Low-temperature conversion of Fe-rich sludge to KFeS2 whisker: a new flocculant synthesis from laboratory scale to pilot scale

Herein, a KFeS2 whisker was formed in mass production at a low temperature, with waste cold-rolling sludge as Fe source, which exhibited good performance in the removal of Zn/Ni from real electroplating effluent. At laboratory scale, KFeS2 was generated at 80 °C by the hydrothermal method, and KFeS2 whisker grew radially with the extension of the reaction time. This method was applied at pilot scale, where a similar KFeS2 whisker was also produced with waste cold-rolling sludge as Fe source, and a residual brownish supernatant was observed after the reaction and then completely recycled in the next round for KFeS2 synthesis. After recycling five times, the produced KFeS2 whisker did not change. The drying and storage of KFeS2 have also been verified. Freeze drying and vacuum drying were applicable, whereas air drying was not profitable. Moreover, the efficiency of Zn/Ni removal using undried KFeS2 was similar to that of dried KFeS2. The efficiencies of Zn/Ni removal using KFeS2 were apparently higher those of common reagents for wastewater treatment.

Low-temperature Conversion of Fe-rich Sludge to KFeS2 Whisker: a New Flocculant Synthesis From Laboratory Scale to Pilot Scale

KFeS2 is a one-dimensional material and commonly used raw material for synthesising AgFeS2 and CuFeS2. With the solvothermal method, KFeS2 cluster could be synthesised at 190 °C with chemically pure grade Fe salt as Fe source. Herein, a KFeS2 whisker was formed in mass production at a low temperature, with waste cold-rolling sludge as Fe source, and exhibited good performance in the removal of Zn/Ni from real electroplating effluent. At laboratory scale, results showed that KFeS2 was not generated after heating at 50 °C for 24 h; however, after heating at 80 °C for 10 h, KFeS2 whisker (diameter and length of 0.2 and 0.5–1 mm, respectively) was produced, which grew radially to 1–4 mm after 24 h. This method was applied at pilot scale, where a similar KFeS2 whisker was also produced with waste cold-rolling sludge as Fe source. At pilot scale, a residual brownish supernatant was observed after the reaction and then completely recycled in the next round for KFeS2 synthesis. After recycling five times, the produced KFeS2 whisker did not change. For KFeS2 drying, freeze-drying and vacuum-drying were applicable, whilst air-drying was not profitable. The prepared KFeS2 was spontaneously hydrolysed in electroplating wastewater to generate Fe/S-bearing oxyhydroxide colloid for Zn/Ni removal. By adding 1 g of KFeS2, the residual levels of Zn/Ni were 0.22 and 0.02 mg/L, met the discharge standard of electroplating wastewater. Undried KFeS2 showed similar efficiencies of Zn/Ni removal to dried KFeS2, whose efficiencies were apparently higher than those with Na2S·9H2O, polymeric ferric sulfuric, sodium diethyldithiocarbamatre and lime. With the method, KFeS2 whisker was produced at pilot scale without generating any secondary waste and exhibited good performance in the treatment of electroplating wastewater.