Coupled Adsorption/Precipitation of Scale Inhibitors: Experimental Results and Modeling

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 modeling approaches in the literature. These approaches have been used quite successfully to model field squeeze treatments. To analyze 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. We present the theory describing the coupled adsorption/precipitation process. In addition, an extensive series of experimental adsorption/precipitation measurements is presented for various mineral separates including sand, chlorite, siderite, muscovite, kaolinite, and feldspar. The coupled adsorption/precipitation model is in very good agreement with the experiment.