minerals Article
Removal of Potassium and Iron in Low Grade Bauxite by a Calcination-Acid Leaching Process Zhuang Li 1,2 , Yijun Cao 3, *, Yuanli Jiang 2 , Guihong Han 1, *, Guixia Fan 1 and Luping Chang 1 1 2 3
*
School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450046, China;
[email protected] (Z.L.);
[email protected] (G.F.);
[email protected] (L.C.) Research Institute of Henan Energy and Chemical Industry Group, Zhengzhou 450046, China;
[email protected] Henan Province Industrial Technology Research Institute of Resources and Materials, Zhengzhou 450046, China Correspondence:
[email protected] (Y.C.);
[email protected] (G.H.); Tel.: +86-371-67781801 (Y.C.); +86-371-6933-7225 (G.H.)
Received: 18 January 2018; Accepted: 16 March 2018; Published: 22 March 2018
Abstract: In order to explore the commercialized applications of the low-grade bauxite in the refractory industry, a calcination integrated with acid leaching method was adopted to remove the potassium (K) and iron (Fe) from the diaspore-illite (DI) type low-grade bauxite. Following calcining the bauxite at different temperatures, the leaching parameters, including the sulfuric acid concentration, temperature, sulfuric acid to bauxite ratio, and reaction time were systematically studied. The appropriate and economical conditions for removing the impurities were found to be calcining the bauxite at 550 ◦ C, and leaching it with a sulfuric acid solution of 1.2 mol/L, sulfuric acid/bauxite ratio of 9 mL/g at a reaction temperature of 70 ◦ C and reaction time of 2 h, under these conditions, the removal efficiency of K and Fe from the bauxite can reach 30.32% and 47.33%, respectively. The treated bauxite was examined by XRD analysis, SEM observations, and chemical analysis. Kinetics of the removing process were calculated by two models, and the results showed that the leaching process was controlled by the mixed shrinking core model, which was affected by both the diffusion through solid layer and the interface transfer. In summary, the approach in this work presents a promising process for comprehensive utilization of the low-grade bauxite. Keywords: low-grade bauxite; potassium and iron removal; calcination; acid leaching; kinetics
1. Introduction Bauxite is an important raw material for the alumina industry, from which more than 90% of the world’s alumina is produced [1]. With the rapid development of the alumina industry, all bauxite-required industries are confronted with the serious shortage of high-quality bauxite resources. Additionally, China, as a large producer and consumer of alumina, has to import a large amount of bauxite each year from other countries like Australia, Guinea, etc. [2,3]. The bauxite found in China, with the mineral feature of diaspore, characterized by high-aluminum, high-silicon, and low ratio of Al2 O3 /SiO2 (Al/Si), is an important raw material for the refractory industry and a strategic resource [4]. High-alumina refractory (HAR) extensive applications in the domestic high-temperature industry such as the metallurgical, ceramic, and glass industries, and also retains a great market share in the international market [5]. Compared with the aluminum industry, the scale of refractory industry is smaller. As a raw material, the consumption of bauxite in the refractory industry is less than that in the aluminum industry. This brings a consequence that the majority of bauxite resources are owned by alumina
Minerals 2018, 8, 125; doi:10.3390/min8040125
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manufactures, and the refractory companies barely have their own bauxite mines [6]. In recent years, the ore-dressing Bayer process, intensified sintering process, and roasting pretreatment for desulphurization process was developed [7–9], following the technology advances in the industry, the Al/Si ratio requirement in Bayer process can be reduced to 4–5, and a large amount of middle-low grade bauxite is being used. Consequently, the extreme shortage of high-alumina bauxite is found in the refractory industry. In addition, there are more mineral processing researches for alumina industry than the refractory. A great number of studies in the literature on the floatation desilicication, desulfurization, and synthesizing mineral processing agents that serve the aluminum industry [10]. However, very few studies report on the purification of bauxite from the refractory point-of-view. To balance the usage of bauxite resources in the two industries and ensure their sustainable developments, it has been suggested by Zhong [11] that the beneficiation and purification should be carried out on the bauxite with low ratio of Al/Si and high content of impurity by the refractory producers. The high-temperature behavior of HAR is based on the mullite (3Al2 O3 ·2SiO2 ) phase, which results from the transformation of kaolinite during the high-temperature thermal cycle [12]. In the bauxite, the main impurities that reduce the performance of refractories include Fe2 O3 , TiO2 , and R2 O (where R = K or Na). These impurities prevent the formation of the mullite and corundum phase [13,14]. It has been found that these impurities form an amorphous phase in the microstructure and that a liquid phase appears easily under high temperature that causes a volume expansion [15]. This leads to degradation of the high-temperature behavior and reduced service life. R2 O almost always forms an amorphous phase and degrades the material properties. Therefore, it is essential to remove the impurities to meet the material requirements for refractory. There are many methods for iron removal or extraction process from bauxite. Reddy et al. [16] studied the removal of iron from a low grade gibbsitic bauxite with hydrochloric acid and it was found 98% of iron could be removed using 4 mol/L acid. Zhao et al. [17] investigated the dissolution of iron from high iron bauxite from Guangxi province by sulfuric acid. Results showed that the quantity of iron leached was 98.68% with acid concentration of 20% and leaching temperature of 100 ◦ C. Hu et al. [18] developed the direct reduction process for utilization of ferric bauxite. The pretreatment used coal as a reductant, then iron powder was obtained by magnetic separation. Papassiopi et al. [19] proposed an innovative process removing iron from bauxite by iron-reducing bacteria. It was found that 95% of amorphous ferrihydrite could be dissolved, whereas the removal efficiency of goethite and hematite was lower than 9% and 1.2%, respectively. Ma [20] adopted active roasting-acid leaching (HCl) to remove iron and potassium from the bauxite tailing, and the Fe2 O3 content in the tailing could be decreased to 0.7%, but only 19.2% of K2 O was leached. However, the removal of potassium in the bauxite has not yet been reported. Since the bauxite studied in this paper is DI type [21] low grade bauxite originating from Dengfeng area, Henan province, and the potassium mainly exists in the illite, the technologies of extracting the potassium from potassium-rich minerals in agriculture can be adopted. There are many relevant studies in this field, including the potassium extraction from mica, nepheline, potassium feldspar, and other potassium-bearing minerals [22–24]. The methods cover soda-sintering, hydrothermal, and acid-leaching technique. Nevertheless, the K2 O content in illite varies from 6% to 9% for agriculture, and it has not reached the industrial requirements (K2 O > 9%) [25]. As a result, the extraction of potassium from illite was barely reported. The objective of this research was to remove iron (Fe) and potassium (K) in low-grade bauxite simultaneously, and a calcination integrated with acid leaching method was adopted. The effects of calcination temperature, sulfuric acid concentration, leaching temperature, sulfuric acid to bauxite ratio, and reaction time on the removal efficiency were studied, and the associated kinetic process was investigated as well. XRD analysis and SEM observations were examined. This study can improve the quality of low -rade bauxite resources and provide better raw materials for the refractory industry.
