In situ AFM imaging of dissolution and growth of struvite surface

Abstract

<p>Phosphorus removal from wastewaters is a great interest to avoid eutrophication of natural waters (i.e. rivers, lakes). Additionally phosphorus recovery is also important due to increasingly limited nutrient resources. Struvite (MgNH<sub>4</sub>PO<sub>4</sub>*6H<sub>2</sub>O) is of current interest as it is considered an alternative way for water remediation and potential use as a renewable fertilizer. Towards environmental sustainability, phosphorus and nitrogen removal and recovery from domestic, industrial, and/ or agricultural inputs, in the form of struvite may be an attractive alternative for the valorization of wastewaters (<strong>Mpountas et al., 2017</strong>).</p><p>Direct observations of crystal dissolution and growth process at the nano- level are possible through the use of Atomic Force Microscopy (AFM). A considerable number of studies have investigated mineral dissolution and growth by in-situ AFM imaging in a fluid-cell (<strong>Vavouraki et al., 2008; 2010</strong>). These direct observations and measurements allow the investigation of possible process mechanisms at the mineral-solution interface. Previous study on AFM imaging indicated struvite micro- to nanocrystal morphology. <strong>Hövelmann & Putnis (2016)</strong> investigated the interactions of ammonium-phosphate solutions with brucite (Mg(OH)<sub>2</sub>) cleavage surfaces by AFM suggesting coupled brucite dissolution and struvite precipitation at the mineral-fluid interface. To the best of our knowledge, there are no records of nanoscale observations of dissolution and/ or growth of struvite surfaces. The aim of this study is to perform in situ AFM experiments using freshly cleaved struvite surfaces at flow conditions. Step retreat and/ or etch pit spreading were observed. Dissolution rates of struvite using doubly deionized water at different pH values were determined  whereas growth rates at different saturation values and pH using magnesium and ammonium-phosphate bearing solutions were also measured . Raman and SEM analyses were carried out to assess chemical structure and morphology of the obtained struvite crystals before and after AFM experiments.</p><p><strong>Acknowledgments: </strong>The work has been supported by IKY-DAAD (2018-4) and KRHPIS II (Action PERAN).                                                                                </p><p><strong>References: </strong>Hövelmann & Putnis, 2016. <em>Env. Sci. Technol.</em> 50, 13032−13041; Mpountas et al., 2017. <em>J. Chem. Technol. Biotechnol.</em> 92, 2075–2082; Vavouraki et al., 2008. <em>Chem. Geol.</em> 253, 243–251; Vavouraki et al., 2010. <em>Cryst. Growth Des.</em> 10, 60–69.</p>

Effect of Operating Parameters and Foreign Ions on the Crystal Growth of Calcium Carbonate during Scale Formation: An Overview

“…For example, at fixed temperature and ionic strength, Karoui et al [50] showed that, the addition of sulphate ions to the CaCO 3 solution increased the induction time and decreased both the crystal growth rate and the amount of the precipitated CaCO 3 . Comparable results were found by Vavouraki et al [57]. However, Tlili et al [64] showed that sulphate ions increase the growth rate of CaCO 3 precipitated electrochemically.…”

“…The presence of mineral ions can significantly influence the crystal growth and microstructure of CaCO 3 [50][51][52][53][54][55][56][57][58][59]. Among mineral ions, sulphate and magnesium ions are widely studied [50,[53][54][55][56][57][58][59] since they are present at significant concentrations in natural waters. Compared to sulphate and magnesium ions, the impact of iron on the precipitation of calcium carbonate seems to be less studied and it appears to be a lack of reliable data on its impact on CaCO 3 precipitation, especially at elevated temperature and different pH.…”

“…(i) increased the nucleation time [50], (ii) decreased the precipitation rate of calcite formation [57] and (iii) promoted the formation of aragonite via a dissolutionÀprecipitation process after long reaction times [55,59].…”