Acid-forming Materials Research Articles

Managing and Reforesting Degraded Post-Mining Landscape in Indonesia: A Review

Tropical forests are among the most diverse ecosystems in the world, completed by huge biodiversity. An expansion in natural resource extraction through open-pit mining activities leads to increasing land and tropical forest degradation. Proper science-based practices are needed as an effort to reclaim their function. This paper summarizes the existing practice of coal mining, covering the regulatory aspects and their reclamation obligations, the practices of coal mining from various sites with different land characteristics, and the reclamation efforts of the post-mining landscapes in Indonesia. The regulations issued accommodate the difference between mining land inside the forest area and outside the forest area, especially in the aspect of the permit authority and in evaluating the success rate of reclamation. In coal-mining practices, this paper describes starting from land clearing activities and followed by storing soil layers and overburden materials. In this step, proper handling of potentially acid-forming materials is crucial to prevent acid mine drainage. At the reclamation stage, this paper sequentially presents research results and the field applications in rearranging the overburden and soil materials, controlling acid mine drainage and erosion, and managing the drainage system, settling ponds, and pit lakes. Many efforts to reclaim post-coal-mining lands and their success rate have been reported and highlighted. Several success stories describe that post-coal-mining lands can be returned to forests that provide ecosystem services and goods. A set of science-based best management practices for post-coal-mine reforestation is needed to develop to promote the success of forest reclamation and restoration in post-coal-mining lands through the planting of high-value hardwood trees, increasing trees’ survival rates and growth, and accelerating the establishment of forest habitat through the application of proper tree planting technique. The monitoring and evaluation aspect is also crucial, as corrective action may be taken considering the different success rates for different site characteristics.

Assessing the acidic potential of waste rock in the Akara gold mine, Thailand

Acid mine drainage (AMD) is the environmental issue that generates the greatest public concern regarding the mining industry. Thus, characterization of mine waste rock according to acid generation potential is necessary for mining operations to ensure proper waste rock storage and to avoid future adverse environmental effects. Therefore, this study was conducted to estimate the potential of AMD generation in the largest operating gold mine in Thailand by using acid base accounting and net acid generation tests. Representative samples of six types of waste rock classified by mining geologists for mineral processing and waste dumping were collected for this study: volcanic clastic, porphyritic andesite, andesite, silicified tuff, silicified lapilli tuff, and sheared tuff. Under various conditions, experimental results indicate that only silicified lapilli tuff and shear tuff are potentially acid-forming materials. The results indicate that AMD generation may possibly occur a long time after mine closure due to the lag time of the dissolution of acid-neutralizing sources. Acidic generation from some waste rocks may occur in the future based on environmental conditions, particularly the oxidation of sulphide minerals by the combination of oxygen and water. Therefore, a proper design for waste rock dumping and storage is necessary to reduce the risk of AMD generation in future. It is advisable to install a surface management system to control the overland flow direction away from the waste dump area and tailing storage facility and to install a second water storage pond next to the main storage pond to store the spilled water during storms and the rainy season. A water quality monitoring plan that focuses on disturbed areas such as water storage ponds and mine pits should be put in place.

Cut‐off Net Acid Generation pH in Predicting Acid‐Forming Potential in Mine Spoils

Acidification of mine wastes can lead to a series of environmental problems, such as acid drainage, heavy metal mobilization, and ecosystem degradation. Prediction of acid-forming potential is one of the key steps in management of sulfide-bearing mine wastes. In this paper, the acid-forming potential of 180 mine waste samples collected from 17 mine sites in China were studied using a net acid generation (NAG) method. The samples contained different contents of total sulfur (ranging from 0.6 to 200 g kg(-1)), pyritic sulfur (ranging from 0 to 100 g kg(-1)), and acid neutralization capacity (ANC, ranging from -41 to 274 kg H2SO4 t(-1)). Samples with high acid-forming potential are generally due to their high sulfur content or low acid neutralization capacity. After the samples were oxidized by H2O2, the amounts of acid generation and the final NAG pH were measured. Results indicated that the final NAG pH gave a well-defined demarcation between acid-forming and non-acid-forming materials. Samples with final NAG pH >or= 5 could be classified as non-acid-forming materials, while those with NAG pH <or= 2.5 could be classified as moderate to strong acid-forming materials. Materials with NAG pH > 2.5, but < 5, had low risk of being acid-forming. The confirmation of cut-off NAG pH will be used as a rapid and cost-effective operational monitoring tool for the in-pit prediction of acid-forming potential of mine wastes and classification of waste types.

