Sand–Attapulgite Clay Mixtures as a Landfill Liner

Absrtract This paper investigates the potential use of sand–attapulgite (palygorskite) mixtures as a landfill liner. The sand and attapulgite clay used in this study were brought from Wahiba (eastern Oman) and Al-Shuwamiyah (southern Oman), respectively. Initially the basic properties of the sand and clay were determined. Then the attapulgite clay was added to the sand at 5, 10, 20 and 30% by dry weight of the sand. The sand–attapulgite clay mixtures were subjected to mineralogical, chemical, microfabric and geotechnical analyses. The X-ray diffraction (XRD) qualitative analysis showed that attapulgite is the major clay mineral. The chemical compounds, exchangeable cations and cation exchange capacity (CEC) for the␣samples were determined. The CEC for the sand–clay mixtures is low but increases with the increase in clay content. The scanning electron microscope (SEM) examination showed that the addition of clay developed coating between and around the sand grains which results in filling the voids and reducing the hydraulic conductivity of the sand–clay mixtures. The hydraulic conductivity values for the pure clay and sand + 30% clay mixture prepared at 2% above optimum water content are slightly higher than hydraulic conductivity requirements for landfill liners but can be acceptable. The geotechnical study which included grain size distribution, Atterberg limits, specific gravity, compaction, hydraulic conductivity and shear strength tests showed that the sand+30% clay mixture prepared at 2% above optimum water content can be considered to satisfy the requirements for landfill liners. For all sand–clay mixtures no swelling was recorded and the addition of clay to the sand improved the shear strength.     

Ferric chloride treatment to control alakli induced heave in weathered red earth

A detailed experimental investigation has been carried out to study the use of ferric chloride salt to control the undesirable volume changes induced by high concentrated alkali contamination on kaolinitic red earth. X-Ray diffraction studies have revealed that soil alkali interactions produce mineralogical changes and formation of new mineral such as zeolite, which are responsible for observed swelling in non-swelling kaolinitic soil. Loss of ferric oxide, which are known cementing agents has been attributed as one of the reasons for swelling in alkali contaminated soils. The consolidation behaviour of soil compacted with 5% ferric chloride solution by weight of solutions and inundated with alkali solutions as well as soil compacted with alkali and inundated with 5% ferric chloride by weight of solutions has been studied. To study the effect of amount of ferric chloride, the volume change behaviour of soil compacted with different weight percentages of ferric salts by weight of soil (1%, 3%, and 5%) and inundated with alkali solutions has also been studied. The swelling of soil compacted with alkali has been checked by inundating with 5% ferric chloride solutions due to neutralization of alkali and is not controlled when soil compacted with 5% ferric chloride solutions is inundated continuously with alkali solutions. Further, even when the soil is treated with higher amounts of ferric chloride, in the range of 1–5% by weight of soil, the swelling is not controlled. X-ray diffraction studies have shown that the formation of zeolite is not inhibited in the presence of ferric salts.This study clearly shows that ferric chloride treatment can overcome the effects of small concentrations of alkali; it is ineffective to overcome the large and continued exposure of soils with alkali contamination.     

Provenance implications of Th–U–Pb electron microprobe ages from detrital monazite in the Carboniferous Upper Silesia Coal Basin, Poland

This paper reports the results of CHIME (chemical Th–U–Pb isochron method) dating of detrital monazites from Carboniferous sandstones in the Upper Silesia Coal Basin (USCB). A total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence. Age distributions were identified in detrital monazites from the USCB sequence and correlated with specific dated domains in potential source areas. Most monazites in all samples yielded ca. 300–320 Ma (Variscan) ages; however, eo-Variscan, Caledonian and Cadomian ages were also obtained. The predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic Bohemian Massif (BM), which suggests that various crystalline lithologies in the BM were the dominant sources of USCB sediments.     

A new interpretation of Stephanian deformation in the Decazeville basin (Massif Central, France): consequences on late Variscan tectonism

Five stages of faulting were observed in and around the Stephanian Decazeville basin, in the SW French Massif Central, at the southern edge of the Sillon houiller fault. The older stage ends during middle Stephanian time, and corresponds to a strike-slip regime with N–S shortening and E–W extension. Before the end of the middle Stephanian, three other stages were recorded: two strike-slip regimes with NW–SE, then E–W compression and NE–SW, then N–S extension; and finally a NNE–SSW extensional regime during the main subsidence of the basin from the end of the middle Stephanian to late Stephanian. Based on mining documents, a new interpretation of the N–S striking folds of the Decazeville basin is proposed. Folding may not be associated with E–W compression but with diapirism of coal seams along syn-sedimentary normal faults during the extensional phase. A last strike-slip regime with N–S compression and E–W extension may be related to Cainozoic Pyrenean orogeny. At a regional scale, it is suggested that from the end of the middle Stephanian to the late Stephanian, the main faults in the Decazeville basin may represent a horsetail splay structure at the southern termination of the Sillon houiller fault.     

