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Foos (1997) determined a first-order rate constant for the removal of Fe2+ from a stream (Case Study 2–1). Discharge from a point source adds Fe2+ to a river. Using the rate constant determined by Foos (1997) and a stream velocity of 0.5 m s–1, calculate the transport distance required to achieve a 90% reduction in the amount of Fe2+ in solution. To do this problem you will first need to find

Foos (1997) determined a first-order rate constant for the removal of Fe2+ from a stream (Case Study 2–1). Discharge from a point source adds Fe2+ to a river. Using the rate constant determined by Foos (1997) and a stream velocity of 0.5 m s–1, calculate the transport distance required to achieve a 90% reduction in the amount of Fe2+ in solution. To do this problem you will first need to find

Principles of Modern Chemistry
Principles of Modern Chemistry
8th Edition
ISBN:9781305079113
Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Chapter20: Molecular Spectroscopy And Photochemistry
Section: Chapter Questions
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33. Foos (1997) determined a first-order rate constant for the removal of Fe2+ from a stream (Case Study 2–1). Discharge from a point source adds Fe2+ to a river. Using the rate constant determined by Foos (1997) and a stream velocity of 0.5 m s–1, calculate the transport distance required to achieve a 90% reduction in the amount of Fe2+ in solution. To do this problem you will first need to find the amount of time required to reduce the iron concentration by 90%.

 

