An official website of the United States government
Slag and Al/Mg oxide modified Douglas fir biochar (AMOB) were compared for their phosphate adsorbing abilities for use individually or in combination for simulated agriculture run-off remediation in wetlands. Aqueous batch and column sorption experiments were performed for both low-cost materials. AMOB was prepared in bulk using a novel green method. Material analyses included XRD, elemental analysis, SEM, EDX, and BET. Biochar and slag have different phosphate removal mechanisms. In short residence times (≤2 h), adsorption phenomena dominate for both adsorbents. Surface area likely plays a role in adsorption performance; slag was measured to be 4.1 m2/g while biochar’s surface area was 364.1 m2/g. In longer residence times (>2 h), the slow leaching of metals (Ca, Al, and Mg) from slag continue to remove phosphate through the precipitation of metal phosphates. In 24 h, slag removed more free phosphate from the solution than AMOB. Preliminary fixed bed column adsorption of slag or AMOB alone and in tandem was performed adopting a scaled-up model that can be used to remediate agricultural runoff with high phosphate content. Additionally, a desorption study was performed to analyze the efficiency of material regeneration. While AMOB does not release any adsorbed phosphates, slag slowly releases 5.7% adsorbed phosphate over seven days.
more »
« less
Modification of Natural Minerals with Technogenic Raw Materials
The presence of uranium-containing wastes from large provinces in the Republic of Kazakhstan significantly complicates the ecological situation, causing damage to the soil and hydrosphere due to the uncontrolled spread of large volumes of natural waters contaminated with radionuclides. They are usually utilized by the sorption method; however, the use of synthesized sorption materials is limited by their high price, and natural minerals are limited by low sorption characteristics. Many modification options are used in order to improve the sorption characteristics, but only a few methods have been found applied in industry. The main disadvantages include the complexity in the application and modification of reagents rarely used in industrial practice, which increases their cost, and is an obstacle to their widespread use. The authors of this research have studied the possibility of using technogenic raw materials—slags of phosphorus production—as a modifier of natural minerals. The methods of slag activation are investigated, the optimal conditions for the modification of the natural minerals zeolite and shungite by activated slag are determined, and the sorption properties of modified sorbents are studied.
more »
« less
- Award ID(s):
- 2113498
- PAR ID:
- 10435218
- Date Published:
- Journal Name:
- Metals
- Volume:
- 12
- Issue:
- 11
- ISSN:
- 2075-4701
- Page Range / eLocation ID:
- 1907
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Geopolymers are structural materials that can be used as a viable alternative to ordinary portland cement concrete. However, their widespread adoption has been limited by the lack of understanding in their fundamental reaction mechanisms. Microwave characterization methods have shown promise at understanding these reaction mechanisms. However, the complex dielectric properties of geopolymer precursor powders and the effect of void content must first be understood. Therefore, in this work, the dielectric properties of two geopolymer precursor powders (blast furnace slag and fly ash) are measured. Then, the effect of void content and particle size distribution (PSD) is considered on the measured dielectric properties. By characterizing the inherent void content of these powder materials, this effect can be removed and therefore the true dielectric properties of the materials can be determined. The results show that the void content has a significant effect on the measured dielectric properties.more » « less
-
null (Ed.)In this study, in situ quasi-elastic neutron scattering (QENS) has been employed to probe the water dynamics and reaction mechanisms occurring during the formation of NaOH- and Na 2 SiO 3 -activated slags, an important class of low-CO 2 cements, in conjunction with isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR) analysis and N 2 sorption measurements. We show that the single ICC reaction peak in the NaOH-activated slag is accompanied with a transformation of free water to bound water (from QENS analysis), which directly signals formation of a sodium-containing aluminum-substituted calcium–silicate–hydrate (C–(N)–A–S–H) gel, as confirmed by FTIR. In contrast, the Na 2 SiO 3 -activated slag sample exhibits two distinct reaction peaks in the ICC data, where the first reaction peak is associated with conversion of constrained water to bound and free water, and the second peak is accompanied