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Kinetics of Red Clay Bluff Dissolution in Western Lake Superior
J. Great Lakes Res., 1979 Internat. Assoc. Great Lakes Res. 5(2):221-224
NOTE KINETICS OF RED CLAY BLUFF DISSOLUTION IN WESTERN LAKE SUPERIOR
Donald A. Bahnick, Thomas P. Markee, and Ronald K. Roubal University of Wisconsin-Superior Superior, Wisconsin
ABSTRACT. The dissolution of red clay bluff samples from the southwestern Lake Superio~ shoreline a~ea in Lake Superior water or deionized water is studied by following the aqueous concentr~tzons of re~ctzve silica over a three month period. The dissolution process is initially rapid, followed by a ftrst-o~der dz~solu tion process (k = 9.4 x 1rr 7 sec-I) up to about thirty days. :ffter about 30 days, the rate ofdzssolutzon of the bluff material follows linear kinetics (k = 5.4 x Irr 8 mg Sz02/gram of bluffper second).
INTRODUCTION Erosion of red clay bluffs along the southwestern Lake Superior shoreline area in Wisconsin results in the major input of eroded material to this lake. Evidence indicates that about 8 million metric tons of material are eroded annually from bluffs into the western portion of Lake Superior (Bahnick et al. 1978). Among the chemical inputs to Lake Superior (resulting from exchange and dissolution processes during suspension of the eroded material) is a large amount of dissolved silica. An estimated 14,000 metric tons of reactive silica enter Lake Superior waters annually due to shoreline erosion, with an additional smaller input arising from periodic resuspension of fine sedimented material al~ng. ~he shoreline area (Bahnick et al. 197 8). This silica input is small, but significant when compared to the total annual reactive silica loading of 4.2 x 10 5 tonnes/yr originating from municipal, industrial, and tributary sources (Upper Great Lakes Reference Group 1976). Diagenesis of the aluminosilicates contained in the sedimented material results in an additional input due to a flux across the sedimentwater interface. This study investigates the dissolution rate of red-elay-containing bluff material suspended in either water from Lake Superior or deionized
water. Rate expressions are obtained by monitoring dissolved reactive silica concentrations in the suspensions over a three month period. METHODOLOGY Bluff material was obtained from an exposed red clay bank along the Lake Superior shoreline 10 km west of the Amnicon River in northwestern Wisconsin. The red clay material was sampled just below the surface and stored in polypropylene containers. Particle size determinations of the bluff material were made by the pipet-sedimentation method (Royse 1970). The bluff sample was used in a three month study of dissolution rates in water from Lake Superior and deionized water. Weighed samples were wet-sieved through a #230 mesh standard sieve (62.5 micron pore) into polypropylene containers and water from Lake Superior or deionized water was added. The coarser particles retained by sieve (sand-size range and larger) were collected, dried at 105°C, and weighed. Unsieved subsamples were also dried at 105°C for the determination of moisture content. The suspensions contained approximately 2000 mg of solids (dry weight) per liter of solution. Each suspension was prepared in duplicate. Blank systems containing Lake Superior water or deionized water in polypropylene containers were used as controls. The suspensions and controls were agitated with teflon stir bars at temperatures which remained between 23 and 27°C during the course of the
Note: This work was supported, in part, by EPA Grant No. ROOS169-01 and the University of Wisconsin-Superior. Periodical Contribution No. 33 from the Center for Lake Superior Environmental Studies.
