Electrochemical acidolysis of magnesite to induce struvite crystallization for recovering phosphorus from aqueous solution

• Published in: Chemosphere (Oxford) 2019-07, Vol.226, p.307-315
• Main Authors: Zhang, Zhiqiang, She, Lu, Zhang, Jiao, Wang, Zuobin, Xiang, Pengyu, Xia, Siqing
• Format: Article
• Language: English
• Subjects: Acidolysis; Electrochemical system; Magnesite; Phosphorus recovery; Struvite crystallization
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2019.03.106

A novel struvite crystallization method induced by electrochemical acidolysis of cheap magnesite was investigated to recover phosphorus from aqueous solution. Magnesite was confirmed to continuously dissolve in the anolyte whose pH stabilized at about 2. Driven by the electrical field force, over 90% of the released Mg2+ migrated to the cathode chamber via passing through the cation exchange membrane. The pH of the phosphate-containing aqueous solution in the cathode chamber was elevated to the appropriate pH fit for struvite crystallization. The products were identified as struvite crystals by scanning electron microscopy and X-ray diffraction. Increasing the magnesite dosage from 0.83 to 3.33 g L−1 promoted the phosphorus recovery efficiency from 2.2% to 78.3% at 3 d, which was attributed to sufficient Mg2+ supply. Increasing the applied voltage from 3 to 6 V improved the recovery efficiency from 43.6% to 76.4% at 1 d, since the enhanced current density of the electrochemical system markedly accelerated both the magnesite acidolysis and the catholyte pH elevation. The initial catholyte pH between 3 and 5 was found to benefit the phosphorus recovery due to the final catholyte pH fit for the struvite crystallization. [Display omitted] •Electrochemical acidolysis of magnesite for struvite way to recover P was achieved.•Magnesite acidolysis inhibited anolyte acidification and continuously released Mg2+.•Driven by electrical field force, Mg2+ migrated to cathode of stainless steel cloth.•Enough Mg2+ and appropriate pH promoted struvite crystallization in cathode chamber.•Increasing either magnesite dosage or applied voltage could enhance the P recovery.