Fine Refuse Research Articles

Long-term leaching characteristic study of coal processing waste streams

A study of the mobility of major and potentially hazardous trace elements from coal processing waste materials was conducted using two types of leaching tests. The baseline leaching test simulates stable waste storage under water, whereas the kinetic test models the storage of waste under more variable conditions including intermittent exposure to air and variations in humidity. Coarse and fine refuse materials were obtained from three commercial coal preparation plants that were being used to upgrade US bituminous run-of-mine coal containing low-to-high amounts of pyritic sulfur. X-ray diffraction analyses revealed a large variation in mineralogy between the coarse and fine refuse streams due to the mineral fractionation that occurs in the processing units and plant. The coarse refuse samples contained higher pyrite contents while the fine refuse samples had high clay content and a minor amount of calcite. This variation in mineralogy resulted in relatively large difference in the leaching characteristics of the waste streams. The most acidic pH and highest release of trace elements were observed in the leachate of coarse refuse containing medium-to-high amounts of coal pyrite, while the fine refuse samples released lower amounts of trace elements in their circumneutral leachate. The least amount of trace elements was observed in the leachate of low pyritic refuse streams. The test data suggested that the most effective disposal practice for coal waste material is segregation and isolation of the coal pyrite and co-disposal of the coarse and fine refuse streams.

Conceptual modifications of coal preparation plants to minimize potential environmental issues associated with coal waste disposal

An environmental concern at coal preparation operations is the release of elements resulting from the oxidation or dissolution of certain minerals contained in the process waste streams. Using a standard conductivity test, the electrical conductivity (EC) of water samples obtained from mixing with various particle size and density fractions of a given plant waste material were measured as an indicator of total dissolved solids. The net neutralization potential (NNP) of the fractions were also measured to predict the pH of the supernatant upon disposal. As a result, the particle size and density fractions contributing to high EC levels were identified with the objective of potentially extracting and isolating these fractions which can significantly reduce the negative environmental impacts. The results showed that the EC generated from coarse refuse streams were significantly higher than the values obtained from fine refuse streams. Based on the NNP values, the coarse refuse stream generates highly acidic pH, while the fine refuse in contact with water produces circumneutral pH. Furthermore, the high specific gravity (>2.68) fractions which comprised less than 10% of the coal waste streams were found to be the primary source of elevated EC levels. The remaining fractions were found to be of minimal environmental concern. Based on the obtained results, modifications to the coal preparation plants were proposed to minimize the environmental concerns of coal waste disposal. Modifications include pyrite removal from the spiral refuse and desulfurization of flotation feed and sieve bend underflow streams using low-cost mineral spiral circuitry. After the segregation, the pyrite (high density) fraction, which encompasses around 1% of the coarse and fine refuse streams, will be isolated/encapsulated and the fine refuse stream dewatered and co-disposed with the coarse refuse stream. The proposed modifications to the processing and disposal practices not only minimize the generation of acid mine drainage thereby reducing the release of trace elements and EC of the discharged water, but also enhances the recovery and quality of the final clean coal product.

Effects of cake thickness and pressure on the filtration of coal refuse slurry

The effects of pressure and cake thickness were studied using a split-plot design for pressure filtration of a fine refuse slurry obtained from a bituminous coal preparation facility. Pressure filtration offers the potential to significantly reduce the moisture content of the fine refuse stream with the addition of little to no flocculants, thereby minimizing the volume of refuse stored in impoundments and providing a recycle water stream for use within the plant. Experimental results showed that the final cake moisture decreased with increase in pressure and decrease in cake thickness. In addition, specific cake resistances calculated for the various tests indicated an increasing trend with increasing pressure and decreasing cake thickness. With increase in cake thickness, an increase in cake moisture and the weight of solids deposited in the cake was observed. An ANOVA analysis indicated that both cake thickness and pressure significantly affected the cake moisture, while only cake thickness statistically influenced the weight of solids in the cake. A regression model was developed with an R2 value of about 0.99 to relate cake thickness, the single largest statistically significant factor, with the weight of solids in the cake. Filter capacities were calculated in terms of the solids deposited per unit time based on a product specification of 25 percent cake moisture, and it was observed that the thinnest cake had the highest filter capacity.