221
BARNICK, MARKEE, and ROUBAL
222
dissolution study. Aliquots of the liquid phases were analyzed for reactive silica over a three month period. At the time of removal of an aliquot, each suspension was allowed to settle for two hours after which one-tenth of the total volume was siphoned and filtered through a 0.45 micron membrane. Reactive silica was determined using the heteropoly blue method (American Public Health Association 1975). The volume removed was replaced by analyzed Lake Superior water (or deionized water). RESULTS Bluff Dissolution The aqueous reactive silica concentrations in the bluff-Lake Superior water suspensions ranged from 2.6 mg/L at the initiation of the experiment to 4.9 mg/L at its conclusion. The release of Si0 2 over the three month period was computed by considering the concentrations of silica in the water at each time and correcting for the silica in the aliquot removed each sampling time and in the water added to replace the aliquot. The details of this calculation have been previously discussed (Bahnick et al. 1978, Bahnick 1977). The total apparent releases of silica (mg), as a function of time were then corrected by subtracting apparent releases of silica in the blanks at each sampling time. This procedure minimized small fluctuations in the bluff release values by helping to eliminate errors due to variations in the conditions of chemical reagents and chemical exchanges between the suspensions and container walls. Data for the bluff-deionized water suspensions were treated in a similar manner. The resulting release values are shown in Figure 1. The results in Figure 1 show a total release of 1.5 mg of Si0 2 per gram of bluff in Lake Superior water and 2.5 mg of Si02 per gram of bluff in deionized water after a 3 month dissolution period. Siever and Woodford (1973) found that the extent of dissolution of kaolinite in distilled water was greater than that found using sea water. This difference was attributed to pH, ionic strength, and composition of the ions in solution. The kinetics of dissolution of the bluff sample in Lake Superior water may be evaluated from the data in Figure 1. Let Rs be the mg of Si0 2 released per gram of bluff sample when steady state conditions are attained from the dissolution process. If Rt is the release at time t, then the quantity R - Rt is the amount of Si0 2 remaining to be reieased at time t until steady state conditions are attained. The integrated form of the first order rate equation is;
Rs - Rt = Rse- kt where k is the specific rate constant. At two different times, t 2 and t 1 (where t 2 > t 1) which differ by a time interval M, Rs - Rtl = Rs e- kt1 R - R = R e- kt2 = R e-k(tl + M) s
t2
S
s
subtracting, (Rs - R ) - (Rs - Rt2 ) =Rse-kt1 (l-e-kM ) t1 or, Rt2 - Rt1 = Rse-kt1 (1-e- klH ) taking natural logarithms of both sides yields In(R - R ) = -kt 1 + In [Rs (1_e- kbot )] t2 t1 Thus for constant time intervals, a plot of In(Rt 2 Rt 1) versus t 1 yields a slope of -k. For our data, time intervals of 5 days were chosen over the 1 to 31 day dissolution period. The first order kinetics fit to the dissolution data is shown by the dashed portion of the release curve in Figure 1. The R2 - R1 values varied progressively from 0.19 to 0.025 mg Si02 /gram in the 5 day intervals from 1-6 to 26-31 days. The slope of the In(R2 - R1) versus t 1 straight line plot indicates a flrst order rate constant of 9.4 x HJ' sec- 1 . At times greater than about thirty days, the dissolution process is best described by linear kinetics. The net release of Si0 2 from the bluff sample versus time in the post 30 day period is shown in Figure 1 to be linear. The rate constant
2.4
2.0
8'. 1.2/-- _------.-----
] 1.6 :
0 ._ _ _ _ _ _ _ _ _ _ _ _ _
. . . ..9---.
~
E ;0.8
'0
0.4
°0~---'-""'2':':0-"""'-4*0-"""'-6*0-"""'-*80~------""'!'00 TIME Id_ysl
FIG. 1. Release of Si0 2 from red clay bluff samples as a [unction of time in Lake Superior (e) and deionized water (0). R is the observed mg of Si02 released per gram of suspended red clay bluff material.
