Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process

Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.

Transformation of hematite in diasporic bauxite during reductive Bayer digestion and recovery of iron

The reductive Bayer digestion by using iron powder as reductant is proposed to convert hematite to magnetite and further to dissociate iron minerals from sodium aluminosilicate hydrate(desilication product,DSP)based on the differences of their surface properties.The results show that the differences of surface properties between magnetite and DSP in zeta potential,wettability and solvation trend facilitate magnetite to agglomerate,grow up and thus to dissociate from DSP.The increments of reductant amount and alkali concentration favor the transformation of hematite in digestion with the relative alumina recovery of98.91%.Processing the resultant red mud can obtain qualified iron concentrate with iron grade of approximate60%and recovery of about86%through magnetic separation,resulting in reduction of red mud emission higher than70%.The results are potential to develop a novel technology for processing high iron diasporic bauxite efficiently and provide references for comprehensive utilization of high iron red mud.

Comparison of the effects of Ti-and Si-containing minerals on goethite transformation in the Bayer digestion of goethitic bauxite

Goethitic bauxite is a widely used raw material in the alumina industry.It is an essential prerequisite to clarify the effect of Ti-and Si-containing minerals on goethite transformation in the Bayer digestion process,which could efficiently utilize the Fe-and Al-containing minerals present in goethitic bauxite.In this work,the interactions between anatase or kaolinite with goethite during various Bayer digestion processes were investigated using X-ray diffraction (XRD),X-ray photoelectron spectroscopy (XPS),transmission electron microscopy (TEM),and scanning electron microscopy (SEM).The results showed that anatase and kaolinite hindered the transformation of goethite.Anatase exerted more significant effects than kaolinite due to the dense sodium titanate layer on the goethite surface after reacting with the sodium aluminate solution.Adding the reductant hydrazine hydrate could eliminate the retarding effect by inducing the transformation of goethite into magnetite.In this process,titanium was embedded into the magnetite lattice to form Ti-containing magnetite.Furthermore,the weakening of the interaction between magnetite and sodium aluminosilicate hydrate reduced the influence of kaolinite.As a validation of the above results,the reductive Bayer method resulted in the transformation of goethite into goethitic bauxite with 98.87% relative alumina digestion rate.The obtained red mud with 72.99wt% Fe2O3could be further utilized in the steel industry.This work provides a clear understanding of the transformative effects of Ti-and Si-containing minerals on iron mineral transformation and aids the comprehensive use of iron and aluminum in goethitic bauxite subjected to the reductive Bayer method.

CONTROL TECHNIQUES FOR DIGESTION IN BAYER PROCESS

The control techniques for indirect heating digestion in Bayer process of alumina production were researched and developed. They include controlling chemical composition of slurry to be digested and controlling digestion status and energy consumption. Very good performances and technical and technical and economical figures for digestion process have been obtained by carefully applying these comprehensive control techniques in Pingguo alumina refinery.

Behavior of silicon-containing minerals during Bayer digestion

Digestion behaviors of several single silicon-containing minerals including kaolinite, illite and pyrophyllite in aluminate solution were investigated. The result shows that the digestion rates of kaolinite, illite and pyrophyllite in aluminate solution were influenced by reaction conditions such as temperature. Adopting quantum chemistry theoretical calculation, using CASTEM procedure module, the slab model of kaolinite, illite, pyrophyllite and their ordinary complete cleavage plane (001) were geometry optimized at GGA-PW91 level. The micro-essence of the different reaction activities among kaolinite, illite, pyrophyllite in aluminate solution was opened out. It is found that the reaction activities of kaolinite, illite, pyrophyllite are obviously different and the reaction activity of pyrophyllite is the highest. The Si—O bond strength of illite is the strongest and its Al—O bond strength is comparatively the weakest, so Si in it is the most difficult to be removed. The Si—O bond strength of pyrophyllite is the weakest, so Si in it is relatively easy to be removed. The micro-electron structure of complete cleavage plane and the Si—O bond strength of kaolinite, illite and pyrophyllite are evidently influenced by the existence of OH-, of which the surface character and the reduction of Si—O bond strength of kaolinite are influenced most greatly by OH-. Therefore, the desilication of kaolinite in alkaline solution at relatively low temperature is easier.

