Irene Lo - Academia.edu (original) (raw)

Papers by Irene Lo

Research paper thumbnail of Remediation of chlorinated aliphatic hydrocarbons in groundwater using Fe° PRB

IAHS-AISH publication, 2005

Research paper thumbnail of Hazardous Waste and Inorganics Removal

Research paper thumbnail of Removals of Chlorinated Aliphatic Hydrocarbons by Fe <sup>0</sup> : Full-scale PRB vs Column Study

American Society of Civil Engineers eBooks, Oct 27, 2006

Research paper thumbnail of Evaluation of the hydraulic performance of a full scale permeable reactive barrier by a tracer study

Investigation of the hydraulic performance of a funnel-and-gate permeable reactive barrier (PRB),... more Investigation of the hydraulic performance of a funnel-and-gate permeable reactive barrier (PRB), packed with zero-valent iron (Fe°) and installed at the Vapokon site, Denmark, has been conducted with a natural gradient tracer study. The purposes of this study were to evaluate the flow pattern and determine the seepage velocity (ν x ) of groundwater through the PRB. After collecting and analysing about 13 000 groundwater samples over a period of 10 months, the moving path of the tracer (i.e. lithium, Li + ) was identified in which the Li + plume was observed passing through the reactive barrier. However, probably owing to clogging caused by mineral precipitates, there was a preferential path inside the Fe 0 PRB. Comparison of the water table contour in the Vapokon site obtained in March 2000 and January 2003 showed formation of a low permeability zone within the reactive barrier, thereby further verifying clogging caused by mineral precipitates. Spatial moments analysis of the Li distribution illustrates the similarity of the maximum Li + mass passing through the upgradient and downgradient locations of the Fe 0 PRB and thereby indicated the conservative of the Li - across the reactive barrier as well as the absence of bypassing flow. Based upon the results of first moment analysis, a ν x of 99.5 m year -1 within the PRB was calculated. The ν x just upgradient of the reactive barrier, however, was only about 6.86 m year -1 , most likely owing to the effect of disturbance exerted by the clogged upgradient interface of the upper part of the Fe 0 PRB.

Research paper thumbnail of Potential and prospects of photocatalytic disinfection: using sustainable solarenergy- driven photocatalysts

Special Issue with Awarded and Shortlisted Papers from the HKIE Outstanding Paper Award for Young Engineers/Researchers 2021, 2021

A new measurement system called Crosshole Sonic Logging Tomography (CSLT) provides information on... more A new measurement system called Crosshole Sonic Logging Tomography (CSLT) provides information on the size, shape, and orientation of defects in a bored pile. The CSLT measurement system has not (yet) been accredited in Hong Kong for foundation testing. Bored piles in Hong Kong are generally wide and deep. Existing measurement accuracy studies do not consider this large type of bored piles. The objective of this research is to quantify the measurement accuracy and precision of the CSLT method for large diameter bored piles (the most common pile type for public housing projects in Hong Kong). A test pile was constructed with known defects and perform experiments with a CSLT measurement system to quantify its accuracy and precision. CSLT is found to be accurate in detecting shape, size, and location of large defects but small defects close to the tube are difficult to detect. Generally speaking, CSLT has satisfactory accuracy and precision for practical use. The use of CSLT can be con...

Research paper thumbnail of Nanotechnologies for Water Environment Applications

This book is useful to undergraduate and graduate students in engineering and practicing engineer... more This book is useful to undergraduate and graduate students in engineering and practicing engineers, as well as educators, scientists, government officials, policymakers, and industrial process managers.

Research paper thumbnail of Rapid disinfection of E. coli by a ternary BiVO4/Ag/g-C3N4 composite under visible light: photocatalytic mechanism and performance investigation in authentic sewage

Environmental Science: Nano, 2019

Z-scheme photocatalyst BiVO4/Ag/g-C3N4 was constructed and applied for rapid disinfection of E. c... more Z-scheme photocatalyst BiVO4/Ag/g-C3N4 was constructed and applied for rapid disinfection of E. coli cells in water and wastewater.

