Pyroaurite-like phases (Mg-Fe3+ LDH) synthesis and solubility
Ellina Bernard, Barbara Lothenbach, Rupert J. Myers, Marcus Yio
Abstract
This study explores different methods for precipitating carbonated Mg-Fe 3+ layered double hydroxides (LDHs) with Mg/Fe 3+ ratios ranging from 2 to 2.5. Two synthesis approaches were investigated: a) CO 3 -Mg-Fe 3+ -LDH co-precipitated directly from MgO, Fe(NO 3 ) 3 and Na 2 CO 3 and b) NO 3 -Mg-Fe 3+ -LDH precipitated by adding NaOH to Mg(NO 3 ) 2 -Fe(NO 3 ) 3 solutions, followed by ion exchange with Na 2 CO 3 to form CO 3 -Mg-Fe 3+ -LDH. The solids were characterised using TGA, XRD and FTIR. For the co-precipitated samples in the presence of Na 2 CO 3 , the formation of carbonate-LDH was accompanied by ~10–30 wt% of hydromagnesite, while CO 3 -Mg-Fe 3+ -LDH modified from the NO 3 -Mg-Fe 3+ -LDH did not show any other Mg‑carbonates but contained Fe hydroxides, as evidenced by their brown coloration. All samples were re-equilibrated at 7, 20 and 50 °C. The solubility product (log Kso) was calculated from solution analysis, and preliminary thermodynamic data are presented. The findings provide insights into the stability and formation conditions of carbonated Mg-Fe 3+ LDH phases in carbonate-rich environments.