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2. Materials and Methods 2. Materials and Methods 2.1. Materials 2.1. Materials The bauxite mineral sample used in this work was sourced from Dengfeng, Henan Province, The bauxite mineral sample work was sourced Dengfeng, Henan Province, China. Sulfuric acid (H 2SO4) used usedinasthis leaching agent is of from analytical grade (provided by China. Aladdin Sulfuric acid (H2 SO used as leaching is of analytical grade Aladdin Biotech Shares in Biotech Shares in4 )Shanghai, China),agent and all the solutions with(provided specified by concentrations were prepared Shanghai, China), and all the solutions with specified concentrations were prepared with deionized water. with deionized water.
2.2.2.2. Experimental Procedure Experimental Procedure The schematic diagram bauxite is is plotted plottedin inFigure Figure1.1.As The schematic diagramofofremoving removingpotassium potassiumand and iron iron from from bauxite Asdescribed describedin inFigure Figure1,1,the thebauxite bauxiteisiscrushed crushed and and milled, milled, and and then then aa muffle muffle furnace furnace was was employed employed to ◦ to calcine calcine the the bauxite airair bauxite at at different different temperatures temperatures (450, (450, 550, 550,650, 650,750, 750,850, 850,950, 950,1050, 1050,1250 1250C) °C)in in atmosphere. After calcination, the sintered specimens were cooled down to room temperature by airair atmosphere. After calcination, the sintered specimens were cooled down to room temperature by and then ground in in a planetary ballball mill forfor 4 h.4 h. and then ground a planetary mill Bauxite Crushing &
Milling
Calcination
Milling
H2SO4 Treated bauxite
Filtering
Leaching
Solution Figure 1. Schematic diagram of removing impurities from bauxite. Figure 1. Schematic diagram of removing impurities from bauxite.
Dilute sulfuric acid (H2SO4) solutions used for leaching were prepared with deionized water. Dilute sulfuric acid (H2were SO4 ) conducted solutions used for mL leaching were withbath deionized The leaching experiments in a 100 conical flaskprepared in the water having water. a digital The leaching experiments were conducted in a 100 mL conical flask in the water bath having a digital temperature controller unit with an accuracy of ±0.5 °C. Also, the experimental device was equipped ◦ C. Also, the experimental device was equipped temperature controller unit with accuracyspeed of ±0.5 with a magnetic stirrer with anan agitation of 300 rpm and a reflux condenser to avoid mass loss with a magnetic stirrer with an agitation speed of 300 rpm and a refluxacid condenser avoid mass resulting from evaporation. A certain amount of specified sulfuric solutiontowas input theloss glass resulting evaporation. A certain amount of temperature, specified sulfuric acid solution input glass reactor.from When it was heated up to the defined the roasted bauxitewas (5 g) was the added into reactor. When it was heated up to the temperature, the roasted (5 g) was added into the flask with constant stirring (300defined rpm). After the desired reactionbauxite time, the leaching slurry was theimmediately flask with constant stirring (300 rpm). desired reaction time, the leaching slurry was filtered through 0.5 μm poreAfter size the white filter paper using a vacuum filtration unit and immediately filtered through 0.5 µm pore size white filter paper using a vacuum filtration unit and washed three times to separate the leached product and the solution. The leach liquor was diluted washed three times to separate and the solution. Theresidue leach liquor was diluted with deionized water to detectthe theleached elementproduct content of K and Fe. The filter was collected, dried, with deionized water to detect the element content of K and Fe. The filter residue was collected, dried, and then characterized. and then characterized. 2.3. Analyzing and Characterizing Methods The K and Fe content were analyzed by atomic absorption spectrophotometer (AAS, 4530F, Shanghai Precision and Scientific Instrument Co., Ltd., Shanghai, China). The removal efficiency (Er) was calculated by the Equation (1):
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2.3. Analyzing and Characterizing Methods The K and Fe content were analyzed by atomic absorption spectrophotometer (AAS, 4530F, Minerals 2018, 8, x FOR PEER REVIEW 4 of 15 Shanghai Precision and Scientific Instrument Co., Ltd., Shanghai, China). The removal efficiency (Er ) was calculated by the Equation (1): C ×V E = × 100% (1) Cm ×MVl Er = × 100% (1) M where Cm, Vl, and M0 represent the concentration0 of ions (Potassium or Iron) in the leachate (mg/L), leachate of element (mg) in the chemical analysis of the where Cmvolume(L), , Vl , and M0mass represent the concentration of ore, ions respectively. (Potassium orThe Iron) in the leachate (mg/L), bauxite volume(L), was performed X-ray fluorescence (XRF, Rigaku ZSX II,analysis Toyko, of Japan). X-ray leachate mass by of element (mg) in the ore, respectively. ThePrimus chemical the bauxite diffraction (XRD) patterns of the solid samples were recorded by a Rigaku D/max-rA diffractometer was performed by X-ray fluorescence (XRF, Rigaku ZSX Primus II, Toyko, Japan). X-ray diffraction with CuKα radiation (40 KV and 100 mA). Data points acquired in the 2θ range of 3 with to 70°, with (XRD) patterns of the solid samples were recorded by a were Rigaku D/max-rA diffractometer CuKα ◦ a step size 0.02°. (TG) and differential (DSC) analysis radiation (40ofKV and Thermogravimetric 100 mA). Data points were acquired in thescanning 2θ range calorimetry of 3 to 70 , with a step size ◦ were performed by the simultaneous thermal analyzer (NETZSCH 449F3, Selb, Germany) at heating of 0.02 . Thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis were performed rate ofsimultaneous 10 °C/min with a temperature range of 20–1200 in air atmosphere. The morphology of the by the thermal analyzer (NETZSCH 449F3,°C Selb, Germany) at heating rate of 10 ◦ C/min ◦ Cscanning solidasamples was observed using the electron microscopy (SEM, of JSM-7500F, JEOL, Japan) with temperature range of 20–1200 in air atmosphere. The morphology the solid samples was equipped with an energy dispersive spectrometer (EDS). The particle distribution of the samples in observed using the scanning electron microscopy (SEM, JSM-7500F, JEOL, Japan) equipped with an energy aqueous solution was observed and analyzed using the optical microscope software (ZEISS Axio dispersive spectrometer (EDS). The particle distribution of the samples in aqueous solution was observed Scope. A1, Oberkochen, Germany). and analyzed using the optical microscope software (ZEISS Axio Scope. A1, Oberkochen, Germany). 3. Results Results and and Discussion Discussion 3.
