Experimental investigation and molecular dynamic simulation of Tannic acid as an eco-friendly inhibitor for calcium carbonate scale

Abstract

The present study aims to assess the performance of Tannic acid (TA), a natural polyphenol, as a new eco-friendly inhibitor on the deposition scale of calcium carbonate. The conductivity test and the Laboratory of Chemistry and Genie of the Environment (LCGE) technique are used to evaluate the anti-scaling property of TA. The dispersion property of CaCO3 is also investigated using UV–visible method. To characterize the morphology and crystal structure of the formed scale during the LCGE tests, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses are utilized. Then, Molecular dynamic simulations are carried out to prove theoretically the ability of TA molecule to inhibit CaCO3 scaling. Results show that the addition of a low concentration of TA (7.8 mg L −1) inhibits completely the precipitation of calcium carbonate of calco-carbonic solution with a hardness of TH = 40 ° F (1 ° F = 4 mg L −1 of calcium ions) at 25 °C. We recorded also that TA has a good dispersion property of CaCO3. It was observed that the scales formed in the absence of TA are regular rhombohedral forms. However, in the presence of a low concentration of TA (2 mg L −1) the significant modification in the crystal morphology and the crystal sizes are noted. XRD diffractogram reveals that CaCO3-calcite is the main polymorph formed during the tests without inhibitor. Nevertheless, in the presence of inhibitor, a mixture of vaterite and calcite was obtained. The geometrical and energetic analyses of the interfacial interactions of TA inhibitor with calcite (110) and (104) surfaces proved its enhanced capacity to interact with calcite crystals. These findings explain the good obtained scale inhibition efficiency of TA. Consequently, we suggest the use of TA as a new eco-friendly inhibitor for calcareous scaling.