Field Investigation of Controlling Acid Mine Drainage Using Alkaline Paper Mill Waste

To verify in situ laboratory test results for the control of acid mine drainage using alkaline paper mill waste, five demonstration cells were built on the Ascot mine site in Sherbrooke (Québec, Canada). A monitoring program was set up to record temperature, leached water quality, oxygen concentration and electrical conductivity.Monitoring results showed that mixing mine residueswith alkaline paper mill waste and covering mine residues with paper mill waste allows an efficient control of acid mine drainage. The paper mill waste cover generates an alkaline front which results in metal precipitation as hydroxides. Also, an increase in pH results in an inhibitionof bacterial catalytic activity. Chemical analyses conducted on the collecting water shows a high reduction of leachingmetals to under ground water. Moreover, a significant reduction of diffusion of oxygen to the mine residue is observed.     

Treatment of Acid Mine Drainage Using Fly Ash Zeolite

In this paper, two Indian fly ashes (from Talcher and Ramagundam) were converted into zeolites and both the raw fly ash and zeolite were used to treat two British acidic mine waters. The results demonstrate that fly ash zeolites are more effective than raw fly ash for treatment of acid mine drainage. Fly ash has been found effective for removal of Pb, but with increased dosing, caused release of Ba, Cr, Sr (both fly ashes) plus Zn, Ni (Talcher), or Fe (Ramagundam) into mine water. In contrast, increased dosing with fly ash zeolite removed 100% Pb, 98.9% Cd, 98.8% Zn, 85.6% Cu, 82.8% Fe, 48.3% Ni, and 44.8% Ba from mine water. Fly ash is amorphous in nature and many metals attached on the surface of the ash particles are easily leached off when ash comes in contact with acidic mine water. However, fly ash zeolite is crystalline in nature and due to its high cation exchange properties, most of the metals present in acid mine water are retained in surface sites.     

Controlling Acid Drainage in a Pyritic Mine Waste Rock. Part II: Geochemistry of Drainage

Mine waste rock can produce acid rock drainage (ARD) when constituent sulphide minerals (for example, pyrite) oxidize upon exposure to the atmosphere. Outdoor experiments were performed to test techniques for preventing and controlling ARD in a pyritic mine waste rock. The experiments involved lysimeter (plastic drum) experiments in which the crushed (25–50 mm particle sizes), amended and unamended waste rock was exposed to natural weather conditions (rain, drying, freezing and thawing) for 125 weeks. The amendments consisted of separately covering the waste rock with compacted soil, wood bark and water and mixing with limestone and phosphate rock at 1 and 3%. Waters draining the various rocks were collected and analyzed for acidity, pH, sulphate and metals. In general, concentrations of SO₄ ^2-, Fe, As, Cu, Al and Mg in the drainage from the control rock increased gradually in the first year, peaked in the second year and increased further in the third year, reflecting increasing acid generation with time. SO₄ ^2- displayed strong positive correlation (0.91 to 0.98) with Al, As, Cu, Fe and Mg.Concentrations of Zn, Mn and Cd reached their maximumin the second year. Geochemical analysis of thecomplete water quality data using the equilibriumspeciation model WATEQ4F suggested waste rockoxidation was most likely controlled by Fe³⁺. Al, SO₄ ^2- and Fe concentrations in thecontrol rock appeared to be controlled by alunite(KAl₃(SO₄)₂(OH)₆), jarosite(KFe₃(SO₄)₂(OH)₆) and amorphousferric hydroxide [(am)Fe(OH)₃] during the firstyear. Ion activity product data (log IAP) forFe³⁺ and OH^- generally ranged between –37and –34 in the first two years but decreased to –39and –40 in the third year, suggesting that amorphousferric hydroxides were beginning to crystallize intomore stable forms such as ferrihydrite (Fe[OH]₃)and goethite (FeOOH) in the third year. The addedlimestone lost its effectiveness after a while,probably because of precipitation of secondaryminerals on the limestone particles. The phosphaterock could not sustain the drainage pH above 6 andlost its effectiveness before the limestone did. Underthe conditions of the experiments, the soil cover didnot work as expected, probably because of sidewallpassage of oxygen and water. The water cover was themost effective control method, reducing the acidproduction rate data from 41 to only 0.08 mgCaCO₃ week^-1 kg^-1 waste rock. The wood bark was theworst performer and accelerated acid production by 170%.     