3.1. 3.1. Analysis Analysis of of Raw Raw Material Material The The chemical chemical analysis analysis performed performed by by XRF XRF indicates indicates that that the thebauxite bauxiteconsists consistsof of57.34% 57.34%Al Al22O O33,, 18.22% SiO , 3.81% Fe O , 3.23% K O, 2.32% TiO , 0.26% Na O, 0.64% CaO, and 0.23% MgO. 18.22% SiO22 3.81% Fe22O3,3 3.23% K2O, Na2O,20.64% CaO, and 0.23% MgO. The 2 2.32% TiO2, 0.26% 2 The sample ofis3.15 is low-grade bauxite. sample withwith A/SA/S (the (the Al2OAl 3-to-SiO 2 mass ratio)ratio) of 3.15 low-grade bauxite. 2 O3 -to-SiO 2 mass According to the XRD pattern given in Figure 2, the mineral phases According to the XRD pattern given in Figure 2, the mineral phases in in the the bauxite bauxite are are mainly mainly diaspore, diaspore,quartz quartzand andillite. illite.No Noiron ironmineral mineralphases phasesare aredetected detectedin inthe theXRD XRDpattern. pattern.As Asthe thecontent contentof of Fe is 3.81 3.81 wt % in the raw material, it suggests the possible iron form Fe22O3 is form is is that that colloidal colloidal iron iron or or the the substitution—isomorphous substitution—isomorphousreplacement replacementof ofaluminium aluminiumatoms atomsby byiron ironatoms atomsin inthe thediaspore diasporeand andillite illite crystal crystallattice. lattice. 12000
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Figure 2. 2. X-ray X-ray diffraction diffraction (XRD) (XRD) pattern pattern of of the thebauxite bauxitesample sample(D, (D,diaspore; diaspore;Q, Q,quartz; quartz;I,I,illite). illite). Figure
The bauxite is calcined and then ground, and the cumulative particle size is shown in Figure 3, from which it can be seen that approximately 60% of the particles were less than 2 μm, and almost 100% of the particles are less than 20 μm.
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The bauxite is calcined and then ground, and the cumulative particle size is shown in Figure 3, from which it can be seen that approximately 60% of the particles were less than 2 µm, and almost Minerals 2018, 8, x FOR PEER REVIEW 5 of 15 100% of the particles are less than 20 µm.
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3.2. Reaction Mechanism 3.2. Reaction Mechanism This research was carried out to determine the optimum parameters of removing impurities This research was carried out to determine the optimum parameters of removing impurities from bauxite. In the calcination process, the main changes are the phase transformation of diaspore, from bauxite. In the calcination process, the main changes are the phase transformation of diaspore, the dehydroxylation of illite and mullitization. The general crystal chemical formula of illite can be the dehydroxylation of illite and mullitization. The general crystal chemical formula of illite can be written as K1.43(Si6.90,Al1.10)(Fe0.40,Al3.27,Mg0.33)O20(OH)4 [26]. The process can be represented by the written as K1.43 (Si6.90 ,Al1.10 )(Fe0.40 ,Al3.27 ,Mg0.33 )O20 (OH)4 [26]. The process can be represented by following: the following: α-AlO2O·3H ·HO(diaspore) 2O(diaspore) → α-Al2O3(corundum) + H2O α-Al → α-Al2 O3 (corundum) + H2 O 2 3 2 K1.43(Si6.90,Al1.10)(Fe0.40,Al3.27,Mg0.33)O20(OH)4 → K1.43(Si6.90,Al1.10)(Fe0.40,Al3.27,Mg0.33)O22+2H2O K1.43 (Si6.90 ,Al1.10 )(Fe0.40 ,Al3.27 ,Mg0.33 )O20 (OH)4 → K1.43 (Si6.90 ,Al1.10 )(Fe0.40 ,Al3.27 ,Mg0.33 )O22 +2H2 O In the second step, the release of soluble potassium and iron into solution occurs through the In theofsecond step, the release potassium and into solutionreactions occurs through reaction calcined bauxite with of Hsoluble 2SO4. Theoretically, theiron main chemical duringthe the reaction of calcined bauxite with H SO . Theoretically, the main chemical reactions during the leaching leaching process can be reflected 2as follows (written as oxide forms): 4 process can be reflected as follows (written oxide + →forms): K2Oas + 2H 2K+ + H2O 3+ Fe 6H++ → 3HO 2O K22O O3 ++ 2H → 2Fe 2K+ ++ H 2
3.3. Effect of Calcination TemperatureFe2 O3 + 6H+ → 2Fe3+ + 3H2 O The thermogravimetric curves of the bauxite are shown in Figure 4. As reported in the literature 3.3. Effect of Calcination Temperature [27], the sample has an obvious weight loss due to the diaspore dehydroxylation at the temperatures The curves of thewater bauxite shownfrom in Figure 4. Asatreported in the literature [27],to from 490thermogravimetric to 580 °C. Chemically bound is are released the illite the temperature from 500 the obvious weight loss duedehydrate to the diaspore dehydroxylation at the temperatures from 700sample °C, andhas theanillite is transformed into illite (not marked in Figure 4 due to low content). ◦ 490 to 580 Chemically bound water vitrification is released from illite at the temperature 500 and to Above 800C.°C, the sintering process, and the high-temperature reactions from (mullite ◦ 700 C, and the illite is transformed into dehydrate illite (not marked in Figure 4 due to low content). corundum formation) take place [28]. AboveFrom 800 ◦ C, the sintering process, vitrification and high-temperature reactions (mullite and°C corundum Figure 5, it can be seen that the mineral phase of the bauxite calcined at 450 does not formation) take place [28]. change compared with the raw sample. As the calcination temperature rises, the new phase of From Figure can be seen that the mineral phase of thediffraction bauxite calcined at 450 ◦ C above does corundum (α-Al25, O3it ) appears in the sample, and the diaspore peaks disappear not change compared with the raw sample. As the calcination temperature rises, the new phase 450 °C. When the temperature rises to 1050 °C, the illite is not observed, and the main phase of of the corundum (α-Al O3 ) appearsdue in the sample, the diaspore diffraction peaks disappear above1100 450 ◦°C, C. solid sample is 2corundum to the high and temperature sintering. As reported in [28], above illite begins to transform into amorphous substance and mullite, while there is no mullite phase discernable in the XRD pattern. The reason for this most likely is that the content of illite is low in the bauxite and only part of illite can transform into mullite.
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When the temperature rises to 1050 ◦ C, the illite is not observed, and the main phase of the solid sample is corundum due to the high temperature sintering. As reported in [28], above 1100 ◦ C, illite begins to transform into amorphous substance and mullite, while there is no mullite phase discernable in the XRD The reason and Minerals 2018,pattern. 8, x FOR PEER REVIEWfor this most likely is that the content of illite is low in the bauxite 6 of 15 only part of illite can transform into mullite. Minerals 2018, 8, x FOR PEER REVIEW 6 of 15 0.4 0.4 0.2 99
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Figure 4. Thermogravimetric (TG) and differential scanning calorimetry (DSC) plots of bauxite Figure (TG) andand differential scanning calorimetry (DSC) plots bauxite Figure4.4.Thermogravimetric Thermogravimetric (TG) differential scanning calorimetry (DSC)ofplots of sample. bauxite sample. sample.
Figure 5.5.XRD XRDpattern pattern of the bauxite calcined at different temperatures. (D, I,diaspore. I, illite. C, Figure of the bauxite calcined at different temperatures. (D, diaspore. illite. C, corundum). Figure 5. XRD pattern of the bauxite calcined at different temperatures. (D, diaspore. I, illite. C, corundum). corundum).
