Reaction behavior of kaolinite with ferric oxide during reduction roasting

The pre-separation of silica and alumina in aluminosilicates is of great significance for efficiently treating alumina-/silica-bearing minerals for alumina production. In this work, the reaction behavior of kaolinite with ferric oxide during reduction roasting was investigated. The results of thermodynamic analyses and reduction roasting experiments show that ferrous oxide obtained from ferric oxide reduction preferentially reacts with alumina in kaolinite to form hercynite, meanwhile the silica in kaolinite is transformed into quartz solid solution and/or cristobalite solid solution. With increasing roasting temperature, fayalite formed by reaction of surplus ferrous oxide with silica at low temperature is reduced to silica and metallic iron in the presence of sufficient carbon dosage. However, increasing roasting temperature and decreasing Fe₂O₃/Al₂O₃ molar ratio favor mullite formation. The complete conversion of kaolinte into free silica and hercynite can be obtained by roasting raw meal of kaolin, ferric oxide and coal powder with Fe₂O₃/Al₂O₃/C molar ratio of 1.2:2.0:1.2 at 1373 K for 60 min. This work may facilitate the development of a technique for comprehensively utilizing silica and alumina in aluminosilicates.     

废旧锂离子电池火法冶炼富锰渣中锰和锂的提取（英文）

开展富锰渣硫酸化焙烧-水浸选择性提取锰和锂的试验,采用XRD、TG-DSC和SEM-EDS详细分析锰和锂的提取机理。结果表明,在酸浓度为82%(质量分数)、酸矿质量比1.5:1、焙烧温度800℃和焙烧时间2 h时,Mn和Li的浸出率分别达到73.71%和73.28%。焙烧过程中,富锰渣首先与浓硫酸反应形成Mn SO₄、MnSO₄·H₂O、Li₂Mg(SO₄)₂、Al₂(SO₄)₃和H₄SiO₄。随着焙烧温度的升高,H₄SiO₄和Al₂(SO₄)₃依次分解,并形成莫来石和尖晶石相。莫来石的形成有利于降低Al和Si的浸出率而增加Li的浸出率;而尖晶石的形成则会降低Mn和Li的浸出率。     

Separation of alumina and silica from metakaolinite by reduction roasting−alkaline leaching process: Effect of CaSO4 and CaO

Limestone (CaCO₃), which could promote sulfur fixation, was added to coal gangue during roasting in a circulating fluidized bed (CFB) boiler. CaO and CaSO₄ were the main Ca-bearing minerals while metakaolinite was the major Al-bearing mineral in CFB slag. The effect of CaSO₄ and CaO on the separation of alumina and silica from metakaolinite by reduction roasting?alkaline leaching process was studied. Results showed that metakaolinite was completely converted into hercynite and silica solid solutions (i.e., quartz and cristobalite solid solutions) by reduction roasting with hematite. More than 95% of silica in the reduced specimen was removed by alkaline leaching. The addition of CaSO₄ and CaO remarkably decreased the separation efficiency of alumina and silica in metakaolinite, which could be attributed to the formation of Si-bearing minerals: (1) Fayalite and anorthite were formed during the reduction roasting process; (2) Fayalite was stable while anorthite was converted into sodalite and wollastonite during the alkaline leaching process. This study demonstrates that sulfur in coal gangue should be fixed by treating the exhaust gas instead of controlling the combustion process of CFB to achieve the comprehensive recovery of silica and alumina from the CFB slag.     

Extraction of valuable metals from Ti-bearing blast furnace slag using ammonium sulfate pressurized pyrolysis–acid leaching processes

A novel method of extracting valuable metals from Ti-bearing blast furnace slag (TBBF slag) via pressure pyrolysis of recyclable ammonium sulfate (AS)–acid leaching process was proposed. The results show that when pressurized roasting at an AS-to-slag mass ratio 3:1 and 370 °C for 90 min, the extraction rates of titanium, aluminum and magnesium reached 94.5%, 91.9% and 97.4%, respectively. The acid leaching solution was subjected to re-crystallization in a boiling state to obtain a titanium product having a TiO₂ content of 94.1%. The above crystallization mother liquor was adjusted to pH=6 and pH≥12.2, respectively, and then qualified Al₂O₃ and MgO products were obtained. The analysis through XRD and SEM–EDS proves that the main phases in roasted samples were NH₄AlSO₄, CaSO₄ and TiOSO₄. The thermodynamic analysis presents that the main minerals of perovskite, spinel and diopside in raw ore could spontaneously react with the intermediate produced by AS under optimal conditions.     

