Comparison of limestone,dolomite and fly ash as pre-treatment agents for acid mine drainage

The physical, chemical and biological nature of Vaal Dam water, the main source of water in Gauteng, South Africa, is often affected by underground water pollution (acid mine water) and industrial effluents. The ecological significance and detrimental effects necessitate investigations into treating the water prior to discharge into public streams. Although several acid mine water treatment techniques and methods exist, they all have certain disadvantages. Lime treatment is the most common approach. In this investigation, limestone, dolomite and fly ash were selected as pre-treatment agents based on their low cost. Simulated acid mine water containing these agents was tested using a Jar Test apparatus. Samples were analyzed before and after treatment for pH, ferrous, ferric, calcium, magnesium and sulphate ions. The study demonstrated that the quality of the water improved with an increase in the amount and surface area of the raw material dosed and an increase in contact time. It was also influenced by the chemical composition of the acid mine water and aeration. Chemical cost savings of 38% are achieved when lime is replaced with limestone, and cost savings of 23% and 48% can be accomplished when limestone is substituted with dolomite and fly ash respectively. This could result in significant savings to the gold and coal mining industries, and could lead to a mutual benefit/gain between industrialists/polluters and the public.     

Neutralizing Coal Mine Effluent with Limestone to Decrease Metals and Sulphate Concentrations

Abstract.   This paper describes pilot scale tests of a novel process for the neutralisation of acidic mine water. Leachate from a waste coal dump was neutralised with limestone, and iron, aluminium, and sulphate were removed. Specific aspects studied were: the process configuration; the rates of iron oxidation, limestone neutralisation, and gypsum crystallisation; the chemical composition of the effluents before and after treatment; the efficiency of limestone utilisation; and the sludge solids content. The acidity was decreased from 12,000 to 300 mg/L (as CaCO₃), sulphate from 15,000 to 2,600 mg/L, iron from 5,000 to 10 mg/L, aluminium from 100 to 5 mg/L, while the pH increased from 2.2 to 7.0. Reaction times of 2.0 and 4.5 h were required under continuous and batch operations respectively for the removal of 4 g/L Fe (II). The iron oxidation rate was found to be a function of the Fe (II), hydroxide, oxygen, and suspended solids (SS) concentrations. The optimum SS concentration for iron oxidation in a fluidised-bed reactor was 190 g/L. Up-flow velocity had no influence on the rate of iron oxidation in the range 5 to 45 m/h. Sludge with a high solids content of 55% (m/v) was produced. This is high compared to the typical 20% achieved with the high density sludge process using lime. It was determined that neutralisation costs could be reduced significantly with an integrated iron oxidation and limestone neutralisation process because limestone is less expensive than lime, and a high-solids-content sludge is produced. Full scale implementation followed this study.     

铀堆浸废水中和沉渣减容与改性方法研究

在传统石灰中和处理法的基础上，提出了酸法难浸废水用“石灰石-石灰两步中和-沉渣循环”的流程进行处理。废水先与廉价的石灰石接触反应，使废水中的强酸中和并使铁、铝等金属离子在较低pH值下形成氢氧化物，再用石灰乳进一步中和到要求的pH。生成的沉淀物（沉渣）在过程中不断循环。该方法与一次石灰中和法相比，试剂费用节省1／3，沉渣生成量（以体积计）减少2／3，并且沉渣的过滤和沉降性能也有所改善。本工作还对沉渣减容与改性的机理进行了研究探讨。     

矿山水污染与酸性矿井水处理

我国矿产资源的不断开采,给矿区带来的不仅是能源与财富,还有环境污染。其中矿山水污染是比较严重的,文章主要介绍了我国矿山水污染的现状与特点,对水污染最严重之一的酸性矿井水进行了重点阐述,并介绍了石灰石中和法、石灰中和法和生物处理法处理酸性矿井水的原理。     

