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 2–1indicating that these species behaved conservatively; i.e., theywere not reacting with their surroundings. However, the modeldid 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 tothe system, and overestimated the concentrations of the otherfour species, indicating that they were being removed from thesystem. Sampling along the length of the discharge streamshowed 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, OhioA serious problem associated with coal mining is the generationof acid mine drainage (AMD). During mining, sulfur-bearingminerals, such as pyrite (FeS2), are exposed to oxygen andwater, leading to a series of oxidation and hydrolysis reactionsthat produce sulfuric acid. The resulting waters are stronglyacidic (pH of 2 or less is possible) and have high concentrationsof SO, Fe²+, Al³+, and Mn²*. Such waters are toxic toaquatic life and vegetation.Foos (1997) investigated the downstream changes in thechemistry of coal mine drainage at Silver Creek Metropark,Summit County, Ohio. The first step was to construct a simplemixing model in which AMD and water discharged from SilverCreek 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 playa role in controlling the concentrations of these species. The re-sults are tabulated here. SI = log(IAP/K»p) and the equilibriumconstants were calculated for a temperature of 11.5°C, the tem-perature of the AMD discharge.PhaseFormulaSIPhaseFormulaSIFe,O3FEOOHHematite14.93QuartzChalcedonySiO2 (aq)AragoniteSiO2SiO2SiO2CACO3CACO3CaMg(CO3)20.53Goethite6.960.06FerrihydritePyrolusiteManganiteRhodochrositeFe(OH)31.07-0.83-14.27-2.09MnO2MNOOH-6.44Calcite-1.94MNCO3-1.17Dolomite-4.61The water was supersaturated with respect to all of the iron-containing phases, and further investigation revealed that about80% of the iron was removed as ferrihydrite. Thus, precipita-tion of iron-containing phases was the cause of the decrease inFe2+ in the downstream direction. The water was undersatu-ganic carbon where the stream flowed from an area of mowedlawn into a wooded area of dense vegetation.The author of the study was able to calculate a rate constantfor the removal of Fe²* assuming a steady-state model. Themodel 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 thedC- kC = 0dxsurface of the iron hydroxides. The water was slightly oversat-urated with respect to the Si-containing phases, so it is possiblethat precipitation of these phases was causing the downstreamdecrease in Si. The waters are undersaturated in terms of thewhere V is the velocity of the stream, C is the concentration, andx is the distance. Solving this equation for k gives a rate constantof 2.9 × 10¬4 s-.carbonate-containing phases, and it was concluded that thedownstream increase in HCO, was due to the addition of or-Source: Foos (1997).

The objective of this question is to determine the first-order rate constant for the removal of Fe2+…

Answered: Foos (1997) determined a first-order…

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Chapter1: Chemical Foundations

Section: Chapter Questions

Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...