The sulfuric acid The effect effect of of calcination calcination temperature temperatureisisstudied studiedwith withleaching leachingin in1.2 1.2mol/L mol/L sulfuric acid solution solution ◦ C for 2 h, and the results according to the liquid/solid (L/S) of 9 mL/g at a reaction temperature of 70 The effect calcination(L/S) temperature is at studied withtemperature leaching in 1.2 mol/L sulfuric acid according to theofliquid/solid of 9 mL/g a reaction of 70 °C for 2 h, and thesolution results are presented ininFigure 6. It be seen that calcination temperature hasof a significant removal according to the liquid/solid of mL/g at a calcination reaction temperature 70 °C afor 2 effect h, andon the results are presented Figure 6. can It(L/S) can be9 seen that temperature has significant effect on
are presented in Figure It can be seen that temperature effectthe on removal efficiency. The 6. removal efficiency of calcination Fe drops sharply from has 94.42a significant to 1.03% when removal efficiency. The increases removal from efficiency of 850 Fe drops sharply 1.03%1.00% whenuntil the calcination temperature 450 to °C. Above 850 from °C, it 94.42 keepstobelow calcinationaround temperature increases at from 850removal °C. Above 850 °C, below until becoming 0 (not detected) 1250450 °C.toThe efficiency of it K keeps increases from1.00% 21.46% at becoming aroundat 0 (not detected) at 1250 °C. The removal efficiency of °C, K increases 21.46% to at 450 °C to 30.32% 550 °C, reaching the maximum value. Beyond 550 it beginsfrom to decrease 450 °C to 30.32% at 550 °C, reaching the maximum value. Beyond 550 °C, it begins to decrease to approximately 3.00% at 1250 °C.
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efficiency. The removal efficiency of Fe drops sharply from 94.42 to 1.03% when the calcination temperature increases from 450 to 850 ◦ C. Above 850 ◦ C, it keeps below 1.00% until becoming around 0 (not detected) at 1250 ◦ C. The removal efficiency of K increases from 21.46% at 450 ◦ C to 30.32% at 550 ◦ C, reaching the maximum value. Beyond 550 ◦ C, it begins to decrease to approximately 3.00% at 1250 ◦ C. The phase transformation Minerals 2018, 8, x FOR PEER REVIEW in Figure 5 can explain the decline of iron removal efficiency as 7 ofthe 15 sintering temperature rises. Specifically, iron enters into the corundum phase and transforms into solid increasing a solidsolution, solution,and andthe thesolid solidsolubility solubilityofofiron iron in in the the corundum corundum increases increases with with the the increasing temperature. Also, small portion portion of of iron iron can can form form aa solid solid solution solution (Fe (Fe22O O33·TiO temperature. Also, aa small ·TiO22)) with with TiO TiO22 [29]. [29]. Therefore, it it is is reasonable reasonable to to deduce deduce that that the the decrease of iron removal efficiency efficiency may may be be attributed attributed to to Therefore, decrease of iron removal the transformation of the the solid solid solution solution at at high high temperature. temperature. the transformation of
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Figure Figure 6. 6. Effect Effect of of calcination calcination temperatures temperatures on on the the removal removal efficiency. efficiency.
The changes of potassium removal efficiency are mainly associated with the illite crystal The changes of potassium removal efficiency are mainly associated with the illite crystal structure. structure. As the calcination temperature rises from 450 to 950 °C, the basic charge balance of the illite As the calcination temperature rises from 450 to 950 ◦ C, the basic charge balance of the illite crystal crystal structure is broken due to the dehydroxylation, causing the adjustment and deformation of structure is broken due to the dehydroxylation, causing the adjustment and deformation of the crystal the crystal structure. He et al. [30] investigated the crystal structure variation of illite in roasting structure. He et al. [30] investigated the crystal structure variation of illite in roasting process. It found process. It found that the interplanar distance d(002), d(004), d(110), d(006), d(131), and d(136) of illite that the interplanar distance d(002), d(004), d(110), d(006), d(131), and d(136) of illite increased, increased, and interlayer space expanded along the direction of c-axis, which leads to weakened and interlayer space expanded along the direction of c-axis, which leads to weakened interlayer force. interlayer force. As a result, the potassium is easily released from the illite,thus we inferred from As a result, the potassium is easily released from the illite, thus we inferred from Figure 5 that the Figure 5 that the bauxite calcined at 550 °C is advantageous for removing potassium, reaching a bauxite calcined at 550 ◦ C is advantageous for removing potassium, reaching a maximum value maximum value (30.32%). Beyond 550 °C, the illite may transform to a solid solution as the calcination (30.32%). Beyond 550 ◦ C, the illite may transform to a solid solution as the calcination temperature temperature rises, and the potassium removal efficiency begins to decline. rises, and the potassium removal efficiency begins to decline. 3.4. Leaching 3.4. Leaching Experiment Experiment Parameters Parameters From the Figure Figure 6, 6, the the removal removal rate rate of of K K reaches reaches the the maximal maximal value value when when the bauxite is is roasted roasted From the the bauxite at 550 °C, and the rate of Fe is 47.33%. Compared with iron, potassium is more disadvantageous ◦ at 550 C, and the rate of Fe is 47.33%. Compared with iron, potassium is more disadvantageous for for the refractory performance, so removing potassium is the first consideration. Hence, the roasting the refractory performance, so removing potassium is the first consideration. Hence, the roasting temperature is selected to to be be 550 550 ◦°C. The leaching leaching experiments experiments are are performed performed to to determine determine the the temperature is selected C. The appropriate parameters of removal impurities from the economical view. appropriate parameters of removal impurities from the economical view. 3.4.1. Effect of Sulfuric Acid Concentration A series of experiments are conducted at c (acid concentration) = 0.4, 0.8, 1.2, 1.6, 2.0, 3.0, 4.0 mol/L to investigate the effect of sulfuric acid concentration on removal efficiency. The reaction temperature, liquid/solid ratio and reaction time are kept constant 70 °C, 9 mL/g and 2 h, respectively. As presented in Figure 7, the removal efficiency of potassium and iron increases gradually with the increasing acid concentration, whose efficiency is raised from 24.71 to 35.54% and 39.71 to 60.78% as the acid concentration is varied from 0.4 mol/L to 4 mol/L, respectively. Higher acid concentration can conduct a strong attack on the minerals and destroy its structure. Besides, for the leaching process,
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3.4.1. Effect of Sulfuric Acid Concentration A series of experiments are conducted at c (acid concentration) = 0.4, 0.8, 1.2, 1.6, 2.0, 3.0, 4.0 mol/L to investigate the effect of sulfuric acid concentration on removal efficiency. The reaction temperature, liquid/solid ratio and reaction time are kept constant 70 ◦ C, 9 mL/g and 2 h, respectively. As presented in Figure 7, the removal efficiency of potassium and iron increases gradually with the increasing acid concentration, whose efficiency is raised from 24.71 to 35.54% and 39.71 to 60.78% as the acid concentration is varied from 0.4 mol/L to 4 mol/L, respectively. Higher acid concentration can conduct a strong attack on the minerals and destroy its structure. Besides, for the leaching process, higher acid concentration increases the H+ activity [31], which may enhance the ion exchange capacity + , resulting in increasing potassium and iron removal efficiency. Minerals 2018, 8, x FOR REVIEW 8 of 15 between metal ion PEER and H 64
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4.0
4.5
Sulfuric acid concentration (mol/L) Figure 7. Effect of sulfuric acid concentration on the removal efficiency. Figure 7. Effect of sulfuric acid concentration on the removal efficiency.