Enhanced conversion mechanism of Al-goethite in gibbsitic bauxite under reductive Bayer digestion process

The conversion mechanism of Al-goethite under the action of different additives(lime or reductant for typical or reductive Bayer digestion)was investigated by thermodynamic calculation,XRD,and SEM-EDS.The results show that the formation of Fe-substituted hydrocalumite is crucial to converting Al-goethite to hematite during Bayer digestion by adding lime.However,the conversion proceeds more easily under the action of reductant due to the rapid formation of magnetite.Additionally,Bayer liquor composition significantly affects the product composition and also the conversion rate of Al-goethite.Compared to typical Bayer digestion with Al-goethite containing gibbsitic bauxite as raw material,the red mud yield of reductive Bayer digestion decreases from 39.02%to 31.19%,and the grade of TFe in red mud increases from 41.66%to 53.80%.

Effect of wall-disruption on nutrient composition and in vitro digestion of camellia and lotus bee pollens

The nutrient digestion,absorption and biological activity of bee pollen may be limited due to the complex pollen wall.Here,the effect of superfine grinding technology on the release of nutrients from bee pollen were investigated,and their antioxidant activities and in vitro digestion were explored in this study.Results showed that the content of nutrients in bee pollen increased after wall disruption.Among them,fat content increased by 22.55%-8.31%,protein content increased by 0.54%-4.91%,starch content increased by 36.31%-48.64%,soluble sugar content increased by 20.57%-29.67%,total phenolic acid content increased by 11.73%-86.98%and total flavonoids content increased by 14.29%-24.79%.At the same time,the antioxidant activity increased by 14.84%-46.00%.Furthermore,the active components such as phenolic compounds in the wall-disruption bee pollen were more readily to be released during the in vitro digestion,and easier to be absorbed because of their higher bioaccessibility.Antioxidant activities during in vitro digestion were also improved in walldisruption bee pollen.These findings provide evidence that bee pollen wall disruption was suggested,thus,it is more conducive to exerting the value of bee pollen in functional foods.

Adsorption,in vitro digestion and human gut microbiota regulation characteristics of three Poria cocos polysaccharides

Poria cocos(PC)is a famous traditional Chinese medicine(TCM)and a widely used healthcare ingredient,which has antiobesity,enhancing immunity and improving sleep effects.Traditionally,only water-soluble poria polysaccharide(WSP)is extracted and applied for clinical application,while insoluble polysaccharide(alkali-soluble poria polysaccharide,ASP)is discarded as herb residue.However,the whole PC has also been historically utilized as functional herbal food.Considering the beneficial role of dietary fiber and the traditional use of PC,ASP may also contribute substantially to the therapy function of PC.Compared to WSP,little attention has been paid to ASP and ASP modified product carboxymethyl poria polysaccharide(CMP)which has been used as an antitumor adjuvant drug.In this study,the oil,cholesterol,metal ions and polyphenols adsorption ability,in vitro simulated digestive and the gut microbiota fermentation characteristics of WSP,ASP and CMP were studied to evaluate the functional values of three P.cocos polysaccharides(PCPs).The results showed that all three PCPs had good adsorption capacity on cholesterol,polyphenols and metal ions(Cd^(2+)/Zn^(2+)/Mg^(2+)),among which ASP showed the highest capacity than WSP and CMP.The adsorption capacity of all three PCPs on heavy metal ions(Cd^(2+)/Zn^(2+))was stronger than that of non-heavy metal ions(Mg^(2+));The in vitro digestibility of all three PCPs was very low,but WSP was slightly higher than ASP and CMP;Moreover,the indigestible residue of all three PCPs could improve the richness and diversity of gut microbiota,among which ASP had the greatest influence.In general,ASP and CMP could significantly promote the proliferation of some probiotics and inhibit the growth of some harmful bacteria.The gut microbiota diversity of CMP was reduced,but the richness of probiotics,especially Parabacteroides distasonis was significantly enhanced compared with the ASP group,and the growth of harmful bacteria Klebsiella pneumoniae was inhibited after CMP treatment.The short-chain fatty acids(SCFAs)analysis results showed that all three PCPs could significantly promote the production of acetic acid,propionic acid and the total acid content compared with blank control group,and SCFAs producing activity was positively correlated with the proliferative capacity of probiotics.Taken together,the good adsorption characteristics and gut microbiota regulatory activity of ASP may lay foundation for its lipid-lowering and immune-improving function.Additionally,the probiotic effect of CMP and ASP indicated that except for only use the water extract of PC in clinic,CMP and ASP also can be used in healthcare to take full advantage of this valuable medicine.