Microsilica role in the CA6 formation in cement-bonded spinel refractory castables

Assisted sintering tests, permanent linear change and microstructural evaluation were carried out in alumina–magnesia and alumina–spinel castables to analyze the microsilica effects on the CA₆ development in each system. Unlike the alumina–magnesia ones, alumina–spinel castables did not present linear changes due to the CaO·2Al₂O₃ (CA₂) formation. The morphology of the calcium hexaluminate (CaO·6Al₂O₃CA₆) grains throughout the castable microstructure was shown to be quite similar for both systems. The CA₆ distribution showed to be dependent not only on the ion diffusion mechanism but also on the in situ spinel formation in the Al₂O₃–MgO castables matrix, which also indicated that by a correct raw material selection, it is possible for the alumina–spinel castables to attain the spinel and CA₆ benefits with very low overall expansion.     

氧化钠对CaO-Al2O3-SiO2三元系铝酸钙形成规律的影响（英文）

利用XRD、SEMEDS和DSCTG技术研究了添加Na2O的CaO-Al2O3-SiO2体系中铝酸钙的形成规律。结果表明,当Al2O3与SiO2的质量比为3.0、CaO与Al2O3的摩尔比为1.0时,在1350°C烧结后的熟料主要由12CaO·7Al2O3、2CaO·Al2O3·SiO2和2CaO·SiO2组成。熟料中12CaO·7Al2O3的含量随着Na2O的增加而增加,2CaO·Al2O3·SiO2的含量随着Na2O的增加而降低。Na2O在12CaO·7Al2O3中形成固溶体,增加了其单位晶胞体积。DSC分析表明,Na2O不仅促进了12CaO·7Al2O3的形成,而且使C12A7的形成温度降低了30°C。烧结熟料中的氧化铝溶出性能随着Na2O的增加而大幅度提高。     

Digestion mechanism and crystal simulation of roasted low-grade high-sulfur bauxite

Low-grade high-sulfur bauxite was pretreated via suspension roasting and muffle furnace roasting to remove sulfur and enhance digestion properties. The results show that sulfur can be efficiently removed, and the alumina digestion properties are significantly improved after suspension roasting. Under optimal conditions (t=70 min, T=280 °C, w(CaO)=8% and N_k=245 g/L), the digestion ratios are 94.45% and 92.08% for the suspension-roasted and muffle-roasted ore, respectively, and the apparent activation energies are 63.26 and 64.24 kJ/mol, respectively. Two crystal models were established by Materials Studio based on the XRD patterns. The DFT simulation shows that the existing Al—O bands after suspension roasting can improve alumina digestion. The (104) and (113) planes of Al₂O₃ after suspension roasting are found to combine with NaOH more easily than those of Al₂O₃ treated in a muffle furnace.     

Silica behavior in the alumina carbothermic reduction-chlorination process

The behavior of silica was investigated experimentally in an alumina carbothermic reduction process and chlorination process in vacuum. The results showed that, first, SiC was produced by SiO₂ and C, and then Al₄SiC₄ was produced by Al₄C₃, Al₄O₄C, C, and SiC during the alumina carbothermic reduction process at about 1,763 K. C, Al₃C₄ and Al₄O₄C decreased and Al₄SiC₄ increased as content of SiO₂ increased. The following chlorination process was blocked, and the recovery rate of aluminum decreased quickly compared with that without silica. It was inferred that silica might be unfavorable for aluminum extracted from alumina by carbothermic reductionchlorination process in vacuum at about 1763 K.     

