Recovery of phosphorus from liquid digestate using waste magnesite dust

Al-Mallahi J., Surmeli R. O. , ÇALLI B.

JOURNAL OF CLEANER PRODUCTION, cilt.272, 2020 (SCI İndekslerine Giren Dergi) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 272
  • Basım Tarihi: 2020
  • Doi Numarası: 10.1016/j.jclepro.2020.122616


Phosphorus recovery through struvite precipitation consumes significant amounts of magnesium, thereby increasing the total cost of the process. Therefore, it is important to find cheaper alternatives than commercial magnesium sources. Processing of magnesite ore to produce magnesium oxide generates waste, the disposal of which can give associated environmental problems. Conversely, this 'waste' material might serve as an appropriate source of magnesium and also as a pH elevator. This study proposes calcination of Waste Magnesite Dust (WMD) to enhance its magnesium release. Calcination was carried out at 500 degrees C, 700 degrees C, 800 degrees C and 900 degrees C for different durations. Fluidized Bed Reactor (FBR) experiments were undertaken to evaluate the performance of calcined WMD compared to raw WMD. This was followed by batch experiments to determine the effect of dosage and pH on phosphorus recovery and to compare the calcined WMD with pure magnesium oxide (MgO). The optimum reaction time was evaluated by running a FBR experiment at optimum dosage. Finally, cost analysis was performed. Complete decomposition could be achieved by calcining at 700 degrees C, 800 degrees C and 900 degrees C for 1, 0.5 and 0.25 h respectively. Calcination converted magnesite to magnesia and enhanced magnesium release. Optimum precipitation conditions were identified to comprise a dosage of 1 g/L of calcined WMD and a reaction duration of 2 h for liquid fraction digestate. Phosphorus removal of 96% for synthetic solution and 75% for real digestate was achieved by WMD which was completely decomposed at 900 degrees C for 0.25 h. Cost analysis revealed the advantage of applying WMD calcined at 700 degrees C for 1 h, which resulted in the highest cost reduction; 38% and 57% compared to magnesium oxide and magnesium chloride respectively. It is considered that this might increase the profitability of magnesite processing companies through allowing them to sell this material, for subsequent use as a cheaper magnesium source for struvite precipitation. (C) 2020 Elsevier Ltd. All rights reserved.