, and the use of a limestone dissolution mechanism before the injection process is carried out to reduce the need for retention time for 216 seconds.

Minimally Active Neutralization of Acid Mine Drainage through the Monte Carlo Method

The necessity of mining valuable metals must be balanced with the safe and effective disposal or remediation of the resulting waste. Water, one of our most valuable resources, is a major component of the mining process, and its post-operation storage often results in acid mine drainage. While many remediation methods have been studied, they have low economic feasibility, as minimally active methods alone were inadequate, and thus required additional, costly active methods for effective neutralization. This study looks to neutralize acid mine drainage with only minimally passive methods, through an optimized dosage of lime, fly ash, and aluminum hydroxide. Wastewater samples of pH 3.62 and 5.03, containing 1.36 and 2.21 percent sulfides, respectively, were experimentally treated, with the utilized dosage parameters generated using the Monte Carlo method for neutralizing acidity. The remediated water samples presented 0.01% and 0.16% sulfur content values, which corresponds to 99.3% and 92.8% reductions, respectively. These results present, for the first time, that minimally active methods could achieve a pH of 8.5 without active methods. While future studies should validate these results and provide a more complete characterization of the water samples, the major challenge of neutralization was addressed, and, thus, these results contribute process incentives for mining companies to economically remediate their waste water in order to safeguard their surrounding communities and return valuable water back to the water cycle.

Simultaneous removal of multiple metal(loid)s and neutralization of acid mine drainage using 3D-printed bauxite-containing geopolymers

The mining industry is one of the largest sources of environmental concern globally. Herein we report for the first time the application of highly porous 3D-printed sorbents containing high amounts (50 wt%) of red mud, a hazardous waste derived from the alumina industry, for the remediation of acid mine drainage (AMD). The sorption capacity of the inorganic polymers was initially evaluated for the simultaneous removal of five metal(loid) elements, namely Cu(II), Ni(II), Zn(II), Cd(II) and As(V) in synthetic wastewater. The effect of the initial concentration, pH and contact time were assessed, reaching removal efficiencies between 64% and 98%, at pH 4 and initial concentration of 50 mg L−1 of each cation, after 24 h of contact time. The 3D-printed lattices were then used for the remediation of the real AMD water samples, and the role of adsorption and acidic neutralization was investigated. Lattices were also successfully regenerated and reused up to five cycles without compromising their performance. This work paves the way for the use of an industrial waste derived from the production of alumina as raw material for the management of the hazardous AMD.

Performance Assessment of Wood Ash and Bone Char for Manganese Treatment in Acid Mine Drainage

Developing efficient methods for Mn separation is the most challenging in exploring innovative and sustainable acid mine drainage (AMD) treatments. The availability and capacity of certain waste materials for Mn removal warrant further exploration of their performance regarding the effect of process factors. This study addressed the influence of AMD chemistry (initial pH and concentrations of Mn, sulfate, and Fe), the solid/solution ratio, and the contact time on Mn separation by wood ash (WA) and bone char (BC). At an equivalent dose, WA displayed higher neutralization and Mn removal capacity over the initial pH range of 2.5–6.0 due to lime, dicalcium silicate, and fairchildite dissolution. On the other hand, at optimal doses, Mn separation by BC was faster, it was less affected by coexisting sulfate and Fe(II) species, and the carbonated hydroxyapatite structure of BC remained preserved. Efficient removal of Mn was feasible only at final pH values ≥ 9.0 in all systems with WA and at pH 6.0–6.4 using BC. These conclusions were confirmed by treating actual AMD with variable doses of both materials. The water-leaching potential of toxic elements from the AMD/BC treatment residue complied with the limits for inert waste. In contrast, the residue of AMD/WA treatment leached non-toxic quantities of Cr and substantial amounts of Al due to high residual alkalinity. To minimize the amount of secondary waste generated by BC application, its use emerges particularly beneficial after AMD neutralization in the finishing step intended for Mn removal.

