•Na3V2 (PO4)3/C composites are synthesized by spray drying-assisted method.•Na3V2 (PO4)3/C composites form porous spherical structure.•Carbon coating and porous spherical structure are favorable for better property.Porous spherical Na3V2(PO4)3/C composites were synthesized by a spray drying-assisted approach combined with microwave calcinations, and then characterized as cathode materials for sodium-ion batteries. The effect of carbon content on Na3V2 (PO4)3/C were investigated by X-ray diffraction, scanning electron microscopy, Brunauer–Emmet–Teller method, charge-discharge test, cyclic voltammetry and electrochemical impedance spectra measurements. The results demonstrate that the Na3V2(PO4)3/C composite with 5wt.% carbon exhibits the best electrochemical performance among the as-prepared three Na3V2 (PO4)3/C samples. It delivers the discharge capacity of 97.9 mAh g− 1, 93.5 mAh g− 1 at 0.2 C and 5 C, respectively. Furthermore, 97.9% of its initial capacity is remained after 500 cycles at a high rate of 5 C. The superior electrochemical performance can be ascribed to the improvement of electronic and ionic conductivity by carbon coating and porous spherical structure.

•Behavior of binary iron-containing nanoparticle mixtures is improved in vibro-fluidized bed.•Plug and channeling can be effectively eliminated with vibration.•The minimum fluidization velocity and the agglomerate size can be reduced significantly.•The R–Z index n/4.65 of iron-containing nanoparticle mixtures is closer to 1.The present work is focused on the fluidization behavior of different mixed binary nanoparticles (Fe2O3 + SiO2, Fe2O3 + TiO2, and Fe2O3 + ZnO) under the influence of a vibrated field. The results reveal that the iron-containing nanoparticle mixtures with different mass fractions can achieve uniform fluidization in the initial bed height of 40 mm, amplitude of 3.0 mm, vibration frequency of 40 Hz, and binary mixtures containing nano-SiO2 and nano-Fe2O3 have commendable fluidization behavior. Richardson–Zaki equation index indicates that the particulate dispersion degree of the different proportion mixtures increases as the mass fraction of APF (agglomerate particulate fluidization) nanoparticle increases. For a binary nanoparticle mixture containing different proportions of high content nano-SiO2 and nano-Fe2O3, n/4.65 is closer to 1 and the relative deviation is smaller than that containing a high content TiO2 and ZnO, indicating that the system has a good dispersibility.

•An ammonia-hydrothermal method was used to prepare hexagonal Mg(OH)2 nanoplates.•Mg(OH)2 particles with good dispersivity and uniform size distribution were prepared.•Optimum operating conditions were determined for preparing nano-sized Mg(OH)2.•Mg(OH)2 crystal growth and size were controlled by MEA concentration.Nanosized dispersive hexagonal magnesium hydroxide (Mg(OH)2) has been prepared using an ammonia-hydrothermal method. Citric acid and monoethanolamine (MEA) were added to the reaction system during the ammonia precipitation and hydrothermal processes, respectively, to improve the crystallinity and dispersion of the (Mg(OH)2) particles. The resulting Mg(OH)2 samples obtained under the optimum preparation conditions were characterized by scanning electron microscopy, X-ray diffraction and thermal gravity analysis, which showed that this newly developed procedure afforded well-dispersed hexagonal nanoplates of Mg(OH)2 with a mean diameter of 246 nm.

