sodium sulfate magnetic separation

effects of sodium salts on reduction roasting and fep separation of high-phosphorus oolitic hematite ore - sciencedirect

Sodium salts react with gangues to destroy the original oolitic structure in the ore.The growth of metallic iron grains is facilitated by sodium salts during reduction.Sodium sulfate and borax improve the reduction and Fe-P separation significantly.

Effects of sodium salts on reduction roasting and FeP separation of high-phosphorus oolitic hematite ore were studied in the process of coal-based direct reduction followed by wet magnetic separation. Various parameters, including reducing temperature and time, type and dosage of sodium salts, grinding fineness of magnetic separation feed and magnetic field intensity were investigated. The results of reduction and FeP magnetic separation are significantly improved by the addition of sodium sulfate and borax, in comparison with those in the absence of additives. A magnetic concentrate with total iron grade of 92.7% and phosphorus content of 0.09% was obtained from an oolitic hematite ore containing 48.96% iron and 1.61% phosphorus when reduced in the presence of 7.5% sodium sulfate and 1.5% borax and wet magnetic separated under the proper conditions. The results of optical microscopy and X-ray diffraction (XRD) analyses of reduced pellet reveal that metallic iron grains exist in sizes of 1020m and are associated with gangue minerals closely when reduced in the absence of sodium salts. By contrast, the oolitic structure is destroyed and metallic iron grains grow markedly to the mean size of 50m when reduced in the presence of sodium sulfate and borax. Sodium salts are capable of destroying the oolitic structure via reacting with gangues, enhancing the reduction of iron oxide and promoting the growth of metallic iron grains during reduction, which is beneficial for FeP separation of the oolitic hematite ore.

reduction roastingmagnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms | springerlink

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90wt% and TiO2 content of 17.40wt%. The results show that after reduction roastingmagnetic separation with sodium sulfate dosage of 2wt% at roasting temperature of 1150C for roasting time of 120min, metallic iron concentrate with total iron grade of 90.20wt%, iron recovery rate of 97.56 % and TiO2 content of 4.85wt% is obtained and high-titanium slag with TiO2 content of 57.31wt% and TiO2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy (SEM) and X-ray diffraction (XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO2 content is obtained.

Wang MC, Huang B, Pu NW, Zhang ZY. Comprehensive utilization of vanadium slag tailings. In: Proceedings of Exchange Conference of Second Session Advanced Vanadium Industry Technology, Kunming; 2013. 72.

Saikat S, Manik CG, Tapan KB, Siddhartha M, Rajib D. Mineralogy and carbothermal reduction behaviour of vanadium-bearing titaniferous magnetite ore in Eastern India. Int J Miner Metall Mater. 2013;20(10):917.

This study was financially supported by the Fundamental Research Funds for the Central Universities (No. 2014zzts273) and the National Professional Senior Researchers and Visiting Scholar Programs (No. [2013]3018).

Sui, YL., Guo, YF., Travyanov, A.Y. et al. Reduction roastingmagnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms. Rare Met. 35, 954960 (2016). https://doi.org/10.1007/s12598-015-0616-0

beneficiation of nickeliferous laterite by reduction roasting in the presence of sodium sulfate - sciencedirect

In this paper, the reduction roasting of laterite ore in the absence or presence of sodium sulfate was carried out for nickel beneficiation by wet magnetic separation. Sodium sulfate is found to be capable of enhancing the reduction of laterite ore through liberating iron and nickel from Ni/Fe substituted-lizardite, as well as increasing the size of ferronickel particles considerably. When the laterite pellets were reduced at 1100C for 60min, the average particle size of ferronickel grains was approximately 50m in the presence of sodium sulfate, which far exceeded the size of 510m in the absence of sodium sulfate. Compared with those reduced without sodium sulfate, the Ni grade of ferronickel concentrate increased from 2.33% to 9.48%, and the magnetic separation recovery of Ni increased from 56.97% to 83.01% with the addition of 20wt.% sodium sulfate. Experimental evidence showed that troilite (FeS) serves as an activating agent to accelerate melt phase formation via a low melting point (985C) FeFeS eutectic. This markedly facilitated the aggregation of ferronickel particles during reduction, along with the selective enrichment of Ni by suppressing the complete metallization of Fe.

Reducing laterite ore in the presence of sodium sulfate, both grade and recovery of Ni in the ferronickel magnetic concentrate increase significantly. The decreasing Fe/Ni ratio in the obtained ferronickel indicates that a greater selective enrichment of Ni than Fe can be achieved with the increase of sodium sulfate dosage.Download : Download full-size image

Ni beneficiation of laterite ore by using direct reduction process is proposed. Sodium sulfate is capable of intensifying the reduction roasting of laterite. Average particle size of ferronickel grows up to 50m when reduced with Na2SO4. Selective enrichment of Ni can be realized by suppressing the metallization of Fe. New-born troilite (FeS) facilitates the aggregation of ferronickel particles.

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advanced method for recycling red mud by carbothermal solid-phase reduction using sodium sulfite | springerlink

The paper presents the results of studying the iron grain growth mechanism during carbothermal solidphase reduction of red mud in the presence of sodium sulfate. It was shown that the main mechanism of iron grain growth involves the formation of low-melting-point surface-active iron-sulfur compounds along the grain boundaries, which significantly accelerates their agglomeration process. The obtained results confirm a positive effect of the sodium sulfate additives on the process of iron grain growth during solid-phase carbothermal reduction of red mud, which makes it possible to improve the efficiency of subsequent magnetic separation.

