Permanent and safe storage of Ba2+ in hardened phillipsite-rich tuff/cement pastes

Ba2+ removal from wastewater by cation exchange using phillipsite-rich tuffs and the subsequent stabilization of the resulting sludge in a cement matrix is reported. Moderate amounts of phillipsite-rich tuff were able to bring, in a short time, the Ba2+ concentration of an experimental wastewater below the legal limits allowed for discharge. Pastes of Portland cement/Ba-loaded tuff were cured for 28 days and characterized from a mechanical and chemical point of view. The compressive strength of the hardened compacts, containing 25-75% of zeolitic material, was much higher than the value of 0.44 MPa, suggested by international protocols for handling and landfilling the solidified wastes. Moreover, experimental leaching of the hardened pastes resulted in a Ba2+ concentration in the leachates much lower than the legal limits allowed for discharge of barium in bodies of water (20 mg/l).