赤泥水浸脱碱实验及动力学研究

赤泥是一种碱性污染物,强碱性是制约其综合利用的关键因素。进行了拜耳法赤泥水浸脱碱实验及动力学研究,实验结果表明：赤泥在水浸次数为4次、液固体积质量比为9 mL/g、反应温度为90 ℃和反应时间为60 min的条件下,赤泥的脱碱率可达71%。采用未反应收缩核模型对水浸脱碱数据进行线性拟合,动力学分析表明：活化焙烧后赤泥的水浸脱碱过程受扩散步骤控制,线性相关系数大于0.97,表观活化能为11.72 kJ/mol。     

Lithium recovery from pretreated α-spodumene residue through acid leaching at ambient temperature

A novel alkaline hydrothermal approach for low-temperature conversion of α-spodumene into Li₂SiO₃ residue was proposed, providing a promising method for extracting lithium from α-spodumene as a pretreatment process. This work proposed a systematic investigation for extracting lithium from the residue by acid leaching and preparing lithium carbonate. The reaction feasibility between Li₂SiO₃ and acids (HCl and H₂SO₄) was first evaluated through thermodynamic calculation. Compared with the leaching effects of hydrochloric acid and sulphuric acid, sulphuric acid is the preferred leaching agent due to its higher extraction efficiency for lithium and lower acid consumption. Lithium extraction efficiency from the residue achieved up to 87.48% under the following optimized conditions: 0.75 mol/L H₂SO₄, 0.4 times the theoretical amount of acid, 10 min, 30°C, and 100 rpm. Based on the optimized conditions, the lithium-containing solution was concentrated through three consecutive cycles of leaching, which obtained a concentration of 17.78 g/L for lithium. The leaching solution was purified by CaO-Na₂CO₃, resulting in the removal rates of SiO₃²⁻, Mg²⁺, and Ca²⁺ of 84.22%, 95.51%, and 90.55%, respectively. Finally, the solution was precipitated with sodium carbonate to prepare Li₂CO₃. This paper facilitates the development of an economical process for efficient lithium extraction from spodumene at low temperatures.     

钛白废酸浸出赤泥脱碱实验研究与动力学分析

依据赤泥强碱性和钛白废酸呈酸性的特点,利用钛白废酸浸出赤泥脱碱。考察了搅拌速率、液固比、浸出温度和浸出时间对赤泥脱碱效果的影响,同时对赤泥脱碱过程进行了理论分析和动力学研究。结果表明:在浸出温度为70 ℃,搅拌速率为400 r/min,液固比为5 mL/g和反应时间为60 min的条件下,赤泥脱碱率大于99%,脱碱液pH值为6.2。利用钛白废酸浸出赤泥,赤泥脱碱率高,脱碱渣中铁品位也得到了富集,可以作为提取回收铁的二次矿产资源。钛白废酸能够显著破坏赤泥中钙霞石的晶体结构,使得结构碱几乎全部溶解,脱碱渣中出现硬石膏衍射峰,赤铁矿衍射峰也可明显分辨。该脱碱过程受未反应核收缩模型(USCM)中的内扩散关键步骤控制,线性相关系数大于0.99,脱碱反应速率常数随着温度升高而增加,表观活化能(E_a)为13.12 kJ/mol。     

Removal of Organic Acids from Wine by Adsorption on Weakly Basic Ion Exchangers: Equilibria for Single and Binary Systems

Abstract

In order to remove or reduce the organic acids from wine and liqueur, we investigated their adsorption on weakly basic resins. CC-S, WA-10, and WA-30, which were made from chitosan, acryl, and styrene, respectively, appeared technically feasible. The concentration of the fixed amino group in CC-S, WA-10, and WA-30 is 3.31, 2.37, and 2.81 kmol/m³, respectively. These resins adsorbed citric acid and malic acid from wine selectively. The equilibrium isotherms for single component systems of citric acid or malic acid were little affected by the initial concentration (C ₀ = 0.01, 0.02, and 0.03 kmol/m³) and by ethanol. The equilibrium data were correlated by the Langmuir equation. The equilibrium data were correlated by the Langmuir equation. The equilibrium isotherms for the binary system of citric and malic acids were affected by the initial concentration (C _A0 = 0.02, C _B0 = 0.03 kmol/m³; C _A0 = 0.014, C _B0 = 0.004 kmol/m³). The equilibrium data were correlated reasonably well by the Markham-Benton equation. The equilibrium constants for citric acid were much larger than those for malic acid. By using these constants, the equilibrium data for adsorption of citric and malic acids from wine could be adequately correlated by the Markham-Benton equation.     

