Shale Disposal Research Articles

Beneficiation of Oil Shale by Froth Flotation: Critical Review

Oil shale beneficiation by froth flotation hasn't received enough attention in the last two decades. The reason was the economics of the process as well as its environmental impact. However, the recent surge in oil price and recent developments in fine grinding technologies may improve the efficiency of oil shale beneficiation by such process. In this work, oil shale concentration by froth flotation technique was critically reviewed. It was found that most of the work was conducted by conventional mechanical flotation using non-ionic collector such as kerosene. Flotation has more pronounced effect on flotation of low grade oil shale; Almost 95% of ash forming minerals were removed to enrich oil shale concentrate by factor of 2-4 with 60-95 % kerogen recovery and approximately 50-300 % increase in oil yield (L/tonne) .Oil shale retorting economics showed that beneficiation reduced the capital cost for pyrolysis and fractionation by 250 % and spent shale disposal by 270%. However, these saving are offset by the cost of beneficiation (grinding, flotation, and dewatering). Therefore, the key for economical oil shale concentration process is the reduction of fine grinding costs.

Ecological rehabilitation and phytoremediation with four grasses in oil shale mined land

Vetiver grass ( Vetiveria zizanioides), bahia grass ( Paspalum notatum), St. Augustine grass ( Stenotaphrum secundatum), and bana grass ( Pennisetum glaucum × P. purpureum) were selected to rehabilitate the degraded ecosystem of an oil shale mined land of Maoming Petro-Chemical Company located in Southwest of Guangdong Province, China. Among them, vetiver had the highest survival rate, up to 99%, followed by bahia and St. Augustine, 96% and 91%, respectively, whereas bana had the lowest survival rate of 62%. The coverage and biomass of vetiver were also the highest after 6-month planting. Fertilizer application significantly increased biomass and tiller number of the four grasses, of which St. Augustine was promoted most, up to 70% for biomass, while vetiver was promoted least, only 27% for biomass. Two heavy metals, lead (Pb) and cadmium (Cd) tested in this trial had different concentrations in the oil shale residue, and also had different contents and distributions in the four grass species. Concentrations of Pb and Cd in the four grasses presented a disparity of only 1.6–3.8 times, but their uptake amounts to the two metals were apart up to 27.5–35.5 times, which was chiefly due to the significantly different biomasses among them. Fertilizer application could abate the ability of the four species to accumulate heavy metals, namely concentration of heavy metals in plants decreased as fertilizer was applied. The total amount of metals accumulated by each plant under the condition of fertilization did not decrease due to an increase of biomass. In summary, vetiver may be the best species used for vegetation rehabilitation in oil shale disposal piles.

Atmospheric oxidation of the pyritic waste rock in Maardu, Estonia. 1 field study and modelling

A field survey and modelling of the oxidation and carbonate buffering reactions inside the alum-shale-containing waste rock dumps located in Maardu, Estonia, was accomplished. In the slope areas, the shale has been altered at high temperatures due to the spontaneous combustion and the pyritic acidity has been eliminated through migration of SOx gases out from the dump. In the central parts of the waste rock plateaus, low temperature pyrite oxidation fronts develop towards the dump depth and towards the centres of individual shale lumps. The main secondary phases precipitating in the weathering profile are gypsum, ferric oxyhydroxide, K-jarosite and smectite. The respective field data made it possible to calibrate the two-stage oxygen diffusion model and the characteristic pyrite oxidation rate 0.06–0.08 mol of pyrite reacted per kg of available water (pyrox/H2O value) was estimated to describe the first tens of years of dump performance. The model is capable to compare different shale disposal strategies that are illustrated with two case scenarios. The buffering of sulphuric acid by Mg-calcite appears to be an incongruent reaction with gypsum precipitating that leads to the build-up of the high Mg/Ca ratio in the leachate. Application of the Mg/Ca method estimates the pyrox/H2O value in the range of 0.05–0.14 mol/kg.