A pilot machine for municipal solid waste separation

The research has developed an innovated pilot machine for separating the recyclable materials of the municipal solid waste. It utilises a rotary screen drum with a length three times its diameter. This drum is divided into two parts, the first part is one metre long, consists of a screen having meshes graduated from 8 to 20 mm to separate the fine refuse. The second part is 3 metre long, consists of a screen having meshes graduated from 20 to 200 mm to separate coarser refuse. The results of treating 30 tons/day of solid waste by separation came with the following rates: metals 10.7%, paper 17.7%, plastics 4.0%, glass 2.0% and textiles 1.3%. In addition, the percentage of organic compostable materials was 58% out of the total solid wastes. Such a pilot machine can be generalised to be applied in similar cities elsewhere.

Environmental Contaminants in Coal Slurry Intended for Underground Injection in the State of West Virginia

AbstractWaste from coal cleaning processes includes coarse size fractions (i.e., coarse refuse) and small particles (i.e., fine refuse). The aqueous suspension of fine refuse, referred to as coal slurry, frequently contains potentially toxic substances, including hydrocarbons, heavy metals, and coal cleaning chemicals. Disposal of coal slurry using underground injection has raised environmental concerns because it may lead to contamination of groundwater and water supplies. In the present study, liquid and solid fractions of coal slurries collected from five underground injection sites and one coal preparation site in West Virginia (WV) were analyzed for a suite of 177 organic and inorganic constituents. The original data presented in this article were all collected by the WV Department of Environmental Protection, Office of Mining and Reclamation, and the U.S. Department of Interior, Office of Surface Mining, with input from the WV Department of Health and Human Resources. Several metals of health and en...

Potential of Breakthroughs of Impounded Coal Refuse Slurry into Underground Mines

On October 11, 2000, an estimated 306 million gallons of water and fine coal refuse slurry broke through a bedrock barrier from an impoundment in Martin County, eastern Kentucky, into an adjacent underground mine. Approximately 260 million gallons of the water and coal slurry discharged from two underground mine portals and affected over 75 miles of streams in Kentucky and West Virginia. As a result of this and several other breakthroughs over just half a decade, the U.S. Office of Surface Mining Reclamation and Enforcement (OSM) and other institutions undertook investigations to assess the causes of the events, the potential for additional breakthroughs in the future, and available methods for preventing them. In addition to needed improvements in the design, construction, and inspection of the facilities, the studies have addressed issues pertaining to the flow characteristics of refuse slurry, not only in impoundments still receiving pumped slurry, but also in “idle” and reclaimed facilities. Related questions concern: (1) the effects on breakthrough potential of the impoundment abandonment process and construction of slurry cells on top of capped structures; and (2) appropriate measures and available methods that may be used to ensure that underground mines adjacent to or underlying impoundments are known and accurately located. Current information on the engineering properties of coal refuse in existing facilities provides no assurance against fine refuse flowability during any stage in the impoundment construction and reclamation process or after reclamation has been completed. Due to this uncertainty, thorough site investigations and conservative measures in design, construction, reclamation, and quality control are of paramount importance.

An Evaluation of a Two-Stage Spiral Processing Fine Anthracite Refuse

Testing was conducted to evaluate the performance of a two-stage Multotec SX7 spiral concentrator treating fine anthracite refuse. Two sets of samples were collected from an anthracite cleaning plant located in eastern Pennsylvania. One sample consisted of the thickener feed slurry (nominal − 1.2 mm) and the other consisted of the thickener underflow slurry. A third sample was prepared by desliming the thickener feed using a 102-mm diameter Krebs cyclone to produce a nominal − 1.2 + 0.025 mm product. The effects of slurry flow rate and solids concentration on spiral performance were investigated. For the + 0.025 mm material, the feed ash value could be reduced from 71% to 21%, while producing a refuse with an ash value of 91%. Regardless of whether the feed slurry was deslimed or undeslimed, the + 0.025 mm material would separate. The separation occurred even with the thickener underflow, which had been treated with flocculant. The − 0.025 mm material split in approximately the same proportion as the water.