NOTE-CLAY DISSOLUTION KINETICS is 5.4 x 10- 8 mg Si0 2 per gram of bluff per second. However the uncertainties in the release values would also allow a first order equation fit. Particle Size and Bluff Mineralogy The particle size distribution within the red clay bluff sample was found to be 8.0 ± 1.1% sand, 6.8 ± 6.3% silt, 25.3 ± 1.3% coarse clay (3.9 to 1.011), and 59.9 ± 4.6% fine clay « 1.011) where the indicated uncertainties are standard deviations for four determinations. The mineralogical compositions of bluff samples from the northern Wisconsin red clay area have been reported by Mengel and Brown (1976). Major quantities of illite, chlorite, and montmorillonite were found to compose 10 to 25% each of the regolith along with traces of kaolinite. Other minerals consisted of quartz (about 20%), plagioclase (about 10%), and 5% each of K feldspar, calcite, and dolomite. DISCUSSION Clay Mineral Dissolution Suspensions of the bluff red clay sample in Lake Superior water and deionized water have been used in a previous seven week study of chemical releases (Bahnicket al. 1978). It was found that the pH of the suspensions prepared with Lake Superior water remained between 7.4 and 7.8 during the seven week period. The pHs of the bluff~eionized water suspensions were initially 5.9 but rapidly rose to 8.7 and remaw.ed about 8 during the remainder of the seven week period. The aqueous dissolved oxygen levels in the suspensions remained high during these studies. Similar pH and oxygen conditions should have existed during the three month bluff dissolution experiment reported in this paper. Busenberg and Clemency (1976) studied the dissolution kinetics of suspensions of K feldspars and plagioclases in distilled water at 1 atm CO 2 partial pressure. The feldspars underwent an initial one minute ion-exchange process with ions in the water followed by a rapid non-parabolic release of cations and silicic acid for a four day period. A diffusion-eontrolled parabolic dissolution stage lasted until 19 days followed by a slow cation and silicic acid release exhibiting linear kinetics. The parabolic kinetics stage of dissolution is believed to result from diffusion from the mineral surface over a thickening product layer. The linear kinetics region results when the rate of formation of a secondary product of the dissolution equals
223
the rate at which this layer dissipates at the liquidproduct layer interface (Paces 1973). Siever and Woodford (1973) studied reactions and sorption of silica by clay minerals in distilled water, buffered distilled water, alkali chloride solutions, and natural and artificial seawater. The authors demonstrated that the release or uptake of Si0 2 by clay minerals depends upon many factors such as the. Si0 2 concentration in the solution phase, pH, composition of the solution, and the degree of grinding. It was found that montmorillonite, kaolinite, and illite will show a net input of Si0 2 into NaHC0 3 pH = 8 buffered distilled water if the concentration of Si0 2 in the water is below the 25 to 40 ppm range. This buffered system is chemically similar (Le. pH and low ionic strength) to Lake Superior water. Dayal (1977) found that diffusion was the rate controlling process in both clay dissolution and clay reconstitution reactions. Helgeson (1971) indicates that the incongruent dissolution of aluminosilicates in neutral aqueous solution proceeds by hydrolysis of silicate tetrahedral units forming Al(OHh at the altered surface of the aluminosilicate. Lerman, MacKenzie, and Bricker (1975) were able to use a combined first order and parabolic rate model for incongruent dissolution of a number of clay minerals, zeolites, and quartz in seawater over an 8-1/2 year period. The first order term is shown to dominate the rate expression resulting in computed first order rate constants in the 10-6 to 10- 7 range. This result agrees with our determination of a first order rate constant of 9.4 x 10- 7 sec- 1 for the one to 31 day dissolution period of the red clay bluff sample in Lake Superior water. The dissolution kinetics for the post 30 day period was shown in our results to follow a linear kinetic expression. The rate constant (5.8 x 10- 8 mg Si0 2 per gram of bluff per second) depends upon the effective surface area of the solid phase. However, this value should give a good estimate of the dissolution rate of eroded red clay bluff suspended in Lake Superior water for relatively long time periods. The red clay bluff material used in this study was composed of a complex mixture of clays, feldspars, and carbonate minerals. Our results demonstrate that the dissolution of this mixture in Lake Superior followed kinetic expressions similar to those determined by other investigators for individual clay minerals, quartz, and K feldspars. The relative contributions of the dissolving phases to the total silica release would be difficult to determine. However the observed rate of silica input due
224
BAHNICK, MARKEE, and ROUBAL
to dissolution of the natural red clay material should be useful in modeling the silica cycle in Lake Superior. REFERENCES American Public Health Association. 1975. Standard Methods for the Examination of Water and Wastewater. 14th ed. APHA, New York. Bahnick, D. A. 1977. The Contribution of Red Clay Erosion to Orthophosphate Loadings into Southwestern Lake Superior.J. Environ. Qual. 6:217-222. _ , Markee, T. P., Anderson, C. A., and Roubal, R. K. 1978. Chemical loadings to southwestern Lake Superior from red clay erosion and resuspension. J. Great Lakes Res. 4(2):186-193. Busenberg, E., and Clemency, C. V. 1976. The Dissolution Kinetics of Feldspars at 25°C and 1 atm CO 2 Partial Pressure. Geochim. Cosmochim. Acta. 40:41-49. Dayal, R. 1977. Kinetics of Silica Sorption and Clay Dissolution Reactions at 1 and 670 atm. Geochim. Cosmochim. Acta. 41:135-141.
