IN SITU LEACHING OF URANIUM USING DILUTE SULFURIC ACID AND MOLECULAR OXYGEN

The technical feasibility of in situ uranium leaching using dilute sulfuric acid and molecular oxygen has been assessed and the important process parameters examined by use of laboratory high pressure leaching columns.

The dilute H₂SO₄/O₂ lixiviant was effective in leaching uranium from the ore samples tested. The leaching process was chemical reaction rate limited and can be represented using pseudo first-order kinetics. The leaching rate constant is proportional to the proton concentration of the lixiviant.

Much of the uranium was leached from the ore before decomposition of carbonate minerals by the acid was complete. Acid consumption per pound of U₃O₈ increased sharply as the uranium recovery level exceeded 70%. There appears to be a minimum oxygen pressure for effective uranium leaching. A pressure of 2758 KPa was adequate for the ore samples tested     

Oxidative leaching kinetics of molybdenum-uranium ore in H2SO4 using H2O2 as an oxidizing agent

The processing of molybdenum-uranium ore in a sulfuric acid solution using hydrogen peroxide as an oxidant has been investigated. The leaching temperature, hydrogen peroxide concentration, sulfuric acid concentration, leaching time, particle size, liquid-to-solid ratio and agitation speed all have significant effects on the process. The optimum process operating parameters were: temperature: 95°C; H₂O₂ concentration: 0.5 M; sulfuric acid concentration: 2.5 M; time: 2 h; particle size: 74 μm, liquid-to-solid ratio: 14 ∶ 1 and agitation speed: 600 rpm. Under these experimental conditions, the extraction efficiency of molybdenum was about 98.4%, and the uranium extraction efficiency was about 98.7%. The leaching kinetics of molybdenum showed that the reaction rate of the leaching process is controlled by the chemical reaction at the particle surface. The leaching process follows the kinetic model 1 ? (1?X)^1/3 = kt with an apparent activation energy of 40.40 kJ/mole. The temperature, concentrations of H₂O₂ and H₂SO₄ and the mesh size are the main factors that influence the leaching rate. The reaction order in H₂SO₄ was 1.0012 and in H₂O₂ it was 1.2544.     

硫酸-糖蜜酒精废液浸出软锰矿的动力学(英文)

The kinetics of reductive leaching of manganese from low grade pyrolusite in dilute sulfuric acid in the presence of molasses alcohol wastewater was investigated. The shrinking core model was applied to quantify the effects of reaction parameters on leaching rate. The leaching rate increases with reaction temperature, concentrations of H 2 SO 4 and organic matter in molasses alcohol wastewater increase and ore particle size decreases. The leaching process follows the kinetics of a shrinking core model and the apparent activation energy is 57.5 kJ·mol –1 . The experimental results indicate a reaction order of 0.52 for H2SO4 concentration and 0.90 for chemical oxygen demand (COD) of molasses alcohol wastewater. It is concluded that the reductive leaching of pyrolusite with molasses alcohol wastewater is controlled by the diffusion through the ash/inert layer composed of the associated minerals.     

硫酸盐熔融反应法从钛铁矿中提取钛的研究

以海南万宁的钛铁矿和硫酸铵为主要原料,通过熔融反应法使钛铁矿中的钛转化为易溶于稀酸的硫酸氧钛,用稀硫酸浸取,达到提高钛浸取率的目的。考察了硫酸铵加入量、焦硫酸钾加入量、反应温度、稀硫酸浸取浓度对钛浸取率的影响。实验结果表明：硫酸铵和焦硫酸钾的加入量、反应温度对钛浸取率的影响较大。提高钛浸取率的最佳条件为：m（钛铁矿）∶m（硫酸铵）∶m（焦硫酸钾）=1∶6∶0.5,反应温度为450 ℃,保温时间为30 min,稀硫酸浸取浓度为2.32 mol/L,在此条件下钛的浸取率达到96.82%。     