CASE STUDY 2–1 indicating that these species behaved conservatively; i.e., they were not reacting with their surroundings. However, the model did not accurately predict the concentrations of HCO, , SO;-, Fe3+, Mn²+, and Si. The model underestimated the concentra- tion of HCO,, indicating that this species was being added to the system, and overestimated the concentrations of the other four species, indicating that they were being removed from the system. Sampling along the length of the discharge stream showed a downstream increase in HCO, and a downstream de- crease in the other four species. There was an excellent correla- tion between Fe²+ concentration and distance. Geochemical Modeling of Coal Mine Drainage, Summit County, Ohio A serious problem associated with coal mining is the generation of acid mine drainage (AMD). During mining, sulfur-bearing minerals, such as pyrite (FeS2), are exposed to oxygen and water, leading to a series of oxidation and hydrolysis reactions that produce sulfuric acid. The resulting waters are strongly acidic (pH of 2 or less is possible) and have high concentrations of SO, Fe²+, Al³+, and Mn²*. Such waters are toxic to aquatic life and vegetation. Foos (1997) investigated the downstream changes in the chemistry of coal mine drainage at Silver Creek Metropark, Summit County, Ohio. The first step was to construct a simple mixing model in which AMD and water discharged from Silver Creek lake were the end members. This model successfully pre- dicted the concentrations of Cl¯, PO-, Ca²+, Mg²+ and Na*, Saturation indices (SI) were calculated, using the water- chemistry program WATEQ4F, for solid phases that could play a role in controlling the concentrations of these species. The re- sults are tabulated here. SI = log(IAP/K»p) and the equilibrium constants were calculated for a temperature of 11.5°C, the tem- perature of the AMD discharge. Phase Formula SI Phase Formula SI Fe,O3 FEOOH Hematite 14.93 Quartz Chalcedony SiO2 (aq) Aragonite SiO2 SiO2 SiO2 CACO3 CACO3 CaMg(CO3)2 0.53 Goethite 6.96 0.06 Ferrihydrite Pyrolusite Manganite Rhodochrosite Fe(OH)3 1.07 -0.83 -14.27 -2.09 MnO2 MNOOH -6.44 Calcite -1.94 MNCO3 -1.17 Dolomite -4.61 The water was supersaturated with respect to all of the iron- containing phases, and further investigation revealed that about 80% of the iron was removed as ferrihydrite. Thus, precipita- tion of iron-containing phases was the cause of the decrease in Fe2+ in the downstream direction. The water was undersatu- ganic carbon where the stream flowed from an area of mowed lawn into a wooded area of dense vegetation. The author of the study was able to calculate a rate constant for the removal of Fe²* assuming a steady-state model. The model is a first-order rate equation that can be written as follows: rated with respect to all Mn-bearing phases, and it was con- cluded that Mn²+ was being removed by adsorption onto the dC - kC = 0 dx surface of the iron hydroxides. The water was slightly oversat- urated with respect to the Si-containing phases, so it is possible that precipitation of these phases was causing the downstream decrease in Si. The waters are undersaturated in terms of the where V is the velocity of the stream, C is the concentration, and x is the distance. Solving this equation for k gives a rate constant of 2.9 × 10¬4 s-. carbonate-containing phases, and it was concluded that the downstream increase in HCO, was due to the addition of or- Source: Foos (1997).
Transcribed Image Text:CASE STUDY 2–1 indicating that these species behaved conservatively; i.e., they were not reacting with their surroundings. However, the model did not accurately predict the concentrations of HCO, , SO;-, Fe3+, Mn²+, and Si. The model underestimated the concentra- tion of HCO,, indicating that this species was being added to the system, and overestimated the concentrations of the other four species, indicating that they were being removed from the system. Sampling along the length of the discharge stream showed a downstream increase in HCO, and a downstream de- crease in the other four species. There was an excellent correla- tion between Fe²+ concentration and distance. Geochemical Modeling of Coal Mine Drainage, Summit County, Ohio A serious problem associated with coal mining is the generation of acid mine drainage (AMD). During mining, sulfur-bearing minerals, such as pyrite (FeS2), are exposed to oxygen and water, leading to a series of oxidation and hydrolysis reactions that produce sulfuric acid. The resulting waters are strongly acidic (pH of 2 or less is possible) and have high concentrations of SO, Fe²+, Al³+, and Mn²*. Such waters are toxic to aquatic life and vegetation. Foos (1997) investigated the downstream changes in the chemistry of coal mine drainage at Silver Creek Metropark, Summit County, Ohio. The first step was to construct a simple mixing model in which AMD and water discharged from Silver Creek lake were the end members. This model successfully pre- dicted the concentrations of Cl¯, PO-, Ca²+, Mg²+ and Na*, Saturation indices (SI) were calculated, using the water- chemistry program WATEQ4F, for solid phases that could play a role in controlling the concentrations of these species. The re- sults are tabulated here. SI = log(IAP/K»p) and the equilibrium constants were calculated for a temperature of 11.5°C, the tem- perature of the AMD discharge. Phase Formula SI Phase Formula SI Fe,O3 FEOOH Hematite 14.93 Quartz Chalcedony SiO2 (aq) Aragonite SiO2 SiO2 SiO2 CACO3 CACO3 CaMg(CO3)2 0.53 Goethite 6.96 0.06 Ferrihydrite Pyrolusite Manganite Rhodochrosite Fe(OH)3 1.07 -0.83 -14.27 -2.09 MnO2 MNOOH -6.44 Calcite -1.94 MNCO3 -1.17 Dolomite -4.61 The water was supersaturated with respect to all of the iron- containing phases, and further investigation revealed that about 80% of the iron was removed as ferrihydrite. Thus, precipita- tion of iron-containing phases was the cause of the decrease in Fe2+ in the downstream direction. The water was undersatu- ganic carbon where the stream flowed from an area of mowed lawn into a wooded area of dense vegetation. The author of the study was able to calculate a rate constant for the removal of Fe²* assuming a steady-state model. The model is a first-order rate equation that can be written as follows: rated with respect to all Mn-bearing phases, and it was con- cluded that Mn²+ was being removed by adsorption onto the dC - kC = 0 dx surface of the iron hydroxides. The water was slightly oversat- urated with respect to the Si-containing phases, so it is possible that precipitation of these phases was causing the downstream decrease in Si. The waters are undersaturated in terms of the where V is the velocity of the stream, C is the concentration, and x is the distance. Solving this equation for k gives a rate constant of 2.9 × 10¬4 s-. carbonate-containing phases, and it was concluded that the downstream increase in HCO, was due to the addition of or- Source: Foos (1997).
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