Session: Fundamental Reactions Driving Macroscopic Geochemical Processes:

The study of mechanisms involving pedological development of soil carbon as facilitated by metal reagents, such as manganese, is a matter that requires detailed investigation for a well-rounded understanding of carbon sequestration and release, as well as how to go about future human conduct. Carbon processing in the pedosphere medium is of scientific significance because the natural phenomena by which carbon is allowed to evolve into its successive forms is impacted by the reality of climate change, industrialization, and human management and development. Manganese oxides are among the most effective oxidizers of Dissolved Organic Carbon (DOC); its presence in many different water bodies, groundwater, and soil make it a critical reactant in reductive kinetic reactions. Manganese(IV) oxide (MnO₂) is both effective and timely when in contact with DOC materials. The two DOC sources chosen for this study were: Oxalic Acid reagent (333 μM, 667 μM), and a locally derived DOC reagent from soils (572 mg L^-1, 161 mg L^-1, 80.7 mg L^-1; all buffered to pH = 4 using an acetic acid/acetate solution). Through implementation of a UV-VIS spectrophotometer, calibration of the reaction was attained and extrapolated to convert observed changes in MnO₂ absorbance to MnO₂ rate loss equations. Initial rates and average rate constants quantify the oxidizing ability of manganese(IV) oxide in reactions with both types of organic ligands. The resulting kinetics of the fastest oxalic acid (667 μM) and MnO₂(66.7 μM) reaction yielded an initial rate of -0.843 μM s^-1, and an average rate constant of -0.0248 s^-1. The resulting kinetics of the fastest DOC (572 mg L^-1) and MnO₂ (66.7 μM) reaction yielded an average rate of -0.920 μM min^-1 and an average rate constant of -0.0241 min^-1. Experimental kinetics data of metal-carbon redox processes can be used to guide remediation and identify lapses and improvements in the management of terrestrial and semi-aquatic portions of the carbon cycle.

Matthew G. Siebecker

Assistant Professor, Texas Tech University

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