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

NH_4HCO_3 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 NH_4HCO_3 conversion, including molar ratio of NH_4HCO_3 to zinc extracted residual,NH_4HCO_3 concentration, conversion temperature, conversion time, and stirring velocity, were discussed, and operating conditions were optimized by the orthogonal test. Experimental results indicate that NH_4HCO_3 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 and13.67 k J·mol~(-1), respectively.     

Reaction condition optimization and kinetic investigation of roasting zinc oxide ore using (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript>

An orthogonal test was used to optimize the reaction conditions of roasting zinc oxide ore using (NH₄)₂SO₄. The optimized reaction conditions are defined as an (NH₄)₂SO₄/zinc molar ratio of 1.4:1, a roasting temperature of 440°C, and a thermostatic time of 60 min. The molar ratio of (NH₄)₂SO₄/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 (NH₄)₂SO₄ 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.     

Thermodynamics and phase transformations in the recovery of zinc from willemite

Willemite is a common component of zinc and lead metallurgical slags that, in the absence of effective utilization methods, cause serious environmental problems. To solve this problem and increase zinc recovery, we proposed a novel extraction method of zinc from willemite by calcified roasting followed by leaching in NH₄Cl-NH₃·H₂O solution. The thermodynamics and phase conversion of Zn₂SiO₄ to zinc oxide (ZnO) during calcified roasting with CaO were investigated. The mechanism of mineralogical phase conversion and the effects of the CaO-to-Zn₂SiO₄ mole ratio (n(CaO)/n(Zn₂SiO₄)), roasting temperature, and the roasting time on zinc-bearing phase conversion were experimentally investigated. The results show that Zn₂SiO₄ was first converted to Ca₂ZnSi₂O₇ and then to ZnO. The critical step in extracting zinc from willemite is the conversion of Zn₂SiO₄ to ZnO. The zinc percent leached in the ammonia leaching system rapidly increased because of the gradual complete phase conversion from willemite to ZnO via the calcified roasting process.     

(NH4)2SO4焙烧?浸出法从氧化锌矿石中提取锌

An improved method of (NH₄)₂SO₄ roasting followed by water leaching to utilize zinc oxidized ores was studied. The operating parameters were obtained by investigating the effects of the molar ratio of (NH₄)₂SO₄ to zinc, roasting temperature, and holding time on zinc extraction. The roasting process followed the chemical reaction control mechanism with the apparent activation energy value of 41.74 kJ·mol?1. The transformation of mineral phases in roasting was identified by X-ray diffraction analysis combined with thermogravimetry–differential thermal analysis curves. The water leaching conditions, including the leaching temperature, leaching time, stirring velocity, and liquid-to-solid ratio, were discussed, and the leaching kinetics was studied. The reaction rate was obtained under outer diffusion without product layer control; the values of the apparent activation energy for two stages were 4.12 and 8.19 kJ·mol?1. The maximum zinc extraction ratio reached 96% while the efficiency of iron extraction was approximately 32% under appropriate conditions. This work offers an effective method for the comprehensive use of zinc oxidized ores.     

Thermodynamics and kinetics of extracting zinc from zinc oxide ore by the ammonium sulfate roasting method

Thermodynamic analyses and kinetic studies were performed on zinc oxide ore treatment by (NH₄)₂SO₄ roasting technology. The results show that it is theoretically feasible to realize a roasting reaction between the zinc oxide ore and (NH₄)₂SO₄ in a temperature range of 573-723 K. The effects of reaction temperature and particle size on the extraction rate of zinc were also examined. It is found that a surface chemical reaction is the rate-controlling step in roasting kinetics. The calculated activation energy of this process is about 45.57 kJ/mol, and the kinetic model can be expressed as follows:1-(1-α)1/3=30.85 exp(-45.57/RT)·t. An extraction ratio of zinc as high as 92% could be achieved under the optimum conditions.     

铁酸锌焙烧后的还原行为及氨浸特性

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.     

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.     

