The Experts below are selected from a list of 18984 Experts worldwide ranked by ideXlab platform
Lei Wang - One of the best experts on this subject based on the ideXlab platform.
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green remediation of as and pb contaminated soil using Cement free clay based stabilization solidification
Environment International, 2019Co-Authors: Lei Wang, Daniel C W Tsang, Zhengtao Shen, Daniel S Alessi, Yong Sik Ok, Chi Sun PoonAbstract:Abstract Stabilization/solidification (S/S) is a low-cost and high-efficiency remediation method for contaminated soils, however, Conventional Cement-based S/S method has environmental constraints and sustainability concerns. This study proposes a low-carbon, Cement-free, clay-based approach for simultaneous S/S of As and Pb in the contaminated soil, and accordingly elucidates the chemical interactions between alkali-activated clay binders and potentially toxic elements. Quantitative X-ray diffraction and 27Al nuclear magnetic resonance analyses indicated that the addition of lime effectively activated the hydration of kaolinite clay, and the presence of limestone further enhanced the polymerization of hydrates. X-ray photoelectron spectroscopy showed that approximately 19% of As[III] was oxidized to As[V] in the alkali-activated clay system, which reduced toxicity and facilitated immobilization of As. During the Cement-free S/S process, As and Pb consumed Ca(OH)2 and precipitated as Ca3(AsO4)2·4H2O and Pb3(NO3)(OH)5, respectively, accounting for the low leachability of As (7.0%) and Pb (5.4%). However, the reduced amount of Ca(OH)2 decreased the degree of hydration of clay minerals, and the pH buffering capacity of the contaminated soil hindered the pH increase. Sufficient dosage of lime was required for ensuring satisfactory solidification and contaminant immobilization of the clay-based S/S products. The leachability of As and Pb in high-Ca S/S treated soil samples was reduced by 96.2% and 98.8%, respectively. This is the first study developing a green and Cement-free S/S of As- and Pb-contaminated soil using clay minerals as an environmentally compatible binding material.
Chi Sun Poon - One of the best experts on this subject based on the ideXlab platform.
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green remediation of as and pb contaminated soil using Cement free clay based stabilization solidification
Environment International, 2019Co-Authors: Lei Wang, Daniel C W Tsang, Zhengtao Shen, Daniel S Alessi, Yong Sik Ok, Chi Sun PoonAbstract:Abstract Stabilization/solidification (S/S) is a low-cost and high-efficiency remediation method for contaminated soils, however, Conventional Cement-based S/S method has environmental constraints and sustainability concerns. This study proposes a low-carbon, Cement-free, clay-based approach for simultaneous S/S of As and Pb in the contaminated soil, and accordingly elucidates the chemical interactions between alkali-activated clay binders and potentially toxic elements. Quantitative X-ray diffraction and 27Al nuclear magnetic resonance analyses indicated that the addition of lime effectively activated the hydration of kaolinite clay, and the presence of limestone further enhanced the polymerization of hydrates. X-ray photoelectron spectroscopy showed that approximately 19% of As[III] was oxidized to As[V] in the alkali-activated clay system, which reduced toxicity and facilitated immobilization of As. During the Cement-free S/S process, As and Pb consumed Ca(OH)2 and precipitated as Ca3(AsO4)2·4H2O and Pb3(NO3)(OH)5, respectively, accounting for the low leachability of As (7.0%) and Pb (5.4%). However, the reduced amount of Ca(OH)2 decreased the degree of hydration of clay minerals, and the pH buffering capacity of the contaminated soil hindered the pH increase. Sufficient dosage of lime was required for ensuring satisfactory solidification and contaminant immobilization of the clay-based S/S products. The leachability of As and Pb in high-Ca S/S treated soil samples was reduced by 96.2% and 98.8%, respectively. This is the first study developing a green and Cement-free S/S of As- and Pb-contaminated soil using clay minerals as an environmentally compatible binding material.
Zhengtao Shen - One of the best experts on this subject based on the ideXlab platform.
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green remediation of as and pb contaminated soil using Cement free clay based stabilization solidification
Environment International, 2019Co-Authors: Lei Wang, Daniel C W Tsang, Zhengtao Shen, Daniel S Alessi, Yong Sik Ok, Chi Sun PoonAbstract:Abstract Stabilization/solidification (S/S) is a low-cost and high-efficiency remediation method for contaminated soils, however, Conventional Cement-based S/S method has environmental constraints and sustainability concerns. This study proposes a low-carbon, Cement-free, clay-based approach for simultaneous S/S of As and Pb in the contaminated soil, and accordingly elucidates the chemical interactions between alkali-activated clay binders and potentially toxic elements. Quantitative X-ray diffraction and 27Al nuclear magnetic resonance analyses indicated that the addition of lime effectively activated the hydration of kaolinite clay, and the presence of limestone further enhanced the polymerization of hydrates. X-ray photoelectron spectroscopy showed that approximately 19% of As[III] was oxidized to As[V] in the alkali-activated clay system, which reduced toxicity and facilitated immobilization of As. During the Cement-free S/S process, As and Pb consumed Ca(OH)2 and precipitated as Ca3(AsO4)2·4H2O and Pb3(NO3)(OH)5, respectively, accounting for the low leachability of As (7.0%) and Pb (5.4%). However, the reduced amount of Ca(OH)2 decreased the degree of hydration of clay minerals, and the pH buffering capacity of the contaminated soil hindered the pH increase. Sufficient dosage of lime was required for ensuring satisfactory solidification and contaminant immobilization of the clay-based S/S products. The leachability of As and Pb in high-Ca S/S treated soil samples was reduced by 96.2% and 98.8%, respectively. This is the first study developing a green and Cement-free S/S of As- and Pb-contaminated soil using clay minerals as an environmentally compatible binding material.