Fluorine and molybdenum solubility relationships in combusted oil shale

Abstract Fluorine (F) and molybdenum (Mo) may adversely affect vegetation, grazing animals, groundwater, and surface waters that are proximate to spent oil shale disposal sites. The chemistry of F and Mo in spent oil shale leachates may be controlled by the precipitation of flu‐orite (CaF2) and powellite (CaMoO4), respectively. Thus, the fate and behavior of these elements may be predicted using equilibrium solubility methods. Recent findings and the examination of methods cast doubt on the interpretations of many spent oil shale solubility studies. Recent research shows that the formation of soluble molybdate species in spent oil shale leachates can be significant. Further, reaction times necessary for equilibrium conditions were not attained in many solubility experiments. Moreover, solubility experiments were only performed on fresh solid waste, yielding little information on element behavior in a disposal site. The objectives of this study were to reexamine spent oil shale literature data and perform ...

Plant Uptake and Cycling of Trace Elements on Retorted Oil Shale Disposal Piles

AbstractThis study considers some of the environmental hazards posed by high trace element concentrations in plants growing on retorted oil shale disposal piles and the potential for surface accumulation of trace elements via biocycling. Arsenic, B, Cu, F, Mo, and Se concentrations in plants growing on six disposal piles were determined 7 yr following site construction. Disposal treatments consisted of leaving Paraho retorted shale exposed at the surface, leaching exposed retorted shale with 760 mm of water, covering retorted shale with 30, 60, or 90 cm of soil, or a 30‐cm rock capillary barrier and 60 cm of soil. These treatments plus a disturbed soil reference plot (no retorted shale) were seeded in 1977 with three mixtures of native and introduced plant species. In 1983, Mo was present in plants at high enough levels to cause molybdenosis in ruminants. Molybdenum, F, As, and Se concentrations in plants decreased as depth of replaced topsoil increased. Leaching only slightly reduced concentrations in plants. Capillary barrier and 90‐cm treatments were the most effective at reducing plant trace elements concentrations; however, shrubs and legumes from these treatments still occasionally had higher trace element contents than plants growing on disturbed soil reference plots. Legumes had higher concentrations of most trace elements than grasses or shrubs. For this reason species composition had a major effect on total trace element content of stands of vegetation. Rates of movement to the surface via biocycling appear to be relatively slow, although they may continue to increase in the future.

Copper Fertilization to Prevent Molybdenosis on Retorted Oil Shale Disposal Piles

AbstractPlants growing on retorted oil shale disposal piles often have Mo concentrations high enough (>8 mg kg−1) and Cu/Mo ratios low enough (<2.0) to cause molybdenosis in grazing ruminants. High Mo concentrations are present in some plant species in spite of 90 cm of topsoil cover. Copper sulfate was broadcast at rates of 0, 8, 16, and 32 kg Cu ha−1 on plots with 30 and 90 cm of topsoil over Paraho retorted oil shale to determine if Cu fertilization can increase Cu/Mo ratios in plants so that molybdenosis is no longer a hazard. Of the plant species studied winterfat [Eurotia lanata (Pursh) Moquin], northern sweetvetch (Hedysarum boreale Nutt.), alfalfa (Medicago sativa L.), native grasses [Agropyron smithii Rydb., A. inerme (Scribn. and Smith) Rydb., A. dasystachium, (Hook.) Scribn. and Poa ampla Merr.], and introduced grasses [A. desertorum (Fisch.) Schult., A. intermedlum (Host Beauv.), and Bromus biebersteinii Roem. & Schult.], all except alfalfa showed increased tissue Cu concentrations during the first growing season. Because of high Mo concentrations, however, only winterfat under high fertilization rates developed Cu/Mo ratios sufficient to prevent molybdenosis (i.e., >2.0). By the end of the second growing season, increases in Cu concentrations due to fertilization had declined approximately 30%. These results indicate that although Cu fertilization can be used for short‐term improvements in Cu/Mo ratios, it should not be relied upon as the sole technique for preventing molybdenosis on retorted shale disposal piles. Instead, maximum feasible topsoil thicknesses should be used and plant species known to concentrate Mo should be eliminated from seeding mixtures.

