Abstract: An apparatus and a process are provided which are particularly suited for treatment of sludge eminating from a metal finishing solution regeneration process, especially aluminum finishing solution. The sludge is washed on a horizontal belt vacuum filter from which a majority of the washing fluid is returned to the regeneration process. A portion of the washing water is wasted. After washing, the sludge is reslurried. Thereafter, the reslurried sludge is pumped to a reaction vessel in the presence of carbon dioxide under pressure. Sufficient carbon dioxide is provided to react with excess lime in the sludge to produce calcium carbonate and a substantially neutral pH. The sludge after carbonation is dewatered in a rotary drum vacuum filter and thereafter is suitable for placement in a landfill.