Hydrogeochemistry,Elemental Flux,and Quality Assessment of Mine Water in the Pootkee-Balihari Mining Area,Jharia Coalfield,India

Ninety nine mine water discharge samples were collected and analyzed for pH, electrical conductivity (EC), major cations, anions, and trace metals in the Pootkee-Balihari coal mining area of the Jharia coalfield. The mines of the area annually discharge 34.80 × 10⁶ m³ of mine water and 39,099 t of solute loads. The pH of the analyzed mine waters ranged from 6.97 to 8.62. EC values ranged from 711 μS cm⁻¹ to 1862 μS cm⁻¹, and reflect variations in lithology, geochemical processes, and hydrological regimes in the mines. The cation and anion chemistry indicate the general ionic abundance as: Mg²⁺ > Ca²⁺ > Na⁺ > K⁺ and HCO₃ ⁻ > SO₄ ²⁻ > Cl⁻ > NO₃ ⁻ > F⁻, respectively. Elevated SO₄ ²⁻ concentrations in the Gopalichuck, Kendwadih, and Kachhi-Balihari mine waters are attributed to pyrite weathering. The water quality assessment indicated that TDS, hardness, Mg²⁺, and SO₄ ²⁻ are the major parameters of concern in the study area. Except for Fe, all of the measured metals in the mine water were well within the levels recommended for drinking water. With only a few exceptions, the mine water is of good to permissible quality and suitable for irrigation.     

Hydrotalcite Formation for Contaminant Removal from Ranger Mine Process Water

Process water from the Ranger Uranium Mine requires treatment to meet stringent environmental water quality criteria. The acidic water contains substantial SO₄, metals, and U. One novel treatment method under consideration is the use of Na-aluminate to both neutralise the process water and precipitate hydrotalcites. Hydrotalcites are a class of Mg–Al layered double hydroxide minerals with a typical endmember chemical composition: Mg₆Al₂(A)(OH)₁₆·n(H₂O), where A = CO₃ ²⁻, SO₄ ²⁻, etc. Many acidic wastewaters contain Mg and/or Al in sufficient abundance for hydrotalcite formation upon addition of alkali to achieve solution pH > 5, and Mg and/or Al to attain a Mg:Al ratio of 2 to 3:1. The utility of hydrotalcites lies in their ability to incorporate a range of cationic (Cu²⁺, UO₂ ²⁺), metalloid (AsO₄ ³⁻), and (oxy)anionic contaminants (CrO₄ ²⁻). The broad spectrum removal of contaminants, including U, also indicates that hydrotalcites and their derivatives could potentially be used as a containment material in nuclear waste repositories. In this study, Ranger process water derived from extraction of U from chloritic schist was treated with Na-aluminate sourced from Bayer process liquor, in combination with NaOH or Ca(OH)₂. Hydrotalcites formed as the primary mineral during process water neutralisation with the ability to simultaneously remove a suite of contaminants from solution.     

Quality Assessment of Mine Water in the Raniganj Coalfield Area,India

In a qualitative assessment of mine water from the Raniganj coalfield, 77 mine water samples were analyzed to assess water quality and suitability for domestic, industrial, and irrigation uses. The pH of the mine water ranged from 6.5 to 8.8. Total dissolved solids (TDS) ranged from 171 to 1,626 mg L⁻¹; spatial differences between the TDS values reflect variations in lithology, activities, and prevailing hydrological regime. The anion chemistry was dominated by HCO₃ ⁻ and SO₄ ²⁻. On average, Cl⁻ contributes 10 and 19% of the total anionic balance, respectively, in the Barakar and Raniganj Formation mine water. F⁻ and NO₃ ⁻ contribute <2% to the total anions. The cation chemistry is dominated by Mg²⁺ and Ca²⁺ in the mine water of the Barakar Formation and Na⁺ in the Raniganj Formation mines. Much of the mine water, especially of the Barakar Formation area, has high TDS, total hardness, and SO₄ concentrations. Concentrations of some trace metals (i.e. Fe, Cr, Ni) were found to be above the levels recommended for drinking water. However, the mine water can be used for irrigation, except at some sites, especially in the Raniganj Formation area, where high salinity, sodium adsorption ratio, %Na, residual sodium carbonate, and excess Mg restrict its suitability for agricultural uses.     