Calcium molybdate solubility in spent oil shale and a preliminary evaluation of the association constants for the formation of CaMoO40(aq), KMoO4-(aq), and NaMoO4-(aq)

In order to better understand the fate and behavior of molybdenum in spent oil shale disposal environments, the equilibrium solubility of CaMoO 4 (c, powellite) in deionized-distilled water, potassium nitrate solutions, and spent oil shale leachates was determined

Trace element mineral transformations associated with hydration and recarbonation of retorted oil shale

A laboratory study was conducted to evaluate the influence of hydration and recarbonation on the solidphase distribution of trace elements in retorted oil shale. The oil shale samples were retorted by the Paraho direct heating process and equilibrated with deionized—distilled water under controlled carbon dioxide conditions. A sequential extraction technique was then used to fractionate trace elements into soluble, KNO3-extractable (easily exchangeable), H2O-extractable (easily adsorbed), NaOh-extractable (organic), EDTA-extractable (carbonate), HNO3-extractable (sulfide), and residual (nonextractable silicate) phases. The chemical fractions present in retorted oil shale and hydrated and recarbonated retorted oil shale were compared to identify trace element mineralogical changes that may occur in retorted oil shale disposal environments.

Availability and Plant Uptake of Trace Elements from Recarbonated Retorted Shale

AbstractOne solution to the management of retorted shale (spent oil shale) is to establish a satisfactory vegetative cover over retorted shale disposal piles. However, the high alkalinity of these waste materials severely hampers direct revegetation efforts. A sample of Lurgi‐Ruhrgas (Lurgi) retorted shale was recarbonated to lower its high alkalinity, by exposing it to 0.04 MPa CO2(g) and moisture for 4 d. A preliminary greenhouse experiment was conducted to examine the uptake of microelements by tall wheatgrass [Agropyron elongatum (Host) Beauv.] grown on this recarbonated shale. Exposing spent Lurgi shale to pressurized CO2(g) and moisture lowered the pH from 11.6 to 8.6 and increased the electrical conductivity (EC) from 4.7 to 15.8 dS/m. Lowering the pH through recarbonation increased ammonium bicarbonate‐diethylenetriaminepentaacetic acid (AB‐DTPA) extractable Fe, Zn, Cu, Mo, and Ni, while extractable B, Sr, Cr, and Mn were decreased. Wheatgrass seeds failed to germinate in spent Lurgi shale, which had no soil cover. Plant growth decreased in the recarbonated shale compared to retorted shale with a soil cover due to higher salinity. Plant tissue grown on the recarbonated shale accumulated lower concentrations of As, Se, Ba, Cd, Sr, and Ti than did plants grown on spent Lurgi shale with a soil cover. Boron concentrations ranged from 7.2 to 13.0 mg/kg in plant tissue, with the lowest concentrations coming from the recarbonated shale. Fluoride concentrations in plant tissue increased with recarbonation but were below the toxic level. Plant uptake of Mo increased with recarbonation. The Cu/Mo ratios of the tall wheatgrass were below 2:1 in all treatments except the control. This preliminary study shows that recarbonated spent shales can be revegetated directly without a soil cover but that some leaching may be advantageous.

Trace Element and Salt Movement in Retorted Oil Shale Disposal Sites

AbstractThe direction and amount of salt and trace element movement within retorted shale disposal piles is a major environmental concern. This study examines the redistribution of soluble salts and trace elements (As, B, Cd, Cu, F, Fe, Mn, Mo, Na, Ni, Pb, Se, and Zn) in retorted shale test plots with different topsoil treatments 6 yr after construction. Topsoil treatments included no topsoil, no topsoil and leached with 76‐cm water, 30‐cm topsoil, 60‐cm topsoil, 90‐cm topsoil, 60‐cm topsoil and capillary barrier, and a disturbed soil control (no retorted shale). Soluble salts (especially Na salts) and F showed considerable movement both upwards and downwards in the profiles. Molybdenum showed some movement in both directions. The remaining elements showed little or no movement out of the shale layer. Increasing topsoil depths resulted in less salt or trace element movement in either direction. Use of a capillary barrier between the topsoil and retorted shale prevented upward migration of salts and trace elements. After 6 yr the exposed shale treatments (both leached and unleached) continued to have considerably higher salt and trace element contents than any other treatment. Because of limited rooting depths, deeper percolation of moisture is occurring on plots containing retorted shale than on the control plot.

