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[Display omitted] • PFS is an effective adsorbent for removal COD. • The treated SFW could be reused in scheelite-flotation system. • Amorphous Fe(OH) 3(s) reacted with oleate to the formation of iron carboxylate. • The COD removal mechanism of PFS was deduced and described. 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. [ABSTRACT FROM AUTHOR]

• CaCl 2 could remove suspended solids in weathered tungsten-ore beneficiation wastewater. • The Ca2+ supplied by CaCl 2 can neutralize the negative charge on suspended solids' surface. • CaCO 3(S) and CaSiO 3(S) were formed by the reaction of Ca2+ with CO 3 2– and SiO 3 2– in wastewater. • The reuse of treated water into tungsten-flotation system did not affect flotation index. The direct reuse of weathered tungsten-ore beneficiation wastewater (WTBW) in tungsten-flotation system seriously deteriorates the flotation index of tungsten because of its high content of suspended solids (SS). In the present study, an innovative technology using calcium chloride (CaCl 2) to remove SS from WTBW was established based on the theory of electroneutralization and chemical precipitation. A series of laboratory tests was performed to determine the optimal conditions for SS removal from WTBW. Species-distribution calculation, zeta potential, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used to analyze the underlying mechanism. Results showed that the content of SS in WTBW decreased from 25.16 × 10 3 mg/L to 22.56 mg/L after CaCl 2 treatment. A concentrate with tungsten grade and recovery of 1.93% and 74.81%, respectively, was obtained by reusing the treated wastewater in the tungsten-flotation system. Compared with untreated wastewater, the tungsten grade and recovery of concentrate increased by 0.45% and 12.20%, respectively. Moreover, the Ca2+ supplied by CaCl 2 can neutralize the negative charge on SS surface and further react with CO 3 2– and SiO 3 2– in solution to form CaCO 3(S) and CaSiO 3(S) , which explained why CaCl 2 can promote the aggregation and sedimentation of SS. [ABSTRACT FROM AUTHOR]

Schematic illustration of combined inhibitory effect of Ca(ClO) 2 and DX on pyrite and galena. • Combined effect of Cp and DX depresses pyrite flotation more strongly than galena. • Calcium hypochlorite (Cp) and dextrin (DX) has synergistic effect on pyrite surface. • Cp and DX could be a new depressant scheme in pyrite-galena flotation systems. Selective separation of pyrite from base minerals is very important and challenging. This research investigates the combined inhibitory effect of two novel reagents on flotation behaviors of pyrite and galena under the low alkaline conditions. The depression and adsorption mechanism of calcium hypochlorite [Ca(ClO) 2 ] and dextrin (DX) on pyrite and galena were systematically studied via the microflotation experiments, reagent adsorption measurements and X-ray photoelectron spectroscopy. Flotation results showed that the combined effect of Ca(ClO) 2 and DX depressed the flotation of pyrite more strongly than that of their individual effect. An improved recovery difference of more than 60% between the galena and pyrite was achieved at pH 10 while using Ca(ClO) 2 and DX as depressant system and diethyldithiocarbamate (DDTC) as collector. Reagent adsorption measurements showed that the adsorption amount of DDTC onto pyrite surface was decreased significantly with the prior addition of Ca(ClO) 2 and DX. On the contrary, the surface of galena remained mildly inert in the presence of Ca(ClO) 2 and DX and thus adsorbed significantly more amount of DDTC. XPS analysis showed that, in the presence of Ca(ClO) 2 , the surface of pyrite was severely oxidized to iron oxide/hydroxide species that promoted the adsorption of DX onto the pyrite surface. Based on the XPS analysis, an adsorption and depression mechanism of Ca(ClO) 2 and DX on pyrite and galena was also proposed. [ABSTRACT FROM AUTHOR]