Dissolution Kinetics of Sulfate from Schwertmannite Under Variable pH Conditions

Sulfate mobilization was investigated under controlled laboratory conditions. Microbially synthesized schwertmannite (14.7 m²/g specific surface area with 4.7 Fe:S molar ratio) was interacted at room temperature for 4 months with aqueous solutions between pH 5 and 8. More than 50% of the solid-phase sulfate was released during the initial 2 months and the rate was positively influenced by pH due to the competition of hydroxyl ions for SO₄ ²⁻. More than 90% of the solid-phase sulfate was released within 4 months at pH 8. Infrared spectra demonstrate diminution and splitting of SO₄ ²⁻ adsorption bands, indicating possible structural changes within the solid phase as a result of SO₄ ²⁻ release. Transformation of schwertmannite to goethite was triggered by pH increase and was primarily responsible for the sulfate mobilization. Thus, schwertmannite that interacts with neutral to alkaline water can add significantly to the sulfate load of a stream.     

The removal of sulfate and metals from mine waters using bacterial sulfate reduction: Pilot plant results

A treatment process that bacterially converts sulfate into elemental sulfur via a hydrogen sulfide intermediate was demonstrated at pilot scale for the treatment of three mine waters that contained metals and sulfate. Ethanol served as the bacterial carbon and energy source. The mine waters were treated at rates that ranged from 50–150 L day⁻¹. Contaminant concentrations up to 13 mg L⁻¹ copper, 0.1 mg L⁻¹ mercury, 0.04 mg L⁻¹ cadmium, 3.5 mg L⁻¹ zinc, 0.68 mg L⁻¹ cobalt, 1.3 mg L⁻¹ nickel, 49 mg L⁻¹ iron, and 63 mg L⁻¹ aluminum were removed to meet water quality effluent limits. Manganese removal was about 80% under normal operating conditions but increased to 96% when the process was optimized for manganese removal. The process was shown to be capable of decreasing sulfate concentrations from 1800 mg L⁻¹ to less than 250 mg L⁻¹, nitrate from 100 mg L⁻¹ to less than 1 mg L⁻¹, arsenic from 8 mg L⁻¹ to less than 0.03 mg L⁻¹, and calcium from 310 mg L⁻¹ to less than 100 mg L⁻¹. Acid mine waters were neutralized using bacterially-generated alkalinity; no external alkalinity source was needed.     

Acid Mine Drainage at the Abandoned Kettara Mine (Morocco): 2. Mine Waste Geochemical Behavior

Weathering and humidity cell tests were used to predict the potential for acid mine drainage (AMD) and to estimate the mineral reaction rates and depletion of fine and coarse tailings from the abandoned Kettara mine, Morocco. The geochemistry of the fine and coarse mine wastes was similar and, as expected by static tests, the wastes produced significant amounts of AMD. The sulfate production rate of both fine and coarse tailings was very high (2,000–8,000 and 2,400–560 mg SO₄/kg/week, respectively) during the first weeks of kinetics tests. After 9 weeks, sulfate release became low, ranging between 600 and 78 mg SO₄/kg/week for fine tailings and 500–120 mg SO₄/kg/week for coarse tailings. Effluent water samples had low pH (2.9–4.2) and elevated concentrations of acidity, sulfate, iron, copper, and zinc. Most or all of the dissolved K, Na, Al, Mg, and Si in the AMD result from the acidic dissolution of silicates (chlorite, talc, muscovite, and albite). Fine tailings produce much higher concentrations of acidity and sulfate than coarse tailings. However, due to greater transport of oxygen and water within the coarse waste, coarse tailings could be of greater environmental significance than fine tailings. The coarse waste continued to release acid after 378 days of leaching, whereas the fine tailings naturally passivates. These laboratory results agree with field observations; the upper profile of the coarse waste rock dam is highly oxidized (75 cm) whereas oxidation in the fine tailings does not extend more than 5–15 cm beneath the surface. A comparison between weathering and humidity cell tests indicated that the general trend of dissolution of metals was essentially similar for both methods. However, sulfate depletion rates were higher for the weathering cell tests. These tests indicate that the Kettara tailings piles and dam will continue to release acid for a long time unless remedial action is taken.     