Effect of simulated gastrointestinal digestion on antioxidant,and anti-inflammatory activities of bioactive peptides generated in sausages fermented with Staphylococcus simulans QB7

Dry-fermented sausages are a good source of bioactive peptides,whose stability against gastrointestinal(GI)digestion determines their bioaccessibility.This study focused on evaluating the effect of peptide extracts from sausages fermented with Staphylococcus simulans QB7 during in vitro simulated GI digestion,including peptide profiles and antioxidant and anti-inflammatory activities.Peptides present in sausages were degraded during digestion,with molecular weight reduced from>12 kDa to<1.5 kDa.Besides,the content of amino acids increased from 381.15 to 527.07 mg/g,especially tyrosine being found only after GI digestion.The anti-inflammatory activities were increased after GI digestion,however,the changes in antioxidant activities were the opposite.A total number of 255,252 and 386 peptide sequences were identified in undigested,peptic-digested and GI-digested samples,respectively.PeptideRanker,BIOPEP-UWM and admetSAR were used to further predict the functional properties and intestinal absorption of the identified peptide sequences from GI digestion.Finally,18 peptides were discovered to possess either antioxidant or anti-inflammatory capacities.

Investigation into IgG/IgE binding capacity and gut microbiota of digestion products derived from glycated ovalbumin

Gut microbiota plays an important role in food allergy.The immunoglobulin G(IgG)/immunoglobulin E(IgE)binding capacity and human gut microbiota changes of digestion products derived from glycated ovalbumin(OVA)were investigated.Gastrointestinal digestion effectively destroyed the primary structure of glycated OVA,resulting in a significantly higher digestibility than gastric digestion,and more abundant peptides<3 kDa.Moreover,gastric and gastrointestinal digestion products have different fluorescence quenching and red shift of fluorescence peaks,and possess different conformational structures.These changes resulted in a decrease in 28.7%of the IgE binding capacity of gastrointestinal digestion products beyond that of pepsin.Moreover,gastrointestinal digestion products of glycated OVA increased significantly the proportion of Subdoligranulum,Collinsella,and Bifidobacterium.Therefore,gastrointestinal digestion products of glycated OVA altered human intestinal microbiota,reducing the risk of potential allergy.

The in vitro digestion fates of diacylglycerol under different intestinal conditions:a potential lipid source for lipid indigestion patients

The in vitro digestion models mimicking the gastrointestinal(GI)tract of general population and lipid indigestion patients(with lower levels of bile salts or pancreatic lipase)were selected to investigate whether diacylglycerols(DAGs)are potential good lipid sources for these patients.Linseed oil-based DAG(LD)and linseed oil(LT)were selected.LD-based emulsion((83.74±1.23)%)had higher lipolysis degree than LT-based emulsion((74.47±1.16)%)when monitoring the GI tract of normal population as previously reported.Indigestion conditions seriously decreased the digestive degree of LT-based emulsion((40.23±2.48)%-(66.50±3.70)%)while showed less influence on LD-based emulsion((64.18±2.41)%-(81.85±3.45)%).As opposed to LT-based emulsion,LD-based emulsion exhibited preference for releasing unsaturated fatty acids(especially oleic acid andα-linolenic acid)due to their different glycerolipid compositions.LD-based emulsion showed potential for providing lipids and nutrients(including essential fatty acids)for lipid indigestion patients.