Efficient and selective recovery of Ni,Cu, and Co from low-nickel matte via a hydrometallurgical process

Low-nickel matte was intensively characterized, and Ni, Cu, and Co were determined to exist mainly as (Fe,Ni)₉S₈ and FeNi₃, Cu₅FeS₄, and (Fe,Ni)₉S₈ and Fe₃O₄ (in isomorphic form), respectively. The efficient and selective extraction of Ni, Cu, and Co from the low-nickel matte in an (NH₄)₂S₂O₈/NH₃·H₂O solution system was studied. The effects of (NH₄)₂S₂O₈ and NH₃·H₂O concentrations, leaching time, and leaching temperature on the metal extraction efficiency were systematically investigated. During the oxidative ammonia leaching process, the metal extraction efficiencies of Ni 81.07%, Cu 93.81%, and Co 71.74% were obtained under the optimal conditions. The relatively low leaching efficiency of Ni was mainly ascribed to NiFe alloy deactivation in ammonia solution. By introducing an acid pre-leaching process into the oxidative ammonia leaching process, we achieved the high extraction efficiencies of 98.03%, 99.13%, and 85.60% for the valuable metals Ni, Cu, and Co, respectively, from the low-nickel matte.     

Effect of modifying agents on the hydrophobicity and yield of zinc borate synthesized by zinc oxide

The aim of this study was to synthesize zinc borate using zinc oxide, reference boric acid, and reference zinc borate (reference ZB) as the seed, and to investigate the effects of modifying agents and reaction parameters on the hydrophobicity and yield, respectively. The reaction parameters include reaction time (1–5 h), reactant ratio (H₃BO₃/ZnO by mass: 2–5), seed ratio (seed crystal/(H₃BO₃+ZnO) by mass: 0–2wt%), reaction temperature (50–120℃), cooling temperature (10–80℃), and stirring rate (400–700 r/min); the modifying agents involve propylene glycol (PG, 0–6wt%), kerosene (1wt%–6wt%), and oleic acid (OA, 1wt%–6wt%) with solvents (isopropyl alcohol (IPA), ethanol, and methanol). The results of reaction yield obtained from either magnetically or mechanically stirred systems were compared. Zinc borate produced was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and contact angle tests to identify the hydrophobicity. In conclusion, zinc borate is synthesized successfully under the optimized reaction conditions, and the different modifying agents with various solvents affect the hydrophobicity of zinc borate.     

Preparation of ultrafine silica from potash feldspar using sodium carbonate roasting technology

A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na₂CO₃ and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows: an Na₂CO₃-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO₂ was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a temperature of 40°C, a CO₂ flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipitation rate and granularity of the SiO₂ particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.     

Recovery of iron and calcium aluminate slag from high-ferrous bauxite by high-temperature reduction and smelting process

A high-temperature reduction and smelting process was used to recover iron and calcium aluminate slag from high-ferrous bauxite. The effects of w(CaO)/w(SiO₂) ratio, anthracite ratio, and reduction temperature and time on the recovery and size of iron nuggets and on the Al₂O₃ grade of the calcium aluminate slag were investigated through thermodynamic calculations and experiments. The optimized process conditions were the bauxite/anthracite/slaked lime weight ratio of 100:16.17:59.37, reduction temperature of 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79wt%, respectively. The calcium aluminate slag mainly comprised Ca₂SiO₄ and Ca₁₂Al₁₄O₃₃, with small amounts of FeAl₂O₄, CaAl₂O₄, and Ca₂Al₂SiO₇.     

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 (R_F/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 R_F/Z of 15:20, the efficiency of zinc extraction from ZnFe₂O₄ reaches 97.2%, and the concentration of ferric ions (Fe3+) 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 (R_{F/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.     

Carbothermal reduction process of the Fe-Cr-O system

Understanding the reduction behaviors and characteristics of the end products of Fe-Cr-O systems is very important not only for maximizing the recovery of metals from stainless steel dust but also for the subsequent reuse in metallurgical process. The present work first predicted the possible products thermodynamically when FeCr₂O₄ was reduced by C. The reduction behaviors by graphite of three kinds of Fe-Cr-O systems, i.e., FeCr₂O₄, Fe₂O₃+Cr₂O₃, and Fe+Cr₂O₃, were then investigated in 1350–1550℃. Further, the microstructures of final products and element distribution conditions were examined. The results suggest that, thermodynamically, the mass of products for the carbothermal reduction of FeCr₂O₄ is a strong function of temperature, and the initial carbon content is used. More Fe-Cr-C solution and less residual carbon content are obtained at higher temperatures and lower n_C:n_O ratios (the initial molar ratio of C to O in the sample). Experimental data show that the sample amount tends to affect the reduction rate, and the residual carbon content strongly depends on n_C:n_O. With regard to the phases present in products during the reaction process, metal carbides tend to form in the initial stage, whereas Fe-Cr-C solution forms when the degree of reduction is sufficiently high.     