I. Oshurkova, Bet on red, in: Rossiyskaya Gazeta Ekonomika URFO, No. 9 (7472) January 17 (2018), [Electronic Resource] URL: https://rg.ru/2018/01/17/reg-urfo/kitajcy-postroiatna-urale-zavod-po-pererabotke-opasnyh-othodov.html (access date: 07.18.2019).

E. Balomnenos, D. Kastritis, D. Panias, et al., The enexal bauxite residue treatment process: industrial scale pilot plant results, in: Light Metals, John Wiley & Sons, Inc., Hoboken, New Jersey, USA (2014), pp. 143-147.

G. S. Podgorodetskii, V. B. Gorbachev, V. V. Korovushkin, et al., Study of the red mud structure currently produced by the Ural Aluminum Plant after thermal treatment in reducing gaseous medium, Izv. Vuzov, Chern. Metallurg., No. 5, 814 (2012).

Ye. V. Shiryaeva, G. S. Podgorodetskii, T. Ya. Malysheva, et al., Effect of low-alkaline red mud on the properties and microstructure of the furnace charge agglomerate of JSC Uralskaya Stal, Izv. Vuzov, Chern. Metallurg., No. 1, 1419 (2014).

P. I. Grudinskii, V. G. Dyubanov, D. V. Zinoveev, et al., Solid-phase reduction and iron grain growth in red mud in the presence of alkali metal salts, Russian Metallurgy (Metally), No. 11, 10201026 (2018).

Z. G. Liu, T. C. Sun, X. P. Wang, et al., Generation process of FeS and its inhibition mechanism on iron mineral reduction in selective direct reduction of laterite nickel ore, Int. J. of Minerals, Metallurgy, and Materials, 22, 9, 901906 (2015).

M. Jiang, T. C. Sun, Z. G. Liu, et al., Mechanism of sodium sulfate in promoting selective reduction of nickel laterite ore during reduction roasting process, Int. J. of Mineral Processing, 123, 3238 (2013).

E. X. Gao, T. C. Sun, Z. G. Liu, et al., Effect of sodium sulfate on direct reduction of beach titanomagnetite for separation of iron and titanium, J. of Iron and Steel Research Int.,23, 5, 428433 (2016).

Grudinskii, P.I., Zinoveev, D.V., Semenov, A.F. et al. Advanced Method for Recycling Red Mud by Carbothermal Solid-Phase Reduction Using Sodium Sulfite. Metallurgist 63, 889897 (2020). https://doi.org/10.1007/s11015-020-00906-z

a novel separation method of the valuable components for activated clay production wastewater

The acidic wastewater produced by the wet production of activated clay contains valuable components such as iron and aluminum. The precipitation method was successfully introduced to separate iron and aluminum from the activated clay production wastewater step by step, which can not only recover the valuable components, but also avoid environmental pollution. In the separation process, gypsum, iron aluminum phosphate, alumina, and sodium sulfate were prepared, and the phase compositions of separation products were analyzed by XRD and IR. The main influencing factors in the separation of iron and aluminum components were studied by single factor experiment. The results show that at the optimized conditions, phosphorus/iron molar ratio 6.0, the system pH 3.0, the reaction temperature 343K, and the reaction time 90min, the iron(iii) ion in the system can form a sodium-containing aluminum iron phosphate double salt, and the filtrate after separating Fe3+ and part of Al3+ can meet the requirements for forming high-purity Al2O3. During the phosphate precipitation process, the hypothesis should be correct that Al3+ reacts with PO 4 3 to form an AlPO4 skeleton, Fe3+ isomorphically replaces Al3+ in the [AlO4] tetrahedron, and adsorption occurs simultaneously, with Na+ occupying the terminal acid sites, P(Al)OH.

Bentonite is a clay rock composed mainly of montmorillonite. Montmorillonite is a 2:1 layered silicate mineral composed of [SiO4] tetrahedral sheet and [AlO6] octahedral sheet [1], its structural formula can be expressed as (Na,Ca)0.30.6{(Al, Mg)2Si4O10(OH)2}nH2O [2,3]. Montmorillonite has many advantages, such as large specific surface area, good adsorption and cation exchange. The activated clay prepared with acid activation can be widely used in the decolorization of edible oil refining [4], sewage treatment [5], petrochemical refining and waste oil regeneration [6] and other fields. However, the wastewater generated during the acid activation process has not been reasonably separated and utilized.

Sulfuric acid [7], nitric acid [8], hydrochloric acid [9], etc. are usually used to activate bentonite for activated clay preparation. The acid activate process is divided into wet method, dry method and semi-dry method [10]. Sulphuric acid wet activation is the most important process for activated clay production. When bentonite is infiltrated in the sulfuric acid solution system, the free H+ quickly produces metal-proton exchange reaction with the interlayer cations Na+, Ca2+ of montmorillonite [11]. The octahedral cations, Al3+, Mg2+, Fe2+, etc., in the montmorillonite structure were partially dissolved out [12], which increased the negative charge of the montmorillonite structure layer and improved the adsorption decolorization performance [13]. Therefore, the acidic wastewater produced by wet process activated clay contains a certain amount of valuable components such as aluminum, iron, and magnesium. The wastwater composition is slightly different due to the raw materials and process.