Controlling Acid Drainage in a Pyritic Mine Waste Rock. Part I: Statistical Analysis of Drainage Data

Field experiments were conducted to evaluate the relativeeffectiveness of several covers and amendment techniques forpreventing or controlling acid generation in a pyritic minewaste rock. The covers and techniques consisted of water cover,soil cover, wood bark cover, limestone addition and phosphaterock addition. Water quality data (pH, sulphate, zinc and ironconcentrations) obtained from the experiments were analyzedusing two-way ANOVA (analysis of variance) with repeatedmeasurements. A 5% test of significance (p-value of 0.05) wasused in the analysis. The results suggested that the covers andamendments should be either compared on a time-by-time basis orgrouped into four, based on their performance: (i) water cover, (ii)1% and 3% limestone, (iii) clay, 1% and 3%PO₄, andcontrol (no cover), and (iv) wood bark. The results did not showany significant difference between the drainage quality from1% and 3% limestone-amended rocks. The drainage quality from the 1%and 3% phosphate and clay-covered rocks did not significantlydiffer from the control (unamended) rock. Water cover was foundto be the most effective, while the wood bark cover proved to bean ineffective method for controlling acid drainage in the wasterock. The statistical analysis also showed good replication inthe experiments, as no significant difference in the quality ofthe drainage from the replicates was observed.     

Treatment of Acid Mine Drainage by Sulphate-reducing Bacteria Using Low Cost Matrices

This paper reports a laboratory-scale investigation concerning the use of sulphate-reducing bacteria (SRB) in a semi-continuous process, where column packed-bed type bioreactors were used for the treatment of acid mine drainage (AMD). The use of different materials as solid matrices was tested and the performance of the bioremediation processes was discussed in terms of sulphate and metals removal and acid neutralization. The behaviour of a reactor filled with acidic soil from a mining area and organic wastes was compared with other three reactors where coarse sand, glass spheres and cereal straw were used as packaging materials. Batch experiments showed the presence and growth of SRB from the acidic soil in different pH conditions and the effect of the absence or presence of several added carbon sources: lactate, ethanol and lactose. The data showed that it is possible to grow SRB using the acidic soil as source of inocula, in the absence and in the presence of the carbon sources tested, since the pH of the media was previously increased to values of 5 or higher. When acidic soil from the mining area and organic wastes were utilised as column matrices, it is possible to remove the metals and to neutralise the acidity of AMD, although an inefficient sulphate removal was observed. When coarse sand or glass spheres were utilised, efficient metals sulphate removal were achieved. However, the incapacity of both systems to generate enough alkalinity does not allow maintaining their good performances in terms of iron removal and sulphate reduction. As a result, the incorporation of materials with neutralizing and buffer capacity to the matrix is recommended. Due to its low density, cereal straw was not suitable to obtain an anaerobic environment inside the column for SRB activity.     

Source Treatment of Acid Mine Drainage at a Backfilled Coal Mine Using Remote Sensing and Biogeochemistry

A biological source treatment (BST) technique using remote sensing and biogeochemistry has been developed to address acid mine drainage (AMD) at its source. The BST technique utilizes down-hole injections of microbial inoculum and substrate amendments to establish a biofilm on the surface of metal sulfides (AMD source material). The treatment results in an elevated groundwater pH (from acidic to circum-neutral levels) and prevents further oxidation of AMD source material. The first 2 years of an ongoing field study of the BST technique at a reclaimed coal mine in central Tennessee (USA) has produced successful results. For instance, the water chemistry in a monitoring well down-gradient from injection wells has improved substantially as follows: the pH increased 1.3 units from 5.7 to 7.3, the dissolved (0.45 µm-filtered) iron concentration decreased by 84% from 93 to 15 mg/l, the conductivity decreased by 379 µS/cm, and sulfate decreased by 78 mg/l. Electromagnetic induction surveys were conducted to identify AMD source material and monitor BST performance by measuring changes in subsurface resistivity throughout the site. These surveys revealed a treatment zone created between injection wells where the resistance of contaminated groundwater from up-gradient AMD sources increased as it flowed past injection wells, thus, suggesting this technique could be used to treat AMD sources directly or to intercept and neutralize sub-surface AMD.     