Extraction and characterization of alumina nanopowders from aluminum dross by acid dissolution process

A significant amount of aluminum dross is available as a waste in foundry industries in Bangladesh. In this study, alumina was extracted from aluminum dross collected from two foundry industries situated in Dhamrai and Manikgang, near the capital city, Dhaka. Aluminum dross samples were found to approximately contain 75wt% Al₂O₃ and 12wt% SiO₂. An acid dissolution process was used to recover the alumina value from the dross. The effects of various parameters, e.g., temperature, acid concentration, and leaching time, on the extraction of alumina were studied to optimize the dissolution process. First, Al(OH)₃ was produced in the form of a gel. Calcination of the Al(OH)₃ gel at 1000℃, 1200℃, and 1400℃ for 2 h produced θ-Al₂O₃, (α+θ)-Al₂O₃, and α-alumina powder, respectively. Thermal characterization of the Al(OH)₃ gel was performed by thermogravimetric/differential thermal analysis (TG/DTA) and differential scanning calorimetry (DSC). The phases and crystallite size of the alumina were determined by X-ray diffraction analysis. The dimensions of the alumina were found to be on the nano level. The chemical compositions of the aluminum dross and alumina were determined by X-ray fluorescence (XRF) spectroscopy. The microstructure and morphology of the alumina were studied with scanning electron microscopy. The purity of the alumina extracted in this study was found to be 99.0%. Thus, it is expected that the obtained alumina powders can be potentially utilized as biomaterials.     

Recycling of Spent Nickel-Cadmium Batteries

A technique for recycling spent nickel-cadmium batteries, which makes separaion of cadmium and nickel possible, is developed by laboratory-scale experiments. NH₃-H₂CO₃ aqueous solution was used in this leaching technique. Since neutralization and/or solvent extraction were not required in the separation procedure of nickel and cadmium, the closed systemizaion of the process becomes possible. Experimental results show that, (1) if the NH₃ concentraion of leaching solution is sufficiently high and the ratio of H₂CO₃ to NH₃ is properly adjusted, both Ni(OH)₂ and Cd(OH)₂ react with NH, and quickly dissolve into leaching solution, and (2) Ni(OH)₂ can be converted into insoluble NiO by calcination at 500℃, and CdO from Cd(OH)₂ by calcination maintains good solubility in NH₃-H₂CO₃ aqueous solution. As a conclusion, the recycling technique characterized by two step leaching can be developed based on such changes in dissolution behavior by calcination. Meanwhile, the yields of 99.8% for nickel and 97.6% for cadmium are obtained, and the purities of recovered nickel and cadmium are 99.9% and 98.6%, respectively.     

SDBS辅助制备的花状ZnO微结构的生长机理及光催化性能评价

Flower-like ZnO microstructures were successfully produced using a hydrothermal method employing ZnSO₄/(NH₄)₂SO₄ as a raw material. The effect of the operating parameters of the hydrothermal temperature, OH?/Zn2+ molar ratio, time, and amount of dispersant on the phase structure and micromorphology of the ZnO particles were investigated. The synthesis conditions of the flower-like ZnO microstructures were: hydrothermal temperature of 160°C, OH?/Zn2+ molar ratio of 5:1, reaction time of 4 h, and 4 mL of dispersant. The flower-like ZnO microstructures were comprised of hexagon-shaped ZnO rods arranged in a radiatively. Degradation experiments of Rhodamine B with the flower-like ZnO microstructures demonstrated a degradation efficiency of 97.6% after 4 h of exposure to sunshine, indicating excellent photocatalytic capacity. The growth mechanism of the flower-like ZnO microstructures was presented.     