Evaluation of the Potential for Beneficial Use of Contaminated Water in a Flooded Mine Shaft in Butte,Montana

The mines of Butte, Montana include over 16,000 km of abandoned underground workings, most of which are now filled with water. The feasibility of using the flooded mine workings as a source of irrigation water was investigated. The geochemistry and stable isotopic composition of water produced during a 59 day pumping test of the flooded Belmont Mine workings are described. Although static water in the pumping well initially met proposed irrigation standards, the quality deteriorated during pumping as water from deeper in the mine complex was drawn into the well. Stable isotopes show that this lower-quality water was not sourced from the nearby Berkeley Pit lake, but most likely came from the mine shaft itself. At steady state, the water pumped to the surface had pH 5.5–6.0 with high concentrations (in mg/L) of dissolved SO₄ (1,600), Fe (160), Mn (19), Zn (15), and As (1.8). Despite substantial bicarbonate alkalinity (≈150 mg/L as CaCO₃), the water became strongly acidic after equilibration with air due to oxidation and hydrolysis of Fe²⁺. Benchtop experiments were performed to test different strategies for low-cost chemical treatment prior to irrigation. The most feasible alternative involved aeration (to remove large quantities of dissolved CO₂) prior to pH adjustment to >9 with lime or NaOH. Further work is needed to see if such treatment is economically viable compared to the cost of using municipal water. Another concern is whether irrigation of grass with high TDS, high sulfate water is sustainable. The mine water reached a steady-state temperature of 19°C during pumping, and therefore the possibility of using this water to help heat nearby buildings should also be explored.     

Passive Treatment of Acidic Coal Mine Drainage: The Anna S Mine Passive Treatment Complex

The Anna S coal mine complex in Tioga County, PA, produces drainage with a pH of 2.8–3.6 containing 3–36 mg/L Al, 1–36 mg/L Fe, and 6–9 mg/L Mn. In 2003, the Babb Creek Watershed Association installed two systems that passively treat three discharges from the mine complex. Both systems contain four parallel vertical flow ponds followed by aerobic wetlands. The vertical flow ponds contain a total of 35,483 t of limestone and 4,913 m³ of organic substrate. During the last 6 years, the systems have treated an average of 1,971 L/min of flow to neutral pH with 135–146 mg/L of alkalinity (as CaCO₃), with less than 1 mg/L of Al and Fe, and 2–4 mg/L of Mn. The vertical flow ponds have generated alkalinity at rates of 32–53 g/m²/day as CaCO₃. No seasonal variation in treatment effectiveness has been observed, despite relatively harsh winter seasons. The total cost of the passive systems was $2.5 million (US). The 20 year projected unit treatment cost, including periodic replacement of the organic substrate, is $2.5 million (US). The 20 year projected unit treatment cost, including periodic replacement of the organic substrate, is 403–618 per t (as CaCO₃) of net alkalinity generated.     

Tracer Test in a Settling Pond: The Passive Mine Water Treatment Plant of the 1 B Mine Pool,Nova Scotia,Canada

In order to verify why the design criteria of the Neville Street well field of the 1 B mine pool passive treatment plant were not being met, four mine water tracer tests with uranine (Na-fluorescein) and rhodamine B were conducted in the system’s settling pond. Both tracers were injected at the pond’s aeration cascade during three separate tracer tests with varying flow conditions (54–158 L s⁻¹). In addition, oxygen saturation and iron concentrations were measured during the first two tests. The aeration cascade works properly; O₂ saturation reaches 81% after less than a second. However, the mean residence time in the settling pond was determined to be only 10–18 h. The plant operator installed five baffle sheets to increase the mean residence time in the settling pond. Tracer tests with uranine after the baffle sheets were installed revealed a new mean residence time of 35 h.     