Synergies between plant antioxidant blends in preventing peroxidation reactions in model and food oil systems

A study was conducted to investigate the oxidative behavior of various mixtures of rosemary, sage, and citric acid in a linoleic acid model system by oxygen consumption measurement and in a palm olein system by differential scanning calorimetry (DSC) analysis. Response surface methodology was used to optimize the use of the mixtures. Results showed that rosemary and sage were two important factors for the protective index (PI). The two antioxidants were highly significantly (P<0.001) in influencing PI values. There was a significant (P<0.01) synergistic effect between rosemary and sage on PI values. Citric acid was also found to be significant (P<0.05) for PI. With respect to onset time (T _o ), all three antioxidants were significant (P<0.05). However, no significant interaction among antioxidants was found for T _o . Mathematical models for both PI and T _o could be developed with confidence. The R ² values for PI and T _o were 0.992 and 0.926, respectively. A combination of 0.078% rosemary, 0.067% sage and 0.037% citric acid was the optimal combination for PI, whereas a combination of 0.068% rosemary, 0.075% sage, and 0.039% citric acid was required to reach the optimal T _o value.     

Bioleaching of acid‐consuming low‐grade nickel ore with elemental sulfur addition and subsequent acid generation

The bioleaching of a nickel concentrate and an acid‐consuming nickel ore was studied using a co‐culture of Acidithiobacillus ferrooxidans and A. thiooxidans, as well as a thermophilic enrichment culture, VS2. The VS2 was dominated by a Sulfolobus species related to Sulfolobus metallicus. Nickel concentrate was readily solubilized with A. ferrooxidans and the VS2, resulting in nickel yields of 56% and 100%, respectively. Low‐grade nickel ore required 350 g H₂SO₄ kg^?1 ore for maintaining the pH of the leaching solution below 3. To overcome the high acid demand, biological elemental sulfur oxidation was combined with the ore leaching. Leaching of a 2% (wt/vol) nickel ore with a co‐culture of A. thiooxidans and A. ferrooxidans resulted in nickel yield of up to 86% with acid supplementation of 290 g H₂SO₄ kg^?1 ore. When coupled with biological sulfur oxidation, an 86% nickel recovery was achieved with 0.5% (wt/vol) ore concentration without further sulfuric acid addition. The VS2 oxidized sulfur at a rate of 0.063 g L^?1 d^?1 and the simultaneous nickel ore leaching resulted in 100% nickel yield. In summary, the potential of using elemental sulfur addition and subsequent biological acid generation to maintain the low pH during bioleaching of an acid‐consuming nickel ore was demonstrated. Copyright © 2005 Society of Chemical Industry     

Chemical structure of poly(β‐cyclodextrin‐co‐citric acid)

We synthesized water‐insoluble polymers, poly(β‐cyclodextrin‐co‐citric acid)s, by heating a mixture of citric acid, cyclodextrin (CD), and Na₂HPO₄ as a catalyst with a 6 : 1 : 2 molar ratio at 160, 170, and 180°C for 10 and 20 min. The chemical composition of the polyesters was determined by high pressure liquid chromatography (HPLC) analysis of the polymer hydrolysates. The crosslinking mechanisms and thermal degradation of the polymers were also investigated. The polyesters contained 30–35% citric acid, 1–4% unsaturated carboxylic acids (i.e., itaconic, cis‐aconitic, trans‐aconitic, and mesaconic acids), and 60–70% CD, whereas about 40% of them were able to form inclusion complexes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photocatalytic degradation of organics in water in the presence of iron oxides: Influence of carboxylic acids

The effects of four carboxylic acids: malic, citric, tartaric and oxalic acids on the leaching of iron from two commercial iron oxides (hematite, α-Fe₂O₃, and magnetite, Fe₃O₄) have been investigated. The variables studied were the doses of iron oxides and carboxylic acids used as well as aqueous pH, temperature and the presence of hydrogen peroxide and/or UV-A radiation. On the whole, Fe₃O₄ led to higher amounts of leached iron than α-Fe₂O₃, and oxalic acid was the most effective carboxylic acid used. The importance of iron leaching has been considered to explain the photodegradation of bisphenol A (BPA) by UV-A/iron oxides systems. The influence of the presence of hydrogen peroxide and/or titania on the efficiency of these oxidation systems was also investigated. At the conditions tested, advanced oxidation with the UV-A/iron oxide/oxalic acid/H₂O₂/TiO₂ system led to the lowest BPA half life (<15 min) among those processes studied.     