Helgeson, H. C. 1971. Kinetics of Mass Transfer Among Silicates and Aqueous Solutions. Geochim. Cosmochim. Acta. 35:421-429. Lerman, A., MacKenzie, F. T., and Bricker, O. P. 1975. Rates of Dissolution of Aluminosilicates in Seawater. Earth Planet. Sci. Lett. 25:82-88. Mengel, J. T., and Brown, B. F. 1976. Red Clay Stability Factors: Douglas County, Wisconsin. Univ. of WISuperior and Univ. of WI-Milwaukee, U.S. EPA G005140-01. Paces, T. 1973. Steady-State Kinetics and Equilibrium Between Ground-Water and Granite Rock. Geochim. Cosmochim. A eta. 34:2641-2663. Royse, C. F., Jr. 1970. An Introduction to Sediment Analysis. Arizona State University Press, Tempe, Ariz. Siever, R., and Woodford, N. 1973. Sorption of Silica by Clay Minerals. Geochim. Cosmochim. Acta. 37:18511880. Upper Great Lakes Reference Group. 1976. The Waters of Lake Huron and Lake Superior. Vols. I, II and III. International Joint Commission, Windsor, Ontario.
NOTE KINETICS OF RED CLAY BLUFF DISSOLUTION IN WESTERN LAKE SUPERIOR
Donald A. Bahnick, Thomas P. Markee, and Ronald K. Roubal University of Wisconsin-Superior Superior, Wisconsin
ABSTRACT. The dissolution of red clay bluff samples from the southwestern Lake Superio~ shoreline a~ea in Lake Superior water or deionized water is studied by following the aqueous concentr~tzons of re~ctzve silica over a three month period. The dissolution process is initially rapid, followed by a ftrst-o~der dz~solu tion process (k = 9.4 x 1rr 7 sec-I) up to about thirty days. :ffter about 30 days, the rate ofdzssolutzon of the bluff material follows linear kinetics (k = 5.4 x Irr 8 mg Sz02/gram of bluffper second).