In industry, the wastewater discharged in activated clay production is mainly neutralized by lime, carbide slag, etc. [14]. Although the neutralization process is simple and has good effects, there are valuable components such as aluminum and iron in the wastewater that cannot be effectively separated and utilized, and the neutralization slag is difficult to handle or use. Although the wastewater produced by the activated clay process has been used to separate valuable components to produce polyaluminum ferric sulfate, aluminum sulfate, alum, cryolite, etc. [15,16], there are still harsh reaction conditions and low product purity, and it is difficult to remove iron impurities. Compared with other chemical precipitation methods, the advantage of phosphate precipitation method is that the product is more stable under acidic conditions, and phosphoric acid, phosphate, phosphorus-containing organic matter, etc. are usually as a precipitant. The report pointed out that under strong acid conditions, Fe3+ was first used to replace Pb2+ in Pb-EDTA solution, and then disodium hydrogen phosphate was used to efficiently recover Pb2+ bearing precipitates [17]. Tang et al. [18] also combined phosphate precipitation with biological adsorption to separate the lead in the solution well. In Amrane and Bouhidel study [19], the valuable components in the acid leaching solution of sludge can be precipitated in steps effectively using different dosage of phosphoric acid.

In this article, the precipitation principle and precipitation-dissolution equilibrium of insoluble electrolyte in supersaturated state were applied. Based on the characteristics of valuable components of acid wastewater generated in the activated clay production process and the needs of production and environmental protection, the separation of iron and aluminum in the wastewater after pre-neutralization treatment was accomplished using phosphate precipitation and alkali precipitation respectively. By means of chemical composition analysis, IR and XRD analysis, the properties of separated product was studied. This paper focuses on achieving the efficient separation of valuable components such as iron and aluminum and solving the worries about the difficulty of acid wastewater handling in the activated clay production process.

The activated clay acidic raw liquid (HWW) is the wastewater generated during the sulfuric acid production process of an enterprise in Jiangxi, China. The main components and pH value of the waste liquid HWW and the solution (HWWS) after neutralization and filtering with calcium hydroxide are shown in Table 1.

The equipment used in experiment mainly includes beaker (100, 250, 1,000, 2,500mL), collector type constant temperature magnetic stirrer (Zhengzhou Yingyu Lingke Instrument Equipment Co., Ltd., China, DF-101S), circulating water type vacuum pump (Gongyi Yuhua Instrument Co., Ltd., China, SHZ-D(iii)), electric heating constant temperature oven (Shanghai Pudong Rongfeng Scientific Instrument Co., Ltd., China, 202-1), box-type resistance furnace (Mianyang Golden Crown Co., Ltd., China, KSD-6-1300), electronic balance (Yuyao JinNuo Balance instrument CO., LTD., China, JT2003), Youpu series ultrapure water machine (Chengdu Ultrapure Technology Co., Ltd., China, UPT-11-10T), digital pH meter (Shanghai Yidian Scientific Instrument Co., Ltd., China, PHS-3C).

The activated clay production wastewater mainly contains Fe3+, Al3+, SO 4 2 , H+. After neutralization for HWW, the iron and aluminum components in wastewater are separated step by step, and the separation theory is based on the metathesis reaction. During the neutralization process, calcium hydroxide interacts with the free acid in the system to produce calcium sulfate and water; when separating iron and aluminum components, it is accomplished by controlling the pH of the system, because the pH of the complete precipitation of iron phosphate is lower than that of aluminum phosphate. The iron and aluminum components can be separated in the form of double salts; Sodium hydroxide is used to produce aluminum hydroxide, which is then calcined to obtain alumina; the sodium sulfate filtrate is evaporated to crystallize. In the separation process of valuable components for HWW, the extraction of iron and aluminum components is the key. The phosphorus/iron molar ratio (nP/nFe = 5.0, 5.5, 6.0, 6.5, 7.0), reaction temperature (T = 313, 323, 333, 343, 353K), reaction time (t = 30, 60, 90, 120, 150min), system pH (pH = 1.5, 2.0, 2.5, 3.0, 3.5), etc. during the separation of iron and aluminum components were studied by single-factor experiment factors.

The separation process of valuable components for the activated clay production wastewater mainly includes: neutralization, separation of iron and aluminum components, aluminum extraction, and evaporative crystallization.

In the neutralization stage, two groups of 600mL HWW were added in a 1,000mL beaker respectively, meanwhile added an appropriate amount of calcium hydroxide (Ca(OH)2) suspension at room temperature to adjust the system pH at the final reaction to about 1.0 under stirring for 2h. After the reaction was completed, the obtained filtrate and the solution produced for washing precipitate were mixed to obtain the acidic waste liquid (HWWS) used in the experiment. The components of HWWS was showed in Table 1 and its pH was 1.08. The filter cake obtained by neutralization was washed and dried at 373K for 12h to obtain a gypsum product (HWWS-PG).