瞬变电磁勘探技术在探测采空区中的应用——以阳煤集团氧化铝厂采空区勘探为例

瞬变电磁法(TEM),是利用不接地回线向地下发送一次脉冲瞬变磁场,再测定一次脉冲瞬变磁场引起的二次涡流场的方法。当地下存在电性不均匀体时,会观测到电性不均匀体的涡流异常场,通过对异常场的分析研究,推断矿体、地下水、采空区等地下盲体的存在和部位。华北石炭-二叠煤系地层的电阻率比非煤系地层的电阻率值高,铝土矿层电阻率相对较低,下伏奥陶系灰岩电阻率最高。地下矿体局部被采出后,对应地层的导电性随采空区的塌陷程度及赋水情况不同,表现为相对较高的电阻率或较低的电阻率值,依据此特征成功地利用瞬变电法应用于采空区探测中。     

The role of sulphide and carbonate minerals in the concentration of chalcophile elements in the bituminous coal seams of a paralic series (Upper Carboniferous) in the Upper Silesian Coal Basin (USCB), Poland

Sulphide and carbonate minerals from nine bituminous coal seams of a Paralic Series were investigated by means of polished-section microscopy, scanning electron microscopy and absorption spectral analyses. In addition to syngenetic accumulations of kaolinite, illite and quartz, diagenetic veinlets of subhedral pyrite and marcasite most often occur in vitrinite clast fissures and in post-tectonic fissures, nests and lenses with fusinite. Epigenetic anhedral and subhedral grains of ankerite, dolomite, siderite and calcite are also frequently found in post-tectonic veins. Pyrite replaced some of the marcasite grains and it dominates in older coal seams in the Flora Beds as compared with the Grodziec Beds. Occasionally there are anhedral and subhedral galena, sphalerite and chalcopyrite grains among coal macerals as well as cerussite among post-tectonic carbonate veins. They all represent the only minerals that are abundant in definite chalcophile elements (Cd, Co, Cu, Ni, Pb, Zn). In addition to the minerals just mentioned, the elements occurred in pyrite and ankerite grains, which contained inclusions of fusinite and other minerals (among others, clay and carbonate minerals in pyrite, pyrite in carbonates). Although there is a low content of minerals accumulating Cd, Co, Cu, Ni, Pb and Zn, the minerals significantly influence the average concentration of elements in the coal seams. In the Grodziec Beds, mineral matter, especially carbonates and sulphides, determines (>50%) the concentration of Cd, Cu, Pb and Zn in coal. The basic part of Cd, Co and Ni in the coal seams of the Grodziec Beds and of Co, Cu, Ni, Pb and Zn in coal seams of the Flora Beds originates from organic matter. These regularities can be important, from an ecological perspective, in stating whether the coals investigated are useful for combustion and in chemical processing.     

Matching gasification technologies to coal properties

The gasification of coal to produce hydrogen for use either in power generation or/and for synthesis applications and transport is attracting considerable interest worldwide. Three types of generic gasifiers (entrained flow, fluidised bed and fixed bed gasifiers) presently in use in commercial gasification plants or under development worldwide are described. Their suitability for processing all types of coals is discussed. This includes an assessment of the impact of some of the major properties of coal on the design, performance and maintenance of gasification processes.     

Hydrogen from coal gasification: An economical pathway to a sustainable energy future

Although hydrogen is the most abundant element in the universe, it does not occur naturally in large quantities or high concentrations on Earth. Hydrogen must be produced from other compounds such as fossil fuels, biomass, or water and is therefore considered an energy carrier like electricity. Gasification of carbonaceous, hydrogen-containing fuels is an effective method of thermal hydrogen production and is considered to be a key technology in the transition to a hydrogen economy. However, for gasification to play a major role during the transition period, capital and operating cost must be reduced and reliability and performance must be improved.Analyses show that hydrogen produced from coal-based gasification can be competitive with production from natural gas provided the cost of natural gas remains above $4/10⁶ Btu and the high reliability of gasification-based processes can be demonstrated. But for coal to be considered in a carbon-constrained environment, the cost of natural gas would have to be greater than $5.50/10⁶ Btu. The development of advanced technologies, however, offers the potential for significant reductions in capital costs, improved thermal efficiencies, and increased reliability. If these advanced technologies are capable of achieving their goals, the cost of producing hydrogen from coal could be reduced by 25–50%, even with the capture and sequestration of CO₂. With these reductions, the cost of natural gas would have to be less than $2.50/10⁶ Btu to compete, a scenario that is very unlikely to occur in the future. This potential cost reduction provides considerable impetus for continuing research and development in the production of hydrogen from coal.     

