Effect of cement kiln dust, lime and fly ash on metal leaching characteristics of oil sands tailings from Alberta, Canada

Effect of cement kiln dust on the low-temperature durability and fatigue life of hot mix asphalt

Heavy metal speciation and leaching behaviors in cement based solidified/stabilized waste materials

Three experiments were conducted to determine (1) the effect of cement kiln dust (CKD) on the growth of lambs fed high- or low-roughage diets, (2) the effect of pelleting on lamb diets which contain CKD, and (3) the effect of different levels of dietary CKD on lamb performance. In exp. 1, lambs were fed complete pelleted diets containing 15 or 45% ground timothy hay with either 0 or 3% CKD. There were no differences in weight gain due to CKD addition. The feed consumed was greater for the high roughage-CKD group (P < 0.05). Feed:gain ratios were greater for the high-roughage groups (P < 0.01). The pH of gastrointestinal tract contents showed an increase due to CKD only in the cecum and colon. The carbohydrate level in the colon of lambs fed the low-roughage rations was lower (P < 0.05) with added CKD. In exp. 2, lambs were fed CKD diets in mash and pelleted form, a complete pelleted CKD diet (including hay) or a mash CKD-free control. All diets except the complete pelleted-CKD diet were fed with hay, ad libitum. Lambs fed the pelleted CKD diet plus hay grew faster than the control group (P < 0.05) with growth in the other groups not different from either extreme. In exp. 3, lambs were fed similar diets containing 0, 1, 2 or 3% CKD. Growth was not different for any of the groups. Fecal pH was elevated in two of the CKD groups. Analysis of feces showed no difference in nitrogen, soluble carbohydrate, ADF or NDF as a percent of organic matter. Fecal ash increased with increasing level of CKD (P < 0.01). Key words: Lamb, cement kiln dust, growth rate, digesta pH

In Alberta, Canada, bitumen production by surface mining followed by ore-water slurry based extraction processes is approaching 2,000,000 bbl/d capacity. The Clark Hot Water Extraction process developed in the 1930s is used at all commercial plants which use caustic NaOH as an additive to boost bitumen recovery efficiency. Use of NaOH as an extraction process additive increases process water salinity, specifically Na+ concentration, promotes dispersion of silt and clay size particles which results in greater production of toxic mature fine tailings. Increase in process water Na+ concentration detrimentally affects the performance of both bitumen extraction and tailings disposal processes. Existing mature fine tailings inventory stored in tailings ponds is exceeding 900x106 m3 and is predicted to grow alarmingly faster by the completion of new plants and by an increase in the production capacity of the existing plants. The Energy Resources Conservation Board of Alberta issued Directive 074 in February, 2009 urging oil sands plants to comply with a 50% reduction in mature fine tailings production. Proposed policies by the oil industry in response to Directive 074 have shown short fallings; which suggests that development of novel bitumen extraction and tailings management processes are needed. To reduce the mature fine tailings inventory, we studied production of nonsegregating tailings by treating a blend of cyclone underflow and thickened cyclone overflow with CaO additive. These tests were made using Albian Sands Muskeg River Mine tailings when the plant was operating at nonadditive and sodium citrate additive extraction modes and using Syncrude Canada Ltd.'s Aurora Mine tailings. Also, we studied the use of CaO as a bitumen extraction process additive replacing NaOH in the Clark Hot Water Extraction process; by which silt-clay size particles dispersion in the extraction process slurry is reduced and accumulation of Na+ in the process water is eliminated. Use of CaO as an extraction additive is considered as a fundamental and a new process alteration by the oil sands operators. Recently, to evaluate this new process the Canadian Oil Sands Innovation Alliance (COSIA) has requested NAIT-NARCOSS, an independent academic and industrial research laboratory, to perform a third party verification study for the use of CaO as a bitumen extraction process additive. The NAIT-NARCOSS test results are completed and are highly encouraging, confirming that use of CaO as an extraction process additive reduces dispersion of silt and clay size particles in the extraction process slurry without harming bitumen recovery efficiency. It also improves process water chemistry by eliminating accumulation of Na+ in the process water. It is concluded that a paradigm change is offered to the oil sands industry to reduce the adverse environmental impacts of oil sands plants in simple, cost effective and environmentally friendly manners; which is the simultaneous implementation of the use of CaO as additives in bitumen extraction and nonsegregating tailings production processes.