The separation process of iron and aluminum components is based on the metathesis reaction. In a 100mL beaker placed in a water bath with a set reaction temperature, 50mL HWWS and a certain amount of trisodium phosphate dodecahydrate (Na3PO412H2O) were added into at the same time, to reaction under stirring for a period of time. During reaction, the sodium hydroxide (NaOH) solution of 100gL1 was applied to adjust the system pH. When the reaction was accomplished, the reaction solution cooled was filtered, washed, and dried to obtain a solid product and a no ferric solution.

The no ferric solution was took as raw material in aluminum extraction process, which was diverted in a 250mL beaker. The 100gL1 NaOH was applied to adjust the system pH to above 5.5. After reaction 60min under stirring, the reaction solution was aged for 60min, then filtered. The no ferric and aluminum filtrate was stored for future use, the filter cake was washed with ultrapure water to neutral and dried in 378K for 2h. The dried filter cake (Al(OH)3, HWWS-AH) was transferred to a ceramic crucible and calcined at 1,273K for 120min to obtain an alumina product (Al2O3, HWWS-AO).

The no ferric and aluminum solution mainly contains sodium sulfate, which is evaporated and crystallized to obtain sodium sulfate containing crystal water. Crystalline hydrate was transferred to a 308K oven and dried for 2h to obtain sodium sulfate product (Na2SO4, HWWS-SS).

The content of iron [20] and aluminum [21] in the sample was analyzed by EDTA titration method, and the sulfate content was determined by barium sulfate gravimetric method [22]. The content of iron [23] and phosphorus [24] in the filtrate was analyzed by ultraviolet-visible spectrophotometry at 510 and 700nm respectively. The instrument (EvolutionTM 300) used was produced by Thermo Corporation of the United States. Ultrapure water was used as the reference solution.

The sample was tested by the infrared spectroscopy (Nicolet-5700) produced by Nicholi Instruments from United States, and the KBr was used for sample preparation. The scanning range is 400 to 4,000cm1.

The Xpert Pro X-ray diffractometer manufactured by PANalytical Company from Netherlands was used for XRD analysis. The test conditions as follows, Cu target, tube voltage 40kV, tube current 40mA, emission slit (DS) (1/2), Anti-scattering slit (SS) 0.04rad, receiving slit (AAS) 5.5mm, scanning step 0.03, scanning range 380, time per step 10s, continuous scanning.

The solid sate 31P NMR experiments were performed on a Bruker AVANCE NEO 400 WB spectrometer operating at 162.02MHz for 31P. A 3.2mm double resonance MAS probe was used for the experiments. The spinning rate was set to 10kHz. The 31P chemical shift was calibrated using H6NO4P = 0.81ppm for 31P.

A total of 41.7g residue (calculated as CaSO42H2O) was obtained by neutralizing from 1,200mL HWW, it is slightly lower than the theoretical value of 4.21g (100mL HWW) 1. Figure 1 is the XRD diffraction pattern of the filter residue sample (HWWS-PG) obtained after neutralization treatment for activated clay production wastewater. It can be seen that the filter residue samples are mainly calcium sulfate dihydrate (CaSO42H2O, PDF # 33-0311) and a small amount of calcium sulfate hemihydrate (CaSO40.5H2O, PDF # 41-0244).

Adding an appropriate amount of calcium hydroxide (Ca(OH)2) in HWW, the reaction (1) mainly reacted. The obtained residue quality is lower than the theoretical value mainly due to calcium sulfate dissolution, transfer loss, and the part residue contains only half of the crystal water. The main reason for the calcium sulfate hemihydrate formation is that in strong acidity systems, the calcium sulfate hemihydrate crystals are more stable, so structural adjustment reaction (2) occurred; on the other hand, during the drying process, part of the calcium sulfate dihydrate will lose crystals water to convert calcium sulfate hemihydrate [25].

Figure 2 shows the iron and phosphorus content changes in the filtrate after the separation of iron and aluminum components under different phosphorus/iron molar ratios. It can be seen from the Figure 2 that as the nP/nFe value increases, the iron ions concentration in the solution decreases linearly and the total phosphorus concentration decreases; when the nP/nFe is 6.0, the iron content in the filtrate is less than 3mgL1, while the total phosphorus content is still at a higher concentration level. In a strong acid system, PO 4 3 can quickly interact with Fe3+. Due to the presence of Al3+ and Na+, insoluble phosphate double salts containing iron, aluminum, and sodium are generated (reactions (3)(5)). When PO 4 3 is excessive, these reactions are promoted forward, which will be beneficial to Fe3+ precipitate. Therefore, by adding an appropriate excess of phosphate, the purpose of Fe3+ precipitation separation in the strong acid system can be achieved.

Figure 3 presents the content changes of iron and phosphorus in the filtrate for the iron and aluminum components separation at different reaction time conditions. With the reaction time extension, the iron and total phosphorus contents in the solution both showed a trend of decreasing first and then increasing. After reaction for 90min, the content of iron and total phosphorus in the system decreased to a relatively low level, which are respectively 4.75 and 88.3mgL1. Due to the low solubility of phosphates containing iron and aluminum, precipitates can be quickly formed during reaction, and there is also a reverse dissolution process, which gradually forms a precipitate-dissolution equilibrium; the excess PO 4 3 and Al3+ in the systemp roduced AlPO4, which has a larger solubility, its partial dissolution and desorption of the partial adsorbed PO 4 3 lead to an increase for total phosphorus content in the system. The main reason for the increase of iron content in the later period is that some iron fails to enter the aluminum phosphate structure and forms iron hydroxide. Due to the poor stability of iron hydroxide in strong acid system, it is converted into iron ions in solution.