Rafat Siddique - One of the best experts on this subject based on the ideXlab platform.
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sustainable geopolymer concrete using ground granulated blast furnace slag and rice husk ash strength and permeability properties
Journal of Cleaner Production, 2018Co-Authors: Ankur Mehta, Rafat SiddiqueAbstract:Abstract The paper presents the utilization of industrial by-products such as ground granulated blast furnace slag (GGBS) and rice husk ash (RHA) for the development of sustainable geopolymer concrete. GGBS-based geopolymer concrete mixture was prepared and the effect of adding RHA as partial replaCement of GGBS, on compressive strength, split tensile strength, chloride permeability and sorptivity were investigated up to the age of 90 days. In addition, SEM, EDS and XRD tests were also performed to observe the microstructure. The results indicate the development of geopolymer concrete using GGBS and RHA with high 3-day compressive strength of approximately 60 MPa, which can replace the Conventional Cement concrete and thus reduce carbon dioxide emissions. Also, the increase in compressive and split tensile strength, and reduction in chloride permeability and sorptivity was observed with the inclusion of RHA up to 15% at all ages. Beyond this optimum content of 15%, RHA inclusion showed negative results. In addition, the results of microstructure analysis showed more compact and dense micrograph of geopolymer concrete with 15% RHA, due to the coexistence of polymerization products with the additional calcium based hydration products.
Elena F. Burguera - One of the best experts on this subject based on the ideXlab platform.
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Injectable and rapid-setting calcium phosphate bone Cement with dicalcium phosphate dihydrate
Journal of biomedical materials research. Part B Applied biomaterials, 2006Co-Authors: Elena F. Burguera, Michael D. WeirAbstract:Calcium phosphate Cement (CPC) sets in situ with intimate adaptation to the contours of defect surfaces, and forms an implant having a structure and composition similar to hydroxyapatite, the putative mineral in teeth and bones. The objective of the present study was to develop an injectable CPC using dicalcium phosphate dihydrate (DCPD) with a high solubility for rapid setting. Two agents were incorporated to impart injectability and fast-hardening to the Cement: a hardening accelerator (sodium phosphate) and a gelling agent (hydroxypropyl methylcellulose, HPMC). The Cement with DCPD was designated as CPCD, and the Conventional Cement was referred to as CPCA. Using water without sodium phosphate, CPCA had a setting time of 82 ± 6 min. In contrast, CPCD exhibited rapid setting with a time of 17 ± 1 min. At 0.2 mol/L sodium phosphate, setting time for CPCD was 15 ± 1 min, significantly faster than 40 ± 2 min for CPCA (Tukey's at 0.95). Sodium phosphate decreased the paste injectability (measured as the paste mass extruded from the syringe divided by the original paste mass inside the syringe). However, the addition of HPMC dramatically increased the paste injectability. For CPCD, the injectability was increased from 65% ± 12% without HPMC to 98% ± 1% with 1% HPMC. Injectability of CPCA was also doubled to 99% ± 1%. The injectable and rapid-setting CPCD possessed flexural strength and elastic modulus values overlapping the reported values for sintered porous hydroxyapatite implants and cancellous bone. In summary, the rapid setting and relatively high strength and elastic modulus of CPCD should help the graft to quickly attain strength and geometrical integrity within a short period of time postoperatively. Furthermore, the injectability of CPCD may have potential for procedures involving defects with limited accessibility or narrow cavities, when there is a need for precise plaCement of the paste, and when using minimally invasive surgical techniques. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
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High early strength calcium phosphate bone Cement: Effects of dicalcium phosphate dihydrate and absorbable fibers†
Journal of biomedical materials research. Part A, 2005Co-Authors: Elena F. Burguera, Shozo Takagi, Laurence C. ChowAbstract:Calcium phosphate Cement (CPC) sets in situ to form resorbable hydroxyapatite with chemical and crystallographic similarity to the apatite in human bones, hence it is highly promising for clinical applications. The objective of the present study was to develop a CPC that is fast setting and has high strength in the early stages of implantation. Two approaches were combined to impart high early strength to the Cement: the use of dicalcium phosphate dihydrate with a high solubility (which formed the Cement CPC(D)) instead of anhydrous dicalcium phosphate (which formed the Conventional Cement CPC(A)), and the incorporation of absorbable fibers. A 2 x 8 design was tested with two materials (CPC(A) and CPC(D)) and eight levels of Cement reaction time: 15 min, 30 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, and 24 h. An absorbable suture fiber was incorporated into Cements at 25% volume fraction. The Gilmore needle method measured a hardening time of 15.8 min for CPC(D), five-fold faster than 81.5 min for CPC(A), at a powder:liquid ratio of 3:1. Scanning electron microscopy revealed the formation of nanosized rod-like hydroxyapatite crystals and platelet crystals in the Cements. At 30 min, the flexural strength (mean +/- standard deviation; n = 5) was 0 MPa for CPC(A) (the paste did not set), (4.2 +/- 0.3) MPa for CPC(D), and (10.7 +/- 2.4) MPa for CPC(D)-fiber specimens, significantly different from each other (Tukey's at 0.95). The work of fracture (toughness) was increased by two orders of magnitude for the CPC(D)-fiber Cement. The high early strength matched the reported strength for cancellous bone and sintered porous hydroxyapatite implants. The composite strength S(c) was correlated to the matrix strength S(m): S(c) = 2.16S(m). In summary, substantial early strength was imparted to a moldable, self-hardening and resorbable hydroxyapatite via two synergistic approaches: dicalcium phosphate dihydrate, and absorbable fibers. The new fast-setting and strong Cement may help prevent catastrophic fracture or disintegration in moderate stress-bearing bone repairs.