Enhancement of Metal Sorption by Composted Paper Mill Waste Following Microbial Manipulation

The biosorptive-capacity of composted paper mill waste (PMW) for the heavy metals [Cd(II), Cu(II), Pb(II) and Zn(II)] was improved by inoculation of sterilized compost with a Bacillus brevis strain followed by incubation. This strain was originally isolated from the compost and adsorbed up to 31% of its dry weight of lead and 28% in copper at an initial concentration of 185.2mg/L and 182.3mg/L respectively. Estimated numbers of the bacterium following 21 days growth in the compost at 25°C reached 10⁹ cells/g. The modified compost exhibited up to a three-fold increase in capacity for removal of lead and up to a two-fold increase in capacity for removal of copper from aqueous solution.     

Fixed Bed Sorption of Phosphorus from Wastewater Using Iron Oxide-Based Media Derived from Acid Mine Drainage

Phosphorus (P) releases to the environment have been implicated in the eutrophication of important water bodies worldwide. Current technology for the removal of P from wastewaters consists of treatment with aluminum (Al) or iron (Fe) salts, but is expensive. The neutralization of acid mine drainage (AMD) generates sludge rich in Fe and Al oxides that has hitherto been considered a waste product, but these sludges could serve as an economical adsorption media for the removal of P from wastewaters. Therefore, we have evaluated an AMD-derived media as a sorbent for P in fixed bed sorption systems. The homogenous surface diffusion model (HSDM) was used to analyze fixed bed test data and to determine the value of related sorption parameters. The surface diffusion modulus Ed was found to be a useful predictor of sorption kinetics. Values of Ed?<?0.2 were associated with early breakthrough of P, while more desirable S-shaped breakthrough curves resulted when 0.2?<?Ed?<?0.5. Computer simulations of the fixed bed process with the HSDM confirmed that if Ed was known, the shape of the breakthrough curve could be calculated. The surface diffusion coefficient D _s was a critical factor in the calculation of Ed and could be estimated based on the sorption test conditions such as media characteristics, and influent flow rate and concentration. Optimal test results were obtained with a relatively small media particle size (average particle radius 0.028?cm) and resulted in 96?% removal of P from the influent over 46?days of continuous operation. These results indicate that fixed bed sorption of P would be a feasible option for the utilization of AMD residues, thus helping to decrease AMD treatment costs while at the same time ameliorating the impacts of P contamination.     

Acid Mine Drainage Treatment Assisted by Lignite-Derived Humic Substances

Rewetting of agriculturally used peatlands has been proposed as a measure to stop soil subsidence, conserve peat and rehabilitate ecosystem functioning. Unintended consequences might involve nutrient release and changes in the greenhouse gas (GHG) balance towards CH₄-dominated emission. To investigate the risks and benefits of rewetting, we subjected soil columns from drained peat- and clay-covered peatlands to different water level treatments: permanently low, permanently inundated and fluctuating (first inundated, then drained). Surface water and soil pore water chemistry, soil-extractable nutrients and greenhouse gas fluxes were measured throughout the experiment. Permanent inundation released large amounts of nutrients into pore water, especially phosphorus (up to 11.7 mg P-PO₄ l^?1) and ammonium (4.8 mg N-NH₄ l^?1). Phosphorus release was larger in peat than in clay soil, presumably due to the larger pool of iron-bound phosphorus in peat. Furthermore, substantial amounts of phosphorus and potassium were exported from the soil matrix to the surface water, risking the pollution of local species-rich (semi-)aquatic ecosystems. Rewetting of both clay and peat soil reduced CO₂ emissions. CH₄ emissions increased, but, in contrast to the expectations, the fluxes were relatively low. Calculations showed that rewetting reduced net cumulative GHG emissions expressed as CO₂ equivalents.     

Sand-Sized Limestone Treatment of Streams Impacted by Acid Mine Drainage

Direct single point, instreamapplications of limestone sand were made in twostreams severely acidified by acid mine drainage. After high flows distributed the sand downstream,dissolution of the limestone significantly reduced theacid loads in both streams. Data from the treatedstream sections and laboratory experiments showed thatthe efficiency of treatment was more dependent onlimestone particle size than CaCO₃ content. Results from the stream treated with a narrow range oflimestone sand-sized particles showed a highutilization efficiency with nearly completedissolution of the limestone. The data indicated thatmonthly addition of limestone sand may be sufficientfor complete treatment of the streams studied. Ananalysis of such a treatment scheme indicated it to behighly cost efficient when compared to other activeand passive treatment systems.     

