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Traditional methods of vanadium recovery from vanadium slag suffer from serious environmental pollution due to the residue and wastewater containing highly toxic V(V) and Cr(VI). To avoid this, a complexation method based on sodium diethyldithiocarbamate (DDTC) complexing agent was proposed to separate and recover V(IV), Fe(II), Cr(III) in the leaching solution directly prepared from vanadium slag. Firstly, the recovery effect of DDTC on metal ions was studied in the imitated solution containing V (IV), Fe (II) and Cr (III), 97.67% vanadium, 99.51% iron and 98.99% chromium were recovered, respectively. In addition, DDTC was recycled in the complexation process. After four cycles, the regeneration rate of DDTC remained above 86%. Then, this method was applied to the leaching solution of vanadium slag, and 97.38% Cr, 97.69% V, 99.66% Fe and 97.64% Mn were recovered, respectively. Chromium was recovered as Cr 2 O 3 with purity of 97.1%. Most iron was recovered as (NH 4) 2 Fe(SO 4) 2 ·6H 2 O with purity of 99.23%. Manganese and a small amount of iron were enriched in the slag, which could be used to produce manganese alloy. Vanadium was recovered as calcium salt, which could be used to produce VOSO 4 electrolyte with purity greater than 99.8%. Without waste water and residue containing highly toxic V(V) and Cr(VI) produced in this new method, which provides a new strategy for cleaner comprehensive utilization of vanadium slag. A novel method for deep separation and recovery of V(IV), Fe(II) and Cr(III) in solution. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, the rapid development of copper indium gallium selenide (GIGS) solar cells makes it necessary to recycle spent CIGS in order to realize circular economy. In this work, a novel and efficient method for comprehensive recovery valuable metals in spent CIGS materials was investigated, mainly including three steps: (1) leaching of spent CIGS with nitric acid to separate indium; (2) precipitating to obtain copper gallium selenite mixture with magnesium oxide as precipitant; (3) calcination of the residue and the precipitation to recover selenium. X-ray photoelectron spectroscopy (XPS) analysis indicates that the valence state of selenium was converted from negative divalent to positive tetravalent after oxidative leaching. In addition, the results of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) shows that the dissolution of metals in CIGS during leaching were significantly different. Copper and gallium were almost completely leached, while indium entered the slag phase as indium selenite, which achieved the separation of indium. Moreover, the reaction mechanism of leaching was analyzed from the perspective of thermodynamics. After leaching, copper, gallium and selenium can be completely recovered from the leach liquor using magnesium oxide as precipitant. Subsequently, the separation of Se in the residue and precipitates can be achieved at 800 °C for 90 min. Finally, the recovery yields of Cu, In, Ga and Se were 99.23%, 96.82, 98.08% and 96.38% respectively. This research represents an important innovation from the perspective of circular economy and provides a new idea for comprehensive utilization of secondary solar cells. [Display omitted] • An innovative technology for treating spent CIGS via HNO 3 leaching was proposed. • Leaching agent (HNO 3) and precipitation agent (MgO) were regenerated and recycled. • Indium was efficiently separated by one-step leaching. • The recovery of selenium was completed quickly at much lower temperatures. [ABSTRACT FROM AUTHOR]

Oil-refinery alkali residue wastewater (ORARW) contains large amounts of phenol and its derivatives, which are highly toxic and valuable but difficult to biodegrade. In this study, using vegetable oil as the liquid membrane phase, a green polypropylene-hollow-fiber supported liquid membrane (SLM) system was constructed to simultaneously separate and recover phenol, m -cresol and o -cresol from aqueous solutions. After screening several types of vegetable oil, linseed oil was selected as the liquid membrane phase. Based on a single SLM module and using a NaOH solution as the stripping reagent with feed phase and stripping phase hydraulic retention times (HRTs) of 7.8 and 6.9 min, respectively, the phenol separation and recovery rates were 92.9% and 88.8%, respectively. The separation rates for m -cresol and o -cresol were both greater than 96%, their recovery rates were approximately 92%, and the membrane separation flux of every phenolic compound exceeded 0.40 g/m2·h. When two SLM modules were operated in series at room temperature for 3 h, the separation efficiency for phenols increased by approximately 9% compared with that obtained with a single SLM module. After applying two SLM modules in series to treat ORARW with an initial concentration of phenols of 4800–5200 mg/L, the simultaneous separation and recovery rates of phenols were near 95% and 92%, respectively. This work concluded that vegetable oil can be used as a nontoxic and renewable green liquid membrane phase and that two SLM modules in series efficiently separated and recovered phenols from aqueous solutions. Image 10784 • Vegetable oil was used as an SLM liquid membrane to separate and recover phenols. • The order of the phenol extraction was linseed oil > sunflower oil > rapeseed oil. • Two membrane modules in series were more effective for the separation of phenols. • The separation and recovery rates for phenols reached 95% and 92%, respectively. • The SLM system can be used in an oil refinery as a cleaner production process. [ABSTRACT FROM AUTHOR]