Mineralization models substrate interactions

Extending this idea one step further, bacteria may have evolved to produce extracellular polymeric substances (EPSs) in order to make mineral surfaces more favorable for attachment. This would be an important evolutionary step, especially if the earliest bacteria utilized minerals for respiration and nutrition.25 According to the present model, oxides other than quartz also have unfavorable entropic interactions with the head group PL (AS°adsi < 0). EPSs should then be exuded on the surfaces of many oxide (and silicate) minerals. As discussed above, quartz is the most harmful, so greater production of EPSs should be expected on quartz, all other factors being equal. Consistent with this hypothesis, the nature of the substrate and of the bacterial surfaces does, in fact, affect the amount of EPS produced.60-62 The idea that surfaces become more hydrophilic by bacterial attachment also underlies the biobeneflciation of ores during mineral separation by floatation. 

The adsorption of ionic surfactants onto mineral substrates is a complex phenomenon simultaneously controlled by the nature of the adsorbing species, the properties of the solid surface and the composition of the aqueous solution. As a consequence, there is no complete theoretical model which can describe, both qualitatively and quantitatively, all the experimental information available. Calorimetry of adsorption may be very useful in studying the nature of the interactions in the adsorption system, but alone it is not capable of solving satisfactorily many detailed problems which still remain to be explained. Hovewer, the evolved model of the phenomenon should be able to contain the experimental results from all the bulk, calorimetric and spectroscopic studies reported on the system. 

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