However, the potassium removal efficiency increases slightly from 30.32 to 35.54% as the acid However,changes the potassium efficiency increases slightly from 30.32 to 35.54% acid concentration from 1.2removal to 4 mol/L due to the main potassium-bearing mineral, illite,asa the layered concentration changes from 1.2 to 4 mol/L due to the main potassium-bearing mineral, illite, a layered silicate with relatively stable Al-Si-O tetrahedron crystal structure. Potassium is stably attached to silicate by with relatively Al-Si-O tetrahedron crystal structure. Potassium is stablytoattached to oxygen ionic bond instable the crystal structure, thereby making it difficult for potassium enter into oxygen by ionic bond in the crystal structure, thereby making it difficult for potassium to enter into the solution. Higher acid concentration cannot promote the removal efficiency greatly. Thus, in the the solution. Higher acid concentration cannot promote removal following experiments, sulfuric acid concentration is keptthe at 1.2 mol/L.efficiency greatly. Thus, in the following experiments, sulfuric acid concentration is kept at 1.2 mol/L. 3.4.2. Effect of Reaction Temperature 3.4.2. Effect of Reaction Temperature The relationship between the reaction temperature (from 30 °C◦ to 90 °C) and the removal The relationship between the reaction temperature (from 30 to 90 C) and the removal efficiency efficiency was investigated with sulfuric acid concentration of 1.2 mol/L, liquid/solid of 9 mL/g and was investigated with sulfuric acid concentration of 1.2 mol/L, liquid/solid of 9 mL/g and reaction reaction time of 2 h. The results are illustrated in Figure 8. As expected, rising temperature is time of 2 h. The results are illustrated in Figure 8. As expected, rising temperature is favorable for the favorable for the removal efficiency of potassium and iron. The efficiency of K and Fe removal is as removal efficiency of potassium and iron. The efficiency of K and Fe removal is as high as 33.74% and high as 33.74% and 57.95% at 90 °C, respectively. Higher temperature can increase the diffusion 57.95% at 90 ◦ C, respectively. Higher temperature can increase the diffusion coefficient of the reaction coefficient of the reaction system and enhance the diffusion of H+ from the surface into the inside + system and enhance the diffusion of H from the surface into the inside channels of the mineral channels of the mineral particles, accelerating the decomposition of bauxite. Other similar particles, accelerating the decomposition of bauxite. Other similar experiments [24] like extraction of experiments [24] like extraction of potassium from phosphorus-potassium associated ore affirmed potassium from phosphorus-potassium associated ore affirmed that rising the reaction temperature that rising the reaction temperature can increase the leaching efficiency. However, higher can increase the leaching efficiency. However, higher temperature may cause an Al loss from the temperature may cause an Al loss from the bauxite, which is disadvantageous considering the bauxite, which is disadvantageous considering the relationship between Al content and refractory relationship between Al content and refractory performance. Therefore, the appropriate temperature performance. Therefore, the appropriate temperature of 70 ◦ C is recommended in this study. of 70 °C is recommended in this study. 3.4.3. Effect of Sulfuric Acid/Bauxite Ratio To observe the effect of liquid/solid ratio on the removal efficiency, the experiments were carried out with four ratio levels ranging from 5 to 11 mL/g at acid concentration of 1.2 mol/L, 70 °C for 2 h. The results plotted in Figure 9 showed that the removal efficiency of K and Fe increases with the increase of the sulfuric acid-to-bauxite ratio. This can be explained that higher acid/bauxite ratio supplies more sulfuric acid to leach the potassium and iron. In addition, higher ratio can reduce
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3.4.3. Effect of Sulfuric Acid/Bauxite Ratio To observe the effect of liquid/solid ratio on the removal efficiency, the experiments were carried out with four ratio levels ranging from 5 to 11 mL/g at acid concentration of 1.2 mol/L, 70 ◦ C for 2 h. The results plotted in Figure 9 showed that the removal efficiency of K and Fe increases with the increase of the sulfuric acid-to-bauxite ratio. This can be explained that higher acid/bauxite ratio supplies more sulfuric acid to leach the potassium and iron. In addition, higher ratio can reduce reaction system viscosity of reactants for improving well mixing and promote diffusion. When the ratio varies from 5 to 11 mL/g, the removal efficiency of potassium and iron only increases from 24.12% to 31.14% and 37.55% to 50.26%, respectively, which does not obviously increase the extent of removing. This reveals that the amount of sulfuric acid is adequate to leach potassium and iron when the ratio exceeds 7 mL/g. Taking the lower acid concentration (1.2 mol/L) into account, the ratio of 9Minerals mL/g2018, is found to PEER be the optimum for leaching. 8, x FOR REVIEW 9 of 15
Removal efficiency (%)
60
K Fe
50 40 30 20 10 0
30
40
50
60
70
Temperature (℃)
80
90
Figure 8. 8. Effect of temperature on the the removal removal efficiency. efficiency. Figure Effect of temperature on
K Fe
Removal efficiency (%)
50
40
30
20 5
6
7
8
9
10
Sulfuric acid/bauxite ratio (mL/g)
11
Figure 9. Effect of sulfuric acid/bauxite ratio on the removal efficiency. Figure 9. Effect of sulfuric acid/bauxite ratio on the removal efficiency.
3.4.4. Effect of Reaction Time The effect of the reaction time on the removal efficiency of potassium and iron was studied at 70 °C with sulfuric acid concentration of 1.2 mol/L and liquid/solid ratio of 9 mL/g. The curves reported in Figure 10 identify that the removal efficiency of K and Fe increases with adding time. The efficiency of Fe increases greatly with the increasing time from 25.09% at 20 min to 60.45% at 360 min. Beyond 360 min, the data increases extremely slowly. The removal efficiency of K displays a similar
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3.4.4. Effect of Reaction Time The effect of the reaction time on the removal efficiency of potassium and iron was studied at 70 ◦ C with sulfuric acid concentration of 1.2 mol/L and liquid/solid ratio of 9 mL/g. The curves reported in Figure 10 identify that the removal efficiency of K and Fe increases with adding time. The efficiency of Fe increases greatly with the increasing time from 25.09% at 20 min to 60.45% at 360 min. Beyond 360 min, the data increases extremely slowly. The removal efficiency of K displays a similar trend, whereas the increasing extent is relatively smaller compared with Fe. This may be due Minerals 2018, 8, x FOR PEER 10 of 15 to the different forms ofREVIEW iron present in the bauxite. 65
K Fe
60
Removal efficiency (%)
55 50 45 40 35 30 25 20
0
100
200
300
400
500
Time (min) Figure 10. Effect of reaction time on the removal efficiency. Figure 10. Effect of reaction time on the removal efficiency.