Effects of mechanical activation on the digestion of ilmenite in dilute H2SO4

The commercial sulfate process for pigment production uses concentrated sulfuric acid(N 85 wt% H_2SO_4) as feeding material and discharges 8–10 tons of spend dilute acid(20 wt% H_2SO_4) per ton of product. Re-using spend acid to leach ilmenite can cut the waste emission and save fresh feeding acid. However, the leaching reaction with dilute acid is very slow and the digestion efficiency is fairly low. This paper describes a wet-milling process to enhance the dilute-acid leaching of ilmenite that makes it possible to produce TiO_2 pigment in a more environmentally benign routine. The leaching kinetic study of unmilled ilmenite, dry milled 60 min ilmenite and wet milled 60 min ilmenite was conducted by revision of the shrinking core model(SCM), incorporation of particle size distribution(PSD) into SCM. The results revealed that mechano-chemical activation method significantly increased the leaching efficiency of titanium from 36% to 76% by reducing the particle size and increasing the reaction contact area. On the other hand, the milling process increased the lattice deformation and amorphization of crystalline, which lowered the activation energies in the leaching process. Compared with dry milling operation, wet milling is more effective, the particle size distribution of wet-milled ilmenite was much narrower, smaller, and more uniform. Wet milling of ilmenite makes the leaching reaction with dilute acid(60 wt% H_2 SO_4) practicable and the re-use of spend acid becomes possible and economical.     

ETHANOL FROM SOUTHERN HARDWOODS: THE ROLE OF PRESULFONATION IN THE ACID HYDROLYSIS PROCESS

A two-stage acid hydrolysis process is currently used in the production of ethanol from hardwoods. In this process, dilute sulfuric acid in water at high pressure and short residence times hydrolyzes the wood and first stage substrate. The chemical action is particularly impeded in the second stage by the presence of acid condensed lignin.

Presulfonation followed by delignification is proposed using a sulfur dioxide/water sulfuric acid/ethanol treatment step in place of the first stage acid hydrolysis step to alleviate this problem.

Results presented include the effects caused by varying treatment time, sulfur dioxide concentration, temperature and ethanol concentration on the degree of delignification, and, on the recovery of C₅ and C₆ sugars in the hydrolysates. A preliminary economic feasibility analysis is made to determine the impact of improved ethanol yields and lignin by-product values in the production of ethanol from hardwoods.     

Manganese leaching in high concentration flue gas desulfurization process with semi-oxidized manganese ore

Manganese leaching during high concentration flue gas desulfurization process with semi-oxidized manganese ore was studied in this paper. It was found that there were different reaction pathways among which MnO_2,Mn_2O_3 and MnCO_3 in semi-oxidized manganese ore during flue gas desulphurization and manganese leaching.High SO_2 concentration facilitated redox reaction between MnO_2 and SO_2, and high concentration of H_2SO_4 accelerated MnCO_3/Mn_2O_3 leaching from semi-oxidized ore. Kinetics study showed that manganese leaching in flue gas desulfurization process with semi-oxidized ore was controlled by a mixed-control model, that is the surface chemical reaction and mass diffusion dominated both the oxidation of SO_2 and manganese leaching process. The apparent activation energy was 13.05 k J·mol~(-1) and the reaction orders with respect to SO_2 and H_2SO_4 concentration were 1.38 and 0.10, respectively. Finally, a semi-empirical rate equation based on shrinking core model was derived to describe the process.     

ACETIC ACID AS AN OXYGEN CARRIER BETWEEN TWO PHASES FOR EPOXIDATION OF OLEIC ACID

Acetic acid was found to be an effective oxygen carrier for epoxidation of oleic acid. The reaction model of oleic acid epoxidation in the two-phase reaction system was systematically analyzed and the rate determining step was experimentally identified.

The results indicated that the rate of oxidation of the unsaturated acid was independent of the concentration of oleic acid and depended on the mixing rate and the rate of formation peracetic acid which in turn depended on the concentration of acetic acid, strength of acid catalyst and the oxygen source, hydrogen peroxide. In the region of reaction control, the rate equation of epoxidation was found to be

$

where k = 2.98 × 10^-2 M^-2 min^-1 at temperature of 35^°C.     

