Abstract
Electroplating sludge is a hazardous waste produced in plating and metallurgical processes which is commonly disposed of in safety landfills. In this work, electroplating sludge containing 25.6% Fe and 5.5% Co (named S1) and another containing 36.8% Fe and 7.8% Cr (S2) were recycled for the preparation of erdite-bearing particles via a facile hydrothermal route with only the addition of Na2S·9H2O. In the sludges, Fe-containing compounds were weakly crystallized and spontaneously converted to short rod-like erdite particles (SP1) in the presence of Co or long nanorod (SP2) particles with a diameter of 100 nm and length of 0.5–1.5 μm in the presence of Cr. The two products, SP1 and SP2, were applied in electroplating wastewater treatment, in which a small portion of Co in SP1 was released in wastewater, whereas Cr in SP2 was not. Adding 0.3 g/L SP2 resulted in the removal of 99.7% of Zn, 99.4% of Cu, 37.9% of Ni and 53.3% of Co in the electroplating wastewater, with residues at concentrations of 0.007, 0.003, 0.33, 0.09 and 0.002 mg/L, respectively. Thus, the treated electroplating wastewater met the discharge standard for electroplating wastewater in China. These removal efficiencies were higher than those achieved using powdered activated carbon, polyaluminum chloride, polyferric sulfate or pure Na2S·9H2O reagent. With the method, waste electroplating sludge was recycled as nanorod erdite-bearing particles which showed superior efficiency in electroplating wastewater treatment.
Highlights
Electroplating is a basic process in the machine manufacturing industry and uses various heavy metals to protect plating pieces [1,2,3,4]
Acidic wastewater is treated through pH adjustment and coagulation, which transfer heavy metals from wastewater to sludges [2,3]
Alkaline wastewater comprises complex agents, such as citric acid, ethylene diamine tetra-acetic acid (EDTA) and tartaric acid [6,7], which react with heavy metals to form heavy metal–organic complexes
Summary
Electroplating is a basic process in the machine manufacturing industry and uses various heavy metals to protect plating pieces [1,2,3,4]. High volumes of electroplating wastewater are generated, which is an extremely hazardous type of wastewater containing multiple heavy metals [5]. Acidic wastewater is treated through pH adjustment and coagulation, which transfer heavy metals from wastewater to sludges [2,3]. Alkaline wastewater comprises complex agents, such as citric acid, ethylene diamine tetra-acetic acid (EDTA) and tartaric acid [6,7], which react with heavy metals to form heavy metal–organic complexes. Heavy metals cannot be hydrolyzed even after adjusting wastewater pH to values above 12. Heavy metals are difficult to precipitate in alkaline wastewater through pH adjustment and are commonly
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