As shown in Figure 10, the removal efficiency of K increases quite slowly as the time increases, Assake shown in Figure 10, the removal efficiency of 2Khincreases slowly as the time increases, for the of energy consumption, reaction time of is chosenquite as the appropriate condition for for the sake of energy consumption, reaction time of 2 h is chosen as the appropriate condition for the the leaching process. leaching process. 3.5. Kinetics Analysis 3.5. Kinetics Analysis The kinetics of removing potassium and iron process were examined at acid concentration of 1.2 The kinetics of removing potassium and iron process were examined at acid concentration of mol/L, 70 °C, and L/S of 9 mL/g. The experimental data was analyzed based on the diffusion shrinking 1.2 mol/L, 70 ◦ C, and L/S of 9 mL/g. The experimental data was analyzed based on the diffusion core model (SCM). Generally, the diffusion through solid layer and the mixed shrinking core model shrinking core model (SCM). Generally, the diffusion through solid layer and the mixed shrinking (diffusion through solid layer integrated with interface transfer) could be the most likely ratecore model (diffusion through solid layer integrated with interface transfer) could be the most likely controlling step during the leaching process. The rate equation for diffusion through solid layer and rate-controlling step during the leaching process. The rate equation for diffusion through solid layer and the mixed shrinking core model can be respectively expressed as Equation (2) and Equation (3) [32,33]. the mixed shrinking core model can be respectively expressed as Equation (2) and Equation (3) [32,33]. (2) 1 + 2(1 − α) − 3(1 − α)2 = 𝑘 × t 3 1 + 2(1 − α) − 3(1 − α) = k 1 × t (2) 1 (3) ln(1 − α) + (1 − α) − 1 = 𝑘 × t 1 13 ln(1 − α) + (1 − α)− 3 − 1 = k2 × t (3) 3 where α is the removal efficiency of potassium or iron, k1 and k2 are the linear rate constants controlled by diffusion layer of and the mixed shrinking model, and rate t is the reaction time in where α is thethrough removalsolid efficiency potassium or iron, k1 andcore k2 are the linear constants controlled minutes. by diffusion through solid layer and the mixed shrinking core model, and t is the reaction time The experimental data of Figure 10 are simulated, and the plots of Equations (2) and (3) versus in minutes. time are in Figures and 12, It can found Figure 12(2) that Equation (3) Thepresented experimental data of11Figure 10respectively. are simulated, andbethe plotsfrom of Equations and (3) versus can describe the leaching potassium and iron the data in 12 Figure are linear timebetter are presented in Figures 11process and 12,of respectively. It can be because found from Figure that 12 Equation (3) with a higher correlation coefficients (R2of ) compared Figure The results indicate that12 theare kinetics can better describe the leaching process potassiumtoand iron11. because the data in Figure linear of the removal of potassium and iron in sulfuric acid is controlled by both the diffusion through solid layer and interface transfer. The rate constant (k2) and intercept are obtained from Figure 12, and the kinetics models for removing potassium and iron are respectively concluded by Equations (4) and (5). 1
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with a higher correlation coefficients (R2 ) compared to Figure 11. The results indicate that the kinetics of the removal of potassium and iron in sulfuric acid is controlled by both the diffusion through solid layer and interface transfer. The rate constant (k2 ) and intercept are obtained from Figure 12, and the kinetics models for removing potassium and iron are respectively concluded by Equations (4) and (5). 1 1 ln(1 − α) + (1 − α)− 3 − 1 = 8.284 × 10−6 × t + 0.00593 3 1 1 ln(1 − α) + (1 − α)− 3 − 1 = 1.382 × 10−4 × t + 0.00332 3 Minerals 2018, 8, x FOR PEER REVIEW
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2
0.07 0.06
R2=0.9799 -5x+0.00963 1. K : y=1.115*10 -4 2 2. Fe :Ry=1.393*10 =0.9799 x+0.00916 2 =0.9580 -4x+0.00916 2. Fe : R y=1.393*10
2
2/3 1+2(1-a)-3(1-a) 1+2(1-a)-3(1-a)2/3
1. K : y=1.115*10-5x+0.00963
0.05 0.04
(5) 11 of 15 11 of 15
0.07
0.06 0.05
(4)
R2=0.9580
0.04 0.03 0.03 0.02
1
0.02 0.01 0.01 0.00 0.00
1 0
100
0
100
200
300
Time (min)300 200
400 400
Time (min) process: 1 + 2(1 − α) − 3(1 − α)2/3 versus Figure 11. The diffusion kinetics model during removing Figure 11. The diffusion kinetics model during removing process: 1 + 2(1 − α) − 3(1 − α)2/3 versus reaction time. Figure 11. The diffusion kinetics model during removing process: 1 + 2(1 − α) − 3(1 − α)2/3 versus reaction time. reaction time.
-1/3 -1/3 1/3ln(1-a)+(1-a) 1/3ln(1-a)+(1-a)-1 -1
2
1. K : y=8.284*10-6x+0.00593
0.06
2
2
R =0.9813-6x+0.00593 1. K : y=8.284*10 -4 2 2. Fe : R y=1.382*10 =0.9813 x+0.00332
0.06 0.05 0.05 0.04
2
R =0.9866 -4x+0.00332 2. Fe : y=1.382*10 2
R =0.9866
0.04 0.03 0.03 0.02 0.02 0.01 0.01 0.00 0.00
1 1 0
0
100 100
200
Time (min) 200
300 300
400 400
(min)process: 1/3ln(1 − α) + (1 − α)−1/3 − 1 versus Figure 12. The diffusion kinetics model duringTime removing reaction time. Figure 12. The diffusion kinetics model during removing process: 1/3ln(1 − α) + (1 − α)−1/3 − 1 versus Figure 12. The diffusion kinetics model during removing process: 1/3ln(1 − α) + (1 − α)−1/3 − 1 reaction time.
3.6. Characterization versus reaction time. of Treated Bauxite
3.6. Characterization of Treated The XRD patterns of the Bauxite roasted bauxites and the leach residues are observed in Figure 13. It can
3.6. Characterization of Treated Bauxite be seen b and c have the same crystal phases withresidues illite and XRD The that XRDa, patterns of the roasted bauxites and the leach arecorundum. observed inThe Figure 13.results It can
indicated that illitec in thethe bauxite has a very stablewith crystal which was destroyed be seen a, the b and have same crystal phases illitestructure, and are corundum. The XRD results The XRDthat patterns of the roasted bauxites and the leach residues observed innot Figure 13. It can even by the 4 mol/L sulfuric acid attack. The stable crystal structure should be responsible for the indicated that the illite in the bauxite has a very stable crystal structure, which was not destroyed be seen that a, b and c have the same crystal phases with illite and corundum. The XRD results lowerby potassium removal efficiency. even the mol/L acid attack. The stable should responsible for the even indicated that the4 illite insulfuric the bauxite has a very stable crystal crystalstructure structure, whichbewas not destroyed The SEM images and corresponding EDS analysis of the roasted bauxite and the leaching residue lower potassium removal efficiency. by theH42SO mol/L sulfuric acid attack. The stable crystal structure should be responsible for the lower 4 are obtained in Figure 14. The fuzzy particle boundary and dendritic shape could be observed The SEM images and corresponding EDS analysis of the roasted bauxite and the leaching residue potassium removal efficiency. in Figure 14a, while in Figure 14b, the dendritic shape disappeared due to acid leaching, and it H2SO4 are obtained in Figure 14. The fuzzy particle boundary and dendritic shape could be observed presents shapes and irregular roughly 0.5–1 μm indue length afterleaching, leaching.and There in Figure different 14a, while in Figure 14b, theparticles dendriticofshape disappeared to acid it are no obvious layer shapes of illite in the SEM images, though the illite phase is identified in Figure presents different shapes and irregular particles of roughly 0.5–1 μm in length after leaching. There 13. no Weobvious can deduce it may be encapsulated into the though transformation the are layerthat shapes of illite in the SEM images, the illiteproduct phase is(corundum), identified in and Figure iron-bearing mineral maybe the similar situation. 13. We can deduce that it mayencountered be encapsulated into the transformation product (corundum), and the iron-bearing mineral maybe encountered the similar situation.