Syngas production from South African coal sources using Sasol–Lurgi gasifiers

Sasol has been operating the Sasol–Lurgi fixed bed coal gasification process for more than fifty years, and with ninety seven units in operation still remains the world's largest commercial application of this technology. The combined operational and engineering expertise vested in Sasol represents a formidable capability in the field of coal and gasification science. Coal is a crucial feedstock for South Africa's unique synfuels and petrochemicals industry, and is used by Sasol as a feedstock to produce synthesis gas (CO and H₂) via the Sasol–Lurgi fixed bed dry bottom gasification process.South Africa, as well as many other countries in the world, will for many years to come rely on its abundant coal resources for energy and specifically for the production of petrochemical products. Synthesis gas production through gasification is growing at a rate of approximately 10% per annum [Office of Fossil Energy, National Energy Technology Laboratory and the Gasification Technologies Council, 2000. Gasification: Worldwide use and acceptance. Contract DE-AMO1-98FE65271], indicating that gasification is definitely not a dying technology. The Sasol plants located in Secunda and Sasolburg (South Africa) gasify > 30 million tons per annum of bituminous coal to synthesis gas, which is converted to fuels and chemicals via the Fischer–Tropsch process. The production of chemicals is currently the dominant application for synthesis gas, followed by power generation, Fischer–Tropsch synthesis and gaseous fuels.Sasol–Lurgi gasifiers are extremely robust devices, and coal from sources with widely varying properties (e.g. ash content < 10% to as high as 35% or “brown coal” with moisture content of approximately 30%) can be gasified provided that certain operational changes are implemented. Other properties, like high caking propensity for example, require blending to acceptable levels and /or mechanical modifications. Interpretation of coal characterization data gives an indication of expected gasifier performance and the suitability of a specific coal source for Sasol–Lurgi Fixed Bed Gasification process. It is therefore critically important to gain an accurate and fundamental understanding of the properties and expected behavior of the targeted coal feedstock in order to (1) prepare a suitable conceptual flow scheme and (2) to maximize the eventual probability of success in any proposed gasification venture and (3) to optimize the operation and profitability of existing plants and (4) effectively address the environmental aspects.It is the view of the authors that fixed bed gasification technology has a bright future in the areas mentioned above and that Sasol has a unique role in the future application and commercialization of gasification technology globally. The unique skills of Sasol could however be complementary to those of other parties who share our view on the future of gasification and related technologies.     

Properties of thermally metamorphosed coal from Tanjung Enim Area, South Sumatra Basin, Indonesia with special reference to the coalification path of macerals

Thermally metamorphosed Tertiary age coals from Tanjung Enim in South Sumatra Basin have been investigated by means of petrographic, mineralogical and chemical analyses. These coals were influenced by heat from an andesitic igneous intrusion. The original coal outside the metamorphosed zone is characterized by high moisture content (4.13–11.25 wt.%) and volatile matter content (> 40 wt.%, daf), as well as less than 80 wt.% (daf) carbon and low vitrinite reflectance (VR_max = 0.52–0.76%). Those coals are of subbituminous and high volatile bituminous rank. In contrast the thermally metamorphosed coals are of medium-volatile bituminous to meta-anthracite rank and characterized by low moisture content (only < 3 wt.%) and volatile matter content (< 24 wt.%, daf), as well as high carbon content (> 80 wt.%, daf) and vitrinite reflectance (VR_max = 1.87–6.20%). All the studied coals have a low mineral matter content, except for those which are highly metamorphosed, due to the formation of new minerals.The coalification path of each maceral shows that vitrinite, liptinite and inertinite reflectance converge in a transition zone at VR_max of around 1.5%. Significant decrease of volatile matter occurs in the zone between 0.5% and 2.0% VR_max. A sharp bend occurs at VR_max between 2.0% and 2.5%. Above 2.5%, the volatile matter decreases only very slightly. Between VR_r = 0.5% and 2.0%, the carbon content of the coals is ascending drastically. Above 2.5% VR_r, the carbon content becomes relatively stable (around 95 wt.%, daf).Vitrinite is the most abundant maceral in low rank coal (69.6–86.2 vol.%). Liptinite and inertinite are minor constituents. In the high rank coal, the thermally altered vitrinite composes 82.4–93.8 vol.%. Mosaic structures can be recognized as groundmasss and crack fillings. The most common minerals found are carbonates, pyrite or marcasite and clay minerals. The latter consist of kaolinite in low rank coal and illite and rectorite in high rank coal. Change of functional groups with rank increase is reflected most of all by the increase of the ratio of aromatic C–H to aliphatic C–H absorbances based on FTIR analysis. The Oxygen Index values of all studied coals are low (OI < 5 mg CO₂/g TOC) and the high rank coals have a lower Hydrogen Index (< 130 mg HC/g TOC) than the low rank coals (about 300 mg HC/g TOC). T_max increases with maturity (420–440 °C for low rank coals and 475–551 °C for high rank coals).Based on the above data, it was calculated that the temperature of contact metamorphism reached 700–750 °C in the most metamorphosed coal.