<p>An experimental study was conducted to determine the effect of cement kiln dust (CKD) and fly ash (FA) on compaction and strength characteristics of the high-plasticity clay obtained from a forest road in North of Iran.  Accordingly, the soil was mixed with 15% CKD by dry weight the soil, and a partial replacement of the CKD with 10, 20, and 30% FA was applied to produce mixtures. The unconfined compressive strength tests were performed on specimens after a curing time 7 and 28 days. Also, the microstructures of untreated and treated specimens were examined using a scanning electron microscope (SEM). It was found that incorporation of CKD and FA leads to a decrease in the volume of pores in the soil matrix, which is due to the formation of calcium silicate hydrates and calcium aluminate hydrates gels. These cementitious compounds in the mixtures were presumed to be the significant factor contributing to strength improvements.</p>

Performance evaluation of intermediate cover soil barrier for removal of heavy metals in landfill leachate

Cement, lime, and Fly Ash (FA) are the major traditional soil stabilizers. Cement production contributes 0.8-0.9 tons of carbon emissions per ton of cement, while lime production generates around 1.2 tons of CO2 per ton of cement. FA is not readily available in all regions, necessitating the exploration of alternative stabilizing agents. Cement Kiln Dust (CKD) and Sugar-Cane Bagasse Ash (SCBA) are waste products from cement and sugarcane production, respectively. This study investigated the use of CKD and SCBA to stabilize black cotton soil. CKD was incorporated into the soil at 0, 2, 4, 6, 8, and 10% for standard Proctor compaction, consistency limits, Free Swell Index (FSI), Unconfined Compressive Strength (UCS), and California Bearing Ratio (CBR) testing. The optimal CKD content based on UCS and CBR was 6%, while the optimal CKD-SCBA composite was 6% CKD and 10% SCBA. The third part of the Kenyan Road Design Manual (KRDM III) categorizes subgrades by strength based on the CBR, ranging from S1 to S6. Subgrades classified as S1 exhibit the lowest strength (CBR of 2-5%), while S6 denotes the highest strength (CBR of 30% or greater). The untreated black cotton soil, with a CBR of less than 2%, was unsuitable as a subgrade. The CKD-SCBA composite improved the soil's CBR to 16.43%, upgrading it to an S4 subgrade, which can reduce the pavement thickness and associated costs. Other enhancements included an increase in UCS from 97.5 kPa to 555.81 kPa, a reduction in the FSI from 86% to 45%, and a reduction in Plasticity Index (PI) from 26.18% to 15.26%.

Cement kiln dust is a potential source of K and Ca for crops on acidic soils in Eastern Canada. The objective of this study was to assess the effect of cement kiln dust on soil chemical properties and potato (Solanum tuberosum L. cv. Superior) yield and quality on two Spodosols. Four rates of cement kiln dust, commercial K fertilizers, and lime were yearly applied and arranged in a randomized complete block design with four replicates. Soil extractable K and Ca increased rapidly after cement kiln dust applications and were comparable to commercial fertilizers or lime treatments. Heavy metal soil contents and plant uptake were not influenced by treatments. Soil metal contents decreased from to initial soil levels and were lower than recommended maximal norms. Tuber yields increased with rates of cement kiln dust and commercial fertilizers but decreased with lime rates. Yields were positively correlated to soil extractable K and partially with extractable Mg. The K and Mg plant uptake increased with cement kiln dust and commercial fertilizers rates but was significantly reduced by liming. Tuber specific gravity decreased with the highest commercial fertilizers and cement kiln dust rates. These results showed that cement kiln dust is an effective source of K and Ca for potato production without short term loss in tuber quality or soil contamination by metals.

Water availability is beginning to impact oil sands development and, as a result, several technologies to increase the percentage of recycled water are being evaluated. One such option being re-evaluated is the use of centrifuges to produce dry tailings that can accommodate overburden and soil replacement. Previous evaluations of centrifuge performance to capture water from the clay and silt tailings (mature fine tailings) components demonstrated some success but, at the time, at unacceptable costs. A better appreciation of the long-term costs of mature fine tailings storage has prompted a re-evaluation of centrifuge technology. The use of additives to improve centrifuge performance has significantly improved the results that can be achieved. Aside from the obvious positive environmental benefit of reclaiming the fluid fine (mature fine) tailings, the increase in the amount of water recycled will reduce the demand for fresh water from the Athabasca River. This paper discusses a laboratory-scale study of the water chemistry and clay/silt feed properties affecting centrifuge performance, as well as the results of a 20 tonne per hour pilot. Introduction The term dry stackable tailings is commonly used in oil sands tailings management to mean a mineral stream left over from the bitumen extraction process which can be stored without the need for dikes or other fluid containment structures. The use of water in the bitumen extraction process results in mineral tailings streams in the form of slurries or suspensions that require containment. In general, surface mined oil sands tailings fall into three categories: sand tailings, fine tailings and froth treatment tailings. Although the froth treatment tailings have important environmental implications due to their contamination with solvents or diluents from the froth treatment process, they are generally combined with the other tailings prior to discharge into the recycle water area (tailings settling pond). It is typically a straightforward process to create dry stackable tailings from the sand tailings, and they are often used to build the containment for the remaining fluid fine tailings. Another common practice in the surface mined oil sands industry is to define sand as mineral particles larger than 44 micrometres (µm). Fines are therefore smaller than 44 µm, and this definition can be useful when discussing the long-term tailings properties during mine planning. It has been demonstrated very clearly, however, that it is the clay content that determines all of the important properties of the fine tailings or fluid fine tailings (or mature fine tailings when the solids content exceeds about 25 wt%)(1–3). Over the entire mine, of course, the average clay-to-fines ratio is fixed and the fines content can be a useful approximation tool for large-scale planning purposes and the prediction of sand volumes and the fine tailings volume that may require containment. The clay content, often expressed as a clay-to-fines ratio, can vary across an oil sands lease by as much as a factor of four. It is therefore essential that the clay content, clay-to-water ratio or clay-to-fines ratio be understood in order to predict the properties of the fluid fine tailings on a daily or monthly basis.