English

Appalachian coal processing wastes are typically acid forming with potential acidities in Virginia ranging from an average of 12 Mg CCE demand/1000 Mg waste up to > 50 Mg/1000 Mg where higher sulfur coal seams are cleaned. Direct seeding of these materials is further complicated by high rock fragment content, low water-holding capacity, and high summer surface soil temperatures. In Virginia, conventional revegetation protocols established by the Virginia Division of Mined Land Reclamation (DMLR) in the early 1980's required the return of 1.2 m of soil cover over all actively permitted coal wastes. Unfortunately, most active piles at the time had no available topsoil reserves, so the only alternative was to disturb adjacent properties via blasting to generate spoil derived topsoil substitutes. Between 1982 and 1990, we investigated a number of direct seeding and reduced topsoil cover alternatives in an effort to determine the optimal combination of soil amendments and cover soil thickness for the successful revegetation of varying coal waste acidity conditions. The centerpiece of this research effort was a series of topsoil wedge experiments established over three different coal waste materials where cover soil depth was varied from 0 to 125 cm, with and without lime (15 to 25 Mg/ha) at the soil/coal waste contact. Multi-year vegetation and soil sampling results indicated that a minimum of 45 to 75 cm of cover soil was required over highly acid-forming refuse (47 Mg CCE demand/1000 Mg), with the shallower depth sufficient when a lime layer was applied at the contact zone. Over moderately acid-forming materials (15 to 35 Mg CCE /1000 Mg), as little as 25 cm of cover soil was adequate as long as lime was added to the soil/waste contact zone. Coal waste materials that are < 15 Mg CCE/1000 Mg net acid forming can be direct seeded if high P applications are coupled with heavy mulch or organic amendments, especially when the fill faces are not south-facing. These results were implemented into permit review and oversight by Virginia DMLR in the early 1990's and over the past 15 years, a wide range of active coal waste piles have been successfully revegetated with soil covers of 50 cm or less.

English

Prevention of acid mine drainage (AMD) at surface coal mines in the Appalachian region relies greatly on minimizing ground-water contact with acid- forming materials and maximizing ground-water contact with alkalinity-yielding materials. Acid-forming materials (AFMs) are often selectively handled to minimize or prevent contact with ground water. Controlling ground-water contact with acidic- or alkaline materials depends on accurate forecasting of the level and range of fluctuation of the post-mining water table and preferred ground water flow paths within the backfill. Physical measurements and aquifer testing of more than 120 wells from 18 reclaimed mines in Kentucky, Ohio, Pennsylvania and West Virginia have improved forecasting of the post-mining ground-water flow system. Flow regime influencing factors include spoil lithology and particle size, age of reclamation, spoil thickness, distance to the final highwall, and pit floor dip angle and direction. Hydraulic conductivity (K) exhibits a broad range of 7 orders of magnitude about a mean K of 1.69 x 10 -5 meters/second. Spoil aquifer saturated thickness is related to the thickness of the spoil, spoil lithology, dip of the pit floor and distance to the highwall. Saturated spoil thickness has a 99% confidence interval of 1.86 to 3.97 meters (m) about a mean of 2.91 m. Spoil saturated zone averages 20% of the total thickness.

Predictability of surface mine spoil hydrologic properties in the Appalachian Plateau.

Prevention of acid mine drainage at surface coal mines in the Appalachian region relies to an extent on minimizing ground water contact with acid-forming materials, and maximizing ground water contact with alkalinity-yielding materials. Acid-forming materials are often selectively handled to minimize or prevent contact with ground water. Controlling ground water contact with acidic or alkaline materials depends on forecasting the level and range of fluctuation of the postmining water table within the mine backfill. Physical measurements and aquifer testing of more than 120 wells from 18 reclaimed mines in Kentucky, Ohio, Pennsylvania, and West Virginia have led to improved forecasting of the postmining ground water system. Factors that influence the ground water regime include spoil lithology and particle size, age of reclamation, spoil thickness, distance from the final highwall, and pit floor dip angle and direction. Spoil hydraulic conductivity (K) exhibits a 95% confidence interval range of six orders of magnitude about a mean K of 1.7 x 10(-5) m/sec. Spoil aquifer saturated thickness is related to the overall thickness of the spoil, the lithology of the spoil, dip of the pit floor, and distance to the highwall. Saturated spoil thickness has a 95% confidence interval of 2.2 to 3.6 m about the mean of 2.9 m. The predicted saturated zone averages 19% of the total spoil thickness.