Research paper thumbnail of Influence of weak magnetic field and tartrate on the oxidation and sequestration of Sb(III) by zerovalent iron: Batch and semi-continuous flow study

Journal of Hazardous Materials, 2017

Oxidation of Sb(III)-tartrate and Sb(III) in the Fe 0-H2O-O2 system was studied. WMF greatly enha... more Oxidation of Sb(III)-tartrate and Sb(III) in the Fe 0-H2O-O2 system was studied. WMF greatly enhanced Sb(III)-tartrate and Sb(III) removal by ZVI. WMF also increased the removal capacity of Sb(III)-tartrate and Sb(III) by ZVI. Tartrate significantly retarded Sb(III) removal by ZVI. The mechanisms of the inhibiting effect of tartrate were clarified.

Research paper thumbnail of Pulverized Fuel Ash Solidification/Stabilization of Waste: Comparison Between Beneficial Reuse of Contaminated Marine Mud and Sediment

JOURNAL OF ENVIRONMENTAL ENGINEERING AND LANDSCAPE MANAGEMENT, 2015

This study aimed to maximize the utilization of contaminated marine mud and sediment for benefici... more This study aimed to maximize the utilization of contaminated marine mud and sediment for beneficial reuse by solidification/stabilization (S/S) treatment with cement and pulverized fuel ash (PFA). For the purposes of waste maximization and enhancing the mechanical property of the S/S mixtures, mixing 75% by mass of either contaminated marine mud or sediment with 20% and 5% of cement and PFA, respectively, was found to be the optimal mix design. Their unconfined compressive strengths reached up to 8.32 MPa and 4.47 MPa, respectively. Apart from the mechanical property, according to the U.S.EPA, the TCLP results show that all regulated heavy metals were immobilized to a safe level and are available for engineering application such as fill material. The results of XRD reveal that the formation of CSH gel in the S/S treated mud and sediment is responsible for the strength development and heavy metal immobilization.

Research paper thumbnail of Design Methodology for the Application of a Permeable Reactive Barrier for Groundwater Remediation

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Research paper thumbnail of Sustainable Wastewater Treatment Using Microsized Magnetic Hydrogel with Magnetic Separation Technology

Industrial & Engineering Chemistry Research, 2014

A novel magnetic polymeric adsorbent, namely magnetic hydrogel, was used to investigate its reusa... more A novel magnetic polymeric adsorbent, namely magnetic hydrogel, was used to investigate its reusability and applicability in Cr(VI)-bearing wastewater treatment using magnetic separation. Different concentrations and amounts of NaCl solution, and a step-wise approach were used for the regeneration experiment. A step-wise adsorption process followed by step-wise 3.0 M NaCl regeneration with 40:1 wastewater-to-recovery volume ratio was found to be the most applicable working condition. The Cr concentration in the recovery solution was increased 25-30 times to 500-600 mg/L. The Cr(VI) removal and recovery performance of magnetic hydrogel was maintained for 20 cycles. An industrial wastewater treatment prototype, including a magnetic separation unit, was developed. The magnetic separation unit was designed to provide a magnetic field at the bottom with a zigzag pathway feature for maximizing the chance of capturing magnetic hydrogel. The separation efficiency for the magnetic hydrogel was above 97% throughout the 20 cycles of treatment. The results of the prototype experiment also indicated that magnetic hydrogel can *Manuscript Click here to view linked References effectively remove Cr(VI) and can also be separated and recovered by the magnetic separation unit in 20 cycles.

Research paper thumbnail of Couples of Precipitation-Dissolution and Reduction-Oxidation Reactions

Natural Processes and Systems for Hazardous Waste Treatment, 2007

Research paper thumbnail of Redox and Precipitation

Remediation Technologies for Soils and Groundwater, 2007

Research paper thumbnail of Chemical Reactive Barriers

Remediation Technologies for Soils and Groundwater, 2007

Research paper thumbnail of Competitive Effects on the Dechlorination of Chlorinated Aliphatic Hydrocarbons by Zero-valent Iron