INTRODUCTION Erosion of red clay bluffs along the southwestern Lake Superior shoreline area in Wisconsin results in the major input of eroded material to this lake. Evidence indicates that about 8 million metric tons of material are eroded annually from bluffs into the western portion of Lake Superior (Bahnick et al. 1978). Among the chemical inputs to Lake Superior (resulting from exchange and dissolution processes during suspension of the eroded material) is a large amount of dissolved silica. An estimated 14,000 metric tons of reactive silica enter Lake Superior waters annually due to shoreline erosion, with an additional smaller input arising from periodic resuspension of fine sedimented material al~ng. ~he shoreline area (Bahnick et al. 197 8). This silica input is small, but significant when compared to the total annual reactive silica loading of 4.2 x 10 5 tonnes/yr originating from municipal, industrial, and tributary sources (Upper Great Lakes Reference Group 1976). Diagenesis of the aluminosilicates contained in the sedimented material results in an additional input due to a flux across the sedimentwater interface. This study investigates the dissolution rate of red-elay-containing bluff material suspended in either water from Lake Superior or deionized
water. Rate expressions are obtained by monitoring dissolved reactive silica concentrations in the suspensions over a three month period. METHODOLOGY Bluff material was obtained from an exposed red clay bank along the Lake Superior shoreline 10 km west of the Amnicon River in northwestern Wisconsin. The red clay material was sampled just below the surface and stored in polypropylene containers. Particle size determinations of the bluff material were made by the pipet-sedimentation method (Royse 1970). The bluff sample was used in a three month study of dissolution rates in water from Lake Superior and deionized water. Weighed samples were wet-sieved through a #230 mesh standard sieve (62.5 micron pore) into polypropylene containers and water from Lake Superior or deionized water was added. The coarser particles retained by sieve (sand-size range and larger) were collected, dried at 105°C, and weighed. Unsieved subsamples were also dried at 105°C for the determination of moisture content. The suspensions contained approximately 2000 mg of solids (dry weight) per liter of solution. Each suspension was prepared in duplicate. Blank systems containing Lake Superior water or deionized water in polypropylene containers were used as controls. The suspensions and controls were agitated with teflon stir bars at temperatures which remained between 23 and 27°C during the course of the
Note: This work was supported, in part, by EPA Grant No. ROOS169-01 and the University of Wisconsin-Superior. Periodical Contribution No. 33 from the Center for Lake Superior Environmental Studies.
221
BARNICK, MARKEE, and ROUBAL
222
dissolution study. Aliquots of the liquid phases were analyzed for reactive silica over a three month period. At the time of removal of an aliquot, each suspension was allowed to settle for two hours after which one-tenth of the total volume was siphoned and filtered through a 0.45 micron membrane. Reactive silica was determined using the heteropoly blue method (American Public Health Association 1975). The volume removed was replaced by analyzed Lake Superior water (or deionized water). RESULTS Bluff Dissolution The aqueous reactive silica concentrations in the bluff-Lake Superior water suspensions ranged from 2.6 mg/L at the initiation of the experiment to 4.9 mg/L at its conclusion. The release of Si0 2 over the three month period was computed by considering the concentrations of silica in the water at each time and correcting for the silica in the aliquot removed each sampling time and in the water added to replace the aliquot. The details of this calculation have been previously discussed (Bahnick et al. 1978, Bahnick 1977). The total apparent releases of silica (mg), as a function of time were then corrected by subtracting apparent releases of silica in the blanks at each sampling time. This procedure minimized small fluctuations in the bluff release values by helping to eliminate errors due to variations in the conditions of chemical reagents and chemical exchanges between the suspensions and container walls. Data for the bluff-deionized water suspensions were treated in a similar manner. The resulting release values are shown in Figure 1. The results in Figure 1 show a total release of 1.5 mg of Si0 2 per gram of bluff in Lake Superior water and 2.5 mg of Si02 per gram of bluff in deionized water after a 3 month dissolution period. Siever and Woodford (1973) found that the extent of dissolution of kaolinite in distilled water was greater than that found using sea water. This difference was attributed to pH, ionic strength, and composition of the ions in solution. The kinetics of dissolution of the bluff sample in Lake Superior water may be evaluated from the data in Figure 1. Let Rs be the mg of Si0 2 released per gram of bluff sample when steady state conditions are attained from the dissolution process. If Rt is the release at time t, then the quantity R - Rt is the amount of Si0 2 remaining to be reieased at time t until steady state conditions are attained. The integrated form of the first order rate equation is;
Rs - Rt = Rse- kt where k is the specific rate constant. At two different times, t 2 and t 1 (where t 2 > t 1) which differ by a time interval M, Rs - Rtl = Rs e- kt1 R - R = R e- kt2 = R e-k(tl + M) s
t2
S
s
subtracting, (Rs - R ) - (Rs - Rt2 ) =Rse-kt1 (l-e-kM ) t1 or, Rt2 - Rt1 = Rse-kt1 (1-e- klH ) taking natural logarithms of both sides yields In(R - R ) = -kt 1 + In [Rs (1_e- kbot )] t2 t1 Thus for constant time intervals, a plot of In(Rt 2 Rt 1) versus t 1 yields a slope of -k. For our data, time intervals of 5 days were chosen over the 1 to 31 day dissolution period. The first order kinetics fit to the dissolution data is shown by the dashed portion of the release curve in Figure 1. The R2 - R1 values varied progressively from 0.19 to 0.025 mg Si02 /gram in the 5 day intervals from 1-6 to 26-31 days. The slope of the In(R2 - R1) versus t 1 straight line plot indicates a flrst order rate constant of 9.4 x HJ' sec- 1 . At times greater than about thirty days, the dissolution process is best described by linear kinetics. The net release of Si0 2 from the bluff sample versus time in the post 30 day period is shown in Figure 1 to be linear. The rate constant
2.4
2.0
8'. 1.2/-- _------.-----
] 1.6 :
0 ._ _ _ _ _ _ _ _ _ _ _ _ _
. . . ..9---.