Figure 4 is a graph showing the reaction temperature effect on the iron and aluminum components separation. As the reaction temperature continues to increase, the residual iron and phosphorus contents in the resulting filtrate rapidly decrease at 313 to 343K, and tend to be stable when it exceeds 343K. The iron concentration in filtrate can be less than 1mgL1. By increasing the reaction temperature, the iron separation effect can be significantly improved, indicating that the formation of phosphates containing iron and aluminum is easy to proceed under higher temperature conditions. The temperature increase effectively accelerates the molecular motion, which increases the effective collisions number and reaction speed. Therefore, increasing temperature has a significant positive effect on the iron and aluminum components separation.

The effect of system pH on the iron and aluminum components separation is depicted in Figure 5. It can be seen from Figure 5 that under low pH conditions, the separation effect of iron components is poor, and as the pH value increases, the separation effect is improved significantly. When the system pH is 3.0, the iron and total phosphorus concentration in the filtrate can reach to after separation 0.56 and 5.86mgL1 respectively. Therefore, the system pH 3.0 is the better operating condition for the follow-up operations. Under low pH conditions, the free H+ in the system can react with OH to generate H2O, which promotes the formation of soluble mono (di) hydrogen phosphate (reactions (6)(9)), in turn making Fe3+ unable to be separated as precipitation. By adjusting the system pH with sodium hydroxide, it can effectively inhibit the progress of the reactions (6) and (7), and promote the precipitation separation of Fe3+ and PO 4 3 as forming insoluble salts.

Based on the single-factor experiments, the iron and aluminum separation results are showed in Table 2 using optimized process conditions, phosphorus/iron molar ratio 6.0, system pH 3.0, reaction temperature 343K, reaction time 90min. It can be seen from Table 2 that under optimized operating conditions, the separation effect is outstanding and relatively stable. The average content of iron and total phosphorus in the filtrate are 0.07 and 0.85mgL1 respectively, and the average iron recovery rate (Fe) is 98.26%. During the iron component separation, the iron concentration in the filtrate after separation has a positive correlation with the total phosphorus content. The more stable the iron-containing phosphate produced in the system, the better the iron separation effect. The optimization experiment results show that it is feasible to separate iron and aluminum components in HWWS by phosphate precipitation method. The iron and total phosphorus content in the filtrate after iron removal are very low, which can meet the needs of subsequent separation to obtain high-purity products.

Figure 6 is the infrared spectrum and solid state 31P NMR spectra of iron aluminum-containing phosphate after calcination, respectively. The filter cake obtained under optimized conditions was washed using ultra-pure water and dried at 378K for 2h to obtain iron aluminum-containing phosphate products (HWWS-FP), and then the intermediate products were calcined in a 923K resistance furnace for 120min to obtain products (HWWS-FPC).

It can be seen from Figure 6a that 1,153cm1 could be ascribed to the PO bond, 1,096, 1,009, 875cm1 could be assigned to the characteristic absorption peaks of POH (Al), 661 and 600cm1 belong to the deformation vibration of OPO, which is slightly smaller than the reported value [26,27], the stretching vibration of OH in OP(OH)2 at 1,621cm1, peaks at 463cm1 belongs to the bending vibration of POAl, the value is less than 486cm1 reported in the literature. The incorporation of iron will cause the characteristic absorption peak of aluminum phosphate to move to a low wave number, because the mass and radius of Fe3+ are larger than Al3+, and the FeO bond is longer than AlO bond [28]. Peaks at 3,556 and 3,611cm1 could be assigned to Al(OH)3 [29], peaks at 1,437 and 3,455cm1 could be ascribed to carbonate and adsorbed water, respectively [30].

In Figure 7, XRD diffraction pattern of iron aluminum-containing phosphate before and after calcination were shown. The result was displayed that the uncalcined iron aluminum-containing phosphates are amorphous, and the crystallization can be ordered through calcination. Due to the presence of sodium in the separation system, the product contains a certain amount of sodium. The sample analysis result of calcinated product is consistent with the standard card of the KFeAlPO4 phase, but the characteristic diffraction peak moves to a high diffraction angle, owing to Na+ radius is less than that of K+, and the sodium isomorphically replaces potassium which causes the spacing between crystal planes to become smaller. When Al3+ reacts with PO 4 3 to produce AlPO4, Fe3+ can participate in the reaction at the same time, so that part of Al3+ is replaced by Fe3+, and the radius of Fe3+ is larger than Al3+, resulting in an increase of interplanar spacing, so the characteristic absorption peak of AlPO4 moves to the direction of low diffraction angle [32]. The detection and analysis also found that there is a small amount of metaphosphate. The main reason for its formation is that orthophosphate will hydrolyze in the solution system to form mono (di) hydrogen phosphate, which will lose water to generate metaphosphate at high temperature (reactions (6)(11)). In order to determine the compound of calcined separation product, the XRF analytical method was adopted. The result (Table 3) showed that in addition to containing phosphorus, iron, aluminum, the product also contains sulfur, sodium, potassium, calcium and silicon. However, in the XRD analysis results, no crystalline iron phosphate or sulfate was detected, so it can be speculated that iron, sodium, and potassium entered the aluminum phosphate skeleton, and the product contained sulfur due to adsorption.