A field test of processed oil shale reclamation strategies designed for minimal use of limited resources

Reclamation of processed oil shale disposal areas in the arid and semi-arid regions of Utah, Colorado and Wyoming faces several challenging problems. Shallow topsoil, harsh climate and limited water supply and low suitability of processed oil shale as a plant growth medium must be addressed if any reclamation plan is to be successful.

Composition and Quality of Mule Deer Diets on Pinyon-Juniper Winter Range, Colorado

Estimates of botanical composition and nutritional quality of mule deer diets on pinyon-juniper winter range in Piceance Basin, Colorado, were based on forage selections of 8 tame animals. Diets contained nearly all browse in early winter, but browse content decreased and forbs increased as winter progressed until April when consumption of new grass growth increased sharply. Dietary crude protein levels were marginally adequate for body maintenance during much of the winter. Levels of dietary in vitro digestible dry matter were inadequate. Browse was considered critical to winter survival of deer in Piceance Basin because it was the most available forage in deep snow. Also, its nutritional value was comparable or better than that of forbs and grasses selected by deer except in April when new plant growth was available. In spite of large variation in diet compositions, deer apparently selected forage mixes to maintain a consistent, although inadequate, diet quality through the critical wintering period. Piceance Basin in northwest Colorado is winter range for a large segment of the White River mule deer (Odocoileus hemionus) population. Impending oil shale development and associated problems of spent shale disposal and reclamation of disturbed areas have created widespread concern for the future welfare of deer in the basin. This future is clouded by the inability to predict how oil shale development will proceed and the eventual course and success of reclamation efforts. A current dilemma involves mitigation for areas already, or soon to be, removed from wildlife use by development. Mitigation is often viewed as some form of habitat improvement. For most wildlife species, particularly mule deer, what should be improved, how it can be improved, or even if improvement is practical or needed are elusive questions. Therefore, knowledge is needed of how deer utilize present winter habitats for both food and cover. This study examines patterns of food use by mule deer in undisturbed habitats. Objectives were to identify major species in winter-long deer diets to estimate quality of those diets on native pinyon-juniper (Pinus edulis-Juniperus

The Establishment of Cheatgrass (Bromus Tectorum L.) on Spent Oil Shale from the Paraho Process

AbstractExperiments were conducted in a greenhouse with the following objectives: (i) to study the emergence and seedling growth of cheatgrass (Bromus tectorum L.) in soil and in Paraho spent oil shale that was either leached, treated with sulfuric acid, covered with soil, or mixed with soil, and (ii) to study emergence and seedling growth of cheatgrass on spent shale that was fertilized with ammonium nitrate and triple superphosphate. The ECe of the spent shale was 14 mmhos/cm, the pH was 9 and the shale was low in plant available N and P. The soil from Federal oil shale lease tract U‐a near Bonanza, Utah was a coarse textured alluvium with low moisture retention. Cheatgrass planted on soil alone and shale covered with soil had the highest emergence rates (75–86%) and produced the greatest total biomass (8.55–13.4 g). Seedling emergence rates on leached and unleached spent shale were 44% and 36%, respectively, and total biomass was <1 g on either treatment. Seedlings failed to emerge on sulfuric acid‐treated spent shale. The addition of sulfuric acid to spent shale increased the ECe of the shale to over 21 mmhos/cm. Leached and unleached spent shale was fertilized with N at rates of 0, 28, and 56 kg/ha and P at rates of 0, 24.4, and 48.8 kg/ha. The total biomass for any fertilizer treatment was <1 g. We conclude that covering shale disposal piles with topsoil may improve the site for successful invasion by a colonizing species such as cheatgrass.