褐铁型高锰红土矿微波预处理-酸浸提取镍钴

以褐铁型高锰红土矿为研究对象,采用微波预处理-酸浸工艺提取Ni、Co。对矿样物相组成及Ni、Co、Fe、Mn等主要元素赋存状态进行X射线衍射（XRD）和电子探针（EPMA）表征,研究常压条件下硫酸浓度、浸出时间、浸出温度等因素对微波预处理矿样中Ni、Co浸出效果的影响。结果表明：矿样中镍钴品位较高但物相结构复杂,Ni主要与Mn以NiMn₃O₇?3H₂O形式赋存,Co伴生于针铁矿和碱式氧化锰中;在最优浸出条件下,即硫酸浓度300g/L、浸出时间5h、浸出温度90℃、液固比6∶1（以mL/g计）、搅拌速度280r/min,Ni、Co浸出率分别达到95.4%和97.1%,与相同浸出条件下未经微波处理的矿样相比,Ni、Co浸出率分别提高了69.4%和70.1%,实现镍钴的高效浸出;对比微波处理前后矿样XRD图谱,发现微波作用下矿物中Ni、Fe、Mn等物相结构出现明显转变,利于Ni、Co酸浸反应。     

预处理对废弃CRT荧光粉中稀土提取的影响

采用稀盐酸预处理工艺,对预处理前后废弃CRT荧光粉中稀土的提取效果进行了比较研究。结果表明,预处理工艺的最佳条件为：盐酸浓度为0.8 mol·L^-1,反应温度为65℃,反应时间为2 h。与未预处理样品相比,预处理样品酸解后得到的浸出液中稀土的浸出率由21.18%提高到60.17%,而杂质的浸出率由45.21%减少到10.43%。经沉淀、煅烧后所得稀土产物为Y₂O₃和Eu₂O₃,总含量为98.20%。其中,Y₂O₃含量为90.25%。稀土产物主要为立方晶型的Y₂O₃,由片状晶体密集堆积而成,片晶之间紧密结合,形成密实的方体结构。稀酸预处理工艺不仅能显著提高废弃CRT荧光粉中稀土提取的效率,实现稀土资源的高效、可持续利用,而且可以减少化学试剂的消耗,为废弃电子产品的综合利用提供研究基础与技术支撑。     

铁强化电解锰阳极液体系中氧化锰矿烟气脱硫和锰浸出工艺

结合电解锰生产工艺,以氧化锰矿为原料,以电解锰生产过程产生的电解阳极液废水配置烟气脱硫浆液,在其中添加FeSO₄强化电解锰阳极液体系下氧化锰矿烟气脱硫及浸锰能力,探讨铁强化氧化锰矿烟气脱硫和浸锰的工艺条件对烟气SO₂脱除和锰浸出的影响机制。研究发现FeSO₄的加入,通过FeSO₄与MnO₂之间的氧化还原反应以及产物三价铁离子和二价锰离子的协同催化作用,可同时提高锰矿烟气脱硫效率和锰的浸出率。锰矿粒径越小,脱硫及浸锰效率越高。温度升高,氧化锰矿浆液烟气脱硫率逐渐下降,浸锰率则先升高后下降,并在60℃时达到最大。浆液液固比和烟气流量的增大均会导致烟气脱硫率的下降,但会提高氧化锰矿浸锰率。进口SO₂浓度过高会导致脱硫率下降,但更有利于浸锰。采用5级逆流吸收对7%的烟气进行铁离子强化氧化锰浆脱硫,得到最终SO₂出口浓度293μL/L,溶液Mn²⁺浓度为44.72g/L,满足电解要求。铁强化电解锰阳极液体系有效回收利用了电解锰生产废水,不仅集脱硫浸锰工艺为一体,且可实现脱硫和浸锰效率的同时提升,为电解锰行业的清洁生产和资源综合利用提供理论依据和技术参考。     