Technology and mechanism of desilication from roasted diasporic bauxite in atmosphere

The leaching desilication technology of roasted diasporic bauxite in atmosphere by caustic soda solution was investigated. The optimum parameters were: the grinding fineness of the roasted bauxite -0. 076 mm and 80 % -85 %,leaching time 2h, Na2Ok100-150g/L, L/S 4-5, leaching temperature 90-95℃. The desilication rate 55.20% and concentrate A/S (mass ratio of A12O3 to SiO2) 9.90, as good as those obtained at pressure, were obtained respectivdy.Investigation of two-stage leaching shows that it can both improve desilication rate of roasted ore and reduce leaching time.When time of the first stage and the second stage is 30 min and 30 min respectively, desilication rate can reach 59.65 %.X-ray diffraction analysis of the concentrate has proved that desilication procedure is accompanied with the formation of sodium aluminosilicate hydrate. X-ray spectra also show that silica removed during leaching is amorphous silica. SiO2 occurrina as ouartz in raw ore or mullite formed during roasting can not dissolve in alkali solution.     

Molybdenite–limestone oxidizing roasting followed by calcine leaching with ammonium carbonate solution

Oxidizing roasting of molybdenite with lime can significantly reduce SO₂ pollution compared with the traditional roasting without lime. However, the calcine is subsequently leached by sulfuric acid, resulting in serious equipment corrosion and abundant non-recyclable CaSO₄ slag. In this work, a novel process, in which the molybdenite was roasted with CaCO₃ followed by (NH₄)₂CO₃ solution leaching, was proposed to improve the art of lime roasting–sulfuric acid leaching. Oxidizing roasting of molybdenite with CaCO₃ was investigated through thermodynamic calculation, thermogravimetric analysis and roasting experiments. The results show that the products of the oxidizing reaction of MoS₂ in the presence of CaCO₃ and O₂ are CaSO₄, CaMoO₄ and CO₂ at 573–1000 K. The MoS₂ conversion rate achieves approximately 99% and the sulfur-retained rate attains approximately 95% with a CaCO₃-to-MoS₂ molar ratio of 3.6 at 500 °C for 1 h by adding 5% mineralizer A (mass fraction). The leaching results show that the leaching rate of Mo reaches 98.2% at 85 °C for 7 h with a (NH₄)₂CO₃ concentration of 600 g/L and a liquid–solid ratio of 10 mL/g. The results presented are potential to develop a novel cleaner technique for ammonium molybdate production.     

Thermodynamic predictions of the behavior of Fe-Cr-Al alloys in coal gasifier environments

The construction of thermodynamic stability diagrams for the Fe-Cr-Al system is discussed. The constructed diagrams are used to predict materials behavior at coal gasifier oxygen and sulfur potentials. Experiments are run to compare predicted results with experimental observations. Powder mixtures of FeS, Cr₂O₃, and Al₂O₃ are used to observe the formation of the iron-chromia and iron-alumina spinels. The spinels are observed at both 871 and 982° C. The formation of an alumina spinel is observed only on the Fe-10Al alloy, whereas no iron-chromia spinel is found on the Fe-Al-Cr alloys.     

Preparation of Ti-rich material from titanium slag by activation roasting followed by acid leaching

A method of activation roasting followed by acid leaching using titanium slag was introduced to prepare Ti-rich material. The effects of H₃PO₄ dosage, roasting temperature, and roasting time on TiO₂ grade were investigated. A Ti-rich material containing 88.54% TiO₂, 0.42% (CaO+MgO) was obtained when finely ground titanium slag was roasted with 7.5% H₃PO₄ at 1000 °C for 2 h, followed by a two-stage leaching in boiling dilute sulfuric acid for 2 h. The XRD patterns show that the product is titanium dioxide with a rutile structure. Mechanism studies show that structures of anosovite solid solution and silicate minerals are destroyed in the roasting process. As a result, titanium components in titanium slag are transformed into TiO₂ (rutile) while impurities are transformed into acid-soluble phosphate and quartz.     