An Efficient Process for Recovery of Fine Coal from Tailings of Coal Washing Plants

Gravity concentration of hard lignites using conventional jigs and heavy media separation equipment is prone to produce coal-rich fine tailings. This study aims to establish a fine coal recovery process of very high efficiency at reasonable capital investment and operational costs. The technical feasibility to upgrade the properties of the predeslimed fine refuse of a lignite washing plant with 35.9% ash content was investigated by employing gravity separation methods. The laboratory tests carried out with the combination of shaking table and Mozley multi-gravity separator (MGS) revealed that the clean coal with 18% ash content on dry basis could be obtained with 58.9% clean coal recovery by the shaking table stage and 4.1% clean coal recovery by MGS stage, totaling to the sum of 63.0% clean coal recovery from a predeslimed feed. The combustible recovery and the organic efficiency of the shaking table + MGS combination were 79.5% and 95.5%, respectively. Based on the results of the study, a flow sheet of a high-efficiency fine coal recovery process was proposed, which is also applicable to the coal refuse pond slurry of a lignite washing plant.

97/01634 Manufacture of fuel briquets

The −0.5 inch (−1.27 cm) and −28 mesh (−600 μm) fractions of the run-of-mine coals from seven western Kentucky preparation plants were crushed to 90 percent passing 200 mesh (75 μm) and processed through high-gradient magnetic separation (HGMS). Petrographic analysis of the clean and refuse fractions indicated that the refuse contained nearly the same amount of vitrinite as the associated clean coal. This contrasts with the findings for other fine coals from the same plants where fine refuse had consistently less vitrinite and more fusinite and semifusinite than fine clean coals. Pyrite remaining in HGMS clean coals was significantly finer than pyrite in the refuse. Most of the pyrite in the clean was less than 5 μm in diameter, and, in all but one case, greater than 98 percent of the “clean” pyrite was less than 10 μm.

Geotechnical characterization of blended coal tailings for construction and rehabilitation work

Abstract Coarse and fine refuse is produced by various coal processing equipment. For instance, fine tailings (100-500µm) are produced by froth flotation cells, whereas coarse fractions (up to 50 mm) constitute cyclone rejects. The relatively wet fine tailings have limited use in construction activities and they are generally pumped as slurries into tailings ponds. The coarse rejects have a greater engineering applicability and are utilized in the construction of tailings dams, mine access roads as well as for landfill and ballast. This study investigates the fundamental engineering properties of blended tailings, where- by appropriate fractions of flotation tailings are mixed with cyclone rejects to produce an acceptable construction or rehabilitation fill. In particular, a practical procedure to optimize the blended ratios is proposed on the basis of fundamental geotechnical testing. The applications of relevant tests are described, including Proctor compaction, California Bearing Ratios, triaxial and consolidation tests. The results confirm that blending of fines with coarse rejects enables enhanced dry densities associated with reduced permeabilities, higher shear and compressive strengths, lower consolidation settlements and increased bearing capacities. The addition of a small quantity of cement (2-5%) further improves the engineering properties of the blended matrix. The practical findings of this study should encourage coal processing plants to modify their existing disposal methods to adopt more efficient co-disposal schemes. Optimization of procedures for discarding fine and coarse rejects together would generate substantial savings, with regard to dewatering of wet tailings and rehandling of distinctly different waste gradations.

Application of electromagnetic techniques in survey of contaminated groundwater at an abandoned mine complex in southwestern Indiana, U.S.A.