Primary beneficiation of tantalite using magnetic separation and acid leaching

Primary beneficiation was successfully performed prior to dissolution of manganotantalite (sample A) and ferrotantalite (sample C) samples obtained from two different mines in the Naquissupa area, Mozambique. Magnetic separation removed the majority of iron and titanium, whereas H₂SO₄ leaching removed a large portion of thorium and uranium in these samples. Analytical results indicated that 64.14wt% and 72.04wt% of the total Fe and Ti, respectively, and ~2wt% each of Nb₂O₅ and Ta₂O₅ were removed from sample C (ferrotantalite) using the magnetic separation method, whereas only 9.64wt% and 8.66wt% of total Fe₂O₃ and TiO₂, respectively, and ~2wt% each of Nb₂O₅ and Ta₂O₅ were removed from sample A (manganotantalite). A temperature of 50°C and a leaching time of 3 h in the presence of concentrated H₂SO₄ were observed to be the most appropriate leaching conditions for removal of radioactive elements from the tantalite ores. The results obtained for sample A under these conditions indicated that 64.14wt% U₃O₈ and 60.77wt% ThO₂ were leached into the acidic solution, along with 4.45wt% and 0.99wt% of Nb₂O₅ and Ta₂O₅, respectively.     

基于优化氧化铁皮和焦粉配比的铁矿烧结过程NOx减排研究

Reducing NO_x emission of iron ore sintering process in a cost effective manner is a challenge for the iron and steel industry at present. Effects of the proportion of mill scale and coke breeze on the NO_x emission, strength of sinter, and sinter indexes were studied by combustion and sinter pot tests. Results showed that the peak value of NO concentration, total of NO emission, and fuel-N conversion rate gradually decreased as the proportions of the mill scale increased because NO was reduced to N₂ by Fe₃O₄, FeO, and Fe in the mill scale. The strength of sinter reached the highest value at 8.0wt% mill scale due to the formation of minerals with low melting point. The fuel-N conversion rate slightly fluctuated and total NO_x emission significantly decreased with the decreased proportions of coke breeze because CO formation and content of N element in the sintered mixture decreased. However, the sinter strength also decreased due to the decrease in the amount of the melting minerals. Furthermore, results of the sinter pot tests indicated that NO_x emission decreased. The sinter indexes performed well when the proportions of mill scale and coke breeze were 8.0wt% and 3.70wt% respectively in the sintered mixture.     

Preparation and characterization of barium strontium titanate/silicon nanoporous pillar array composite thin films by a sol-gel method

Barium strontium titanate (Ba_0.5Sr_0.5TiO₃, BST)/silicon nanoporous pillar array (Si-NPA) thin films were prepared by a spin-coating/annealing technique based on Si-NPA with micro/nano-structure. Both the isomer conversion of acetylacetone and the network structure combined by enol and Ti-alkoxide facilitate the formation of the BST sol and the subsequent crystallization. Before the perovskite BST begins to form, the intermediate phase (Ba,Sr)Ti₂O₅CO₃ is found. The boundary between BST and Si-NPA is of clarity and little interface diffusion, disclosing that Si-NPA is an ideal template substrate in the preparation of multifunctional composite films.     

Bioleaching of vanadium from barren stone coal and its effect on the transition of vanadium speciation and mineral phase

This study determined the optimal conditions required to obtain maximum vanadium extraction and examined the transition of mineral phases and vanadium speciation during the bioleaching process. Parameters including the initial pH value, initial Fe2+ concentration, solid load, and inoculum quantity were examined. The results revealed that 48.92wt% of the vanadium was extracted through bioleaching under optimal conditions. Comparatively, the chemical leaching yield (H₂SO₄, pH 2.0) showed a slower and milder increase in vanadium yield. The vanadium bioleaching yield was 35.11wt% greater than the chemical leaching yield. The Community Bureau of Reference (BCR) sequential extraction results revealed that 88.62wt% of vanadium existed in the residual fraction. The bacteria substantially changed the distribution of the vanadium speciation during the leaching process, and the residual fraction decreased to 48.44wt%. The X-ray diffraction (XRD) and Fourier transform infrared (FTIR) results provided evidence that the crystal lattice structure of muscovite was destroyed by the bacteria.