Cement stabilization of tannery sludge using quaternary ammonium salt exchanged bentonite as pre-solidification adsorbent

In this paper a cement-based cementitious system is studied for the stabilization of tannery sludge. Two binders were used as stabilizing matrices: pozzolanic cement alone and a 3.7 cement/blast furnace slag mixture. Due to the high organic content of the sludge, organophilic bentonite was added to the stabilization system; the modified bentonite was obtained by ionic exchange with benzyldimethyloctadecylammonium chloride and proved to be an effective sorbent of the organic components of the sludge. The different process steps were arranged to minimize the water requirement. The process was evaluated from three different points of view: chemical, environmental and technological. From the chemical point of view, it was found that the binder hydration products are unaffected by the presence of sludge, although the hydration process is retarded. From the environmental and technological points of view, it was found that the presence of organophilic bentonite strongly enhances process performance. In fact, the release of both organic carbon and chromium is greatly reduced and the unconfined compressive strength of the stabilized products is increased. According to Italian standards, the stabilized products are suitable for the manufacture of pre-formed building blocks.