Phosphorus Removal by Sediment in Streams Contaminated with Acid Mine Drainage

Acid mine drainage (AMD) affects thousands of stream miles in the Appalachian region of the USA and results in elevated concentrations of iron and aluminum in the stream water and sediments and wide ranging pH values. It was hypothesized that these conditions would lead to increased P buffering capacity of the sediments which in turn would cause a decrease in dissolved reactive phosphorus (DRP) in the water column. In the lab fresh Fe, Al, and Mn oxide precipitates all adsorbed DRP strongly but over different pH ranges. Sulfate and calcium ions inhibited adsorption of DRP with Fe oxides but the effect was less apparent with Al oxides. In the field DRP concentration was reduced 54–90% just downstream of an AMD input compared to upstream of the input. In addition the sediment buffering capacity increased and equilibrium phosphate concentration decreased dramatically downstream of the AMD inputs. The strength of the effect and the widespread occurrence of AMD suggest that AMD could be altering the P dynamics of streams and rivers throughout the Appalachian region.     

Bioremediation of Pulp and Paper Mill Effluent by Tannic Acid Degrading Enterobacter sp.

Wastewaters from pulp and paper mills are highly toxic and around 250 xenobiotic compounds have been reported in the effluents. Tannic acid degrading bacterium, Enterobacter sp. was isolated from soil by tannic acid enrichment. This isolate was used for bioremediation of pulp and paper mill effluents. Parameters like temperature, agitation, inoculum size and treatment duration were optimized by using Qualiteck-4 software. Reduction in lignin 73% and colour up to 82% was also observed. Encouraging results were observed is reduction of COD, BOD with 16-h retention time in batch culture.     

Bioremediation of Acid Mine Drainage Using Acidic Soil and Organic Wastes for Promoting Sulphate-Reducing Bacteria Activity on a Column Reactor

Acid mine drainage (AMD) is a serious environmental problem resulting from extensive sulphide mining activities. The old copper mine of S. Domingos in Southeast Portugal is an example of such a situation. The abandoned open-pit from the mining operations resulted in the creation of a large pit lake with acidic water (pH～2) and high contents of sulphate and heavy metals. Sulphate-reducing biological processes have been studied as a remediation technology for this problem. A new application based on a simple and semi-continuous process for the treatment of S. Domingos AMD has been presented herein. Experiments using bench scale fixed-bed column bioreactors were carried out to evaluate the efficiency of the process. Sewage, anaerobic sludge and soil from the mining area were tested as solid matrices and/or inocula, as well as sources of complex organic substrates. The addition of lactose as a supplementary carbon source, easily available at zero cost or at negative cost in the effluents of the local cheese industries, was also tested. The data obtained indicate that it is possible to use the matrices tested for the production of sulphide by sulphate reduction, and that the regular addition of lactose is effective. Results showed that the process is efficient for the precipitation of the main dissolved metals, for the reduction in the sulphate content and, most importantly, for the neutralization of the AMD. Moreover, the use of soil as solid support also showed the possibility of using this process for the decontamination of both waters and soils.     

基于沟渠库厂联合运用的金属矿区酸性废水防控措施研究

[目的]金属矿区酸性矿山废水外排防控一直是个难题。探索酸性矿山废水源头控制与末端治理相结合的防控技术体系,为金属矿区酸性废水的防控提供新的解决思路。[方法]以广东省大宝山矿区为研究案例,坚持"源头防控,末端治理"的原则,构建基于沟渠库厂联合运用的酸性废水综合防控技术体系。[结果]建设截排水系统实施雨污分流,从源头上减少酸性废水产生量;清淤腾空拦泥库调蓄库容2.81×106 m3,并建设4.50×104 t/d处理规模的污水处理厂,对酸性废水进行未端治理,达到在5a一遇降雨条件下丰水期酸性废水不外排的防控目标。[结论]通过沟(截水沟)、渠(排水渠)、库(拦泥库)、厂(污水处理厂)的联合运用,可以控制酸性矿山废水在设计标准下不外排,该技术体系可用于类似矿山酸性废水的治理。     

Repeatability Evaluation of Instrumented Column Tests in Cover Efficiency Evaluation for the Prevention of Acid Mine Drainage

Instrumented column tests are often used to assess the effectiveness of methods to prevent acid mine drainage (AMD). These tests are seldom duplicated, and this lack of duplicate can cast some doubt about their repeatability and reliability. This paper provides an analysis of column test studies (with duplicates) performed with a commonly used methodology. The paper presents the analysis of two multi-layer covers with capillary barrier effects in which the water retention layer was made of a non-plastic silt and of two cover scenarios involving a single-layer low sulphide cover. The first study compared the cover performance to limit AMD when different cover materials are used, while the second study compared the thickness of covers on cover performance. Statistical comparison between duplicates was made using available geochemical data, hydro-geotechnical data, and gas concentrations. Student??s t-test statistical tools and analysis of variances were used to determine the repeatability of the data. The results indicate that a good reproducibility of the column tests can be achieved with a good set-up methodology and rigorous control of the boundary conditions.     