The filtrate after iron and aluminum components separation under optimized conditions was used for aluminum extraction experiment. A total of about 200mL of filtrate was collected, in which the aluminum content was 2.43gL1. According to the aluminum extraction step shown in section 4.3. The total mass of aluminum oxide prepared is 1.17g, which was lower than the theoretical value of 1.84g owing to transfer loss.

Figure 8 is the XRD patterns of aluminum hydroxide and alumina products. It can be seen that the aluminum hydroxide produced by adding sodium hydroxide is amorphous (Figure 8a). After calcination, a well-crystallized alumina can be obtained (Figure 8b), mainly occurs reactions (12) and (13). Due to the good adsorption and flocculation of aluminum hydroxide [33], sodium sulfate co-precipitation occurs during the precipitation process, resulting in a small amount of sodium sulfate in the calcined product alumina (PDF # 10-0173). The high-purity alumina can be obtained by washing and drying for calcined product (Figure 8c).

The solution after aluminum extraction is about 250mL. Due to the incorporation of the solution for washing aluminum hydroxide and the loss in the operation process, the SO 4 2 concentration in the system has dropped significantly to 67gL1. The total mass of sodium sulfate product obtained by evaporation, crystallization and drying is 23.65g.

The XRD pattern of sodium sulfate obtained by evaporation and crystallization for the solution after aluminum extraction was depicted in Figure 9. The filtrate is concentrated by evaporation and cooled to crystallize for producing sodium sulfate containing crystal water (reaction (14)), Through drying, the crystal water will lost (reaction (15)). The characteristic diffraction peaks of anhydrous products completely match with the standard card (PDF # 37-1465). In figure, no other substances diffraction peaks are found, which means the product purity is high.

Owing to the solubility product of iron phosphate and aluminum phosphate are very small, about Ksp,iron phosphate = 1.3 1022 and Ksp,aluminum phosphate = 5.8 1019 respectively at 298K, so the PO 4 3 in the solution system rapidly reacts with Fe3+ and Al3+ to produce a pale yellow or white precipitate, which is sodium-containing iron aluminum phosphate. The product can be judged to be NaFeAlPO4 phase by XRD analysis,that is consistent with XRF analysis results. The solid state 31P NMR results showed that it mainly contains AlPO4, and contains PO, POH, OPO, OP(OH)2, POAl and other chemical bonds by IR analysis, but the absorption peaks of aluminum-containing chemical bonds move to a low wave number due to iron intervention. During the iron aluminum phosphate formation, aluminum phosphate is first generated. According to the Lowenstein rule [34], [PO4] and [AlO4] tetrahedrons in the aluminum phosphate skeleton are alternately connected by sharing vertex, so there is only AlOP bonding without AlOAl and POP bonds, and there is only even-numbered rings in the skeleton structure. For the macro ring, its generation needs a template agent to construct [35]. In the aluminum phosphate framework, a part of Fe3+ isomorphous replaces Al3+ in the [AlO4] tetrahedron, some are adsorbed in the pores, and there are acid sites at the end positions, like POH and AlOH, which partly occupied by Na+. Therefore, in the strongly acidic system, iron aluminum phosphate double salt mainly forms small ring compounds, as shown in Figure 10. At the same time, due to the hydrolysis of PO 4 3 , a certain amount of HPO 4 2 and H 2 PO 4 can be produced in the system. For (Al3+, Fe3+)2(HPO4)3, it is easier to hydrolyze to produce (Al, Fe)(OH)3 and H 2 PO 4 . During precipitation calcination at high temperature, (Al3+, Fe3+)(H2PO4)3 entrained will lose water and convert to (Al3+, Fe3+)(PO3)3 [36].

In this paper, based on the characteristics of strongly acidity, complex components, and difficulty in separation and comprehensive utilization for the activated clay production wastewater, and results of chemical composition analysis, the valuable components in the wastewater are separated successfully by stepwise precipitation. The influencing factors of the iron and aluminum components separation process were studied by single factor experimental method. The separation conditions were selected based on the iron and phosphorus content of target filtrate, and the phase composite of solid products in the separation process were analyzed. The main conclusions are as follows.

The phosphate precipitate produced during the iron and aluminum components separation changes from disorder to order under high temperature conditions; according to the analysis results of IR and XRD, it is conjectured that in a strongly acid sulfate system, when Al3+ reacting with PO 4 3 to form AlPO4 skeleton, Fe3+ can isomorphously replaces Al3+ in [AlO4] tetrahedron, and partly adsorbed in the pores, meanwhile, Na+ occupies the acid site at the terminal position. The molecular structure of sodium-containing iron aluminum phosphate double salt is speculated.

The precipitation method was used to successfully separate valuable components such as iron and aluminum from the acid wastewater produced by activated clay. Gypsum, sodium-containing iron aluminum phosphate, aluminum oxide, and sodium sulfate were prepared. The comprehensive utilization of wastewater and no waste production in separation process are achieved.

The operating conditions of the separation process for iron and aluminum components were investigated using the single factor experimental method. The optimized operating parameters were: phosphorus/iron molar ratio 6.0, system pH 3.0, reaction temperature 343K, and reaction time 90min. Under optimized conditions, the phosphate precipitation method can be used to effectively separate iron and produce sodium-containing iron aluminum phosphate double salts. The filtrate after iron separation can meet the requirements for the subsequent generation of high purity products.

