In situ AFM imaging of dissolution and growth of struvite surface
Authors: Vavouraki Aikaterini , King Helen , Putnis Christine , Koutsoukos Petros 
Published: March 2020

&lt;p&gt;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&lt;sub&gt;4&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;*6H&lt;sub&gt;2&lt;/sub&gt;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/&amp;#160;or agricultural inputs, in the form of struvite may be an attractive alternative for the valorization of wastewaters (&lt;strong&gt;Mpountas et al., 2017&lt;/strong&gt;).&lt;/p&gt;&lt;p&gt;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 (&lt;strong&gt;Vavouraki et al., 2008; 2010&lt;/strong&gt;). 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. &lt;strong&gt;Ho&amp;#776;velmann &amp; Putnis (2016)&lt;/strong&gt; investigated the interactions of ammonium-phosphate solutions with brucite (Mg(OH)&lt;sub&gt;2&lt;/sub&gt;) 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&amp;#160; 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.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgments: &lt;/strong&gt;The work has been supported by IKY-DAAD (2018-4) and KRHPIS II (Action PERAN).&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&amp;#160;&lt;/strong&gt;Ho&amp;#776;velmann &amp; Putnis, 2016. &lt;em&gt;Env. Sci. Technol.&lt;/em&gt; 50, 13032&amp;#8722;13041;&amp;#160;Mpountas et al., 2017. &lt;em&gt;J. Chem. Technol. Biotechnol.&lt;/em&gt; 92, 2075&amp;#8211;2082;&amp;#160;Vavouraki et al., 2008. &lt;em&gt;Chem. Geol.&lt;/em&gt; 253, 243&amp;#8211;251;&amp;#160;Vavouraki et al., 2010. &lt;em&gt;Cryst. Growth Des.&lt;/em&gt; 10, 60&amp;#8211;69.&lt;/p&gt;