Passive aerobic treatment of net-alkaline,iron-laden drainage from a flooded underground anthracite mine,Pennsylvania, USA

This report evaluates the results of a continuous 4.5-day laboratory aeration experiment and the first year of passive, aerobic treatment of abandoned mine drainage (AMD) from a typical flooded underground anthracite mine in eastern Pennsylvania, USA. During 1991–2006, the AMD source, locally known as the Otto Discharge, had flows from 20 to 270 L/s (median 92 L/s) and water quality that was consistently suboxic (median 0.9 mg/L O₂) and circumneutral (pH ≈ 6.0; net alkalinity >10) with moderate concentrations of dissolved iron and manganese and low concentrations of dissolved aluminum (medians of 11, 2.2, and <0.2 mg/L, respectively). In 2001, the laboratory aeration experiment demonstrated rapid oxidation of ferrous iron (Fe²⁺) without supplemental alkalinity; the initial Fe²⁺ concentration of 16.4 mg/L decreased to less than 0.5 mg/L within 24 h; pH values increased rapidly from 5.8 to 7.2, ultimately attaining a steady-state value of 7.5. The increased pH coincided with a rapid decrease in the partial pressure of carbon dioxide (PCO₂) from an initial value of 10^−1.1 atm to a steady-state value of 10^−3.1 atm. From these results, a staged aerobic treatment system was conceptualized consisting of a 2 m deep pond with innovative aeration and recirculation to promote rapid oxidation of Fe²⁺, two 0.3 m deep wetlands to facilitate iron solids removal, and a supplemental oxic limestone drain for dissolved manganese and trace-metal removal. The system was constructed, but without the aeration mechanism, and began operation in June 2005. During the first 12 months of operation, estimated detention times in the treatment system ranged from 9 to 38 h. However, in contrast with 80–100% removal of Fe²⁺ over similar elapsed times during the laboratory aeration experiment, the treatment system typically removed less than 35% of the influent Fe²⁺. Although concentrations of dissolved CO₂ decreased progressively within the treatment system, the PCO₂ values for treated effluent remained elevated (10^−2.4 to 10^−1.7 atm). The elevated PCO₂ maintained the pH within the system at values less than 7 and hence slowed the rate of Fe²⁺ oxidation compared to the aeration experiment. Kinetic models of Fe²⁺ oxidation that consider effects of pH and dissolved O₂ were incorporated in the geochemical computer program PHREEQC to evaluate the effects of detention time, pH, and other variables on Fe²⁺ oxidation and removal rates. These models and the laboratory aeration experiment indicate that performance of this and other aerobic wetlands for treatment of net-alkaline AMD could be improved by aggressive, continuous aeration in the initial stage to decrease PCO₂, increase pH, and accelerate Fe²⁺ oxidation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Alkalinity generation and metals retention in a successive alkalinity producing system