单家村煤矿八采区奥灰突水机理研究

本文以单家村煤矿八采区奥灰滞后突水实例为主,分析了大小组合断层共同作用形成地垒、造成奥灰上抬出露于巷道,引发滞后出水的突水原因;结合奥灰水文观测孔长期、动态观测数据,分析得出了八采区奥灰含水层特征,最终研究得出地质资料不准确导致采掘活动直接揭露奥灰引发突水、断层抬升奥灰含水层,导致3煤层与下部含水层之间隔水层厚度不足引发奥灰突水、采掘活动引起断层活化,改变其导水性引发奥灰滞后突水三条奥灰突水机理。研究成果填补了兖州煤田区域巷道掘进过程中断层导致奥灰滞后突水方面的空白,为八采区水害防治工作提供了技术依据,也为同类受水害威胁的矿井提供了重要借鉴。     

Reclamation of Abandoned Coal Mine Waste in Korea using Lime Cake By-Products

Abstract.  There are hundreds of abandoned coal mines in Korea's steep mountain valleys. Enormous amounts of coal waste from these mines were dumped on the slopes, contaminating streams with sediment and acid mine drainage. A limestone slurry by-product (lime cake), which is produced during the manufacture of soda ash, was investigated for its potential use in reclaiming the coal waste. The lime cake is fine grained, has low hydraulic conductivities (10^-8 to 10^-9 cm sec^-1), high pH, high electrical conductivity, and trace amounts of heavy metals. A field experiment was conducted; each plot was 20 x 5 m in size on a 56% slope. Treatments included a control (waste only), lime (CaCO₃), and lime cake. The lime requirement (LR) of the coal waste to pH 7.0 was determined; treatments consisted of adding 25, 50, and 100% of the LR. The lime cake and lime were applied either as a layer between the coal waste and topsoil or mixed into the topsoil and waste. Each plot was hydroseeded with grasses, and planted with trees. In each plot, soils, surface runoff, and subsurface water were collected and analyzed, and plant cover was measured. Lime cake treatments increased the pH of the coal waste from 3.5 to 6, and neutralized the pH of the runoff and leachate of the coal waste from 4.3 to 6.7. Moreover, the surface cover of seeded species was significantly increased; sufficient acidity in the coal waste was neutralized in the 25% LR plots to allow seed germination.     

Downflow Limestone Beds for Treatment of Net-Acidic, Oxic, Iron-Laden Drainage from a Flooded Anthracite Mine, Pennsylvania, USA: 2. Laboratory Evaluation

Acidic mine drainage (AMD) containing elevated concentrations of dissolved iron and other metals can be neutralized to varying degrees by reactions with limestone in passive treatment systems. We evaluated the chemical and mineralogical characteristics and the effectiveness of calcitic and dolomitic limestone for the neutralization of net-acidic, oxic, iron-laden AMD from a flooded anthracite mine. The calcitic limestone, with CaCO₃ and MgCO₃ contents of 99.8 and <0.1 wt%, respectively, and the dolomitic limestone, with CaCO₃ and MgCO₃ contents of 60.3 and 40.2 wt%, were used to construct a downflow treatment system in 2003 at the Bell Mine, a large source of AMD and baseflow to the Schuylkill River in the Southern Anthracite Coalfield, in east-central Pennsylvania. In the winter of 2002–2003, laboratory neutralization-rate experiments evaluated the evolution of effluent quality during 2 weeks of continuous contact between AMD from the Bell Mine and the crushed calcitic or dolomitic limestone in closed, collapsible containers (cubitainers). The cubitainer tests showed that: (1) net-alkaline effluent could be achieved with detention times greater than 3 h, (2) effluent alkalinities and associated dissolution rates were equivalent for uncoated and Fe(OH)₃-coated calcitic limestone, and (3) effluent alkalinities and associated dissolution rates for dolomitic limestone were about half those for calcitic limestone. The dissolution rate data for the cubitainer tests were used with data on the volume of effuent and surface area of limestone in the treatment system at the Bell Mine to evaluate the water-quality data for the first 1.5 years of operation of the treatment system. These rate models supported the interpretation of field results and indicated that treatment benefits were derived mainly from the dissolution of calcitic limestone, despite a greater quantity of dolomitic limestone within the treatment system. The dissolution-rate models were extrapolated on a decadal scale to indicate the expected decreases in the mass of limestone and associated alkalinities resulting from the long-term reaction of AMD with the treatment substrate. The models indicated the calcitic limestone would need to be replenished approaching the 5-year anniversary of treatment operations to maintain net-alkaline effluent quality.     