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by zero-valent iron (Fe 0 ) was found... more Dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by zero-valent iron (Fe 0 ) was found to be influenced by the competitive effects exerted by other groundwater contaminants. Laboratory column study of the competitive effects on CAH dechlorination by Fe 0 indicated that the presence of 1,1,1-trichloroethane (1,1,1-TCA) in the trichloroethylene (TCE)-contaminated groundwater could decrease the normalized dechlorination rate constant (k SA ) of TCE from 3.04 x 10 -2 to 2.74 x 10 -2 mL m -2 hr -1 . In a similar fashion, introduction of chloroform (TCM) into the synthetic groundwater containing TCE and 1,1,1-TCA led to a 40 to 54% drop in TCE and 1,1,1-TCA k SA , thus indicating competition among TCE, 1,1,1-TCA and TCM during dechlorination reactions induced by Fe 0 . Activation energy ranging from 34.3 to 53.7 kJ/mol for the simultaneous dechlorination of TCE, 1,1,1-TCA and TCM by Fe 0 showed that the process of the electron transfer from Fe 0 to the CAHs is the dominant step limiting the rate of the dechlorination reactions so that the electron released from Fe 0 is most likely in competition with TCE, 1,1,1-TCA and TCM during the dechlorination reactions. In addition to CAHs, abiotic reduction of hexavalent chromium [Cr(VI)] by Fe 0 also exerted effects on TCE dechlorination leading to a 31% drop in TCE k SA after the addition of Cr(VI) into the TCE-contaminated groundwater. Groundwater geochemical factors such as alkalinity and contaminant concentration could potentially influence competition among TCE, 1,1,1-TCA, TCM and Cr(VI) during the abiotic reduction of chemical substances by Fe 0 .

Research paper thumbnail of Hydraulic Studies of Zero-Valent Iron in Permeable Reactive Barriers Using Tracer Experiment

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Research paper thumbnail of Configuration and Construction of Zero-valent Iron Reactive Barriers

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Research paper thumbnail of Some Bounds on the Rainbow Connection Number of 3-, 4- and 5-connected Graphs

Cornell University - arXiv, Dec 24, 2012

The rainbow connection number, rc(G), of a connected graph G is the minimum number of colors need... more The rainbow connection number, rc(G), of a connected graph G is the minimum number of colors needed to color its edges so that every pair of vertices is connected by at least one path in which no two edges are colored the same. We show that for κ = 3 or κ = 4, every κ-connected graph G on n vertices with diameter n κ − c satisfies rc(G) ≤ n κ + 15c + 18. We also show that for every maximal planar graph G, rc(G) ≤ n κ + 36. This proves a conjecture of Li et al. for graphs with large diameter and maximal planar graphs.

Research paper thumbnail of Dynamic Matching in School Choice: Efficient Seat Reassignment after Late Cancellations

SSRN Electronic Journal, 2017

In the school choice market, where scarce public school seats are assigned to students, a key ope... more In the school choice market, where scarce public school seats are assigned to students, a key operational issue is how to reassign seats that are vacated after an initial round of centralized assignment. Practical solutions to the reassignment problem must be simple to implement, truthful and efficient while also alleviating costly student movement between schools. We propose and axiomatically justify a class of reassignment mechanisms, the Permuted Lottery Deferred Acceptance (PLDA) mechanisms. Our mechanisms generalize the commonly used Deferred Acceptance (DA) school choice mechanism to a two-round setting and retain its desirable incentive and efficiency properties. School choice systems typically run DA with a lottery number assigned to each student to break ties in school priorities. We show that under natural conditions on demand, the second round tie-breaking lottery can be correlated arbitrarily with that of the first round without affecting allocative welfare, and reversing the lottery order between rounds minimizes reassignment among all PLDA mechanisms. Empirical investigations based on data from NYC high school admissions support our theoretical findings.

Research paper thumbnail of Study of zinc in cementitious material stabilised/solidified wastes by sequential chemical extraction and microstructural analysis

Chemical Speciation & Bioavailability, 2001

In the present study, a five step sequential chemical extraction (SCE) procedure was employed to ... more In the present study, a five step sequential chemical extraction (SCE) procedure was employed to investigate the binding mechanisms and chemical partitioning of zinc in cement-based stabilised waste materials. After each step of SCE, scanning electronic microscope with energy dispersive spectrometer (SEM/EDS) and X-ray diffraction (XRD) were used to assess the microstructural and chemical changes of the waste materials. The results showed that the leaching of Zn from the cement based stabilised waste mainly took place at the second and the third extraction steps at pH 5.0 and 2.0, respectively. The addition of pulverised fly ash (PFA) increased the leachability of Zn at the second extraction step. The SCE results also indicated the hydration of cement was greatly retarded by the incorporation of zinc waste. The SEM and XRD analysis of the samples after each extraction step demonstrated that zinc leached at the second step extraction was partially due to the dissolution of the new crystalline phase (ZnO) in the waste materials. Since large amounts of zinc were leached out only at the third extraction step at pH 2.0, these stablised waste materials may be relatively stable under a normal disposal environment.