This research was financially supported by the Programs of the National Natural Science Foundation of China (grant number 41972042); the National Key R&D Program of China (grant number 2018YFC1802902); the Scientific and Technological Innovation Team Foundation of Southwest University of Science and Technology, China (grant number 17LZXT11); the Program Projects Funded of Sichuan University of Arts and Science (grant number 2018SCL001Y); the Project of Dazhou Science and Technology Bureau (grant numbers18ZDYF0008, 19YYJC0020).

Funding information: This research was financially supported by the Programs of the National Natural Science Foundation of China (grant number 41972042); the National Key R&D Program of China (grant number 2018YFC1802902); the Scientific and Technological Innovation Team Foundation of Southwest University of Science and Technology, China (grant number 17LZXT11); the Program Projects Funded of Sichuan University of Arts and Science (grant number 2018SCL001Y); the Project of Dazhou Science and Technology Bureau (grant numbers18ZDYF0008, 19YYJC0020).

Author contributions: L. S. Zhoumethodology, experiment, characterization, writingoriginal draft preparation, T. J. Pengconceptualization, funding acquisition, project administration, supervision, writingoriginal draft preparation, H. J. Sunfunding acquisition, project administration, supervision, writingreview & editing, D. Fucharacterization, writingreviewing and editing, C. Laifunding acquisition, writingreviewing and editing.

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synthesis of new type of au-magnetic nanocomposite and application for protein separation thereof | nanoscale research letters | full text

We present a different strategy for synthesizing the Au--Fe2O3 bifunctional nanoparticle by using a larger (50nm) Au nanoparticle as the core surrounded by smaller (10nm) -Fe2O3 nanoparticles. The synthesis of the composite nanoparticles is quite facile based on a simple redox process whereby Fe2+ is used to reduce Au3+. The morphology and composition of the product is measured by transmission electron microscopy, X-ray powder diffraction and UVvis spectroscopy. We demonstrate the utility of these as-prepared Au--Fe2O3 nanoparticles by showing they can be used to separate proteins in solution. For example, bovine serum is efficiently removed from an aqueous solution with the simple addition of the NPs and application of a small magnet. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis is performed to evaluate the fidelity and efficiency of the protein separation procedure.

Nanoparticles (NPs) containing two completely different elemental compositions (i.e., bifunctional nanomaterials) enable a single particle to have physical properties vastly superior to those made solely from the individual elements. Due to their increased versatility, such bifunctional nanomaterials have enhanced potential for the development of new applications in many different areas, especially in biotechnology. For example, a single composite nanoparticle derived from gold (Au) and iron oxide nanoparticle subunits is quite versatile, having excellent surface chemistry, superior optical characteristics of gold and superparamagnetic properties of iron oxide [17].

Commonly, such Au-maghemite (-Fe2O3) bifunctional nanoparticles have a -Fe2O3 core, either a solid Au shell or smaller Au nanoparticles surrounding the core [8, 9]. We present a different strategy for synthesizing the Au--Fe2O3 bifunctional nanoparticle by using a larger (50nm) Au nanoparticle as the core surrounded by smaller (10nm) -Fe2O3 nanoparticles. The synthesis of the composite nanoparticles is quite facile based on an easy redox process whereby Fe2+ was used to reduce Au3+. One advantage of this composition is that the size of the bifunctional nanoparticle is easily tuned by changing the size of the Au nanoparticle core while still maintaining a strong magnetic response since a significant amount of magnetic material composes the single particle.

We demonstrate the utility of these as-prepared Au--Fe2O3 nanoparticles by showing they can be used to separate proteins in solution. For example, bovine serum is efficiently removed from an aqueous solution with the simple addition of the NPs and application of an external magnetic field. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) is performed to evaluate the fidelity and efficiency of the protein separation procedure.

All chemicals were purchased from Sigma-Aldrich Corporation (MO, USA) and used as received without further purification. Deionized water was used throughout. The TEM images were taken using a JEOL 2000EX transmission electron microscope (JEOL Ltd., Tokyo, Japan) at an accelerating voltage of 200 kv. The UVvis spectra were taken by Lambda 950 UVvis spectrometer (PerkinElmer, MA, USA).

In this method, magnetite nanoparticles were prepared first in water solvent by the chemical precipitation method. Then, gold precursor was added in the solution and reduced by Fe2+ which was oxidized to Fe3+. Magnetite change to maghemite and attach on gold nanoparticles (as shown in Figure 1). In a typical process, a mixture of 0.1mmol of FeCl23H2O, 0.2mmol of FeCl36H2O and 0.1mmol D-lysine in 50ml deionized water was stirred and bubbled with N2 for 30min, and then, 0.6ml of 5N ammonium was added in the mixture under N2 protection. The color of the mixture changed to black immediately while the mixture was continually stirred for another 30min and added with 2ml of 0.05M HAuCl4 aqueous solution drop by drop into the black mixture. The color changed to purple black slowly while on continuous stirring for 60min. Separated by external magnate, the liquid was almost colorless, and the paste was purple black which was washed by deionized water and separated by external magnate three times. The final product, which was purple black solution, was redispersed in deionized water for further measurement. Figure 1 shows the procedure of formation of maghemite-gold bifunctional nanomaterials. Inset photo is the final product in water, which shows the purple-black solution.