酸法浸铀与生物浸铀浸泡试验的对比研究

近年来,生物技术在我国低品位砂岩型铀矿及老采区残留难浸铀矿的开发研究已开始起步。凭借生物浸铀具有的氧化性强、浸出液铀浓度及浸出率高等特点而成为开采该类铀矿的重要手段。文章以新疆某砂岩型难浸铀矿石浸泡浸出试验为例,系统开展了不同酸度条件下酸法浸出及不同Fe3+浓度条件下细菌浸铀试验。试验结果表明,生物浸铀在浸出液平均铀浓度、铀浸出率及浸出量等方面均高于酸法试验结果。     

多金属复杂硫化铜矿中有价金属的分离研究现状与进展

综述了复杂铜铅硫化矿中铜锌及铅等有价金属的分离回收技术。通过阐述最近的几种处理复杂硫化铜矿的方法,分析和比较了各处理方法的特点,展望了研究趋势。指出:氧化焙烧预处理-浸出法和硫酸化焙烧-水浸法尽管工艺流程短且简单,但焙烧过程产生的SO₂气体对环境污染严重;硫化焙烧-酸浸法能有效降低SO₂气体的排放量,但其焙烧条件苛刻,难以实现工业化;高价铁盐浸出法存在高价铁盐损耗大、再生难的问题;使用氯盐体系直接浸出时还存在Cl^-对设备腐蚀严重等问题;而氧压浸出和微生物浸出虽然也存在一些不足,但在处理复杂硫化铜矿过程中无有害废气产生,环境友好并且硫以单质硫的形式回收,能有效解决硫酸储存难问题,相信其在今后处理复杂多金属硫化矿中具有广阔的发展前景。     

铬铁矿无钙焙烧渣的SO2还原解毒

系统地对铬铁矿无钙焙烧渣进行了表征,并研究了SO₂还原解毒铬渣,提出了机械活化与SO₂还原相结合的解毒工艺。结果表明,该铬渣主要物相组成是（Fe,Mg）（Cr,Fe）₂O₄和MgAlFeO₄,铬渣中Cr₂O₃含量为12.23%,铬渣粒径越小,含有的总Cr（Ⅵ）、水溶性Cr（Ⅵ）、难溶性Cr（Ⅵ）量越小。SO₂还原解毒铬渣工艺过程中搅拌能有效强化外扩散过程,液固比增大有利于铬渣中Cr（Ⅵ）的浸出,铬渣中Cr（Ⅵ）的浸出随温度升高先增加后急剧降低,反应体系中压力变化对铬渣还原解毒效果影响不大。优化的SO₂还原解毒铬渣条件为：压力0.1 MPa、温度60℃、搅拌速度500 r·min^-1、反应时间60 min,此时铬渣中Cr（Ⅵ）的去除率达90%;机械活化90 min的铬渣进行SO₂还原解毒60 min后,渣中的Cr（Ⅵ）去除率达到98.1%,含量降至25 mg·kg^-1以下,达到国家排放标准。     

天青石锶废渣氯化钡浸出及其动力学研究

天青石生产碳酸锶后剩下的锶废渣,因含有大量的锶资源,属于一种二次资源。目前天青石锶废渣主要通过碳酸盐转化-盐酸浸出两步法来制备SrCl₂,制备过程复杂。实验以BaCl₂为浸出剂,浸出酸预处理后的天青石锶废渣中的SrSO₄,通过一步浸出得到SrCl₂。分别考察了浸出时间、浸出温度、BaCl₂/SrSO₄摩尔比、液固比对锶浸出率的影响。结果表明：浸出时间120 min,浸出温度90℃,BaCl₂/SrSO₄摩尔比2.0,初始液固比10 ml/g时的锶浸出率达到了68.79%。该浸出过程符合未反应核缩模型,且主要受BaSO₄产物层扩散控制,其表观活化能为38.75 kJ/mol。Ba²⁺部分或全部取代SrSO₄中的锶,使得锶废渣中的锶以SrCl₂的形式被浸出。     