Remediation of acid mine drainage and immobilization of rare earth elements: Comparison between natural and residual alkaline materials

Acid mine drainage (AMD) is a well-known source of toxic trace metals in freshwaters. Traditional passive treatment systems rely on AMD neutralization with limestone and removal of most common toxic transition metals such as Cu and Zn with little attention to rare earth elements (REE). Alkaline waste materials now receive increasing attention as low cost AMD treatment alternatives in the circular economy. This study was set up to identify the efficiency of alkaline waste materials remediating AMD and scavenging REE in addition to other toxic trace elements. An AMD sample was collected from a lixiviate coming from pyrite heaps in the Iberian Pyrite Belt (pH = 1.8, 30 μM ∑REY). The sample was treated with either blast furnace slag (BFS) generated during smelting of iron ore in a blast furnace or biomass ashes (BA) derived from combustion of biomass, thereby using analytical grade CaCO3, and NaOH as reference products. The batch alkalinization experiments were conducted by adding each alkaline material at an amount to obtain an equal pH to ≈6.5. The required amounts of the products were NaOH < CaCO3<BFS < BA in line with their acid neutralizing capacities. The largest removal of sulfate from water was obtained in the CaCO3 treatment suggesting gypsum precipitation which was lower with BA and BFS and virtually absent with NaOH, these trends were confirmed by SEM-EDX and XRD. Both BFS and BA removed more Fe than CaCO3 and NaOH. The REE elements were well removed by all treatments (>99%) and the remaining REE concentrations in the solutions were clearly lower than values for Cu and Zn. The Zn and Cu removals were not consistently high enough (except with NaOH) to meet environmental limits in the discharge waters. The largest efficiency for REE removals was obtained with CaCO3. Indirect evidence here suggests that gypsum is a better host for the trivalent REE than Fe(III) minerals in the precipitates. The ionic radii of trivalent REE are more similar to Ca2+ than to Fe3+, explaining the better potential of gypsum as REE host. This study showed also the potential of BFS as alkaline agent for the remediation of AMD in terms of its higher alkalinity generation potential as compared to BA, thus making BA less promising than BFS.

Process and mechanism of recovering layered double hydroxides (LDHs) from acid mine drainage (AMD) and synergetic removal of manganese

The neutralization-precipitation method is widely used for treating acid mine drainage (AMD). However, the accumulation of sludge and the requirement for a high pH for the precipitation of Mn2+ limit the widespread application of this technology. In this work, layer double hydroxides (LDHs) were obtained by chemical neutralization of AMD, and the mechanism of LDHs for synergistic removal of Mn2+ was investigated by studying the morphological of metal elements during the neutralization process. The results showed that pH=8.5 was the critical condition for the formation of LDHs, and the sludge mainly consisted of Mg-Al-LDHs and manganese oxides. With increasing pH, Mn2+ was synergistically removed by LDHs through ion exchange (at the site 6) and complexation (with Mg-O). At pH=9.0, the concentration of Mn2+ was reduced to 1.5 mg/L, but it should be noted that high pH could destroy the structure of LDHs. Moreover, LDHs recovered from actual AMD were also found to have the ability to remove environmental pollutants. These findings not only enhance our understanding of the morphological change of metal elements during the neutralization process and the mechanism of Mn2+ removal, but also provide new insights for the recycling and utilization of neutralized sludge.

Rationale for alternative water sources for mining regions with high environmental footprint on the example of Levikha village of the Sverdlovsk region

