A novel hydrothermal method for zinc extraction and separation from zinc ferrite and electric arc furnace dust

A novel hydrothermal process was developed to extract zinc from pure zinc ferrite（ZnFe2O4） nanopowder and zinc-containing electric arc furnace（EAF） dust using hexahydrated ferric chloride（FeCl3-6H2O） as a decomposing agent.The effects of solid FeCl3-6H2O to ZnFe2O4 ratio by mass（RF/Z）,hydrothermal reaction temperature,and time on zinc extraction were systematically investigated.In the results,when the hydrothermal reaction is conducted at 150℃ for 2 h with RF/Z of 15：20,the efficiency of zinc extraction from ZnFe2O4 reaches97.2%,and the concentration of ferric ions（Fe^3＋） in the leaching solution is nearly zero,indicating a high selectivity for zinc.In addition,the zinc extraction efficiency from the EAF dust reaches 94.5%in the case of the hydrothermal reaction performed at 200℃ for 10 h with the solid FeCl3-6H2O to EAF dust ratio by mass（RF/EAF dust） of 15：10.Zinc and iron separation is achieved by adjusting the pH value of the leaching solution according to the different precipitation pH values of metal hydroxides.

Extraction and kinetic analysis of Pb and Sr from the leaching residue of zinc oxide ore

NH4HCO3 conversion followed by HCl leaching was performed and proven to be effective in extracting Pb and Sr from zinc extracted residual.The mechanism and operating conditions of NH4HCO3 conversion,including molar ratio of NH4HCO3 to zinc extracted residual,NH4HCO3 concentration,conversion temperature,conversion time,and stirring velocity,were discussed,and operating conditions were optimized by the orthogonal test.Experimental results indicate that NH4HCO3 conversion at temperatures ranging from 25 to 85°C follows the shrinking unreacted core model and is controlled by inner diffusion through the product layer.The extraction ratios of Pb and Sr under optimized conditions reached 85.15%and 87.08%,respectively.Moreover,the apparent activation energies of Pb and Sr were 13.85 and 13.67 kJ·mol^−1,respectively.

Characteristics of the reduction behavior of zinc ferrite and ammonia leaching after roasting

A novel method for recovering zinc from zinc ferrite by reduction roasting–ammonia leaching was studied in this paper. The reduction thermodynamic of zinc ferrite by CO was analyzed. The effects of roasting parameters on the phase transformation and conversion rate of zinc ferrite, and the leaching behavior of zinc from the reductive roasted samples by ammonia leaching, were experimentally investigated. The mineralogical phase compositions and chemical compositions of the samples were characterized by X-ray diffraction and chemical titration methods, respectively. The results showed that most of the zinc ferrite was transformed to zinc oxide and magnetite after weak reduction roasting. 86.43% of the zinc ferrite was transformed to zinc oxide under the optimum conditions: CO partial pressure of 25%, roasting temperature of 750°C, and roasting duration of 45 min. Finally, under the optimal leaching conditions, 78.12% of zinc was leached into the solution from the roasted zinc ferrite while all iron-bearing materials were kept in the leaching residue. The leaching conditions are listed as follows: leaching duration of 90 min,ammonia solution with 6 mol/L concentration, leaching temperature of 50°C, solid-to-liquid ratio of 40 g/L, and stirring speed of 200 r/min.

Reaction condition optimization and kinetic investigation of roasting zinc oxide ore using (NH_4)_2SO_4

An orthogonal test was used to optimize the reaction conditions of roasting zinc oxide ore using（NH_4）_2SO_4. The optimized reaction conditions are defined as an（NH_4）_2SO_4/zinc molar ratio of 1.4：1, a roasting temperature of 440°C, and a thermostatic time of 60 min. The molar ratio of（NH_4）_2SO_4/zinc is the most predominant factor and the roasting temperature is the second significant factor that governs the zinc extraction. Thermogravimetric-differential thermal analysis was used for（NH_4）_2SO_4 and zinc mixed in a molar ratio of 1.4：1 at the heating rates of 5, 10, 15, and 20 K·min-1. Two strong endothermic peaks indicate that the complex chemical reactions occur at approximately 290°C and 400°C. XRD analysis was employed to examine the transformations of mineral phases during roasting process. Kinetic parameters, including reaction apparent activation energy, reaction order, and frequency factor, were calculated by the Doyle-Ozawa and Kissinger methods. Corresponding to the two endothermic peaks, the kinetic equations were obtained.

Effect of CacO_(3) on volatilization of self-reduced zinc from blast furnace dust

To solve the problem of low reduction extraction rate of zinc from blast furnace dust,the effects of CacO3 addition,reduction temperature,and reduction time on self-reduction zinc extraction were studied through high-temperature reduction experiment,and the mechanism of how CaCO_(3) addition promotes zinc ferrite reduction was analyzed.The zinc removal rate can reach 98.82%when the blast furnace dust is reduced at 1000℃ for 25 min by adding 10 mass%CaCO_(3).At low temperature,CaCO_(3) can enhance the reduction and decomposition of ZnFe_(2)O_(4)(which is difficult to reduce)into ZnO and low-valent iron oxides.After CaCO_(3) is decomposed at high temperature,CO_(2) is produced to undergo gasification reaction with carbon in blast furnace dust,and co is generated to provide more reducing agents for the whole reduction system.CaO generated by decomposition can also catalyze the gasification reaction of carbon,thus improving the removal rate of zinc in the reduction process of dust.

Antibacterial and Antioxidant Activities of ZnO Nanoparticles Synthesized Using Extracts of Allium sativum,Rosmarinus officinalis and Ocimum basilicum

ZnO nanoparticles（ZnO NPs） were synthesized by chemical method（coprecipitation） and biological method using aqueous extracts of garlic（Allium sativum）,rosemary（Rosmarinus officinalis） and basil（Ocimum basilicum）.The influence of plant extract on the antibacterial and antioxidant activities of green synthesized nanoparticles was investigated.The X-ray diffraction studies reveal that all ZnO samples have hexagonal wurtzite structure.The particle size of ZnO NPs estimated by transmission electron microscopy analysis（between 14 and 27 nm） varies depending on the synthesis method of nanoparticles and the type of extracts from the plants used.The functional groups involved in the biosynthetic procedure were evidenced by Fourier transform infrared spectroscopy.The presence of Mn^（2＋）ions,Zn vacancy complexes and oxygen vacancies in ZnO samples was highlighted by electron paramagnetic resonance spectroscopy.The green synthesized ZnO NPs have shown a good bactericidal activity against Staphylococcus aureus,Bacillus subtilis,Listeria monocytogenes,Escherichia coli,Salmonella typhimurium and Pseudomonas aeruginosa bacterial strains.ZnO NPs synthesized using extracts of the selected plant species have been found to exhibit more enhanced antibacterial and antioxidant activities as compared to chemical ZnO NPs.