Preparation of Co–Mo/B2O3/Al2O3 catalysts for hydrodesulfurization: Effect of citric acid addition

The effect of citric acid (CA) addition was studied on the HDS of thiophene over Co–Mo/(B)/Al₂O₃ catalysts. The catalysts were characterized by means of LRS, Mo K-edge EXAFS, NO adsorption capacity measurements, and UV–vis spectra. The catalysts were subjected to a chemical vapor deposition (CVD) technique using Co(CO)₃NO as a precursor of Co in order to get deeper insights into the effect of citric acid addition. It was shown that the HDS activity was enhanced by the citric acid addition up to the CA/Mo mole ratio of around 1 and leveled off with further addition. The amount of Co anchored by the CVD was increased by the addition of citric acid, suggesting an increase in the dispersion of MoS₂ particles on the catalyst by the simultaneous presence of Co, Mo and citric acid, in conformity with the increase in the NO adsorption capacity. In contrast to Co–Mo catalysts, the edge dispersion of MoS₂ particles in Mo/B/Al₂O₃ was not affected by the addition of citric acid. The LRS, UV–vis spectra and Mo K-edge EXAFS showed that Co–CA and Mo–CA surface complexes are formed by the addition of citric acid. The Co–CA surface complex is more preferentially formed on CoMo/Al than on CoMo/B/Al, in agreement with a greater promoting effect of citric acid at a lower CA/Mo mole ratio for CoMo/Al than for CoMo/B/Al.     

Removal of citric acid from aqueous solution by catalytic wet peroxidation using effective mesoporous Fe‐MCM‐41 molecular sieves

The presence of citric acid in decontamination waste can cause complexation of radioactive cations, resulting in interferences in their removal by various treatment processes such as chemical precipitation and ion exchange, and may pose a potential danger to the environment. Mesoporous Fe‐MCM‐41 molecular sieves (Si/Fe = 25, 50, 75 and 100) were synthesized hydrothermally and characterized by X‐ray diffraction, N₂ adsorption studies, diffuse reflectance UV‐visible spectroscopy, electron paramagnetic resonance and transmission electron microscopy to evaluate the removal of citric acid from aqueous solution by the wet peroxidation method. The effect of time, pH, Si/Fe ratios of Fe‐MCM‐41 and temperature has been studied to achieve efficient removal of citric acid from the aqueous solution. Unlike homogeneous Fe³⁺ catalysis, more mineralization of citric acid was achieved by heterogeneous catalysis with Fe‐MCM‐41 with the percentage removal of total organic carbon of citric acid following the order Fe‐MCM‐41 (Si/Fe = 25) > Fe‐MCM‐41 (Si/Fe = 50) > Fe‐MCM‐41 (Si/Fe = 75) > Fe‐MCM‐41 (Si/Al = 100). Moreover, it was also observed that during the reaction only a minimum amount of iron is leaching from Fe‐MCM‐41. Copyright © 2007 Society of Chemical Industry     

Porous phosphatic materials of agronomical interest:Synthesis and study of their dissolution

Phosphatic materials of agronomic interest were synthesised. These materials of good mechanical quality and of significant porosity show high P₂O₅ contents (up to 28%). They have been prepared by treatment of volcanic pumices with a solution of phosphoric acid (1N, 5N or 10N) at 200°C in a closed system for 72h using a mass solid/liquid ratio of 1:3.After reaction, the precipitation of amorphous phosphates and crystalline aluminium phosphates has been detected by XRD both outside and inside of the material. The morphological study by SEM reveals several crystalline forms of aluminium phosphates: crystals of small size migrate into the internal porosity of the pumices and crystals of berlinite appear (AlPO₄) well developed in a matrix of amorphous phosphate overlapping the initial material.Normal tests of reactivity in water and in 2% citric acid show that the percentages of released P₂O₅ in solution are greater after treatment with weak concentrations of phosphoric acid. Lixiviation of treated materials with citric acid reagent shows that, after three days of reaction, losses in weight are considerable and the kinetic curves of phosphorus liberation present a linear evolution.The fertilizing value of these materials did not decrease during the leaching; so phosphorus will be solubilized with time thus allowing these materials to gain a good agronomical availability and to propose their use as delayed fertilizer types for tropical agricultural soils.     