Introduction. Mine drainage has always been one of the main threats to the hydrosphere of mining areas, both during and after active mining. The most common method of mine water neutralization is associated with the slaked lime. On the abandoned Levikha copper-sulphide mine territory (Sverdlovsk region), acid mine drainage discharge reaches 3,000 m³/day. To neutralize acid waters, more than 400 m³/day of water with a neutral pH is required (to produce the slaked lime). Due to the worn out state of water pipe from the river Tagil, heavy losses, and frequent accidents, the neutralization station receives no more than half of the required amount of water. As a result, the neutralization technology is violated, acid mine drainage is not properly cleaned, the regulatory requirements for wastewater are not achieved, and sulfate waters with increased mineralization and metal concentrations are discharged into the river Tagil. Research objective is to substantiate the possibility of finding sources of drinking, household and process water supply for Levikha village and acid mine drainage neutralization stations by applying groundwater. Methods of research include a comprehensive approach containing research results analysis and field and laboratory research data processing. Results and discussion. Promising areas have been identified representing private catchment areas of potential water intakes with the most favorable conditions for underground runoff. A combination of the following factors was the criterion for promising areas and load points: favorable geological and tectonic conditions (the presence of tectonic faults); groundwater inflow testing results (relatively high specific flow rates of wells); geomorphological position (confinement to low relief areas, location near surface sources of groundwater recharge); hydrochemical sampling data (satisfactory chemical composition of groundwater); sanitary and hygienic situation (absence of potential sources of pollution in the local catchment area). Conclusions. The total resources of the five promising sites are 1,340 m3 /day, including 282 m3 /day for drinking purposes. Exploration and development of promising areas no. II (favorable geological and tectonic conditions within it are confirmed by the groundwater inflow testing results) and no. III (favorable sanitary and hygienic conditions) seem to be the most reasonable. These sites might cover half of the village water needs for drinking and household purposes.

Isotope provenance of AMD and treatment options for large, abandoned mines: A case study of the abandoned Dashu pyrite mine, Southwest China

Discharge of acid mine drainage (AMD) along with heavy metals mobilization is a critical environmental concern. An urgent need is to manage or treat AMD in the minefield effectively. To this end, based on a hydrogeological investigation, the d-T (deuterium excess parameter-Tritium content) technique was adopted to trace the recharge, runoff, and discharge of AMD in the abandoned Dashu pyrite mine in China. The results reveal that AMD in the minefield originates from local precipitation and shallow groundwater and exhibits apparent seasonal runoff variations. The AMD is associated with shallow groundwater from the top of the Quaternary platform on the axis of the Dashu anticline, and protons could originate from the pyrite oxidation. Therefore, an engineering practice to purify the AMD is combined with (1) water diversion to stop AMD formation and blockage of the AMD outlets. (2) Acceleration of Fe(II) oxidation through aeration promotes the precipitation of Fe-oxide and hydroxide. (3) Neutralization of AMD using Karst water from the Maokou Formation (P2m). This study provides a new research idea and tracing method for improving hydrogeological surveys and effectively handling environmental problems related to AMD of abandoned mines.

Impacts of coexisting mineral on crystallinity and stability of Fe(II) oxidation products: Implications for neutralization treatment of acid mine drainage.

The neutralization treatment of acid mine drainage involves the oxidation of Fe(II), but little is known about the effects of co-existing minerals on the oxidation and hydrolysis of Fe(II) to iron oxides. Here we investigated the transformation of fresh and heated Fe(II) oxidation coprecipitates, which were synthesized in the presence and the absence of five co-existing minerals (montmorillonite, kaolin, quartz (SiO2), aluminium oxide (Al2O3) and calcium carbonate (CaCO3)). In the FeSO4 system with montmorillonite or kaolin, the formation of lepidocrocite was inhibited with the increase of clay mineral contents. In the same system, heated coprecipitates of montmorillonite were mainly comprised of amorphous ferrihydrite and its transformation was retarded by the excess montmorillonite. In the FeCl2 system with SiO2, Al2O3 or CaCO3, akaganeite formation was inhibited with the increase in the corresponding mineral contents. In the same system, goethite formation was blocked by either CaCO3 or Al2O3 and the growth of lepidocrocite was inhibited by CaCO3 or SiO2. However, magnetite formation was enhanced by addition of CaCO3. These findings are important for predicting products of abiotic Fe(II) oxidation during the neutralization of acid mine drainage and for better understanding the transformation of amorphous iron oxides in the complicated environmental matrix.