Salt Release and Movement in Processed Oil Shale

AbstractSalts present as a component of processed, discarded oil shale represent not only a potential environmental hazard, but also a detrimental influence in the reestablishment of vegetation on processed shale disposal sites. The saline characteristics of Paraho processed oil shale were investigated in a two‐phase series of laboratory experiments. The first phase studied the release of salts from two naturally distributed shale particle sizes packed in lysimeters constructed of plastic pipe and subjected to five leaching situations. All the lysimeters were instrumented with a porous‐cup‐vacuum system that allowed periodic nondestructive sampling of the soil solution with depth and time. Electrical conductivity and specific ion concentrations were measured. The second phase of the experiments involved subjecting three particle sizes of shale to a variety of shale/water ratios. The subsequent solutions were analyzed for electrical conductivity (EC) and concentrations of Ca, Mg, Na, K, Cl, and SO4.The lysimeter experiments demonstrated the highly soluble nature of the salts present in the Paraho processed shale. These salts are primarily composed of Mg, Na, and SO4 and are predominately in the precipitated form, existing external to the shale. The most efficient treatments for removing salt from the upper 60 cm of the shale were those in which large (about 0.5 pore volumes) pulses of water were applied. To reduce the EC to acceptable levels (<4.0 mmho/cm) required application of approximately 2 pore volumes of water.Results of the batch studies indicate a proportional relationship between dilution ratios and EC on a log‐log scale. Similar EC and dilution ratio relationships were observed for the cation sums. Ion analysis showed Mg and Na to be as much as 93% of the total water‐soluble cations and SO4 to be the dominant anion.

Salt Tolerance of Two Saltbush Species Grown in Processed Oil Shale

The tolerance of fourwing saltbush (A triplex canescens) and cuneate saltbush (Atriplex cuneata) to the salts in processed oil shale was studied in a greenhouse experiment over an ECe range of 4 to 38 mmho/cm. Growth responses differed, depending on the species and the particular salt or salts in the soil solution. Cuneate saltbush was more salt tolerant than fourwing saitbush, but both species survived and grew at salinities as high as 38 mmho/cm. Because of their high salt tolerance these saltbush species may be very important for use in the rehabilitation of processed oil shale disposal sites. Commercial scale surface retorting of oil shale will result in large amounts of processed shale that may be deposited in canyons as land fill. Any lessee of federal prototype oil shale lands is required to rehabilitate affected lands to a useable and productive condition. .compatible with existing adjacent undisturbed natural areas. .that will support fauna of the same kinds and in the same numbers as existing at the time the basline data were obtained. . (Federal Register 1973). Establishment of vegetation must be considered as one of the prime steps of rehabilitation. One of the major obstacles to successful plant establishment on processed oil shale is high salinity. Electrical conductivities of saturation extracts (ECe's) of several processed shale samples ranged from 9 to 26 mmho/ cm in studies of Schmehl and McCaslin (1973) and from 5 to 22 mmho/cm in our studies (Institute for Land Rehabilitation 1979). Soils are usually considered saline when ECe values reach 4 mmho/cm (Richards 1954). In addition to the total salinity, as measured by EC, the specific ion composition of the shale may have important effects on plant growth as well. The predominant soluble salts in processed oil shale are sodium sulfate and magnesium sulfate, while concentrations of chloride salts are relatively low (Schmehl and McCaslen 1973). For example, the first liter of leachate obtained from columns of paraho processed oil shale at Utah State University contained 509 milliequivalents per liter (meq/ l)Na +, 436 meq/ 1 Mg++, 882 meq/ 1 SO4'and only 14.1 meq/ 1 CL(Institute for Land Rehabilitation 1979). The leachate also contained 23.5 meq/l Ca,19.3 meq/ I K+, and 1.6 meq/l HCO3 Two plant species of interests for rehabilitating processed oil shale in Utah are fourwing saltbush (Atriplex canescens) and cuneate saltbush (Atriplex cuneata). Both species are native to the federal oil shale lease tracts, U-a and U-b, in eastern Utah (VTN Colorado, Inc. 1977). The species are noted for their salt and drought tolerance and their forage value (Blauer et al. 1976). These two species occupy different Authors are research associate and director, Institute for Land Rehabilitation, Utah State University, Logan 84322. This study was conducted as a project of the Institute for Land Rehabilitation, Utah State University, and was supported by funds from the White River Shale Project, Vernal, Utah. Manuscript received July 13, 1979. habitats and may have different soil requirements and salt