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The SEM images and corresponding EDS analysis of the roasted bauxite and the leaching residue H2 SO4 are obtained in Figure 14. The fuzzy particle boundary and dendritic shape could be observed in Figure 14a, while in Figure 14b, the dendritic shape disappeared due to acid leaching, and it presents different shapes and irregular particles of roughly 0.5–1 µm in length after leaching. There are no obvious layer shapes of illite in the SEM images, though the illite phase is identified in Figure 13. We can deduce that it may be encapsulated into the transformation product (corundum), and the Minerals 8, PEER 12 Minerals 2018, 2018, 8, xx FOR FORmaybe PEER REVIEW REVIEW 12 of of 15 15 iron-bearing mineral encountered the similar situation.
Intensity
(c) (c)
C C C C C II C
C C C C II IIII
C C C C C C
C C
II
I=Illite I=Illite C=Corundum C=Corundum (b) (b)
(a) (a) 10 10
20 20
30 30
40 40
50 50
60 60
70 70
22θθ ((°°)) ◦ C. Figure 13. XRD patterns treated roasted at leached with Figure 13. The The XRD patternsofof oftreated treated bauxites bauxites ((a): ((a): bauxite roasted at 550 550 °C. (b): leached with 1.2 1.2with Figure 13. The XRD patterns bauxites ((a):bauxite bauxite roasted at°C. 550(b): (b): leached mol/L H 22SO 44,, (c): leached with 44 mol/L H 22SO 44). mol/L H SO (c): leached with mol/L H SO ). 1.2 mol/L H2 SO4 , (c): leached with 4 mol/L H2 SO4 ).
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Figure Figure 14. 14. Scanning Scanning electron electron microscopy microscopy (SEM) (SEM) images images and and energy energy dispersive dispersive spectrometer spectrometer (EDS) (EDS)
Figure 14. Scanning electron microscopy (SEM) images and energy dispersive spectrometer (EDS) analysis analysis of of the the treated treated bauxite. bauxite. (a): (a): Bauxite Bauxite roasted roasted at at 550 550 °C; °C; (b): (b): leaching leaching residue; residue; (c) (c) and and (d): (d): EDS EDS ◦ analysis of the bauxite. analysis assigned zone. analysis for fortreated assigned zone. (a): Bauxite roasted at 550 C; (b): leaching residue; (c) and (d): EDS analysis for assigned zone. The The combined combined EDS EDS analysis analysis results results in in Figure Figure 14c 14c illustrates illustrates there there are are still still quantities quantities of of K K and and Fe Fe distribution distribution in in the the residue, residue, which which also also suggests suggests the the mineral mineral embedded embedded characteristics characteristics are are complex complex and and itit is is difficult difficult to to remove remove the the impurities. impurities. The The chemical chemical analysis analysis of of the the treated treated and and raw raw bauxite bauxite is is presented presented in in Table Table 1. 1. The The equivalent equivalent content content of of K K22O O and and Fe Fe22O O33 reduces reduces to to 2.09 2.09 and and 1.78%, 1.78%, respectively. respectively. The The treated treated bauxite bauxite with with relatively relatively low low impurities impurities (about (about 2% 2% of of R R22O) O) can can be be used used to to produce produce homogenized homogenized bauxite bauxite [34]. [34]. Notably, Notably, the the
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The combined EDS analysis results in Figure 14c illustrates there are still quantities of K and Fe distribution in the residue, which also suggests the mineral embedded characteristics are complex and it is difficult to remove the impurities. The chemical analysis of the treated and raw bauxite is presented in Table 1. The equivalent content of K2 O and Fe2 O3 reduces to 2.09 and 1.78%, respectively. The treated bauxite with relatively low impurities (about 2% of R2 O) can be used to produce homogenized bauxite [34]. Notably, the content of Al2 O3 is not decreased after leached, which is advantageous for the use in refractory applications. Table 1. The X-ray fluorescence (XRF) results of bauxite samples, presented as oxides. Sample
Al2 O3 (%)
SiO2 (%)
TiO2 (%)
Fe2 O3 (%)
K2 O (%)
Na2 O (%)
CaO (%)
MgO (%)
Treated Raw
58.17 57.34
20.56 18.22
1.82 2.32
1.78 3.81
2.09 3.23
0.07 0.26
0.09 0.64
0.15 0.23
4. Conclusions In order to explore a method to apply low-grade bauxite in the refractory industry, a calcination followed by acid leaching process for the impurity removal of low-grade bauxite is proposed. Sulfuric acid is used as a leaching agent in this work. The results prove that raising the calcination temperature is disadvantageous for removing iron, but the removal efficiency of potassium can reach its maximum value when the calcination temperature is 550 ◦ C. The influencing factors including acid concentration, temperature, sulfuric acid–to-bauxite ratio, and reaction time are investigated. It is found that when a sulfuric acid (1.2 mol/L) to bauxite ratio of 9 mL/g and a temperature of 70 ◦ C and a residence time of 2 h are used, the potassium- and iron-removing efficiency from the bauxite calcined at 550 ◦ C can reach 30.32% and 47.33%, respectively, and the treated bauxite can be used to produce homogenized bauxite. The kinetics formulas are calculated, and the results showed that the leaching reaction is controlled by both the diffusion through solid layer and interface transfer. In summary, this research provides prospects for a more comprehensive utilization of low-grade bauxite. Acknowledgments: The financial support from the National Nature Science Foundation of China (No. U1704252 and 51704263) is gratefully acknowledged. We also thank the Development Fund for Outstanding Young Teachers of Zhengzhou University (No. 1421324065) and the China Postdoctoral Science Foundation (No. 2017M622375). Author Contributions: Zhuang Li, Yijun Cao, and Yuanli Jiang conceived and designed the experiments; Zhuang Li, Guixia Fan, and Guihong Han performed the experiments; Luping Chang, Guihong Han, and Zhuang Li analyzed the data; Luping Chang and Guixia Fan contributed reagents, materials, and analysis tools; Zhuang Li, Yijun Cao, and Yuanli Jiang wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.
References 1. 2. 3. 4. 5. 6. 7.
Paz, S.P.A.; Angélica, R.S.; Kahn, H. Optimization of the reactive silica quantification method applied to Paragominas-type gibbsitic bauxites. Int. J. Miner. Process. 2017, 162, 10–15. [CrossRef] Zhang, B.; Jiang, Y.; Guo, S.; Zhou, F. The influence of bauxite resource change in China on layout of world alumina industry. Lightmedals 2014, 26, 1–5. Fan, Z.L.; Ma, Z.H. Countermeasures and safety evaluation on the use of foreign bauxite resources. China Min. Mag. 2010, 19, 13–15. Zhong, H.; Liu, G.Y.; Xia, L.Y.; Lu, Y.P.; Hu, Y.H.; Zhao, S.G.; Yu, X.Y. Flotation separation of diaspore from kaolinite, pyrophyllite and illite using three cationic collectors. Miner. Eng. 2008, 21, 1055–1061. Pan, S.X.; Wang, R.; Zhang, Z.Q.; Chu, G.S.; Wang, T.Z. Export and import situation of refractories and refractory raw materials in China. China Refract. 2000, 3, 11–15. Shi, G. Discussion on current situation of China’s refractories resources and development. Naihuo Cailiao 2007, 41, 63–67. Fang, C.J.; Chang, Z.Y.; Feng, Q.M.; Xiao, W.; Yu, S.C.; Qiu, G.Z.; Wang, J. The Influence of Backwater Al3+ on Diaspore Bauxite Flotation. Minerals 2017, 7, 195.