Alkalinity generation and metals retention were evaluated during the initial year of operation of a treatment wetland, consisting of four 185 m² inseries cells comprised of alternating vertical-flow anaerobic substrate wetlands (VFs) and surface-flow aerobic settling ponds (SFs). The substrate in the VFs consists of spent mushroom substrate (SMS) and limestone gravel, supplemented with hydrated fly ash in a 20∶10∶1 ratio by volume. Approximately 15±4 L/min of acid mine drainage (AMD) from an abandoned underground coal mine in southeastern Oklahoma, USA, was directed to the system in October 1998 (mean influent water quality: 660 mg L⁻¹ net acidity as CaCO₃ eq., pH 3.4, 215 mg L⁻¹ total Fe, 36 mg L⁻¹ Al, 14 mg L⁻¹ Mn, and 1000 mg L⁻¹ SO₄ ⁻²). Flow through the first VF resulted in substantial increases in alkalinity, decreased metal concentrations and circumneutral pH. 258±84 mg L⁻¹ of alkalinity was produced in the first VF by a combination of processes. Final discharge waters were net alkaline on all sampling dates (mean net alkalinity=136 mg L⁻¹). Total Fe and Al concentrations decreased significantly from 216±45 to 44±28 mg L⁻¹ and 36±6.9 to 1.29±4.4 mg L⁻¹, respectively. Manganese concentrations did not change significantly in the first two cells, but decreased significantly in the second two cells. Mean acidity removal rates in the first VF (51 g m⁻² day⁻¹) were similar to those previously reported.     

Iron Removal by a Passive System Treating Alkaline Coal Mine Drainage

The Marchand passive treatment system was constructed in 2006 for a 6,000 L/min discharge from an abandoned underground bituminous coal mine located in western Pennsylvania, USA. The system consists of six serially connected ponds followed by a large constructed wetland. Treatment performance was monitored between December 2006 and 2007. The system inflow was alkaline with pH 6.2, 337 mg/L CaCO₃ alkalinity, 74 mg/L Fe, 1 mg/L Mn, and <1 mg/L Al. The final discharge averaged pH 7.5, 214 mg/L CaCO₃ alkalinity, and 0.8 mg/L Fe. The settling ponds removed 84% of the Fe at an average rate of 26 g Fe m⁻² day⁻¹. The constructed wetland removed residual Fe at a rate of 4 g Fe m⁻² day⁻¹. Analyses of dissolved and particulate Fe fractions indicated that Fe removal was limited in the ponds by the rate of iron oxidation and in the wetland by the rate of particulate iron settling. The treatment effectiveness of the system did not substantially degrade during cold weather or at high flows. The system cost $1.3 million (2006) or $207 (US) per L/min of average flow. Annual maintenance and sampling costs are projected at $10,000 per year. The 25-year present value cost estimate (4% discount rate) is $1.45 million or $0.018 per 1,000 L of treated flow.     

The Combined Impact of Mine Drainage in the Ankobra River Basin,SW Ghana

This study assessed the combined effects of seven large-scale gold mines, one manganese mine, and scattered artisanal gold mining sites on the quality of water in the Ankobra Basin in a geologically complex terrain. Water samples from streams, boreholes, hand dug wells, and mine spoil were analysed. Scatter plots of trends among measured parameters were used to assess drainage quality and differential impacts. Drainage quality exhibits wide seasonal and spatial variations; the geology strongly influences the water chemistry. Areas with low pH (<5.5), and high sulphate ions and trace ions are suggestive of acid mine drainage while sites with high pH (>7.5), HCO₃ ⁻, subdued SO₄ ²⁻, and high trace ions are suggestive of sites where acid neutralization is effective. High metal sources are largely confined to mining operations in the Birimian formation with ores containing more than 2% sulphides. However, restricted high metal regimes are observed in drainage in the Tarkwaian formation associated with scatted sulphide-bearing dolerite dykes in the operational areas of the Tarkwa and Damang mines. Earlier studies disputed sulphides in the Tarkwaian formation until recently, when acid-generating dykes were discovered in operating pits. The most degraded waters emanate from the Prestea and Iduapriem mines, and to a lesser extent, the Nsuta mine sites, all mining Birimian rocks. The Tarkwa mine showed minimal metal loading. Zn, Cu, Ni, As, SO₄, pH, and specific conductance are essential and adequate parameters in determining if acid drainage is taking place at these sites, and are recommended for routine mine environmental monitoring.     

