Study on the influence and mechanism of polyferric sulfate on COD removal and reuse of scheelite flotation wastewater

This study investigated an efficient method for removal COD of scheelite flotation wastewater (SFW) with polyferric sulfate (PFS) and the reuse of the treated water into the flotation system. The mechanism of COD removal was studied by scanning electronmicroscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transforminfrared spectroscopy, species distribution calculation and kinetics. Results showed that 66.85 % COD removal was achieved with PFS treatment under the optimum conditions (Contact time: 30 min, PFS dose: 1.5 g/L, and initial solution pH: 8). The COD of SFW was reduced from 207.36 mg/L to 68.75 mg/ L and the COD removal capacity could reach 92.41 mg/g. The treated SFW could be reused in scheelite-flotation system without affecting index of scheelite. In addition, amorphous ferric hydroxide (Fe(OH)3(s)) was formed during Fe(III) hydrolysis, and it could reacted with oleate to the formation of iron carboxylate, resulting the removal of COD in SFW. The kinetic analysis of PFS treatment process showed that the removal of COD obeyed the pseudo-second-order kinetic model, and the main rate-limiting step of the adsorption of amorphous Fe(OH)3 (s) was chemisorption.