In this paper, results are presented on the general mechanisms by which scale inhibitors (SIs) are retained within porous media. There is a generally accepted view that the main two mechanisms of SI retention are "adsorption" and "precipitation" and these are described by different but related modelling approaches in the literature. These approaches have been used quite successfully to model field squeeze treatments. To analyse in a detailed and unambiguous manner where a given retention mechanism (e.g. pure adsorption) or mechanisms (e.g. coupled adsorption and precipitation) are operating requires that we carry out careful laboratory experiments under "field relevant" conditions.

In this work, we study adsorption vs. adsorption/ precipitation by performing a series of experiments where we know that the system exhibits either (a) adsorption only or (b) coupled adsorption/precipitation. Experimentally it is straightforward to determine which regime the system is in, as explained below. We present the theory describing the coupled adsorption/precipitation process. In addition, an extensive series of experimental adsorption/precipitation measurements are presented for various mineral separates including sand, chlorite, siderite, muscovite, kaolinite, feldspar and montmorillonite. The coupled adsorption/ precipitation model is in very good agreement with experiment.

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