Analysis of the Mechanism of Acid Mine Drainage Neutralization Using Fly Ash as an Alternative Material: A Case Study of the Extremely Acidic Lake Robule in Eastern Serbia

Acid mine drainage (AMD) is a waste from mining sites, usually acidic, with high concentrations of sulfates and heavy metal ions. This study investigates the AMD neutralization process using fly ash (FA) as an alternative material. Samples of FA from coal-fired power plants in Serbia (“Nikola Tesla” (EF) and “Kostolac” (KOST)) were analyzed and used. The results were compared with the treatment efficiency of commercial neutralization agent (NaOH). The alkaline nature of FA was the basis for use in the treatment process of the extremely acid Lake Robule (pH 2.46), located in the mining areas of eastern Serbia. The optimal S/L ratio for the AMD neutralization process determined for EF was 25 wt.%, and for KOST it was 20 wt.%. The mechanism of the neutralization process was analyzed using the ANC test and PHREEQC program. The element concentrations and pH values in solutions indicated that FA samples could neutralize Lake Robule with more than 99% of Al, Fe, Cu, Zn, and more than 89% of Pb precipitated. Formation of insoluble (oxy)hydroxide forms (Fe3+ and Al3+ ions) creates favorable conditions for co-precipitation of other trace metals (Cu, Zn, Ni, Pb, and Cd) from AMD, which is further enhanced by cation adsorption on FA particles. FA proved to be a more effective neutralization agent than NaOH due to its adsorption effect, while among the FA samples, KOST was more effective due to the aging process through the carbonization reaction. Using FA as an alternative material is a promising and sustainable method for treating AMD, with economic and environmental benefits.

Lignite fly ash utilization for acid mine drainage neutralization and clean-up

Two fly ashes (FAs) originating from Kardia and Megalopolis power plants are used for the first time to amend the acid mining drainage (AMD) from the abandoned Ermioni and the active Kassandra Greek mining sites. The fly ashes employed are of type C, with Kardia fly ash (KFA) being mostly calcareous and Megalopolis’ (MFA) mostly siliceous. Both FAs were tested for their pH-regulating and metal-ions-removal efficiency. Regarding the acidity reduction both FAs proved equally efficient; by regulating the FA to AMD solution ratio, final pH values between 6 and 12.5 were attained using KFA while weakly acidic (pH = 6) to neutral solutions were produced in the case of MFA. Except for chromium ions, both FAs, also, proved equally effective in (heavy-)metal-removal for loadings higher than 5 g/50 mL acid waters. KFA, particularly, cleaned up the acid mine drainage solution from all metals even at a 0.5 g/50 mL loading. For KFA, metal removal was attributed to precipitation while in the case of MFA retention was found to occur via adsorption and/or complexation as well. Both FAs and AMD are largely produced as side effects of the two major Greek economic activities, i.e., electricity production and mining; using FAs to assess the AMD environmental impact can contribute to circular economy and, therefore, is of significant financial interest for Greece.

Comparative study of acid mine drainage neutralization by calcium hydroxide and concrete sludge–derived material

A novel neutralizing agent (PAdeCS) was produced from concrete sludge generated during the production of secondary concrete products by centrifugal molding, and the effect on actual acid mine drainage (AMD) was evaluated. The effect was compared with a conventional neutralizing agent (i.e., calcium hydroxide). Nine reaction tanks were temporarily installed and operated, imitating the treatment of actual AMD. The amount of discharged water and sediment generated was evaluated. The amount of PAdeCS required to neutralize the actual mine wastewater was 1.5 times that of Ca(OH)2, and the amount of sludge generated was less with PAdeCS than with Ca(OH)2. The coagulation sedimentation performance of PAdeCS is greater than that of Ca(OH)2, determined by comparing the thickness of the sludge layer and the transparency of the supernatant. The reduction of CO2 emissions for the substitution of Ca(OH)2 and CaCO3 by PAdeCS was evaluated, and the neutralization performance of this novel neutralizing agent prepared from concrete sludge in AMD was determined.