Insights into sensitizing and eliciting capacity of gastric and gastrointestinal digestion products of shrimp(Penaeus vannamei)proteins in BALB/c mice

Shrimp(Penaeus vannamei)proteins have been shown an allergenic potential;however,little information is available on the sensitizing and eliciting capacity of shrimp protein digestion products.In this study,a BALB/c mice model was used to explore the allergenicity of shrimp protein sample(SPS)and their gastric and gastrointestinal digestion products(GDS/GIDS).As compared with the SPS groups,the GDS/GIDS groups caused lower specific immunoglobulins(Ig E/Ig G1)levels(P<0.05),but higher than the control groups,indicating that the digestion products sensitized the mice.Meanwhile,spleen index,mouse mast cell protease-1(m MCP-1)concentration and proportion of degranulated mast cells were significantly reduced in the GDS/GIDS groups(P<0.05);simultaneously,allergic symptoms,vascular permeability and histopathological changes of tissues were alleviated.Nevertheless,the allergenicity of digestion products cannot be eliminated and still cause systemic allergic reactions in mice.The study showed that the digestion products of shrimp still had high sensitizing and eliciting capacity.

Simultaneous determination of typical toxic aldehydes formed during food frying and digestion using isotope dilution UHPLC-QqQ-MS/MS

An isotope dilution ultra-performance liquid chromatography-triple quadrupole mass spectrometry method was developed to simultaneously detect two typical kinds ofα,β-unsaturated aldehydes,namely 4-hydroxy-2-hexenal(4-HHE)and 4-hydroxy-2-nonenal(4-HNE),in foods.The proposed method exhibited a linear range of 10-1000 ng/mL with a limit of detection of 0.1-2.0 ng/g and a limit of quantification of 0.3-5.0 ng/g.The recovery rates of these typical toxic aldehydes(i.e.,4-HHE,4-HNE)and their d3-labeled analogues were 91.54%-105.12%with a low matrix effect.Furthermore,this proposed method was successfully applied to a real frying system and a simulated digestion system,wherein the contents of 4-HHE and 4-HNE were determined for both.Overall,the obtained results provide strong support for further research into the production of 4-HHE and 4-HNE resulting from foods during oil digestion and frying.

Changes in Polyphenols and Antioxidant Activities of Yingshan Yunwu Tea during Digestion in Vitro

[Objectives]To explore the change rule of polyphenol content and antioxidant activity of coarse old leaves of Yingshan Yunwu Tea in the process of human digestion.[Methods]The coarse and old leaves of Yunwu tea in Yingshan,Huanggang,Hubei Province were selected as the research object,and their digestion in vitro was simulated.The total polyphenol content was determined by Folin-phenol reagent colorimetric method,and the DPPH radical scavenging activity and total antioxidant activity were determined.[Results]After simulated gastrointestinal digestion in vitro,the polyphenol content and antioxidant activity of coarse old leaf tea soup showed a downward trend.After gastrointestinal digestion,the polyphenol content in tea infusion separately decreased by 31.8%and 8.5%;the scavenging rate of DPPH free radical was 97%before digestion,decreased to 92%after gastric digestion and 65%after intestinal digestion,which decreased by 5%and 27%,respectively;after gastrointestinal digestion,the total antioxidant capacity of tea soup decreased by 4.7%and 3.1%,respectively.[Conclusions]This study provided a reference for the development and application of coarse old leaves of Yingshan Yunwu tea,and provided a reference for the nutritional value evaluation and comprehensive utilization of coarse old leaves,so as to make the best use of coarse tea leaves and reduce the waste of resources.

Bayer图像色彩还原线性插值方法

基于Bayer模板的单CCD相机通过彩色滤波阵列采集图像数据,图像中的每个像素只有红、绿、蓝3种颜色分量中的一种,为提高图像分辨率,获取高质量的彩色图像,需要通过色彩还原方法恢复另外两种颜色分量。线性插值方法算法简单、运算速度快,在数字图像色彩还原中经常采用。文章结合Bayer模板结构特点,介绍目前常用的3种色彩还原插值算法,包括基于像素复制法、双线性插值法和高质量插值法,分析和讨论了这些算法的思路和性能特点。通过样本图像色彩还原对比实验,对各种算法进行了图像质量和处理速度性能比较,结果表明,高质量插值法还原图像细节丰富,具有最佳的色彩还原性能。文中最后对色彩还原技术的未来发展趋势进行了展望。