~
E ;0.8
'0
0.4
°0~---'-""'2':':0-"""'-4*0-"""'-6*0-"""'-*80~------""'!'00 TIME Id_ysl
FIG. 1. Release of Si0 2 from red clay bluff samples as a [unction of time in Lake Superior (e) and deionized water (0). R is the observed mg of Si02 released per gram of suspended red clay bluff material.
NOTE-CLAY DISSOLUTION KINETICS is 5.4 x 10- 8 mg Si0 2 per gram of bluff per second. However the uncertainties in the release values would also allow a first order equation fit. Particle Size and Bluff Mineralogy The particle size distribution within the red clay bluff sample was found to be 8.0 ± 1.1% sand, 6.8 ± 6.3% silt, 25.3 ± 1.3% coarse clay (3.9 to 1.011), and 59.9 ± 4.6% fine clay « 1.011) where the indicated uncertainties are standard deviations for four determinations. The mineralogical compositions of bluff samples from the northern Wisconsin red clay area have been reported by Mengel and Brown (1976). Major quantities of illite, chlorite, and montmorillonite were found to compose 10 to 25% each of the regolith along with traces of kaolinite. Other minerals consisted of quartz (about 20%), plagioclase (about 10%), and 5% each of K feldspar, calcite, and dolomite. DISCUSSION Clay Mineral Dissolution Suspensions of the bluff red clay sample in Lake Superior water and deionized water have been used in a previous seven week study of chemical releases (Bahnicket al. 1978). It was found that the pH of the suspensions prepared with Lake Superior water remained between 7.4 and 7.8 during the seven week period. The pHs of the bluff~eionized water suspensions were initially 5.9 but rapidly rose to 8.7 and remaw.ed about 8 during the remainder of the seven week period. The aqueous dissolved oxygen levels in the suspensions remained high during these studies. Similar pH and oxygen conditions should have existed during the three month bluff dissolution experiment reported in this paper. Busenberg and Clemency (1976) studied the dissolution kinetics of suspensions of K feldspars and plagioclases in distilled water at 1 atm CO 2 partial pressure. The feldspars underwent an initial one minute ion-exchange process with ions in the water followed by a rapid non-parabolic release of cations and silicic acid for a four day period. A diffusion-eontrolled parabolic dissolution stage lasted until 19 days followed by a slow cation and silicic acid release exhibiting linear kinetics. The parabolic kinetics stage of dissolution is believed to result from diffusion from the mineral surface over a thickening product layer. The linear kinetics region results when the rate of formation of a secondary product of the dissolution equals
223
the rate at which this layer dissipates at the liquidproduct layer interface (Paces 1973). Siever and Woodford (1973) studied reactions and sorption of silica by clay minerals in distilled water, buffered distilled water, alkali chloride solutions, and natural and artificial seawater. The authors demonstrated that the release or uptake of Si0 2 by clay minerals depends upon many factors such as the. Si0 2 concentration in the solution phase, pH, composition of the solution, and the degree of grinding. It was found that montmorillonite, kaolinite, and illite will show a net input of Si0 2 into NaHC0 3 pH = 8 buffered distilled water if the concentration of Si0 2 in the water is below the 25 to 40 ppm range. This buffered system is chemically similar (Le. pH and low ionic strength) to Lake Superior water. Dayal (1977) found that diffusion was the rate controlling process in both clay