Extraction of hydrogen cyanide from waste solutions of cyaniding circuit for sulfide flotation concentrates

The process for extraction of hydrogen cyanide to decontaminate solutions produced at cyaniding of sulfide flotation concentrates is developed. The centrifugal-bubbling apparatus is employed as a reactor. The regularities of HCN formation in an acid medium are established in investigation into kinetics of SCN⁻ thiocyanate oxidation by hydrogen peroxide H₂O₂ in presence of Fe²⁺, Fe³⁺ and pH ≤ 3.5. In the process proposed the evolved HCN is adsorbed by NaOH solution and returned to the circuit of leaching of gold and silver as NaCN, and the waste cyaniding solution is discharged into a waste dump, where it is mixed with industrial water to be utilized to transport flotation tailings. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 98–105, January–February, 2009.     

Impact of lead/zinc ore mining on groundwater quality in Trzebionka mine (southern Poland)

The intensive mining activity carried out by “Trzebionka” zinc-lead mine causes changes in the hydrodynamic regime of the triassic aquifer as well as essential changes in the chemical composition of the groundwater. The mine water, in comparison with groundwaters collected directly from fractures and Karstic channels and with groundwaters pumped out from wells situated in Chrzanow region, is characterized by higher contents of almost all major dissolved constituents as, well as, many trace elements. Hydrogeochemical background of triassic carbonate series aquifer has been elaborated. Largest anomalies in extent of almost all elements have occurred in area of the “Trzebionka” mine. In this water general trend of increase of pH, total dissolved solids and SO₄ ²⁻ concentration with simultaneous trends of decrease of Zn²⁺ and Pb²⁺ concentrations have been noticed. Water pumped out from the mine in spite of its low quality, is utilized in about 80% as potable water after undergoing complicated treatment.     

Research on mechanism of groundwater pollution from mine water in abandoned mines

In order to understand the mechanism and regularity of the groundwater contamination from mine water of abandoned mines, experiments were conducted on an abandoned coal mine in Fuxin, a representative city with lots of mine water in northeast China. The groundwater pollution from different contaminants of coal-mining voids (total hardness, SO₄²⁻, Cl⁻ and total Fe) and pollution factors transportation situation in the coal rock were simulated by soil column experiment under the conditions of mine water leaching and main water leaching (similar to rainwater leaching), and the water-rock interaction mechanism was discussed during mine water infiltration through saturated coal rock by application of principle of mass conservation, based on physical properties of coal rock, as well as monitored chemical composition. The results show that, compared with the clear water leaching process, trends of change in pollutant concentrations presented different characteristics in the mine water leaching process. Groundwater is contaminated by the water rock interactions such as migration & accumulation, adsorption & transformation, dissolution & desorption and ion exchange during the mine water permeation. The experiments also suggest that at first dissolution rate of some kinds of dissoluble salts is high, but it decreases with leaching time, even to zero during both the mine water leaching and main water leaching. Supported by the National Natural Science Foundation of China(50434020, 50374042), Science & Technology Found of Liaoning Province (20022155); Specialized Research Fund for the Doctoral Program of Higher Education (20040147003)     

Hydrologic Characteristics of a 35-Year-Old Underground Mine Pool

The hydrology of a 14,672 acre (5,940 ha) coal mine complex in Cambria County, Pennsylvania, USA, was characterized. This flooded mine complex was evaluated to determine the potential of using the mine water for downstream agricultural purposes in an adjoining watershed. The hydrologic characteristics of the mine complex dictate the amounts and rates of mine water discharge that are available. The original coal extraction rate was known to be 63%, but post-mining subsidence has reduced the effective porosity to a mean of 11%. Thus, the mine stores considerably less mine water than was anticipated, a priori. The mine receives vertical recharge averaging 0.27 gallons (gal) per minute per acre (24.6 L/s per ha), which is equivalent to 11.6% of the mean precipitation. The recharge rate fluctuates about the mean by ±22%. The low storage capacity combined with the moderately low recharge rates allow the large mine complex to be rapidly drawn down when the pumping rate is raised from 4.68 to 9.36 × 10⁶ gal (17.7–35.4 × 10⁶ L/day). Conversely, the mine refills rapidly, up to 0.8 ft (0.24 m) or spatially 33 acres (13.4 ha) per day, once the pumping rate is reduced back to 4.68 × 10⁶ gal/day (17.7 × 10⁶ L/day), which is well below the total recharge rate. In addition to vertical recharge, 6.3–40.4% of the inflow into the mine pool complex occurs from coal barrier seepage from an adjacent flooded mine. The seepage rates are relatively constant and are estimated to be insensitive to changes in head up to 50 ft (15.2 m).     

