Treatment of nanowaste via fast crystal growth: With recycling of nano-SnO2 from electroplating sludge as a study case

The treatment of industrial sludge containing amorphous/nanophase metal oxides or hydroxides is one of the vital issues in hazardous waste disposal. In this work, we developed a strategy to recycle nano-SnO2 from tinplate electroplating sludge. It revealed that the major components of this sludge were acid soluble Sn and Fe amorphous phases. By introducing NaOH as a mineralizer, a fast growth of amorphous Sn compound into acid-insoluble SnO2 nanowires was achieved selectively. Thus, the as-formed nano-SnO2 could be recycled via dissolving other solid compositions in the sludge by using acid. The role of NaOH on accelerating both the Oriented Attachment (OA) and Ostwald Ripening (OR) growth of SnO2 was discussed, which was regarded as a critical factor for treating the sludge. A pilot-scale experiment was conducted to treat 2.3 kg original sludge and the recycling of about 90 g nano-SnO2 was achieved. We anticipate this work can provide a good example for the recycling of valuable metals from industrial sludge containing fine metal oxides or hydroxides.