טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLehmann Katan Orly
SubjectSelective Magnetic Separation of MG+2 Ions from SWRO
Brine by Adsorption on Magnetite Crystals
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Ori Lahav
Full Thesis textFull thesis text - English Version


Abstract

A new approach was developed for cost effective recovery of Mg(II) from 1st stage seawater reverse-osmosis brines (salinity: twice seawater concentration) as well as seawater and seawater reverse-osmosis brine nanofiltration brines. The process is based on precipitation of Mg(OH)2(s) on the surface area of self-synthesized magnetite (Fe3O4) micro-particles and magnet-assisted separation of the solids-slurry from the Mg(II)-depleted brine. Once separated from solution, the solids slurry is subjected to acidic conditions (pH~4-6) under which Mg(OH)2(s) is recovered as Mg(II) with the counter anion being either SO42-, Cl- or HCO3-, depending on the choice of strong acid used in the dissolution step. The magnetite solids are then used in the following adsorption cycle. This research focused on proof-of-concept of the suggested process and on defining ranges for the major process operational conditions (Fe3O4 particle concentration; pH range maintained during Mg(OH)2(s) dissolution step; determination of the favorable solid-aqueous separation technique, etc.). Once defined, the chosen operational conditions were applied and shown to result in three high purity (>97%) Mg(II) solution products at costs which are comparable with equivalent commercial products. A possible application of replenishing Mg in desalinated water is presented. Two options were tested: dosing a produced MgSO4 rich solution to the desalinated water and direct integration into the post treatment process with dissolution of the Mg(OH)2(s) into the calcite reactor effluent. Both options are shown to be a valid among other known post-treatment technologies, both cost- and water quality wise. The latter option was found to reduce chemical demand in the overall post treatment process, thus lowering costs and improving water quality.