Comparison of the fluoride, arsenate and nitrate anions water depollution potential of a calcined quintinite, a layered double hydroxide compound

The potential for removing anionic pollutants such as F⁻, HAsO ₄ ²⁻ , and NO ₃ ⁻ from water by mixed oxides issued from the moderate thermal treatment of quintinite (Mg₄Al₂ LDH) has been studied. This compound shows good trapping properties for F⁻ and HAsO ₄ ²⁻ , and a low potential for NO ₃ ⁻ , due to the competition with OH⁻. The competition between these three anions and CO ₃ ²⁻ has been envisaged and shows that CO ₃ ²⁻ is able to easily replace F⁻ and NO ₃ ⁻ , making the mixed oxides issued from MgAl LDH an inappropriate trap for F⁻ and NO ₃ ⁻ . However, only small amounts of arsenic are released after the CO ₃ ²⁻ introduction in water. Moreover, arsenates are able to replace carbonates even at lower concentrations. This means that HAsO ₄ ²⁻ anions present a stronger affinity than CO ₃ ²⁻ for the LDH structure. This makes mixed oxides issued from MgAl LDH very promising materials for the removal of arsenic in polluted waters.