混酸提纯制备高纯石英砂及浸出动力学分析

以江苏省东海县石英砂为原料,盐酸、草酸及柠檬酸为浸出剂,混酸浸出法制备高纯石英砂,研究了酸液浓度、液固质量比、酸浸温度和酸浸时间对石英砂物相结构及提纯效果的影响,推导了盐酸、草酸及柠檬酸混酸浸出石英砂的动力学模型.结果表明:酸液浓度、液固质量比、酸浸温度及酸浸时间均对酸浸除杂效率有明显影响,混酸浸出符合扩散控制模型,E...     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

赤泥脱碱方法及其机理研究进展

赤泥是氧化铝生产过程中产生的强碱性废弃物,其强碱性是制约自身大规模综合利用的重要因素。因此十分有必要对赤泥进行脱碱,以期实现赤泥的综合利用,保障铝工业可持续发展。论文综述了国内外赤泥脱碱方法,如水洗法、酸浸法、石灰法、盐类浸出法、CO₂法、生物法等;同时从自由碱和化学结合碱的角度分析了各种脱碱方法的特点及主要脱碱机理,总结出赤泥脱碱的原理主要是中和反应、沉淀反应及钠置换反应。最后剖析了各种脱碱方法存在的问题,并对赤泥脱碱的研究提出了建议,这将为赤泥脱碱技术的进步以及赤泥的综合利用提供参考。     

Equilibria,Kinetics, and Modeling of Extraction of Citric Acid from Aqueous Solutions with Alamine 336 in 1-Octanol

Experimental equilibrium and kinetic data on the extraction of citric acid from aqueous solutions using Alamine 336 in 1-octanol have been determined. The distribution coefficient has increased from 0.029 to 71.727 with increase of Alamine 336 concentration from 0 to 30% (v/v). The chemical equilibria was interpreted as a result of consecutive formation of acid-amine species with 1:1 stoichiometry and the equilibrium complexation constant, K _E1 , has been estimated as 20.186 m³ kmol^?1. The mass-transfer coefficients of citric acid, Alamine 336, and 1:1 acid-alamine complex in 1-octanol were calculated from acetic acid mass-transfer coefficient, which was determined by measuring its fluxes of simple diffusion from kerosene to water. Based on the Hatta number and the criterion given by Doraiswamy and Sharma, the reaction regime has been found to be instantaneous reaction regime occurring at the interface on the organic phase side. An extraction model comprising 1:1 equilibrium complextion constant, K _E1 , and complex mass-transfer coefficient, k _BA (3.79 × 10^?6 m s^?1), has been developed, and it explained the present system satisfactorily.     

Effect of fuel type on structural and physicochemical properties of solution combustion synthesized CoCr2O4 ceramic pigment nanoparticles

Due to importance and wide applications, CoCr₂O₄ ceramic pigment nanoparticles were synthesized via low-temperature solution combustion route by different fuels including ethylenediamine/oxalic acid, ethylenediamine/citric acid, oxalic acid/citric acid and ethylenediamine/oxalic acid/citric acid. Physicochemical properties of the synthesized samples were determined by different techniques such as fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX) and color/optical properties were evaluated based on CIELAB system by spectrophotometer. Moreover, thermodynamic considerations of combustion reactions for CoCr₂O₄ nanopigments formation in terms of calculated adiabatic flame temperature and enthalpy of combustion reaction were studied. The Comparison of results and data showed that cobalt chromite pigment nanoparticles synthesized by using ethylenediamine/citric acid and ethylenediamine/oxalic acid/citric acid fuels exhibited higher purity, smaller crystallite size and lower degree agglomeration.     

