Biodegradation and adsorption of crude oil hydrocarbons supported on “homoionic” montmorillonite clay minerals

• Interlayer cations are crucial for both adsorption and biodegradation of hydrocarbons.
• Na+, Ca2 +, and Fe3 + as interlayer cations stimulate biodegradation of hydrocarbons.
• K+, Zn2 + and Cr3 + as interlayer cations inhibit the biodegradation of hydrocarbons.
• K+ and Zn2 + as interlayer cations effect significant hydrocarbon adsorption.
• Hydrolysis of interlayer water is suggested to be inhibitory to biodegradation.

The role of “homoionic” montmorillonites in hydrocarbon removal during biodegradation was investigated in aqueous clay/oil microcosm experiments with a hydrocarbon degrading microorganism community. The clay mineral used for this study was montmorillonite which was treated with the corresponding metal chloride salt to produce Na-, K-, Mg-, Ca-, Zn-, Al-, Cr-, and Fe-montmorillonites used in this study. The study indicated that Zn- and K-montmorillonites were inhibitory to biodegradation of the crude oil hydrocarbons and appears to do so as a result of extensive adsorption of the hydrocarbons. However, Na-, Ca- and Fe-montmorillonites with relatively high surface area and cation exchange capacity (CEC) were stimulatory to biodegradation of the crude oil hydrocarbons. This study reveals that whereas surface area and the ‘local bridging effect’ were important factors from the clay minerals that conferred stimulatory effect on the biodegradation of the hydrocarbons, the hydrolysis of the interlayer water by trivalent cations of the clay to generate protons and increase acidity of the medium is suggested to be inhibitory to biodegradation of the crude oil hydrocarbons. The interlayer cations (trivalent cations) that impart the highest local bridging effect which is stimulatory to biodegradation also impart the highest hydrolysis of interlayer water which is inhibitory. This study showed that interlayer cations play a crucial role on the ability of the clay mineral to influence biodegradation of the hydrocarbons.