A CONCISE METHOD FOR MINE SOILS ANALYSIS

A large number of abandoned hard rock mines exist in Colorado and other mountain west states, many on public property. Public pressure and resulting policy changes have become a driving force in the reclamation of these sites. Two of the key reclamation issues for these sites in the occurrence of acid forming materials (AFMs) in mine soils, and acid mine drainage (AMD) issuing from mine audits. An AMD treatment system design project for the Forest Queen mine in Colorado's San Juan mountains raised the need for a simple, useable method for analysis of mine land soils, both for suitability as a construction material, and to determine the AFM content and potential for acid release. The authors have developed a simple, stepwise, go - no go test for the analysis of mine soils. Samples were collected from a variety of sites in the Silverton, CO area, and subjected to three tiers of tests including: paste pH, Eh, and 10% HCl fizz test; then total digestion in HNO{sub 3}/HCl, neutralization potential, exposure to meteoric water, and toxicity content leaching procedure (TCLP). All elemental analyses were performed with an inductively-coupled plasma (ICP) spectrometer. Elimination of samples via the first two testing tiers leftmore » two remaining samples, which were subsequently subjected to column and sequential batch tests, with further elemental analysis by ICP. Based on these tests, one sample was chosen for suitability as a constructing material for the Forest Queen treatment system basins. Further simplification, and testing on two pairs of independent soil samples, has resulted in a final analytical method suitable for general use.« less

ACID/BASE ACCOUNT AND MINESOILS: A REVIEW

Generation of acidity from the oxidation of iron sulfides (FeS{sub 2}) is a common feature of geological materials exposed to the atmosphere by mining activities. Acid/base accounting (ABA) has been the primary method to evaluate the acid- or alkaline-potential of geological materials and to predict if weathering of these materials will have an adverse effect on terrestrial and aquatic environments. The ABA procedure has also been used to evaluate minesoils at different stages of weathering and, in some cases, to estimate lime requirements. Conflicting assessments of the methodology have been reported in the literature. The ABA is the fastest and easiest way to evaluate the acid-forming characteristics of overburden materials; however, accurate evaluations sometimes require that ABA data be examined in conjunction with additional sample information and results from other analytical procedures. The end use of ABA data, whether it be for minesoil evaluation or water quality prediction, will dictate the method`s interpretive criteria. Reaction kinetics and stoichiometry may vary and are not clearly defined for all situations. There is an increasing awareness of the potential for interfering compounds, particularly siderite (FeCO{sub 3}), to be present in geological materials associated with coal mines. Hardrock mines, with possible mixed sulfide mineralogy,more » offer a challenge to the ABA, since acid generation may be caused by minerals other than pyrite. A combination of methods, static and kinetic, is appropriate to properly evaluate the presence of acid-forming materials.« less

The impact of acid soil volume of reclaimed minesoils on plant growth in minilysimeters

ABSTRACT Limited data are available to assess the influence of randomly distributed acid soil, produced from acid forming materials (AFM), on growth and productivity of crops. This study evaluated the effect of amount and volume of acid soil on die growth of an acid tolerant plant (Coastal bermudagrass, Cynodon dactylon, L) and an acid intolerant plant (Yuchi arrowleaf clover, Trifolium vesiculosum, Savi.) in greenhouse lysimeters. Acid soil (pH=2·5) volumes up to 20 % for Yuchi arrowleaf clover and up to 40% for Coastal bermudagrass did not significantly decrease dry matter yield. Concentrations of Al and Mn in plant tissue of clover and bermudagrass were below the toxicity level. In the presence of randomly distributed acid soil, plant roots continued to elongate in non-acid soil, by evading localized areas of low soil pH. These results suggest that the federally mandated zero tolerance for AFM in the top 1.2 m of reclaimed lands may not be reasonable.

Effects of Selective Handling of Pyritic, Acid-Forming Materials on the Chemistry of Pore Gas and Ground Water at A Reclaimed Surface Coal Mine, Clarion County, PA, USA

Effects of Selective Handling of Pyritic, Acid-Forming Materials on the Chemistry of Pore Gas and Ground Water at A Reclaimed Surface Coal Mine, Clarion County, PA, USA

Reclamation of Acid-Forming Materials in the Colorado Alpine

Reclamation of Acid-Forming Materials in the Colorado Alpine