by conversion of free water to bound and constrained water (from QENS analysis). The second conversion is attributed to formation of the main reaction product ( i.e. , C–(N)–A–S–H gel) as confirmed by FTIR and N 2 sorption data. Analysis of the QENS, FTIR and N 2 sorption data together with thermodynamic information from the literature explicitly shows that the first reaction peak is associated with the formation of an initial gel (similar to C–(N)–A–S–H gel) that is governed by the Na + ions and silicate species in Na 2 SiO 3 solution and the dissolved Ca/Al species from slag. Hence, this study exemplifies the power of in situ QENS, when combined with laboratory-based characterization techniques, in elucidating the water dynamics and associated chemical mechanisms occurring in complex materials, and has provided important mechanistic insight on the early-age reactions occurring during formation of two alkali-activated slags.more » « less
-
The mineral carbon sequestration capacity of basic oxygen furnace (BOF) slag offers great potential to absorb carbon dioxide (CO2) from landfill emissions. The BOF slag is highly alkaline and rich in calcium (Ca) containing minerals that can react with the CO2to form stable carbonates. This property of BOF slag makes it appealing for use in CO2sequestration from landfill gas. In a previous study, CO2and CH4removal from the landfill gas was investigated by performing batch and column experiments with BOF slag under different moisture and synthetic landfill gas exposure conditions. The study showed two stage CO2removal mechanism: (1) initial rapid CO2removal, which was attributed to the carbonation of free lime (CaO) and portlandite [(Ca(OH)2)], and (2) long-term relatively slower CO2removal, which was attributed to be the gradual leaching of Ca2+from minerals (calcium-silicates) present in the BOF slag. Realising that the particle size could be an important factor affecting total CO2sequestration capacity, this study investigates the effect of gradation on the CO2sequestration capacity of the BOF slag under simulated landfill gas conditions. Batch and column experiments were performed with BOF slag using three gradations: (1) coarse (D50 = 3.05 mm), (2) original (D50 = 0.47 mm), and (3) fine (D50 = 0.094 mm). The respective CO2sequestration potentials attained were 255 mg g−1, 155 mg g−1, and 66 mg g−1. The highest CO2sequestration capacity of fine BOF slag was attributed to the availability of calcium containing minerals on the slag particle surface owing to the highest surface area and shortest leaching path for the Ca2+from the inner core of the slag particles.more » « less
-
Fugitive methane (CH4) and carbon dioxide (CO2) emissions at municipal solid waste (MSW) landfills constitute one of the major anthropogenic sources of greenhouse gas (GHG) emissions to the atmosphere. In recent years, biocovers involving the addition of organic-rich amendments to landfill cover soils is proposed to promote microbial oxidation of CH4 to CO2. However, most of the organic amendments used have limitations. Biochar, a solid byproduct obtained from gasification of biomass under anoxic or low oxygen conditions, has characteristics that are favorable for enhanced microbial oxidation in landfill covers. Recent investigations have shown the significant potential of biochar-amended cover soils in mitigating the CH4 emissions from MSW landfills. Although the CH4 emissions are mitigated, there is still considerable amount of CO2 that is emitted to the atmosphere as a result of microbial oxidation of CH4 in landfill covers as well as the CO2 derived from MSW decomposition. Basic oxygen furnace (BOF) slag is a product of steel making has great potential for CO2 sequestration due to its strong alkaline buffering and high carbonation capacity. In an ongoing project, funded by the U.S. National Science Foundation, the potential use of BOF slag in landfill covers along with biochar-amended soils to mitigate both CH4 and CO2 emissions is being investigated. This paper presents the initial results from this study and it includes detailed physical and chemical and leachability characteristics of BOF slag, and a series of batch tests conducted on BOF slag to determine its CH4 and CO2 uptake capacity. The effect of moisture content on the carbonation capacity of BOF slag was also evaluated by conducting batch tests at different moisture contents. In addition, small column experiments were conducted to evaluate the gas migration, transport parameters and the CO2 sequestration potential of BOF slag under simulated landfill gas conditions. The result from the batch and column tests show a significant uptake of CO2 by BOF slag for the tested conditions and demonstrates excellent potential for its use in a landfill cover system.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/met12111907