通过选择性浸出、结晶和沉积回收废重整催化剂中的镍和铝

研究和优化不同工艺条件下硫酸(3.0~5.5 mol/L)浸出回收Ni和Al的工艺。浸出实验表明,在H₂SO₄浓度5.5 mol/L、反应时间4 h、固液比0.2 g/mL、温度358 K、粒径<100μm、搅拌速度200~250 r/min、催化剂用量5.0 g的条件下,可提取98.5%的NiO和40.7%的Al₂O₃。浸出液中的Al用1.4 mol/L KOH选择性结晶分离,Ni用0.3 mol/L H₂C₂O₄选择性沉淀分离。此法可回收约97.9%的NiO,纯度达98.3%;约25%的Al₂O₃以明矾(纯度为99%)形式回收,14.7%的Al₂O₃以Al-K-C₂O₄-SO₄盐的形式回收。研究结果表明,硫酸是一种合适的选择性浸出溶剂,而且可以从硫酸盐溶液中选择性结晶出明矾。TG-DTA/DTG和XRD表征研究证明,本工艺可以有效地提取和回收镍和铝。     

Physico-Chemical Characterization of Modified Tunisian Kaolin by Phosphoric Acid

In this study, crude Tunisian kaolin clay (from the Tabarka region—North of Tunisia) was subjected to refluxing with phosphoric acid under different operating conditions. Acid activation was carried out with H₃PO₄ (28 and 54 wt % P₂O₅), at temperatures of 60 and 90°C, with the time of treatment ranging from 2 to 12 h. The structure of acid leached kaolinite clay was characterized by; the XRD, FTIR, SEM, ²⁹Si and ³¹P NMR techniques and the Brunauer Emmett Teller theory was uses as the base for respective calculations. The chemical composition was determined by ICP. The results of XRD show that the kaolin acid treatment at 90°C provoked a destruction of clay structure after 6 h with phosphoric acid 28 wt % P₂O₅ and after 4 h with phosphoric acid 54 wt % P₂O₅. Hereafter, the forming of an amorphous silica phase is detected, whose confirmation is effected by the ²⁹Si NMR analysis. FTIR studies indicate that acid treatment under reflux conditions leads to the removal of the octahedral Al³⁺ cations for the two types of phosphoric acid. In fact, the chemical analysis shows that the leaching of Al³⁺ ions increases progressively with severity and the time of the reaction. The acid treatment with H₃PO₄ 54 wt % P₂O₅ at 90°C, enlarged the surface area from 24 to 150 m²/g. Thus, the solids obtained by the acid treatments can be used as promising adsorbents and catalyst supports.     

Post-mortem analysis of high alumina brick attacked by vanadium and titanium bearing slag after service in torpedo ladle

Abstract

High alumina brick after service in a torpedo ladle was analysed by means of atomic emission spectroscopy, X-ray diffraction, electron probe microanalysis and themochemical analysis in order to determine the corrosion mechanism during industrial application in a steel works. The results showed that slag containing vanadium and titanium oxide is more corrosive than common silica slags, and that this facilitates corrosion and penetration into the high alumina brick. Mineralogical observation confirmed that V₂O₅, TiO₂, MnO and FeO and MgO in the slag reacted with native phases presented in high alumina brick to form complex spinel, corundum and anorthite solid solution, etc. The dissolved content of V₂O₅ in the spinel decreased from 6·08 to 2·78 wt-% from the working face to the inner area. However, the FeO and MnO content in the spinel varied little with a slight increase in the TiO₂ content. The expansion coefficient mismatch between the penetrated zone and cold face zones, which results in densification spalling and increased porosity, play a key role in the failure of the high alumina brick.     

Extraction of alumina from fly ash by ammonium hydrogen sulfate roasting technology

NH₄HSO₄ roasting technology was used for preparing Al₂O₃ from fly ash. First, Al and Fe were extracted from fly ash by NH₄HSO₄ roasting and deionized water leaching. Then, the Al and Fe in the leached liquid were precipitated by adding NH₄HCO₃ solution. After the mixed precipitations of Al(OH)₃ and Fe(OH)₃ were leached by NaOH solution, the NaAl(OH)₄ solution was decomposed by carbonation. Finally, the pure Al(OH)₃ was calcined to α-Al₂O₃. The optimal conditions of the whole technology were determined by experiments. The quality of α-Al₂O₃ product is up to the technical indicator of YS/T 274-1998 standard.     

