A pilot-plant for the selective recovery of magnesium and calcium from waste brines

Abstract

The problem of brines disposal has raised great interest towards new strategies for their valorisation through the recovery of minerals or energy. As an example, the spent brine from ion exchange resins regeneration is often discharged into rivers or lakes, thus impacting on the process sustainability. However, such brines can be effectively reconcentrated, after removal of bivalent cations, and reused for the resins regeneration. This work focuses on developing and testing a pilot plant for selective recovery of magnesium and calcium from spent brines exploiting a novel proprietary crystallization unit. This is part of a larger treatment chain for the complete regeneration of the brine, developed within the EU-funded ZERO BRINE project. The pilot crystallizer was tested with the retentate of the nanofiltration unit processing the spent brine from the industrial water production plant of Evides Industriewater B.V. (Rotterdam, The Netherlands).Magnesium and calcium hydroxide were selectively precipitated by adding alkaline solution in two consecutive steps and controlling reaction pH. Performance was assessed in terms of recovery efficiency and purity of produced crystals, observing in most investigated cases a recovery of about 100% and 97% and a purity above 90% and 96%, for magnesium and calcium hydroxide, respectively.

Analysis of particles size distributions in Mg(OH)2 precipitation from highly concentrated MgCl2 solutions

“…Vassallo et al [19] presented a novel pilot plant for the selective recovery and removal of magnesium and calcium from retentate brines of a nanofiltration unit processing spent brines from the industrial water production plant of Evides Industriewater B.V. More than 90% of magnesium ions contained in the treated brine were recovered with magnesium hydroxide purities above 90%.…”

Influence of Operational Strategies for the Recovery of Magnesium Hydroxide from Brines at a Pilot Scale

“…Results marked the possibility of achieving high values of mineral recovery: 100 and 97% for magnesium and calcium hydroxides, respectively. High purity of these final products (>98%) was another successful accomplishment …”

“…The novel reactive crystallizer under investigation in this work is the MF-PFR introduced by Vassallo et al , Figure presents (a) a picture of the developed MF-PFR pilot plant and (b) a simplified P&ID describing all the features of the plant.…”

“…(a) MF-PFR prototype developed at the Brine Excellence Centre satellite laboratory of the University of Palermo and (b) simplified P&ID of the MF-PFR prototype. Figure 1a was adapted from Vassallo et al …”

“…As schematically illustrated in Figure , the two feed streams enter in contact with each other with a multiple inlet arrangement which is employed in order to favor a better supersaturation homogenization all over the reactor volume. In addition, each inlet is equipped with nozzles, purposely designed to promote the fast mixing of the two streams. , When the two reactants meet, Mg 2+ present in the feed solution (brine) react with the hydroxyl ions (OH – ) of the alkaline solution, promoting the precipitation of Mg­(OH) 2 according to the following chemical reaction eq …”