Mineralogically and biologically assisted oxidation of arsenic (As) was investigated using batch techniques. Direct assessment of As speciation in complex environmental systems is crucial in predicting its fate, transport, and bioavailability. The two most prominent As species in soil systems are arsenate [As(V)] and arsenite [As(III)]. The former is less mobile and toxic than As(III). Redox processes, that are affected by an array of environmental factors and type of mineral surface, control the speciation of As. Arguably the most important soil component in As oxidation is manganese oxides. Additionally, soil microbes play an important role in oxidation and reduction of As species. Macroscopic based experiments were carried out to determine the contribution of manganese oxides, specifically Random Stacked Birnessite (RSB), and Alcaligenes faecalis in oxidizing As(III). Reactions were conducted in a batch reactor to first, evaluate As(III) oxidation by RSB and Alcaligenes faecalis separately at circumneutral pH. Second, batch experiments were executed using RSB and Alcaligenes faecalis in a mixed solution as oxidants for As(III). As(III) and As(V) were measured by Hydride Generation– Inductively Coupled Plasma–Optical Emission Spectrometry (HG-ICP-OES) in all experiments. The results from batch investigations will be coupled with concurrent research using bench and synchrotron-based infrared and Raman spectroscopic techniques to generate a comprehensive understanding of As dynamics in contaminated soil systems.