Protein separation is one of the basic applications of this kind of bifunctional nanomaterials. To use these materials for protein separation, the sample was washed several times to make sure there is no free gold nanoparticle in the solution, and bovine serum solution was added in the sample. Then, by using external magnetic separation, the sample was divided to liquid and paste, which was redispersed in water, for SDS-PAGE electrophoresis gel stained by Coomassie blue. Figure 2 shows the mechanism for protein separation by the bifunctional nanocomposite.

To compare with the bifunctional nanocomposite, gold (50nm) and magnetite (10nm) nanoparticles were synthesized and characterized separately. From TEM images and AFM image (Figure 3), the morphology of Fe3O4 (magnetite) and Au nanoparticle is shown clearly. After the addition of gold precursor to the magnetite solution, the structure of 50-nm gold nanoparticle surrounded by 10-nm maghemite nanoparticles was formed (Figure 4). Due to this kind of structure, the UV peak for gold shifted to 565nm.

The composition of the synthesized materials was identified by XRD, as shown in Figure 5. The left pattern is the data for magnetite (Fe3O4) (black line in left figure), which is before the addition of Au precursor, and the right pattern is the data for Au--Fe2O3 composite (black line in right figure). The results match the data in the 2003 JCPDS-International Centre for Diffraction Data for magnetite (890951) (red line in left figure), maghemite (895894) (blue line in right figure) and gold (893697) (red line in right figure). These results can provide two facts: first is after magnetic separation; the gold is still in the sample. Second is that magnetite was reduced to maghemite.

To test these materials for protein separation, bovine serum solution was added in the sample. Then, by using external magnetic separation, the sample was divided to liquid and paste which was redispersed in water for SDS-PAGE electrophoresis gel.

The Bradford protein assay protocol (Coomassie Blue G-250) was used as an instant method to examine for the existence of protein in those two parts of sample [10]. If a certain part contains proteins, it will turn the originally brown Coomassie Blue G-250 solution into a blue color, while the part without protein in it will leaves Coomassie Blue G-250 brown. As shown in the above photos of Figure 6, sample 1 is the original sample solution which was before the magnetic separation. It contained protein since the color of Coomassie Blue solution was turned into blue. Sample 2 is the supernatant part after magnetic separation. It contained no protein since the color of Coomassie Blue solution remained brown. Sample 3 is the solid part after magnetic separation which was redissolved in buffer. It contains proteins since it turned the solution into blue.

Bradford protein assay of the separation efficiency (top photos). SDS-PAGE analysis of the separated protein: lane 0, marker; lane 1, original protein and particle mixture solution; lane 2, supernatant part after separation; lane 3, solid part after separation, which was redissolved in buffer.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was then applied according to the literature [11]. As shown in Figure 6, compared to the marker in lane 0, the original mixture solution (as shown in lane 1) contained proteins of various molecular sizes. After magnetic separation, those proteins were removed from the solution (lane 2). For the solid sample after separation, the proteins were obtained again (lane 3), so the protein was effectively separated and collected.

We reported the synthesis of gold-maghemite nanoparticles and their use in separating proteins. The as-prepared nanocomposites combined the merits of both gold and magnetic nanoparticles, and were produced by a very easy method. Furthermore, this experiment has also suggested a new way to synthesize various bifunctional or multifunctional composite nanomaterials through simple redox process.

YS is a an MD and a pharmacist-in-charge. YS's research areas are pharmaceutics and Chinese medicine pharmacology, and is affiliated to Department of Pharmacy, Third Affiliated Hospital of Southern Medical University, Guangzhou, 510630, China. LT is an MD whose research is on pharmaceutics and Chinese medicine pharmacology, and is affiliated to the Research Division of Pharmacology, Guiyang Medical College, Guiyang, 550004, China. XS is also an MD and PI whose research areas are on nanotechnology, pharmaceutics and Chinese medicine pharmacology. XS is affiliated to the Research Division of Pharmacology, Guiyang Medical College, Guiyang, 550004, China.

Park H, Schadt MJ, Wang L, Lim S, Njoki PN, Kim SH, Jang M, Luo J, Zhong C: Fabrication of magnetic [email protected] Fe [email protected] nanoparticles for interfacial bioactivity and bio-separation. Langmuir 2007, 23(17):90509056. 10.1021/la701305f

This research is funded by the National Natural Science Foundation of China (grant no.: 30701024), Guizhou Province Special Assistant to Funding High-Level Talent (TZJF-2006-13), Guizhou International Technology Cooperation Fund (grant no.: G [2009] 700115); and the Provincial Key Technologies R&D Program of Guizhou (grant no.: S [2011] 3010).

YS carried out the synthesis, TEM and XRD measurements. LT carried out Bradford protein assay and SDSPAGE, and participated in the design of the study. XS conceived of the study, participated in its design and coordination, and drafted the manuscript. All authors read and approved the final manuscript.

Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License ( https://creativecommons.org/licenses/by/2.0 ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Song, Y., Tao, L. & Shen, X. Synthesis of new type of Au-magnetic nanocomposite and application for protein separation thereof. Nanoscale Res Lett 7, 369 (2012). https://doi.org/10.1186/1556-276X-7-369

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