Research paper thumbnail of Remediation of chlorinated aliphatic hydrocarbons in groundwater using Fe° PRB

IAHS-AISH publication, 2005

Research paper thumbnail of Hazardous Waste and Inorganics Removal

Research paper thumbnail of Removals of Chlorinated Aliphatic Hydrocarbons by Fe <sup>0</sup> : Full-scale PRB vs Column Study

American Society of Civil Engineers eBooks, Oct 27, 2006

Research paper thumbnail of Evaluation of the hydraulic performance of a full scale permeable reactive barrier by a tracer study

Investigation of the hydraulic performance of a funnel-and-gate permeable reactive barrier (PRB),... more Investigation of the hydraulic performance of a funnel-and-gate permeable reactive barrier (PRB), packed with zero-valent iron (Fe°) and installed at the Vapokon site, Denmark, has been conducted with a natural gradient tracer study. The purposes of this study were to evaluate the flow pattern and determine the seepage velocity (ν x ) of groundwater through the PRB. After collecting and analysing about 13 000 groundwater samples over a period of 10 months, the moving path of the tracer (i.e. lithium, Li + ) was identified in which the Li + plume was observed passing through the reactive barrier. However, probably owing to clogging caused by mineral precipitates, there was a preferential path inside the Fe 0 PRB. Comparison of the water table contour in the Vapokon site obtained in March 2000 and January 2003 showed formation of a low permeability zone within the reactive barrier, thereby further verifying clogging caused by mineral precipitates. Spatial moments analysis of the Li distribution illustrates the similarity of the maximum Li + mass passing through the upgradient and downgradient locations of the Fe 0 PRB and thereby indicated the conservative of the Li - across the reactive barrier as well as the absence of bypassing flow. Based upon the results of first moment analysis, a ν x of 99.5 m year -1 within the PRB was calculated. The ν x just upgradient of the reactive barrier, however, was only about 6.86 m year -1 , most likely owing to the effect of disturbance exerted by the clogged upgradient interface of the upper part of the Fe 0 PRB.

Research paper thumbnail of Potential and prospects of photocatalytic disinfection: using sustainable solarenergy- driven photocatalysts

Special Issue with Awarded and Shortlisted Papers from the HKIE Outstanding Paper Award for Young Engineers/Researchers 2021, 2021

A new measurement system called Crosshole Sonic Logging Tomography (CSLT) provides information on... more A new measurement system called Crosshole Sonic Logging Tomography (CSLT) provides information on the size, shape, and orientation of defects in a bored pile. The CSLT measurement system has not (yet) been accredited in Hong Kong for foundation testing. Bored piles in Hong Kong are generally wide and deep. Existing measurement accuracy studies do not consider this large type of bored piles. The objective of this research is to quantify the measurement accuracy and precision of the CSLT method for large diameter bored piles (the most common pile type for public housing projects in Hong Kong). A test pile was constructed with known defects and perform experiments with a CSLT measurement system to quantify its accuracy and precision. CSLT is found to be accurate in detecting shape, size, and location of large defects but small defects close to the tube are difficult to detect. Generally speaking, CSLT has satisfactory accuracy and precision for practical use. The use of CSLT can be con...

Research paper thumbnail of Nanotechnologies for Water Environment Applications

This book is useful to undergraduate and graduate students in engineering and practicing engineer... more This book is useful to undergraduate and graduate students in engineering and practicing engineers, as well as educators, scientists, government officials, policymakers, and industrial process managers.

Research paper thumbnail of Rapid disinfection of E. coli by a ternary BiVO4/Ag/g-C3N4 composite under visible light: photocatalytic mechanism and performance investigation in authentic sewage

Environmental Science: Nano, 2019

Z-scheme photocatalyst BiVO4/Ag/g-C3N4 was constructed and applied for rapid disinfection of E. c... more Z-scheme photocatalyst BiVO4/Ag/g-C3N4 was constructed and applied for rapid disinfection of E. coli cells in water and wastewater.

