Divalent ion uptake of heavy metal cations by (aluminum + alkali metals) – substituted synthetic 1.1 nm-tobermorites

Abstract

The reactions of Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺ or Hg²⁺ synthetic (Al + alkali metal) – substituted tobermorites were studied. Among these cations, Mn²⁺, Fe²⁺, Cu²⁺, Zn²⁺, pb²⁺ and Hg²⁺ appears to exchange with outer planar surface of Ca²⁺ of tobermorites due to the break down of structural Ca-O bonds, in addition to the substituted alkali metals in the structure. But it is difficult to delineate the extent of this reaction from the precipitation of the concerned ions as carbonates, hydroxy carbonates, hydroxy nitrates or hydroxides. The uptake of metal ions by these solids led to their amorphization in many cases due to the partial exchange and the acidic nature of metal solutions, and hence their reactions are not strictly analogous to cation exchange in zeolites and clays. The order of ion uptake has been found in the following order: Fe²⁺ > Ni²⁺ > Co²⁺ > Zn²⁺ > Cu²⁺ > Mn²⁺ > Hg²⁺ > Cd²⁺ > pb²⁺.