MIXED COBALT-BASED CATALYSTS IN AUTOXIDATION OF AQUEOUS SO2

The kinetics of aqueous sulphur dioxide autoxidation catalyzed simultaneously by ions of two different transition metals was studied. Basing on the mechanism of a chain reaction the rate equation for oxygen consumption has been derived. Interaction of the ions in redox steps was assumed. The equation was tested against experimental data collected during oxygen absorption performed in a gas-liquid reactor with a plane interface. Two catalytic systems were used in the experiments: CoSO₄-Fe₂(SO₄)₃ and CoSO₄-MnSO₄

The predicted occurrence of a minimum value of oxygen absorption rate at a certain concentration ratio of metal ions constituting a mixed catalyst was confirmed for both systems. Other phenomena related to the possible removal of a catalyst or sulphite from the place of reaction were also discussed.     

COMPARATIVE LIMITING FLUX ANALYSIS OF BLACK LIQUOR AND POLYETHYLENE GLYCOL IN ULTRAFILTRATION

Ultrafiltration of black liquor was carried out using an asymmetric membrane and the results were compared with that of polyethylene glycol, a standard macromolecule, in a stirred batch cell. The effects of system parameters, e.g., pressure, concentration and stirrer speed on permeate flux and solute rejection were studied extensively for both the solutes.

An osmotic pressure model was used to analyze experimental results. To take into account the phenomena of concentration polarization, an extra resistance term, called the polarization layer resistance (R_p), was incorporated into the model. The polarization layer resistance was found to be a function of flow regime and concentration at the membrane. To correlate these, the following two types of relationship were examined and tested with the experimental results,

and

where a, b, c, a₁, b₁, are constants.     

废弃CRT荧光粉中稀土的提取工艺与技术

以废弃CRT荧光粉为原料,在前期稀盐酸预处理工艺的基础上,通过进一步深入研究,开发出从废弃CRT荧光粉中提取稀土的完整工艺路线。结果表明:稀酸预处理后,盐酸酸浸剩余荧光粉固体的最佳浓度为5 mol·L^-1,最佳反应温度为80℃;酸浸后稀土浸出液净化除杂的pH控制为5.5,DDTC最佳用量比为6:1;稀土净化液经草酸沉淀后煅烧的最佳温度为900℃。从废弃CRT荧光粉中提取到稀土产物Y₂O₃和Eu₂O₃的总含量为99.2%,其晶粒由若干片状晶体密实堆积成多面体结构,晶粒之间相互嵌入,呈镶嵌式接触。     

KINETICS OF THE CLAY ROOFING TILE CONVECTION DRYING

Kinetics of the convection drying process of flat tile has been investigated experimentally in an industrial tunnel dryer. Several velocities of wet tile movement through the dryer were tested to obtain maximum allowable drying rate curve. As there are various models to describe the kinetics of convection drying, finding a model that would fairly well approximate the kinetics of the whole drying process was part of the research. Especially the polynomial and exponential models were tested.

It was found that exponential model of the type: B(t) = (a-B_e. EXP(-bt²) +B_et (-dB(t)/dt) = 2bt(B(t)-B_e significantly correlates the kinetics of the whole tile drying process.

Applying the maximum allowable drying rate curve obtained for flat tile in the first period of drying, a grapho-analytic model for the optimal conducting of the process has been developed.     

ESTIMATION OF EFFECTIVE SHEAR RATE FOR AERATED NON-NEWTONIAN LIQUIDS IN AIRLIFT BIOREACTOR”“

Effective shear rate is one of the indispensable parameters for the design of aerobic fermentors using a viscous non-Newtonian system. The estimation of effective shear rate in airlift loop bioreactors has been investigated with liquid circulation velocity. An empirical correlation of effective shear rate in airlift loop reactors is proposed.

γ_eπ= 3.26-3.51 ; 10²U_G + 1.48 10⁴U²_G

It is found that the effective shear rate is lower in airlift reactors than in bubble columns. This equation can be used for the cultivation of cells sensitive to shear stress.