新疆某选厂选矿废水处理及回用试验研究

研究了新疆某选厂选矿废水的处理方法,并对处理后的废水进行了选矿验证试验。确定采用"化学氧化还原法+中和沉淀法+活性炭吸附法"联合处理选矿废水。结果表明,当初始废水pH值在2左右,FeSO4·7H2O投加量为理论值,石灰乳调节溶液pH值于7～8,活性炭的投加量为0.3g/L时,废水中重金属以及COD的去除率最高。处理后的选矿废水中Cr、Cu、Pb以及COD的含量均低于国家污水排放标准,选矿验证试验结果表明,处理后的废水可循环利用。     

采煤坑水处理方法研究

采煤坑酸性水的治理是国内外攻关的重要课题.介绍了采煤坑水酸性起因,并对酸性采煤坑水的处理方法进行了试验研究.同时也介绍了处理酸性水的流程.阐述通过添加碳酸钙和石灰,可使酸性采煤坑水得到很好治理.该工艺既能有效地保护环境,又可以使水资源得到合理利用,还可以综合回收矿产资源,意义重大.     

加药方式对铜萃余液中和处理的影响

本文验证一段石灰中和工艺,通过调整加药方式、药剂混配、用水类型、加药次数等方式对铜萃余液的pH值的影响,初步对各种中和工艺下的中和渣产量及药剂成本进行分析。结果表明,湿法加药方式比干法的加药方法对铜萃余液的中和效果更好。与现有中和工艺比较,采用石灰乳分两段中和工艺具有药剂成本低和时间短特点,而石灰石-石灰两段中和工艺属于石灰石药剂耗量易控制,理论渣量较小,综合药剂成本较低。      

并流蓄热式双膛竖窑生产活性石灰的探讨

目前国外用于煅烧细粒石灰的竖窑主要窑型为瑞士麦尔兹窑炉公司设计建造的并流蓄热式细粒石灰双膛竖窑,该窑用于煅烧20～40mm小粒度石灰石,可以充分利用目前我国石灰石矿许多丢弃的细粒石灰石,为我国石灰石矿的资源综合利用开辟了新途径。煅烧好的石灰石用于转炉炼钢,可以降低石灰石的消耗量,提高废钢的加入量,具有显著的经济效益。     

Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca²⁺. This resulted in increased removal of sulphate as CaSO₄·2H₂O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO₄·2H₂O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.     

Limestone Drain Design Parameters for Acid Rock Drainage Mitigation

Abstract.  Limestone drains are an integral component of some of the most efficacious passive systems for the treatment of acid rock drainage (ARD). A critical design parameter for a limestone drain is the mass of limestone that will be required for effective treatment. This in turn depends on the flow rate, limestone dissolution rate, and associated hydraulic detention time necessary to achieve a certain effluent alkalinity for a given design life. Rates of alkalinity generation and limestone dissolution, and the quality of the limestone in terms of weight fraction of CaCO₃ and percentage CaCO₃ available must be known to determine the required mass of limestone. These parameters were experimentally determined for a natural and synthetic suite of ARD waters. The experimental results show that the empirical change in the alkalinity over time cannot simply be modeled as a first-order process. During the initial stage, the concentration increase is extremely fast, giving a linear and steep rise in the alkalinity. Alkalinity concentrations peaked at elapsed times of 90 to 180 minutes and then declined to a nearly constant value. The decline in alkalinity corresponds with a decline in concentrations of dissolved iron and aluminum, implying that the consumption of alkalinity by the hydrolysis of these metals is faster than the rate of alkalinity production by the dissolution of limestone, so that the reaction appears zero order in the early stage and pseudo-first order later. Because the changes in concentration were complex, considerable uncertainty exists in the rate constants for estimating alkalinity concentration. This causes problems in design equations based solely on a limestone dissolution rate that is estimated from alkalinity generation rates. A more applicable design procedure, combining the kinetics of alkalinity production and consumption with the hydraulics and chemical equilibrium of the system, is illustrated. Research was conducted while the first and third authors were with Ecology and Environment, Inc, Dallas, TX, USA;     