Water quality implications of the neutralization of acid mine drainage with coal fly ash from India and the United States

Subsurface coal mining often induces the formation of acid mine drainage (AMD) in active and abandoned coal mines while coal combustion generates coal combustion residuals (CCR), including fly ash (FA), with elevated levels of toxic metals. Decades of AMD and CCR production have caused major environmental and human health impacts. Given the typically elevated level of oxides in FA, previous studies have examined its potential to neutralize AMD and remove the associated metals. While the neutralization of AMD through reaction with FA has been demonstrated to successfully remove cationic metals, the fate of oxyanion forming elements are less well studied and is the focus of this study. Here we conducted 49 different experiments in which simulated AMD solutions were interacted with representative U.S. (n = 7) and Indian (n = 6) FA samples through controlled liquid to solid ratios in short-term (24 h) and long-term (up to 5 weeks) lab-scale experiments. We show that Class-F FA, originating from Gondwana and Northeastern Tertiary coals in India, has limited neutralization capacity, while Class-C FA, with high CaO and MgO contents from Powder River coals in the U.S. has the greatest AMD neutralization capacity among the studied fly ashes. The neutralization experiments show that AMD-FA reactions cause the removal of cationic elements (i.e., Fe, Mn, and Al) from solution, while at the same time, leaching oxyanion forming elements (i.e., As, Se, Mo, Cr, B, Tl, and Sb) from the FA, increasing the potential environmental risks from the treated leachates. The magnitude of mobilization of these elements depends on their concentrations in the FA and the pH conditions. We show that using FA from the Appalachian and Illinois coals efficiently neutralizes AMD, but also results in secondary contamination of the treated effluents with oxyanion forming elements to levels exceeding drinking water and ecological standards, which could contaminate the ambient environment, whereas neuralization with Powder River Basin Class-C FA induces only limited contamination.

Effective and simultaneous removal of heavy metals and neutralization of acid mine drainage using an attapulgite-soda residue based adsorbent

Implementing an economical and effective measure for treating acid mine drainage (AMD) from abandoned mines using low-cost restoration reagents present a significant challenge. In this study, natural attapulgite (AT) and soda residue (SR) composite particles (AT-SR) were firstly prepared and utilized in AMD treatment. The efficiencies and mechanisms of AT-SR composites for regulating acidity and removing metals in AMD, the critical factors influencing the treatment efficiencies, and the regeneration performance and environmental risk were investigated. It is illustrated that AT and SR quality ratio of 5:5, dosage of 0.5 g L−1, particle size < 1.5 mm, concentrations of 150 mg L−1 for Fe, 75 mg L−1 for Mn and 100 mg L−1 for Cu, Zn, Cd and Pb, and adsorption time of 120 min were the optimized conditions. The maximum adsorption capacities of Fe, Mn, Cu, Zn, Cd and Pb under single metal scenarios were 51.61, 22.30, 37.05, 40.21, 37.39 and 49.53 mg g−1, respectively. Under the mixed metal scenarios, competitive adsorption was predominated with the rate constants in the reducing order of 3.169 for Fe > 0.841 for Cu > 0.657 for Pb > 0.083 for Zn > 0.024 for Cd > 0.006 for Mn. The experimental data was fitted well with the pseudo-second-order and the Freundlich isotherm models. AT-SR is an outstanding neutralizer for AMD due to its richness in calcium and magnesium oxides and the spent AT-SR composites could be easily regenerated while maintaining high metal removal efficiencies under the subsequent usages. It is determined under the aqua regia digestion and Toxicity Characteristic Leaching Procedure (TCLP) tests that AT-SR can be used safely without posing environmental risks, thus promoting the resource recovery and utilization of soda residue and providing a green and effective method for treating AMD.

Development of Artificial Geochemical Filter to Treat Acid Mine Drainage for Safe Disposal of Mine Water in Salt Range Portion of Indus Basin—A Lab to Pilot Scale Study