The Effects of Sulfate on the Physical and Chemical Properties of Actively Treated Acid Mine Drainage Floc

It is important to consider floc properties when designing acid mine drainage treatment (AMD) systems. Relatively few studies have evaluated the effects of neutralizing base, neutralization pH, and sulfate in solution on floc properties in active treatment systems. We used NaOH and NH₄OH as neutralizing bases, 0:1, 2.5:1, and 5:1 SO₄:Fe molar ratios, and neutralization pH of 7, 8, and 9 in laboratory studies. Neutralizing cation, sulfate content, and neutralization pH had significant effects on floc mass and volume, but SO₄:Fe ratio was the most important parameter. Settled floc volumes were slightly larger in the sodium system. Floc mass and volume both decreased with increasing pH. Floc generated in the presence of sulfate required significantly more time to reach a total suspended solids discharge limit of 70 mg L⁻¹, had slower initial settling rates, and smaller settled volumes than floc generated without sulfate. The systems we studied were less complicated than actual AMD, but understanding the effects of sulfate, neutralizing cation, and neutralization pH on floc properties may help to design more efficient treatment systems. Choosing the appropriate treatment chemical and designing adquate pond sizes will ultimately increase treatment efficiency and improve stream water quality.     

Alkalinity Generation in a Novel Multi-stage High-strength Acid Mine Drainage and Municipal Wastewater Passive Co-treatment System

Passive co-treatment of high-strength acid mine drainage (AMD) and municipal wastewater (MWW) was examined in a laboratory-scale, four-stage continuous flow reactor system with a total residence time of 6.6 d. Synthetic AMD of pH 2.60 and an acidity of 1,870 mg/L (as CaCO₃) was mixed at a 1:2 ratio with raw MWW (pH 7.67, 288 mg/L alkalinity (as CaCO₃), and 265 mg/L BOD₅) from the City of Norman, Oklahoma and introduced into the system. Alkalinity generated by limestone dissolution and bacterial SO₄ ²⁻ reduction (BSR) processes was sufficient to support various metal removal processes and produce an effluent with circumneutral pH (6.98) and a net alkalinity of 10.4 mg/L (as CaCO₃). Alkalinity generation from limestone dissolution was comparable with conventional AMD passive treatment systems. BSR proceeded at a relatively high rate (0.56 mol/m³ day) despite inhibitory pH and metals concentrations. Results indicate that the diverse electron donors in the MWW may be as suitable for BSR and their supporting microbial communities as commonly used substrates, presenting an opportunity to use a common waste as a resource for passive treatment.     

Detoxification of Cyanide in a Gold Processing Plant Tailings Water Using Calcium and Sodium Hypochlorite

In laboratory experiments, cyanide in waste water from the Muteh gold mine in Iran was oxidized by sodium and calcium hypochlorite to cyanate (CNO⁻), which is 1,000 times less environmentally hazardous than cyanide. Experiments were conducted using waste water containing 270 mg/L cyanide over a pH range of 6–13 and temperatures between 25 and 50°C. Cyanide was removed completely at a pH of 12.3 at the higher temperatures. The experimental results were simulated in Visual MINTEQ 2003 EPA software using all of the components in the waste water. The model readily predicted most of the chemical reactions in the experiments and explained the mechanism of complexation of cyanide with metals, free cyanide, and cyanide acid formation. An erratum to this article can be found at