A feasibility study of an integrated process for solid waste utilization

ABSTRACT

Pre-combustion coal cleaning and post-combustion flue gas desulfunzation (FGD) using lime or limestone are often used to reduce sulfur dioxide (SO₂) emission from high-sulfur coal combustion. These processes generate voluminous pyrite and gypsum solid wastes that are usually landfilled, occupying thousands of acres of land and creating serious land and water pollution problems due to the release of acids and toxic substances. An integrated thermochemical process has been developed for the combined utilization of gypsum and pyrite wastes by converting them into useful products including lime, sulfur, and direct reduced iron (DRI). The thermochemical reactions involved in the process were studied using thermogravimetric analysis (TGA) for reaction kinetics and X-ray diffraction (XRD) technique for product characterization. Reaction rate constant and activation energy were determined for individual reactions. Process variables studied included reaction temperature, time, reactant composition, and the purity of reactants.     

Groundwater Source Discrimination and Proportion Determination of Mine Inflow Using Ion Analyses: A Case Study from the Longmen Coal Mine,Henan Province,China

Complex hydrogeological conditions in China’s coal mines have contributed to frequent mine water disasters. A simple and effective method to determine water inflow sources and paths is therefore essential. The Longmen Mine, located in Henan Province, in central China was used as a case study. A Piper diagram and cluster analysis were used to screen the characteristic values of 18 water samples from potential aquifers. A comprehensive fuzzy evaluation of the groundwater ions was carried out to determine the main source of the total mine inflow. Then, based on conservation of ionic masses, a matrix function was established to calculate the groundwater recharge composition. Finally, using measured water inflows for the Cambrian limestone aquifer, the calculated and observed results were compared. The results showed that the Carboniferous Taiyuan Formation limestone aquifer (the L₇ limestone aquifer) accounts for 60.8% of the total mine inflow, while the Cambrian limestone and roof sandstone aquifers account for 34.8 and 4.4% of the inflow, respectively. The normal mine inflow totals about 19,200 m³/day, of which 6,840 m³/day is from the Cambrian limestone aquifer. This agrees well with the calculated value of 6,720 m³/day. Thus, the method is feasible and reliable.     

Treatment of acid mine water by use of heavy metal precipitation and ion exchange

Acid mine water from a South African gold mine was characterised and treated by the precipitation of heavy metals with lime and sulphides, followed by ion exchange. The novelty of the proposed process lies in the use of carrier magnetic materials for more effective separation of water and solids, as well as the oxidation pretreatment that is also used to sterilize the water. The process can generate very, pure water from acid mine water with a great flexibility and an acceptable cost. The oxidation and precipitation of heavy metals with lime and subsequent sulphide-carrier magnetic separation appeared to be particularly suitable for the removal of heavy metal ions from the effluent of the particular gold mine that was investigated. The cation exchange resin IR120 can be used to reduce the salinity of the effluent of mine water after removal of heavy metals by precipitation. Low cost sulphuric acid can be used as the cation resin regenerator. The anion exchange resin A375 could reduce the anions (sulphate, chloride, bromide and fluoride) to acceptably low levels in the mine water after precipitation of heavy metals. A combination of sodium hydroxide and saturated lime solution can be used as the anion resin regenerator. A mixture of acidic gypsum from the cation elution section and alkaline gypsum from the anion elution section could generate high quality gypsum as byproduct, which could be sold as a valuable raw material to the gypsum industry, to offset process cost. Although these experiments were conducted on the acid mine water of a specific mine, the process could be extended to other mine waters contaminated with heavy metals and high salinities.     