In this study, a green process with prospective environmental and economic significance has been experimentally and theoretically established for the sustainable recovery of metals from spent lithium-ion batteries (LIBs). Three leaching systems were explored for the application of different biomass as reductants. According to leaching results, H3Cit (citric acid) and tea waste and H3Cit/H2O2 systems reveal similar leaching abilities (96% Co and 98% Li; 98% Co and 99% Li, respectively), while the H3Cit/Phytolacca Americana system shows inferior leaching performance (83% Co and 96% Li) under the optimized conditions. Tentative exploration of oxidation mechanism for different biomass indicates that potential reducing substances contained in biomass can be employed as efficient reductants during leaching. Then both metal ions and waste citric acid can be simultaneously recovered by selective precipitation. About 99% Co and 93% Li could be recovered as CoC2O4·2H2O and Li3PO4, and the recycled citric acid demonstrates similar leaching capability as fresh acid according to circulatory leaching experiments. Finally, solution chemistry theory and waste stream analysis were investigated to provide theoretical foundation for the recovery process.Keywords: Green process; Leaching; Metals; Precipitation; Recovery; Spent lithium-ion batteries

•A combined hydrometallurgical process was proposed.•Fe, Mn, Ni and Li were selectively precipitated and recovered.•Cu was selectively extracted and recovered by Mextral®5640H.•Nickel loaded Mextral®272P was employed to recover Co.•All metals can be effectively separated and recovered.Present study was focused on a hydrometallurgical process for the separation and recovery of copper, manganese, cobalt, nickel and lithium from leaching liquor of spent lithium-ion batteries. First, copper ions were selectively extracted using Mextral®5640H as extraction reagent after the removal of impurity ions. Manganese ions were then selectively separated and precipitated using KMnO4 solution and about 99.2% manganese was removed and precipitated as MnO2 and Mn2O3. Subsequently, nickel loaded Mextral®272P was used as a new extraction reagent to separate and recover cobalt from the leaching liquor. Finally, nickel and lithium ions left in the leachate were successively precipitated using NaOH and Na3PO3 solutions. Nickel and lithium were recovered as Ni(OH)2 and Li3PO4 after filtration and drying. Recovery efficiencies could be attained as follows: 100% for copper; 99.2% for manganese, 97.8% for cobalt, 99.1% for nickel and 95.8% for lithium under their optimized experimental conditions. McCabe–Thiele extraction isotherm study was conducted for the extraction of copper and cobalt to predict the extraction stages required. It is expected that this hydrometallurgical process can be a candidate for the effective separation and comprehensive recovery of all metals from the leaching liquor.

•A combined hydro-metallurgical process has been proposed.•Nickle, cobalt and lithium were recovered by selective precipitation method.•Manganese was recovered by solvent extraction method.•This process was a relatively simple and environment-friendly route.•About 98%, 97%, 97% and 89% of Ni, Co, Mn and Li could be recovered.In this study, a hydro-metallurgical process has been proposed to separate and recover valuable metals from citric acid leach solution of waste lithium nickel cobalt manganese oxide based cathodes. Nickel, cobalt, manganese and lithium were effectively separated and recycled by a combined method of selective precipitation and solvent extraction. First, about 98% of nickel was selectively precipitated by dimethylglyoxime reagent under conditions of equilibrium pH of 6 and molar ratio of Ni2+ to dimethylglyoxime of 0.5, with little loss of other metals. Then about 97% of cobalt was precipitated by ammonium oxalate and recovered as CoC2O4·2H2O under conditions of equilibrium pH of 6, reaction temperature of 55 °C and molar ratio of C2O42+ to Co2+ of 1.2. The recovery of manganese was conducted by solvent extraction method using D2EHPA with 70–75% saponification rate. About 97% of manganese was extracted under optimal experimental conditions and recovered as MnSO4 after stripped with sulfuric acid solution. The McCabe–Thiele isotherm indicated that three extraction stages were needed for complete extraction of manganese at specific extraction condition. Finally, about 89% of lithium was precipitated and recovered as Li3PO4 by 0.5 mol L−1 Na3PO4 solution. This combined hydro-metallurgical recovery process is a relatively simple and environment-friendly route, which all metal values in the leach liquor can be effectively separated and recovered and both dimethylglyoxime and D2EHPA can be recycled and re-used.