Extraction of molybdenum and nickel from roasted Ni–Mo ore by hydrochloric acid leaching,sulphation roasting and water leaching

To extract molybdenum and nickel from the roasted Ni–Mo ore, a process of hydrochloric acid leaching, sulphation roasting and water leaching was investigated. The results showed that this process could get a high leaching rate of Mo and Ni. Under the optimum conditions of hydrochloric acid leaching (roasted Ni–Mo ore leached with 0.219 mL/g hydrochloric acid addition at 65 °C for 30 min with a L/S ratio of 3 mL/g), sulphation roasting (51.9% sulfuric acid addition, roasting temperature 240 °C for 1 h), followed by leaching with the first stage hydrochloric acid leaching solution at 95 °C for 2 h, the leaching rates of Mo and Ni reached 95.8% and 91.3%, respectively.     

Effect of surfactant on the alumina dispersion and corrosion behavior of electroless Ni?P?Al2O3 composite coatings

Electroless Ni? P? Al₂O₃ composite coatings have been synthesized on mild steel shafts using surfactant cetyltrimethyle ammonium bromide (CTAB) as dispersant. The effects of the surfactant on the alumina dispersion, weight fraction in coatings, and corrosion resistance of the composite coatings under salt spray test were investigated. Results showed that alumina dispersion was improved, whereas weight fraction was decreased, with the increasing concentration of the dispersant CTAB. The corrosion resistance of the composite coatings was found to increase with the increase in CTAB concentration up to a certain optimum of 20 mg/L, beyond which a decreasing trend of corrosion resistance was observed under salt spray test. Compared with Ni? P coating, all the Ni? P? Al₂O₃ composite coatings showed improved corrosion‐resistant properties.     

Preparation of sodium manganate from low-grade pyrolusite by alkaline predesilication–fluidized roasting technique

Low concentration alkaline leaching was used for predesilication treatment of low-grade pyrolusite. The effects of initial NaOH concentration, liquid-to-solid ratio, leaching temperature, leaching time and stirring speed on silica leaching rate were investigated and the kinetics of alkaline leaching process was studied. The results show that silica leaching rate reached 91.2% under the conditions of initial NaOH concentration of 20%, liquid-to-solid ratio of 4:1, leaching temperature of 180 °C, leaching time of 4 h and stirring speed of 300 r/min. Shrinking-core model showed that the leaching process was controlled by the chemical surface reaction with activation energy E_a of 53.31 kJ/mol. The fluidized roasting conditions for preparation of sodium manganate were optimized by the orthogonal experiments using the desiliconized residue. The conversion rate of sodium manganate was obtained to be 89.7% under the conditions of silica leaching rate of 91.2%, NaOH/MnO₂ mass ratio of 3:1, roasting temperature of 500 °C and roasting time of 4 h, and it increased with the increase of silicon leaching rate.     

Process optimization and modeling of recycling Mo (VI) from spent Mo-Fe2O3/Al2O3 catalyst by roasting with sodium carbonate using response surface methodology (RSM)

The oil-containing spent Mo-Fe₂O₃/Al₂O₃ catalyst can be deemed as an environmental threat and an attractive source of minerals that can reduce the consumption of natural resources. Herein, recovery of Mo from spent Mo-Fe₂O₃/Al₂O₃ catalyst was conducted by the Na₂CO₃ roast-leach process, response surface methodology (RSM) coupled with central composite design (CCD) was employed to optimize the roasting process and a polynomial equation was derived to predict the response. The three roasting independent variables the roasting temperature, the Na₂CO₃/sample weight ratio, and the roasting duration were investigated in the Na₂CO₃ roasting process while water-leaching parameters were identical. The predictions of model showed that the roasting temperature had a major effect on the response with respect to other parameters. According to analysis of variance (ANOVA), the proprosed model equation had shown satisfactory agreement with the experimental data with a correlation coefficient (R²) of 0.9811. The optimum conditions for Mo recovery were predicted to be as the roasting temperature of 771.2 °C, the Na₂CO₃/sample weight ratio of 2.09 and the roasting duration of 93.56 min. Under the optimum conditions, maximal value of Mo recovery rate was reached as 92.58%.