Differential Precipitation of Mg(OH)2 from CaSO4·2H2O Using Citrate as Inhibitor—A Promising Concept for Reagent Recovery from MgSO4 Waste Streams

Abstract

In hydrometallurgical processing and acidic wastewater treatment, one of the neutralizing agents employed is MgO or Mg(OH)2. At the end of this process, the resulting solution, which is rich in SO42− and Mg2+ is treated with lime to remove (or minimize the amount) of these ions via the precipitation of Mg(OH)2 and CaSO4·2H2O (gypsum). In our work, an attempt was made to separate the two solids by increasing the induction time of the gypsum precipitation, thus regenerating relatively pure Mg(OH)2 which could be reused in wastewater treatments or hydrometallurgical processing circuits, and in this way, significantly enhancing the economic viability of the process. During our experiments, the reaction of an MgSO4 solution with milk of lime prepared from quicklime was studied. The effects of a range of organic additives, which can slow down the precipitation of gypsum have been assessed. The process was optimized for the most promising inhibiting agent—that is, the citrate ion. The reactions were continuously monitored in situ by conductometric measurements with parallel monitoring of solution pH and temperature. ICP-OES measurements were also carried out on samples taken from the reaction slurry. The composition of the precipitating solids at different reaction times was established by powder XRD and their morphology by SEM. Finally, experiments were carried out to locate the additive after the completion of the precipitation reaction to get information about its potential reuse.

Reaction Layer Formation on MgO in the Presence of Humidity

“…However, there is also no evidence of crystallinity in the BF-TEM images. Further research is needed to conclusively determine if the reaction layer is a crystalline phase or not, but previous studies have observed precipitation of amorphous magnesium hydroxide during reactions between magnesium sulfate and calcium hydroxide, as well as precipitation of amorphous phases during the reaction of MgO in ambient conditions for time periods shorter than 2 months. ,, …”

Phosphorus availability from magnesium‐modified P‐enriched Douglas fir biochar as a controlled release fertilizer

“…In contrast, the low release of Mg could possibly be because of the precipitation of Mg 2+ in the form of less soluble forms such as Mg(OH) 2 (pK SP = 10.86) (Ziegenheim et al, 2020) at increased Mg 2+ and OH − concentration. Angst and Sohi (2013) in their study to establish K, Mg and P released by biochar noted that both P and Mg were gradually released from biochar suggesting its suitability for use as a slow-release fertilizer.…”

Valorization of Seawater Reverse Osmosis Brine by Monovalent Ion-Selective Membranes through Electrodialysis

“…The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/membranes13060562/s1, Figure S1: Custom-made frame set-up for membrane fabrication through interfacial polymerization, Figure S2: XRD spectra of the product obtained as a result of electrodialysis. References [46,47]…”