Minerals 2018, 8, 125
8. 9. 10. 11. 12.
13. 14. 15.
16. 17. 18. 19. 20. 21. 22. 23. 24.
25.
26. 27. 28. 29. 30. 31. 32.
14 of 15
Li, X.B.; Liu, X.M.; Liu, G.H.; Peng, Z.H.; Liu, Y.X. Study and application of intensified sintering process for alumina production. Chin. J. Nonferr. Met. 2004, 14, 1031–1036. Lü, G.Z.; Zhang, T.A.; Li, B.; Dou, Z.H.; Zhang, W.G. Roasting Pretreatment of High-sulfur Bauxite. Chin. J. Process. Eng. 2008, 8, 892–896. Zhao, Q.; Miller, J.D.; Wang, X.M. Recent Developments in the Beneficiation of Chinese Bauxite. Miner. Process. Extr. Metall. Rev. 2010, 31, 111–119. Zhong, X.C. Strategic thoughts on innovative development of Chinese bauxites. Naihuo Cailiao 2009, 43, 241–243. Amrane, B.; Ouedraogo, E.; Mamen, B.; Djaknoun, S.; Mesrati, N. Experimental study of the thermo-mechanical behaviour of alumina-silicate refractory materials based on a mixture of Algerian kaolinitic clays. Ceram. Int. 2011, 37, 3217–3227. [CrossRef] Cheng, H. Influence of K2 O on Sintering-Synthesizing Mullite with Bauxite. Chin. Ceram. 2013, 49, 48–50. Sadik, C.; Amrani, I.E.; Albizane, A. Recent advances in silica-alumina refractory: A review. J. Asian Ceram. Soc. 2014, 2, 83–96. [CrossRef] Stjernberg, J.; Ion, J.C.; Antti, M.L.; Nordin, L.O.; Lindblom, B.; Odén, M. Extended studies of degradation mechanisms in the refractory lining of a rotary kiln for iron ore pellet production. J. Eur. Ceram. Soc. 2012, 32, 1519–1528. [CrossRef] Reddy, B.R.; Mishra, S.K.; Banerjee, G.N. Kinetics of leaching of a gibbsitic bauxite with hydrochloric acid. Hydrometallurgy 1999, 51, 131–138. [CrossRef] Zhao, A.C.; Zhang, T.A.; Lü, G.Z.; Dou, Z.H. Study on the leaching rules of aluminum and ferrum from high iron bauxite by acid leaching at low temperature. J. Funct. Mater. 2012, 43, 105–108. Hu, W.T.; Wang, H.J.; Liu, X.W.; Sun, C.Y.; Duan, X.Q. Restraining Sodium Volatilization in the Ferric Bauxite Direct Reduction System. Minerals 2016, 6, 31. [CrossRef] Papassiopi, N.; Vaxevanidou, K.; Paspaliaris, I. Effectiveness of iron reducing bacteria for the removal of iron from bauxite ores. Miner. Eng. 2010, 23, 25–31. [CrossRef] Ma, D.Y. Preparation of Mullite-Based Complex Refractory from Bauxite Tailings. Ph.D. Thesis, University of Science and Technology Beijing, Beijing, China, 2015. Gao, Z.X.; Li, G.P. On the classification of Chinese bauxites. J. Chin. Ceram. Soc. 1984, 2, 115–122. Zheng, L.; Yang, Y.; Ma, H.W.; Liu, M.T.; Ma, X. Recovery of magnesium and potassium from biotite by sulfuric acid leaching and alkali precipitation with ammonia. Hydrometallurgy 2015, 157, 188–193. Yuan, B.; Li, C.; Liang, B.; Lü, L.; Yue, H.R.; Sheng, H.Y.; Ye, L.P.; Xie, H.P. Extraction of potassium from K-feldspar via the CaCl2 calcination route. Chin. J. Chem. Eng. 2015, 23, 1557–1564. [CrossRef] Zhang, Y.F.; Ma, J.Y.; Qin, Y.H.; Zhou, J.F.; Li, Y.; Wu, Z.K.; Wang, T.L.; Wang, W.G.; Wang, C.W. Ultrasound-assisted leaching of potassium from phosphorus-potassium associated ore. Hydrometallurgy 2016, 166, 237–242. [CrossRef] Ma, H.W.; Yang, J.; Su, S.Q.; Liu, M.T.; Zheng, H.; Wang, Y.B.; Qi, H.B.; Zhang, P.; Yao, W.G. 20 Years Advances in Preparation of Potassium Salts from Potassic Rocks: A Review. Acta Geol. Sin-Engl. 2015, 89, 2058–2071. Drits, V.A.; Zviagina, B.B. Trans-vacant and cis-vacant 2:1 layer silicates: Structural features, identification, and occurrence. Clays Clay Miner. 2009, 57, 405–415. [CrossRef] Yang, H.M.; Yang, W.G.; Hu, Y.H.; Qiu, G.Z. Kinetics analysis of thermal decomposition reaction of diaspore. Chin. J. Nonferr. Met. 2003, 55, 9750–9757. Wattanasiriwech, D.; Srijan, K.; Wattanasiriwech, S. Vitrification of illitic clay from Malaysia. Appl. Clay Sci. 2009, 43, 57–62. [CrossRef] Wang, J.X.; Zhong, X.C. The effects of potassium oxide and iron oxide additions on the phase composition of sintered bauxites (DK type). J. Chin. Ceram. Soc. 1984, 12, 77–84. He, D.S.; Feng, Q.M.; Zhang, G.F.; Long, S.S.; Ou, L.M.; Lu, Y.P. Effect of roasting on dissolution behavior of illite in acid solution. J. Cent. South Univ. 2011, 42, 1533–1537. Bibi, I.; Singh, B.; Silvester, E. Dissolution of illite in saline–acidic solutions at 25 ◦ C. Geochim. Cosmochim. Acta 2011, 75, 3237–3249. [CrossRef] Çalban, T.; Kaynarca, B.; Ku¸slu, S.; Çolak, S. Leaching kinetics of Chevreul’s salt in hydrochloric acid solutions. J. Ind. Eng. Chem. 2014, 20, 1141–1147. [CrossRef]
Minerals 2018, 8, 125
33. 34.
15 of 15
Dickinson, C.F.; Heal, G.R. Solid–liquid diffusion controlled rate equations. Thermochim. Acta 1999, 340, 89–103. [CrossRef] Lin, B.Y.; Hu, L. Raw Materials of Refractory; Metallurgical Industry Press: Beijing, China, 2015; pp. 137–166. ISBN 978-7-5024-7038-8. © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