Heavy metals in urban soils may pose risks to both urban environment and human health. However, only a fraction of heavy metals in soil is mobile and/or bioavailable for plant uptake and human ingestion. This study evaluates the chemical fraction and potential mobility and bioaccessibility of heavy metals (Cd, Cr, Cu, Pb, and Zn) in the contaminated urban topsoils from steel-industrial city (Anshan), Northeastern China. Chemical forms of heavy metals in soils are determined using Tessier sequential extraction technique. The toxicity characteristic leaching procedure (TCLP), ethylenediaminetetraacetic acid (EDTA), and US Pharmacopeia methodology (USPM) are used to determine the operationally defined potentially mobile and bioaccessible metal fractions, respectively. Sequential extraction results show that Cd has the highest percentage of exchangeable form, whereas Cr primarily exists in residual form. The non-residual fraction of heavy metals increases in the order of Cr < Cu < Pb < Zn < Cd. The leachability of heavy metals evaluated by TCLP test indicates that Cd, Zn, Cu, and Pb have much higher mobile than Cr. The bioavailability of heavy metals determined by EDTA extraction decreases in the order of Pb > Cu ≅ Zn > Cd > Cr. The order of bioaccessibility determined by USPM extraction is Pb = Cu > Zn > Cd > Cr. The Cr exhibits the lowest leachability and bioaccessibility among the investigated metals. The Pb has the highest bioaccessibility, indicating higher potential hazard for the human health. There are significant relationships between the EDTA- and USPM-extractable metals (Cd, Cu, Pb, and Zn) and the sum of first three steps of sequential extraction. Highly significant correlation is found between amounts of EDTA-extractable Cd, Cu, Pb, and Zn and USPM-extractable metals. The result suggests that EDTA extraction can be helpful to estimate the bioaccessibility of heavy metals for human ingestion. Introduction of mobile and human bioaccessible concentrations into risk assessments can give more realistic implications for urban environmental management.

This paper investigated the effect of cement kiln dust (CKD) on the geotechnical properties of clay. Soil sample was collected from clay deposit at Ede North Local Government Area, Osun State, which lies within the geographical coordinates of 7N and 4E, was treated with up to 10% CKD. Sieve analysis, specific gravity, consistency limits, compaction (British Standard Light, BSL and West African Standard, WAS) and California Bearing Ratio (CBR) tests were carried out on both treated and untreated soil samples. Results showed that Ede clay is an A-7- 6 soil. Specific gravity increased from 2.61 to 2.91 with increase in CKD from 0 to 10%, maximum dry density (MDD) of the natural soil sample increased from 1.72 and 1.76 g/m’ to 1.84 and 1.85 g/m’ at 8% CKD for BSL and WAS, respectively. The unsoaked CBR of the specimen increased from 17 to 35% for 0-10% addition of CKD, and a similar trend was observed for the 24 hours soaked CBR values. This study indicated that CKD, though regarded as waste material, can be used to improve the geotechnical properties of Ede clay.

Study of the effect of cement kiln dust on the mechanical, thermal and durability properties of compressed earth blocks

Assessment of cement kiln dust (CKD) for stabilization/solidification (S/S) of arsenic contaminated soils

As traditional petroleum supplies dwindled and prices soared over the past few years, oil companies have shifted their attention to oil sands, a mix of sand, water, and a heavy, viscous hydrocarbon called bitumen that can be converted to oil. With the plunge in oil prices in fall 2008, many producers began canceling or postponing plans to expand oil sands development projects, but this turn of events could yet reverse, as Canada’s vast oil sands deposits are lauded as a secure source of imported oil for the United States. At the same time, however, oil sands present troubling questions in terms of the environmental health effects associated with their development.

A retrofit of the San Francisco Oakland Bay Bridge involves more than 30 different concrete mixes, each of which confers specific advantages.For instance, according to the U.S. EPA, concrete containing more than 50% fly ash resists the cracking and corrosion associated with seawater.