In part of a large abandoned mining complex, electromagnetic geophysical surveys were used along with data derived from cores and monitoring wells to infer sources of contamination and subsurface hydrologic connections between acidic refuse deposits and adjacent undisturbed geologic materials. Electrical resistivity increases sharply along the boundary of an elevated deposit of pyritic coarse refuse, which is highly contaminated and electrically conductive, indicating poor subsurface hydrologic connections with surrounding deposits of fine refuse and undisturbed glacial material. Groundwater chemistry, as reflected in values of specific conductance, also differs markedly across the deposit's boundary, indicating that a widespread contaminant plume has not developed around the coarse refuse in more than 40 yr since the deposit was created. Most acidic drainage from the coarse refuse is by surface runoff and is concentrated around stream channels. Although most of the contaminated groundwater within the study area is concentrated within the surficial refuse deposits, transects of apparent resistivity and phase angle indicate the existence of an anomalous conductive layer at depth (>4 m) in thick alluvial sediments along the northern boundary of the mining complex. Based on knowledge of local geology, the anomaly is interpreted to represent a subsurface connection between the alluvium and a flooded abandoned underground mine.

Maceral Partitioning through Beneficiation of Illinois Basin Coals

Coals from 28 Illinois Basin preparation plants, primarily in western Kentucky, were studied for maceral partitioning around several unit operations. Consideration was also given to two sets of plants with similar designs; in one case cleaning the same seam and in the other case cleaning three different seams. More consistent maceral partitioning was exhibited in the finer fractions than in the coarse coal with the fine clean coal being enriched in vitrinite and the fine refuse being enriched in fusinite plus semifusinite. Comparison of coals prepared through similar operations indicated that a significant difference existed in the maceral partitioning both between different coals cleaned in one plant and between the same coal seam (different mines) beneficiated through similar design plants. The petrographic characteristics of each coal appear to be site specific and include inherent factors, such as maceral-mineral associations, as well as factors imposed during mining.

Maceral and pyrite partitioning through high-gradient magnetic separation of selected western kentucky coals

The −0.5 inch (−1.27 cm) and −28 mesh (−600 μm) fractions of the run-of-mine coals from seven western Kentucky preparation plants were crushed to 90 percent passing 200 mesh (75 μm) and processed through high-gradient magnetic separation (HGMS). Petrographic analysis of the clean and refuse fractions indicated that the refuse contained nearly the same amount of vitrinite as the associated clean coal. This contrasts with the findings for other fine coals from the same plants where fine refuse had consistently less vitrinite and more fusinite and semifusinite than fine clean coals. Pyrite remaining in HGMS clean coals was significantly finer than pyrite in the refuse. Most of the pyrite in the clean was less than 5 μm in diameter, and, in all but one case, greater than 98 percent of the “clean” pyrite was less than 10 μm.

Sludge to Fertile Soil—Research Results

Abstract This paper reports on work done by Dravo Lime Co. in the Dravo Corporation Research Facilities with the cooperation of the U.S. Environmental Protection Agency, Project R803999-01-0. The primary purpose of this study has been to combine flue gas desulfurization (FGD) sludges with municipal waste to produce fertile soils. A second objective has been to stabilize and combine coal fine refuse with municipal waste to identify potential stabilization and revegetation techniques. Testing on the FGD municipal waste mixtures has included seedings both under greenhouse conditions and in outdoor test plots. Coal fine refuse-municipal waste sludge mixtures have also been successfully stabilized and have been successfully seeded and tested under greenhouse conditions. Plant varieties that have been growth in these combined waste products include corn, soybeans, oats, ryegrass, and crown vetch.

OBSERVATIONS ON THE FUNCTIONING OF THE ALIMENTARY SYSTEM OF THE SNAIL LYMNAEA STAGNALIS APPRESSA SAY

1. A balanced physiological salt solution was developed which maintains contractions of the vas deferens for approximately 66 hours.2. Cathepsin was found in greatest concentration in the liver and no activity could be ascertained in the gut fluids. Some trypsin was indicated in the salivary glands. Amylase showed greatest activity in the salivary glands and the liver.3. Muscular activity of the alimentary system involves the manipulation of the mouth parts in the buccal mass, peristalsis in the remainder of the tract, marked pulsatory movements of the postesophagus, crop, pylorus and liver, and a kneading motion of the gizzard. The radula is moved principally by the action of the odontophore but also operates independently of it.4. The entire alimentary system, with the exception of the gizzard and parts of the buccal cavity, is ciliated. The cilia show definite directional streams which function in propelling food particles, in sorting food and in consolidating fine refuse particles with the aid of muco...