Research paper thumbnail of Influence of weak magnetic field and tartrate on the oxidation and sequestration of Sb(III) by zerovalent iron: Batch and semi-continuous flow study

Journal of Hazardous Materials, 2017

Oxidation of Sb(III)-tartrate and Sb(III) in the Fe 0-H2O-O2 system was studied. WMF greatly enha... more Oxidation of Sb(III)-tartrate and Sb(III) in the Fe 0-H2O-O2 system was studied. WMF greatly enhanced Sb(III)-tartrate and Sb(III) removal by ZVI. WMF also increased the removal capacity of Sb(III)-tartrate and Sb(III) by ZVI. Tartrate significantly retarded Sb(III) removal by ZVI. The mechanisms of the inhibiting effect of tartrate were clarified.

Research paper thumbnail of Pulverized Fuel Ash Solidification/Stabilization of Waste: Comparison Between Beneficial Reuse of Contaminated Marine Mud and Sediment

JOURNAL OF ENVIRONMENTAL ENGINEERING AND LANDSCAPE MANAGEMENT, 2015

This study aimed to maximize the utilization of contaminated marine mud and sediment for benefici... more This study aimed to maximize the utilization of contaminated marine mud and sediment for beneficial reuse by solidification/stabilization (S/S) treatment with cement and pulverized fuel ash (PFA). For the purposes of waste maximization and enhancing the mechanical property of the S/S mixtures, mixing 75% by mass of either contaminated marine mud or sediment with 20% and 5% of cement and PFA, respectively, was found to be the optimal mix design. Their unconfined compressive strengths reached up to 8.32 MPa and 4.47 MPa, respectively. Apart from the mechanical property, according to the U.S.EPA, the TCLP results show that all regulated heavy metals were immobilized to a safe level and are available for engineering application such as fill material. The results of XRD reveal that the formation of CSH gel in the S/S treated mud and sediment is responsible for the strength development and heavy metal immobilization.

Research paper thumbnail of Design Methodology for the Application of a Permeable Reactive Barrier for Groundwater Remediation

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Research paper thumbnail of Sustainable Wastewater Treatment Using Microsized Magnetic Hydrogel with Magnetic Separation Technology

Industrial & Engineering Chemistry Research, 2014

A novel magnetic polymeric adsorbent, namely magnetic hydrogel, was used to investigate its reusa... more A novel magnetic polymeric adsorbent, namely magnetic hydrogel, was used to investigate its reusability and applicability in Cr(VI)-bearing wastewater treatment using magnetic separation. Different concentrations and amounts of NaCl solution, and a step-wise approach were used for the regeneration experiment. A step-wise adsorption process followed by step-wise 3.0 M NaCl regeneration with 40:1 wastewater-to-recovery volume ratio was found to be the most applicable working condition. The Cr concentration in the recovery solution was increased 25-30 times to 500-600 mg/L. The Cr(VI) removal and recovery performance of magnetic hydrogel was maintained for 20 cycles. An industrial wastewater treatment prototype, including a magnetic separation unit, was developed. The magnetic separation unit was designed to provide a magnetic field at the bottom with a zigzag pathway feature for maximizing the chance of capturing magnetic hydrogel. The separation efficiency for the magnetic hydrogel was above 97% throughout the 20 cycles of treatment. The results of the prototype experiment also indicated that magnetic hydrogel can *Manuscript Click here to view linked References effectively remove Cr(VI) and can also be separated and recovered by the magnetic separation unit in 20 cycles.

Research paper thumbnail of Couples of Precipitation-Dissolution and Reduction-Oxidation Reactions

Natural Processes and Systems for Hazardous Waste Treatment, 2007

Research paper thumbnail of Redox and Precipitation

Remediation Technologies for Soils and Groundwater, 2007

Research paper thumbnail of Chemical Reactive Barriers

Remediation Technologies for Soils and Groundwater, 2007

Research paper thumbnail of Competitive Effects on the Dechlorination of Chlorinated Aliphatic Hydrocarbons by Zero-valent Iron