石灰絮凝法去除矿坑废水中锰离子的研究

采用石灰絮凝法对福建潘洛铁矿矿坑废水中Mn离子进行了去除试验研究。石灰用量为150 g/m³, 阴离子PAM用量为0.5 g/m³, 98%硫酸用量为20 g/m³, 处理后出水达到GB8978-1996一级排放标准。通过对石灰沉淀除锰机理分析, 锰从废水中沉淀析出适宜的pH值应大于8.5, 而要使处理后废水锰含量达标(Mn含量低于2.0 mg/L), 则废水pH值应控制在10.0以上。实验室试验研究结果为后续的工程设计提供了较为合理的工艺流程。     

Removal of trace elements from acid mine drainage

The mine drainages in some coal mines of North Eastern India, are found to be highly acidic and contain trace elements which are highly undesirable for drinking purposes. This water requires neutralization together with trace metal removal prior to its supply to the public. This paper describes the results of a study conducted to determine the ability of lime neutralization to remove inorganic trace elements from acid mine drainage under different operating conditions. The specified trace elements were arsenic, cadmium, chromium, copper, mercury, lead, zinc, manganese, aluminium, iron and nickel etc. Results of this study indicate that treatment by lime neutralization was very effective in removing these trace metals from acid mine drainage.     

Evaluation of municipal solid waste (MSW) compost as a soil amendment for acidic,metalliferous mine tailings

ABSTRACT

Four 0·5 ha plots were established on freshly dried tailings of INCO Ltd. near Sudbury, Ontario, Canada and received the following treatments: 1) 125 t/ha Municipal Solid Waste (MSW) compost, 2) 250 t/ha MSW compost, 3) INCO's standard application of crushed limestone, fertilizer and hay mulch and 4) control - no application of compost. Application of compost at a rate of 250 t/ha yielded the same increase in tailings pH (from 2·80 to 4·65) as that achieved with the typical INCO application of 40 t lime/ha. The INCO treatment with lime and fertilizer resulted in no initial input of organic matter; whereas, a 250 t/ha application of compost increased organic content by 8·3%. Moisture retention in tailings at the two compost-treated plots was significantly higher (26%) than that of the INCO treated plots (<10%). Application of lime as part of the INCO treatment reduced levels of water soluble Cu and Ni from 22·8 pgCu/g to 0·4 pgCu/g and from 35·5 pgNi/g to 5·2 ngNi/g. Similar reductions in water soluble copper and nickel in tailings were achieved with the 250 t/ha application of compost. It was concluded that tailings amelioration with MSW compost is superior to the INCO treatment because it more rapidly increases pH, moisture content and organic content, and reduces concentrations of water soluble (plant available) Cu and Ni.     

Influent Water Quality Affects Performance of Passive Treatment Systems for Acid Mine Drainage

Passive treatment of acid mine drainage (AMD) relies on biological, geochemical, and gravitational processes to neutralize acidity. Published design guidelines use sizing ‘rules of thumb’ based on AMD loadings at design flows. Using average performance data for 82 treatment systems, we used regression modeling to investigate the influence of influent net acidity and water loading on alkalinity generation by five treatment system types. Alkalinity generation increases with influent net acidity loading for all system types. Influent net acidity loading can be deconstructed into concentration and water loading components. In bivariate models, water loading was a predictor of alkalinity generation for all five system types but net acidity was significant only for vertical flow systems (VFs). In multivariate models using both components as performance predictors, both influenced alkalinity generation. These relationships were strongest for anaerobic wetlands (AWs), VFs, and open limestone channels; anoxic limestone drains and limestone leach beds demonstrated these influences less consistently. These results reflect the geochemical mechanisms governing the performance of limestone-based passive treatment system: solubility of limestone decreases as dissolved reaction products and pH increase.