Laboratory Investigation of the Geochemical Behavior of Metals in Paddy Soils Contaminated with Mine Tailings

The geochemical behavior of metals, including Fe, Mn, Pb and Zn, in contaminated paddy soils was investigated during the cultivation of rice crops through laboratory microcosm experiments. From the two paddy fields contaminated by mine tailings, Siheung and Deokeum in Korea, paddy soils were collected and analyzed for their geochemical characteristics. The Siheung paddy soil showed higher levels of heavy metals, whereas the higher potential for the release of metals was anticipated due to the extremely acidic conditions at Deokeum. In microcosm experiments of flooded paddy soils over 18 weeks, Fe and Mn were released in subsurface pore waters by reductive dissolution, and Pb and Zn were dissolved in high amounts at the surface by oxidation of sulfides. Although amorphous Fe oxide-rich layers were formed at the surface of both paddy soils, the release of Pb and Zn were controlled at the surface by these layers only under slightly alkaline conditions at Siheung. Lead and Zn were associated with the reducible and carbonate fractions at the surface paddy soil of Siheung from the sequential extraction on core samples collected during the flooded period. In the acidic conditions at Deokeum, Pb and Zn were continuously released until the late stage of flooding. A great increase in the exchangeable fraction of metals was observed after the soils had drained. The bioavailability of metals for rice crops would be high under acidic conditions at Deokeum, despite the lower levels of heavy metal contamination.     

Valuable Metal Recovery During the Bioremediation of Acidic Mine Drainage Using Sulfate Reducing Straw Bioremediation System

Recovery of valuable metals from acidic mine drainage (AMD) during bioremediation using straw bioremediation system was investigated, with observation of efficient metal recovery. The recovery loading rates of Cu and Zn were 46.19?±?6.13 and 43.86?±?6.76?mg?m^?3?h^?1, respectively. More than 97.0% of Cu and more than 87.0% of Zn were recovered from AMD during bioremediation. The recovery loading rate of Cu increased by 4.54?mg?m^?3?h^?1 for each 1?mg?L^?1 increase in influent concentration while that of Zn increased by 4.08?mg?m^?3?h^?1. Heavy metal toxic effect on the metal recovery in the straw bioremediation system could be neglected in most cases. Low pH could severely decrease recovery rate of Zn, while it had no influence on that of Cu. The recovery loading rate of Zn decreased by almost 70% when the influent pH decreased from 7.0 to 3.0. Cu could be recovered efficiently even at a short hydraulic residence time (HRT) of 18?h, while Zn could only be efficiently recovered at a relatively long HRT of 80?h, indicating that selective metal recovery might be achieved with relatively short HRT and bioreactor process optimization. These findings suggested the feasibility of using sulfate-reducing straw bioremediation system to recover valuable metals during bioremediation of AMD.     

In-Vessel Cocomposting of Green Waste With Biosolids and Paper Waste

In comparison to traditional windrow composting, in-vessel composting techniques often represent more effective waste management options due to the reduced production of bioaerosols and leachate and the potential for better process control. Chemical processes occurring during the cocomposting of three common wastes (green waste, biosolids and paper processing waste) were studied using the forced aeration, static pile, in-vessel EcoPOD® composting system. Since no turning of the compost occurs within the static piles, spatial differences in the vessel were also monitored. These measurements revealed significant spatial gradients in temperature; however, this did not result in spatial differences in nutrients within the composting vessel. Significant differences in soluble N production were observed during the composting process following the series: green plus paper waste < green waste < green waste plus biosolids. After the active compost phase was over, and the compost was removed from the vessel and matured outside, we demonstrated that covering the compost was essential to preserve compost quality. Our study clearly shows that cocomposting of common waste feedstocks can be used to successfully manipulate the chemistry of the final compost making it suitable for multiple end uses. In addition, our study demonstrated that careful management of the compost maturing phase is also required to maximise quality and minimize pollution.