Electrochemical and surface properties of aluminium in citric acid solutions

The electrochemical and surface properties of aluminium in 0.05 M citric acid solutions of pH 2–8 were studied by means of open circuit potential (OCP), potentiodynamic polarization and potentiostatic current–time transient measurements. The OCP reached a steady-state value very slowly, probably due to the slow rate of detachment of surface complexes into the solution. Aluminium exhibits passive behaviour in citric acid solutions of pH 4–8. Tafel slopes b _c were characteristic for hydrogen evolution on aluminium covered by an oxide film. The corrosion kinetic parameters E _corr, i _corr and b _a suggest that surface processes are involved in the dissolution kinetics, especially in the pH range 3–6. Current–time transient measurements confirm that, in citric acid solutions of pH 3–6, the dissolution is controlled by surface processes, that is, by the rate of detachment of surface complexes, while in solutions of pH 2, 7 and 8 dissolution is under mass-transport control. The addition of fluoride ions to citric acid changes the controlling steps of the dissolution process. Citrate and fluoride ions compete for adsorption sites at the oxide surface, and adsorption of these ions is a competitive and reversible adsorption.     

湿化学法回收污泥水热炭中磷的潜能研究

以富含磷的污泥水热炭为研究对象,用SMT法分析磷的形态分布,以盐酸和柠檬酸为浸提剂,探究湿化学法回收磷的潜能。结果表明,污泥经水热碳化后,总磷含量上升,有机磷朝着无机磷转化,非磷灰石无机磷朝着磷灰石无机磷转化,水热炭中磷形态以无机磷和非磷灰石磷为主。适宜酸浸条件下（盐酸浓度0.3 mol/L、液固比50 ml/g、酸浸时间240 min,柠檬酸浓度0.1 mol/L、液固比50 ml/g、酸浸时间600 min）,盐酸和柠檬酸对磷的浸出效率分别可达94.34%、88.78%,准二级动力学模型能较好地拟合磷的浸出过程;同时,金属浸出能力随酸浸时间延长而逐渐上升,与磷浸出能力呈线性相关,由大到小依次为Fe>Ca>Al>Mg;重金属浸出能力由大到小依次为Zn>Mn>Cr>Cu>Pb;酸浸残渣有望成为性能良好的吸附材料。     

钙基水热浸出赤泥脱碱试验及机制分析

以Ca(OH)₂为脱碱剂水热浸出赤泥脱碱,考察了Ca(OH)₂掺量、反应温度、液固比对赤泥脱碱率的影响,同时对赤泥脱碱过程进行机理分析和浸出动力学分析。研究结果表明,在Ca(OH)₂掺量为60%(质量分数)、反应温度为250 ℃、液固比为8 mL/g的条件下,赤泥脱碱率可达到96.3%。Ca(OH)₂可有效脱除赤泥中的游离碱和结构碱,赤泥中的钙霞石和水钙铝榴石被分解,脱碱渣中新相铁钙榴石(水合的)是主要的衍射峰,并且赤铁矿的衍射峰明显减弱,方解石的衍射峰增强。该脱碱过程受固膜内扩散关键步骤控制,线性相关系数都大于0.97,特征常数n<1,表观活化能为5.20 kJ/mol。     

一步法回收和再生废旧钴酸锂电池中的钴酸锂

采用酸浸法和溶胶-凝胶法耦合的一步法技术路线回收和再生LiCoO₂，简化了流程。先使用柠檬酸浸出正极材料中的Co和Li元素，然后采用溶胶-凝胶法从浸出液中直接再生LiCoO₂，柠檬酸在过程中起到了浸出剂和螯合剂的双重作用，简化了回收和再生流程。摸索了柠檬酸浓度、固液比、浸出温度、H₂O₂体积浓度和浸出时间对Co和Li浸出效率的影响规律，探究了煅烧温度对再生钴酸锂结构组成、颗粒形貌以及电化学性能的影响规律。结果表明，最佳浸出条件为：柠檬酸浓度为1.5mol/L，固液比为20g/L，浸出温度为80℃，H₂O₂体积分数为2%，浸出时间为60min。在此条件下，Co和Li的浸出率分别达到93.7%、98.2%。通过电化学分析表明，在700℃下煅烧得到的再生LiCoO₂电化学性能最佳，在1C下经50次循环后可逆放电比容量为118.7mA·h/g，容量保持率为93%。