Several passive and active treatment approaches are available for dealing with Acid Mine Drainage (AMD). Despite a range of newly emergent techniques for the treatment of AMD, pH control using low-cost neutralizing reagents has been the most common and economical technique for the treatment of AMD. Thereby, owing to their widespread availability, ease of use, and cost effectiveness, active treatment techniques utilizing calcium-based reagents (particularly limestone) are considered the prime choice for treating AMD. Limestone is a well-known option worldwide for AMD neutralization thanks to its easy availability, low cost, and excellent efficiency. Generally, acidity is reduced by the presence of CaCO3 and alkalinity (i.e., HCO−3) is increased. pH can be increased from 2.5 to 7.5 by using limestone as a treating agent, resulting in the precipitation of heavy metals, which can then be removed by precipitation and sorption. Wargal limestone, a well-known limestone from the Salt Range, Indus basin, Pakistan, has high potential for neutralization and treatment of PTEs present in mine water or AMD. After selecting a suitable neutralization material at pilot scale, two different filters were designed using selected Wargal limestone: Filter 1 A (Oxic-based, Vertical bed-type Wargal Limestone Filter) and Filter 1 B (Anoxic-based Vertical bed-type Wargal Limestone Filter with Compost). The pH of the AMD under study was elevated from 2.5 to 7.65 and 7.60, respectively, in uncoated and coated media of limestone. Although the neutralization potential decreased over time, as an overall phenomenon the Ca concentration and net alkalinity (280–360 mg/L) were increased with the removal of metals such as Fe, Cu, Pb and Mn. The respective removal efficiency of these metals was 98%, 99%, 99% and 60%, with a threshold residence time of 5 h. in all columns of the developed filters.

Fe(II)-mediated transformation of schwertmannite associated with calcium from acid mine drainage treatment

Schwertmannite is an important Fe(III)-oxyhydroxysulfate in acid mine drainage (AMD) polluted areas and its stability depends on surrounding environmental factors and previously bound elements. The treatment and neutralization of AMD normally involve the use of lime, which leads to the discharge of abundant Ca in the mining area. Such an environmental disturbance brings up an important and less considered problem of how the reductive transformation of schwertmannite associated with coexisting Ca occurred. Here, the Fe(II)-mediated transformation of Ca-adsorbed schwertmannite and subsequent Ca repartitioning behaviors were investigated. Results showed that adsorbed Ca had a weak inhibitory effect on Fe(II)-mediated schwertmannite transformation. Release of SO42− and SEM images both indicated that transformation rates of schwertmannite decreased under the influence of adsorbed Ca. XRD patterns indicated that adsorbed Ca altered schwertmannite transformation pathways and product compositions upon treatment with 0.4 mmol/L Fe(II). The end products of Sch notably contained both goethite and lepidocrocite; however, transformation products of SchCa only contained goethite all along. Approximately 33.5% of the surface adsorbed-Ca was released into solution within 6 hr after Fe(II) injection. Aqueous Ca behaved in a “first release and then im-mobilization” manner, which indicated dissolution and secondary mineralization drove Ca migration during the Fe(II)-mediated transformation of SchCa. Adsorbed Ca blocked the surface sites for subsequent Fe(II) adsorption, limited the Fe(II)-Fe(III) ETAE, and decreased the transformation rates. This work sheds light on the complex geochemical behavior of schwertmannite under the influences of environmental perturbations in AMD environments.

Emerging remediation potentiality of struvite developed from municipal wastewater for the treatment of acid mine drainage

The valorisation of wastewaters for minerals recovery and their potential beneficiation has gained enormous attention recently. In this study the removal of phosphate and ammonia from municipal wastewater using activated magnesite resulted in the formation of struvite. The optimum conditions for the synthesis of struvite were 60 min of mixing, 300 rpm mixing speed, 1 g of activated magnesite and room temperature, whilst optimum conditions for the treatment of acid mine drainage (AMD) using the synthesized struvite were 45 min of mixing, 20 g of struvite dosage, 1000 mL, and 300 rpm mixing speed. The efficacy of struvite for neutralisation of AMD and attenuation of inorganic contaminants were ≥98.99% for metals (Al3+, Fe3+, and Mn2+) and ≥30% for SO42−. Traces of other metals such as Zn, Cu, Ni, Pb, and Cr were significantly attenuated. Phosphate was fully attenuated from the aqua-sphere. PHREEQC predicted the removal of minerals as oxy-(hydro)-sulphates, oxy-(hydro)-phosphate, metals hydroxides, and other complexes. FE-SEM equipped with FIB and an EDX, XRD, XRF, and FTIR confirmed the synthesis of struvite and fate of chemical species after treatment. This study confirmed the feasibility of recovering phosphate and ammonia as struvite which can be employed for the treatment of AMD.