基于Bayer滤波的彩色面阵CCD调制传递函数

介绍了基于Bayer滤波获取彩色图像的方法。根据CCD离散采样的工作特点,构建了采用Bayer滤波的彩色面阵CCD的调制传递函数(MTF)。通过数值计算和实验对基于Bayer滤波的彩色面阵CCD和单色面阵CCD的MTF值进行了对比分析。结果表明,基于Bayer滤波的彩色面阵CCD的MTF值显著低于单色面阵CCD的MTF值。当像元边长与对应中心距相等时,基于Bayer滤波的彩色面阵CCD在Nyquist频率处的MTF为0.067 6,单色面阵CCD在Nyquist频率处的MTF值为0.405 3;分辨率板成像实验表明,相同成像条件下,前者的分辨率比后者的分辨率降低约40%,基本符合MTF对比分析结论。

应用字典学习算法改善Bayer格式图像彩色恢复效果

利用单片探测器获取彩色图像,插值算法的优劣对结果起着决定性的作用。为了改善恢复效果,该文设计了一种基于字典学习的非线性Bayer格式图像彩色插值算法。根据图像梯度的变化,首先,在上下左右方向利用局部方向插值方法(LDI)对Bayer格式图像进行合并计算,用高斯混合模型(GMM)分类法训练字典,运用主分量分析(PCA)方法提取训练结果中的主要分量为学习提供样本,通过学习,得到R,B通道缺失的G分量。然后,应用G分量,插值得到另外两种缺失分量R和B,从而得到彩色图像。选取McMaster图像集作为字典,分别用算法对标准图像和使用DALSA公司彩色CMOS探测器开发的相机实际拍摄的图像进行插值恢复,较其它几种算法,视觉上伪彩色最少,峰值信噪比最优。整体性能优于现有的很多其它插值算法。

视频卫星影像的Bayer插值重建

视频卫星在成像过程中一般采用Bayer模板,地面处理时需要通过Bayer插值处理才可恢复全彩色的影像。针对视频卫星影像Bayer插值重建中容易出现拉链、噪点和边缘伪彩色等问题,提出一种改进的基于亮度、色度信号重建的滤波方法。首先,通过24张标准柯达影像训练得出Bayer插值重建的带通滤波器;其次,通过带通滤波器提取色度信号,并根据Bayer模型获取初始的重建结果;然后,在绿色空间中,利用梯度信息进行均值区域判断,并在均值和非均值区域中分别进行边缘方向插值和色差域中值滤波更新,有效减少均值区域的插值拉链和噪点现象;最后,在新的色差域中进行红光、蓝光波段的导向插值和中值滤波更新,进一步提升插值精度。采用吉林一号01星和03星的4幅视频影像数据验证本文方法的有效性,结果表明与2种经典的Bayer插值方法相比,提出的改进方法在定性和定量评价上均最优,影像边缘更加锐利、清晰,无明显噪点和伪彩色现象,可用于卫星视频数据的后续处理和应用。

低复杂度Bayer图像色彩重建算法

针对Bayer图像色彩重建效果越好的算法需要越多计算量,占用越多硬件资源问题,提出了一种低复杂度的色彩重建算法。首先使用Hamilton-Adam(H-A)算法对Bayer图像进行预插值并求出色差通道,接着通过求出5×5模板内判断插值方向的综合梯度因子,重新更新G通道缺失像元值,最后利用已重建的G通道求出缺失的R和B通道颜色。柯达测试图仿真结果表明,相对于其他算法,所提出的算法在PSNR上有较大优势;相机输出图像的色彩重建结果表明,本文算法在判断插值方向上的准确率更高;可抑制其他算法插值后出现的斑点现象,图像边缘清晰、完整。平均每个像元,本文算法只需要56次算数运算,不需要乘法和除法运算,减轻了FPGA算法实现中IP核的负担,易于硬件实现,完全满足项目需要。

一种改进的Bayer图像彩色恢复差值算法

图像传感器采集到的都是经过滤波镜.片后的Bayer格式马赛克图像,为了恢复丢失掉的色彩信息,必须经过插值计算。针对图像采集系统处理的实时性要求,结合自适应插值法和三角函数法则,提出了一种适用于硬件实现的新算法。给出对算法性能的评估数据和MATLAB仿真图片,对比了算法的处理效果,最后基于实际应用的需求对该算法的硬件实现难度进行了分析。实验结果证明,改进算法在图像边缘的处理上效果更好,基于硬件的实现方式也能保证系统的实时性。