Pickering, Rebecca A.

Razumov, Peter M

Taylor, Lucy C.

English

ScholarWorks @ Georgia State University

TITLE: Clay Synthesis: Modeling the Uptake of K+ during Low-Temperature Illitization of Smectite AUTHORS: Peter Razumov, Lucy Taylor, Rebecca Pickering FACULTY SPONSOR: Daniel Deocampo, PhD, Associate Professor, Department of Geosciences   Introduction: Authigenic lacustrine clay sediments have long been recognized as important chemical precipitates in sedimentary environments in East African Neogene lakes. Understanding how these minerals form is important to understanding the paleohydrologic, paleoclimate, and diagenetic histories of lake basins. We designed a suite of clay synthesis experiments to test the role of varying K concentrations during the process of illitization, after layer charge has been increased through Fe reduction. Specifically we are testing the hypothesis that elevated aqueous K concentration leads to enhanced illitization, and that this effect is greater with clays in which Fe has been reduced. Method: To test this hypothesis, the Clay Minerals Society Fe-rich nontronite clay standard (NAu-1) was artificially reduced by mixing with a sodium dithionite (Na2S2O4) solution buffered to neutral pH with sodium citrate – sodium bicarbonate buffer fallowing the methods of Stucki et al., 1993. Clay aliquots were then exposed to solutions of increasing K concentrations in a flask under a nitrogen rich atmosphere. Solution concentrations were based on Lake Dabusun, China, a K-rich saline lake (Spencer et al., 1990). Fluid chemistry was monitored though AA spectroscopy for both reduced and non-reduced samples, before and after experiments. XRD analysis was used for identifying mineralogy (before and after experiments) and XRF analysis was used to identify major element composition (before and after experiments). Results: Element ratios K2O/Al2O3 and K2O/TiO2 in the clay fractions provide evidence of effective uptake of K by the clay minerals. K2O/Al2O3 ratios using raw NAu-1 clay fraction separates were 0.05, 0.19, and 0.93, representing increasing dissolved K concentrations. With reduced nontronite, K2O/Al2O3 was 0.17, 0.45, and 1.47. Therefore, exposure to greater K concentrations leads to greater K uptake, and the effect is stronger in the reduced clay. Further experimentation may focus on microbial reduction of Fe-rich nontronite as opposed to artificial reduction.     Conclusion: The results of the experiments may be used to interpret the geochemistry of paleoclays as well as, in the field of petroleum geology to show the association between the smectite to illite transition and the thermal maturation of organic compounds in the production of petroleum and natural gas.   

Clay Synthesis: Modeling the Uptake of Potassium during Low Temperature Illitization of Smectite

Georgia State University

TITLE: Clay Synthesis: Modeling the Uptake of K
+
 during Low-Temperature Illitization of 
Smectite 
AUTHORS: Peter Razumov, Lucy Taylor, Rebecca Pickering 
FACULTY SPONSOR: Daniel Deocampo, PhD, Associate Professor, Department of Geosciences 
  
Introduction: Authigenic lacustrine clay sediments have long been recognized as important chemical 
precipitates in sedimentary environments in East African Neogene lakes. Understanding how these 
minerals form is important to understanding the paleohydrologic, paleoclimate, and diagenetic histories 
of lake basins. We designed a suite of clay synthesis experiments to test the role of varying K 
concentrations during the process of illitization, after layer charge has been increased through Fe 
reduction. Specifically we are testing the hypothesis that elevated aqueous K concentration leads to 
enhanced illitization, and that this effect is greater with clays in which Fe has been reduced. 
Method: To test this hypothesis, the Clay Minerals Society Fe-rich nontronite clay standard (NAu-1) was 
artificially reduced by mixing with a sodium dithionite (Na2S2O4) solution buffered to neutral pH with 
sodium citrate – sodium bicarbonate buffer fallowing the methods of Stucki et al., 1993. Clay aliquots 
were then exposed to solutions of increasing K concentrations in a flask under a nitrogen rich 
atmosphere. Solution concentrations were based on Lake Dabusun, China, a K-rich saline lake (Spencer 
et al., 1990). Fluid chemistry was monitored though AA spectroscopy for both reduced and non-reduced 
samples, before and after experiments. XRD analysis was used for identifying mineralogy (before and 
after experiments) and XRF analysis was used to identify major element composition (before and after 
experiments). 
Results: Element ratios K2O/Al2O3 and K2O/TiO2 in the clay fractions provide evidence of effective 
uptake of K by the clay minerals. K2O/Al2O3 ratios using raw NAu-1 clay fraction separates were 0.05, 
0.19, and 0.93, representing increasing dissolved K concentrations. With reduced nontronite, K2O/Al2O3 
was 0.17, 0.45, and 1.47. Therefore, exposure to greater K concentrations leads to greater K uptake, and 
the effect is stronger in the reduced clay. Further experimentation may focus on microbial reduction of 
Fe-rich nontronite as opposed to artificial reduction.     
Conclusion: The results of the experiments may be used to interpret the geochemistry of paleoclays as 
well as, in the field of petroleum geology to show the association between the smectite to illite 
transition and the thermal maturation of organic compounds in the production of petroleum and 
natural gas.  
 


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Clay Synthesis: Modeling the Uptake of Potassium during Low Temperature Illitization of Smectite

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