A modified model is established according to the analysis of energy balance acting on an agglomerate of binary mixed nanoparticles in a vibrated fluidized bed (VFB). The sizes of agglomerates of binary mixed nanoparticles are calculated with this model. The average agglomerate size estimated by the model of energy balance decreases with increasing superficial gas velocity. The vibration frequency had a comparatively significant impact on agglomerate sizes that seemed to change regularly and decreased with higher frequency. Both of the experimental and theoretical results showed that vibration led to a smaller agglomerate size, and the average agglomerate sizes calculated by this model provided the closest fit to those determined experimentally.

•The behavior of mixed nanoparticles can be improved by adding coarse particles.•The minimum fluidization velocities can be decreased by adding coarse particles.•The R–Z exponents can characterize the fluidization behavior of binary mixtures.Fluidization behavior of binary mixed SiO2 and ZnO nanoparticles by adding 3 different fluid catalytic cracking (FCC) or Al2O3 coarse particles was studied. The Richardson–Zaki exponents of the single and binary mixtures were calculated by using linear regression. The results showed that the improvement of the fluidization behavior of mixed nanoparticles by adding Al2O3 coarse particles was not obvious. Fluidization behavior of mixed nanoparticles can be improved significantly by adding FCC coarse particles. However, the effect of adding FCC2 (61–90 μm) and FCC3(38–61 μm) coarse particles is better than that of adding FCC1(90–109 μm) coarse particles. The order of degree of agglomerate particulate fluidization of beds by adding the same amount of FCC coarse particles is pure SiO2, 70% SiO2 and 30% ZnO, 50% SiO2 and 50% ZnO, 30% SiO2 and 70% ZnO and pure ZnO nanoparticles.Fig. 12 Agglomerate sizes of mixed nanoparticles by adding FCC coarse particles. (The ratio in the fig is mass ratio.).

•Selective precipitation and solvent extraction were adopted.•Nickel, cobalt and lithium were selectively precipitated.•Co-D2EHPA was employed as high-efficiency extraction reagent for manganese.•High recovery percentages could be achieved for all metal values.Environmentally hazardous substances contained in spent Li-ion batteries, such as heavy metals and nocuous organics, will pose a threat to the environment and human health. On the other hand, the sustainable recycling of spent lithium-ion batteries may bring about environmental and economic benefits. In this study, a hydrometallurgical process was adopted for the comprehensive recovery of nickel, manganese, cobalt and lithium from sulfuric acid leaching liquor from waste cathode materials of spent lithium-ion batteries. First, nickel ions were selectively precipitated and recovered using dimethylglyoxime reagent. Recycled dimethylglyoxime could be re-used as precipitant for nickel and revealed similar precipitation performance compared with fresh dimethylglyoxime. Then the separation of manganese and cobalt was conducted by solvent extraction method using cobalt loaded D2EHPA. And McCabe–Thiele isotherm was employed for the prediction of the degree of separation and the number of extraction stages needed at specific experimental conditions. Finally, cobalt and lithium were sequentially precipitated and recovered as CoC2O4⋅2H2O and Li2CO3 using ammonium oxalate solution and saturated sodium carbonate solution, respectively. Recovery efficiencies could be attained as follows: 98.7% for Ni; 97.1% for Mn, 98.2% for Co and 81.0% for Li under optimized experimental conditions. This hydrometallurgical process may promise a candidate for the effective separation and recovery of metal values from the sulfuric acid leaching liquor.

Nano-sized dispersive hexagonal magnesium hydroxide (Mg(OH)2) was prepared by an ammonia-hydrothermal method. To improve the crystalline and dispersivity of magnesium hydroxide, citric acid was introduced into the reaction system at ammonia precipitation process and monoethanolamine (MEA) was introduced at hydrothermal process, respectively. In this study, the optimal parameters of nano-sized Mg(OH)2 preparation were obtained. The as-prepared Mg(OH)2 was characterized by SEM, XRD, TGA and etc. The results showed that the sample was hexagonal plates and had the mean diameter of 246 nm.