dissolution and clay reconstitution reactions. Helgeson (1971) indicates that the incongruent dissolution of aluminosilicates in neutral aqueous solution proceeds by hydrolysis of silicate tetrahedral units forming Al(OHh at the altered surface of the aluminosilicate. Lerman, MacKenzie, and Bricker (1975) were able to use a combined first order and parabolic rate model for incongruent dissolution of a number of clay minerals, zeolites, and quartz in seawater over an 8-1/2 year period. The first order term is shown to dominate the rate expression resulting in computed first order rate constants in the 10-6 to 10- 7 range. This result agrees with our determination of a first order rate constant of 9.4 x 10- 7 sec- 1 for the one to 31 day dissolution period of the red clay bluff sample in Lake Superior water. The dissolution kinetics for the post 30 day period was shown in our results to follow a linear kinetic expression. The rate constant (5.8 x 10- 8 mg Si0 2 per gram of bluff per second) depends upon the effective surface area of the solid phase. However, this value should give a good estimate of the dissolution rate of eroded red clay bluff suspended in Lake Superior water for relatively long time periods. The red clay bluff material used in this study was composed of a complex mixture of clays, feldspars, and carbonate minerals. Our results demonstrate that the dissolution of this mixture in Lake Superior followed kinetic expressions similar to those determined by other investigators for individual clay minerals, quartz, and K feldspars. The relative contributions of the dissolving phases to the total silica release would be difficult to determine. However the observed rate of silica input due
224
BAHNICK, MARKEE, and ROUBAL
to dissolution of the natural red clay material should be useful in modeling the silica cycle in Lake Superior. REFERENCES American Public Health Association. 1975. Standard Methods for the Examination of Water and Wastewater. 14th ed. APHA, New York. Bahnick, D. A. 1977. The Contribution of Red Clay Erosion to Orthophosphate Loadings into Southwestern Lake Superior.J. Environ. Qual. 6:217-222. _ , Markee, T. P., Anderson, C. A., and Roubal, R. K. 1978. Chemical loadings to southwestern Lake Superior from red clay erosion and resuspension. J. Great Lakes Res. 4(2):186-193. Busenberg, E., and Clemency, C. V. 1976. The Dissolution Kinetics of Feldspars at 25°C and 1 atm CO 2 Partial Pressure. Geochim. Cosmochim. Acta. 40:41-49. Dayal, R. 1977. Kinetics of Silica Sorption and Clay Dissolution Reactions at 1 and 670 atm. Geochim. Cosmochim. Acta. 41:135-141.
Helgeson, H. C. 1971. Kinetics of Mass Transfer Among Silicates and Aqueous Solutions. Geochim. Cosmochim. Acta. 35:421-429. Lerman, A., MacKenzie, F. T., and Bricker, O. P. 1975. Rates of Dissolution of Aluminosilicates in Seawater. Earth Planet. Sci. Lett. 25:82-88. Mengel, J. T., and Brown, B. F. 1976. Red Clay Stability Factors: Douglas County, Wisconsin. Univ. of WISuperior and Univ. of WI-Milwaukee, U.S. EPA G005140-01. Paces, T. 1973. Steady-State Kinetics and Equilibrium Between Ground-Water and Granite Rock. Geochim. Cosmochim. A eta. 34:2641-2663. Royse, C. F., Jr. 1970. An Introduction to Sediment Analysis. Arizona State University Press, Tempe, Ariz. Siever, R., and Woodford, N. 1973. Sorption of Silica by Clay Minerals. Geochim. Cosmochim. Acta. 37:18511880. Upper Great Lakes Reference Group. 1976. The Waters of Lake Huron and Lake Superior. Vols. I, II and III. International Joint Commission, Windsor, Ontario.