Synthesis and Characterisation of Struvite Family Crystals by An Aqueous Precipitation Method

¹ Departement of Chemical Engineering, University of Pembangunan Nasional “Veteran” Jatim.
² Center for Waste Management, Mechanical Engineering Graduate Program, Diponegoro University, Tembalang Campus, Semarang 50275, Indonesia.
³ Office of Research and Department of Chemical Engineering, UNTAG, Bendhan Dhuwur Campus, Semarang 50233, Indonesia

E-mail: apbayuseno@gmail.com

Abstract

Struvite (NH₄MgPO₄•6H₂O) is a mineral often found as a scale deposit in an industrial process and piping. The common occurrence of struvite formation is a wide variety of environments. pH solution and environmental temperature are important parameters that control precipitation and subsequent decomposition of struvite. The study aims to characterise the struvite precipitated out the solution through chemical and mineralogical analysis. In this work, struvite solution was prepared by mixing NH₄OH , MgCl₂ and H₃PO₄ with the different purity grade (A and B) in the mol ratio of 1 : 1 : 1 in the stirred glass vessel tank with volume of 500 ml, and then stirred at 200 rpm for 70 minutes. Temperature of 3°C and an initial pH of 10 were selected. The precipitated deposit was dried at room temperature for 48 hours of being analyzed. Material characterization of the deposits was conducted using XRPD Rietveld method of qualitative and quantitative mineralogical phase analysis. XRF was employed for bulk chemical elemental analysis of the scale obtained. The sample A using analytical grade powder provided the major phases of struvite-(K) and struvite. In constrast, the major phase of newberyite and minor phases of lepidocrocite (FeOOH) and niter (KNO₃) was observed by following changes in the lowest purity of powder (Sample B). Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.