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by zero-valent iron (Fe 0 ) was found... more Dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by zero-valent iron (Fe 0 ) was found to be influenced by the competitive effects exerted by other groundwater contaminants. Laboratory column study of the competitive effects on CAH dechlorination by Fe 0 indicated that the presence of 1,1,1-trichloroethane (1,1,1-TCA) in the trichloroethylene (TCE)-contaminated groundwater could decrease the normalized dechlorination rate constant (k SA ) of TCE from 3.04 x 10 -2 to 2.74 x 10 -2 mL m -2 hr -1 . In a similar fashion, introduction of chloroform (TCM) into the synthetic groundwater containing TCE and 1,1,1-TCA led to a 40 to 54% drop in TCE and 1,1,1-TCA k SA , thus indicating competition among TCE, 1,1,1-TCA and TCM during dechlorination reactions induced by Fe 0 . Activation energy ranging from 34.3 to 53.7 kJ/mol for the simultaneous dechlorination of TCE, 1,1,1-TCA and TCM by Fe 0 showed that the process of the electron transfer from Fe 0 to the CAHs is the dominant step limiting the rate of the dechlorination reactions so that the electron released from Fe 0 is most likely in competition with TCE, 1,1,1-TCA and TCM during the dechlorination reactions. In addition to CAHs, abiotic reduction of hexavalent chromium [Cr(VI)] by Fe 0 also exerted effects on TCE dechlorination leading to a 31% drop in TCE k SA after the addition of Cr(VI) into the TCE-contaminated groundwater. Groundwater geochemical factors such as alkalinity and contaminant concentration could potentially influence competition among TCE, 1,1,1-TCA, TCM and Cr(VI) during the abiotic reduction of chemical substances by Fe 0 .

Research paper thumbnail of Hydraulic Studies of Zero-Valent Iron in Permeable Reactive Barriers Using Tracer Experiment

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Research paper thumbnail of Configuration and Construction of Zero-valent Iron Reactive Barriers

Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 2006

Research paper thumbnail of Some Bounds on the Rainbow Connection Number of 3-, 4- and 5-connected Graphs

Cornell University - arXiv, Dec 24, 2012

The rainbow connection number, rc(G), of a connected graph G is the minimum number of colors need... more The rainbow connection number, rc(G), of a connected graph G is the minimum number of colors needed to color its edges so that every pair of vertices is connected by at least one path in which no two edges are colored the same. We show that for κ = 3 or κ = 4, every κ-connected graph G on n vertices with diameter n κ − c satisfies rc(G) ≤ n κ + 15c + 18. We also show that for every maximal planar graph G, rc(G) ≤ n κ + 36. This proves a conjecture of Li et al. for graphs with large diameter and maximal planar graphs.

Research paper thumbnail of Dynamic Matching in School Choice: Efficient Seat Reassignment after Late Cancellations

SSRN Electronic Journal, 2017

In the school choice market, where scarce public school seats are assigned to students, a key ope... more In the school choice market, where scarce public school seats are assigned to students, a key operational issue is how to reassign seats that are vacated after an initial round of centralized assignment. Practical solutions to the reassignment problem must be simple to implement, truthful and efficient while also alleviating costly student movement between schools. We propose and axiomatically justify a class of reassignment mechanisms, the Permuted Lottery Deferred Acceptance (PLDA) mechanisms. Our mechanisms generalize the commonly used Deferred Acceptance (DA) school choice mechanism to a two-round setting and retain its desirable incentive and efficiency properties. School choice systems typically run DA with a lottery number assigned to each student to break ties in school priorities. We show that under natural conditions on demand, the second round tie-breaking lottery can be correlated arbitrarily with that of the first round without affecting allocative welfare, and reversing the lottery order between rounds minimizes reassignment among all PLDA mechanisms. Empirical investigations based on data from NYC high school admissions support our theoretical findings.

Research paper thumbnail of Study of zinc in cementitious material stabilised/solidified wastes by sequential chemical extraction and microstructural analysis

Chemical Speciation & Bioavailability, 2001

In the present study, a five step sequential chemical extraction (SCE) procedure was employed to ... more In the present study, a five step sequential chemical extraction (SCE) procedure was employed to investigate the binding mechanisms and chemical partitioning of zinc in cement-based stabilised waste materials. After each step of SCE, scanning electronic microscope with energy dispersive spectrometer (SEM/EDS) and X-ray diffraction (XRD) were used to assess the microstructural and chemical changes of the waste materials. The results showed that the leaching of Zn from the cement based stabilised waste mainly took place at the second and the third extraction steps at pH 5.0 and 2.0, respectively. The addition of pulverised fly ash (PFA) increased the leachability of Zn at the second extraction step. The SCE results also indicated the hydration of cement was greatly retarded by the incorporation of zinc waste. The SEM and XRD analysis of the samples after each extraction step demonstrated that zinc leached at the second step extraction was partially due to the dissolution of the new crystalline phase (ZnO) in the waste materials. Since large amounts of zinc were leached out only at the third extraction step at pH 2.0, these stablised waste materials may be relatively stable under a normal disposal environment.