On the characteristic properties of oxidation of sulfide minerals exposed to nanosecond electromagnetic pulses

High-power nanosecond electromagnetic pulses cause changes in the chemical and phase surface composition of sulfide minerals (pyrrhotite and pentlandite) and their sorption, flotation, and chemical activities. The influence of the conditions and parameters of the electric-pulse effect on the change in the amount of elemental sulfur and iron oxide on the surface of mineral particles, as well as the concentration of iron and sulfoxide ions in the aqueous mineral suspension, has been studied. The parameters of preliminary pulsed treatment of pyrrhotite and pentlandite that lead to improvement of flotation separation of minerals have been determined.     

Ilmenite Mineral's Recovery from Beach Sand Tailings

The mineral ilmenite is the major source of rutile for industrial use and is of interest to paint and fertiliser industries. Enormous unutilised tailing dams lie on the eastern coast of the South Africa. Although covered by a simulation of the original indigenous vegetation, these tailings are still ilmenite bearing and of economic value. Tailings emanating from beach sand mineral slimes dams of the Kwazulu-Natal area (South Africa) have been processed. Screening, flotation, spiral concentration and magnetic separation methods were used either separately or successively. The present work sheds light on alternative routes for the extraction of the ilmenite, from these tailings. It moreover points out the usefulness of the Mössbauer spectroscopy in the mineral processing product monitoring. Tailings from the beach sands were used in the present study after the economic industrial minerals zirconia, ilmenite and rutile had been extracted in previous mining operations. About 61% natural ilmenite recovery was observed in the flotation concentrate of a Humphrey Spiral concentrate while a 62% recovery of hematite was found in the flotation tailings. The combination of screening, spiral concentration and magnetic separation, and flotation yielded a product with the highest ilmenite and hematite concentration being 71% and 19%, respectively. A natural ilmenite mineral, containing 87% ilmenite and 13% hematite, could be produced and extracted from the tailings of the flotation process, collected subsequently to the spiral concentration and the initial screening.     

Enrichment of microplastic pollution by micro-nanobubbles

Microplastic pollution has become a global environmental concern. It has been reported that microplastics are easily accessible to a wide range of aquatic organisms and ultimately enter the human body along the food chain. They pose a severe threat to ecosystems, organisms and even human health due to their durability and persistence. However, how to reduce microplastic pollution still remains a challenge in terms of scientific techniques and policy-making. There is currently still a lack of effective methods for microplastic recycling and removal. Luckily, a new technique, micro-nanobubbles (MNBs), may provide a possible and highly effective method to enrich microplastic pollution: their great advantages^[1] include a high specific surface area, long lifetime and ability to adsorb microplastics of the same size and hydrophobicity. Then they further adsorb on larger bubbles such as microbubbles or millimeter bubbles and float to the water surface together. In this study, we present a new method using MNBs to enrich microplastic pollution with high efficiency. Two types of microplastics, millimeter-scale plastic fragments and microplastic particles, were chosen as the model microplastic pollution systems to study the enrichment efficiency of MNBs on microplastics. Results showed that MNBs can efficiently enrich these microplastics. The enrichment efficiency increases with flotation time until a maximum value is reached. It is proved that MNBs not only collect the microplastic pollution but also reduce detergent use in domestic laundry sewage. This is because detergent, as a surfactant, is easily absorbed on the surface of MNBs and can be collected together with the microplastic pollution. Our research has demonstrated that the MNB technique could be promising for use in microplastic recycling and reducing detergent pollution in daily life.     

Effect of the ultrasonic standing wave frequency on the attractive mineralization for fine coal particle flotation

Froth flotation for mineral beneficiation is one of the most important separation techniques; however, it has several challenges for processing fine and ultrafine particles. Attractive mineralization between particles and bubbles by ultrasonic standing wave (USW) is a novel and high-efficiency method that could assist fine particle flotation. Frequency is an important ultrasound parameter, whose effectiveness mechanisms on the attractive mineralization did not compressively address. This study explored the effect of the USW field with various frequencies on the fine coal flotation for filling this gap. Herein, a high-speed camera and a focused beam reflectance measurement (FBRM) were used to analyze three sub-processes of the attractive mineralization, including the microbubbles’ formation, the conventional flotation bubbles (CFBs)’ dispersion, and the particles’ movement. It was found that the maximum flotation metallurgical responses were obtained under the highest examined USW frequency (600 kHz). However, the flotation outcomes by a low USW frequency (50 kHz) were even lower than the conventional flotation tests. Observation and theoretical calculation results revealed these results were originated from the influence of frequency on the carrier bubbles’ formation and the action of the secondary acoustic force during USW-assisted flotation. These outcomes demonstrated that frequency is a key factor determining the success of attractive mineralization for fine particles’ flotation.     

Monitoring the Dynamics of Concentrated Suspensions by Enhanced Backward Light Scattering

The shear-induced flocculation of kaolin-polymer flocs in a stirred tank is investigated at medium to high solids concentrations (ϕ=1−10% w/w). The evolution of the average floc size is monitored by the change in intensity of laser light scattered in the 180° direction. The measurements reflect the change in particle number concentration as flocculation proceeds. As flocculation begins, coagulation dominates and the floc size increases (total particle number decreases) and then levels off at a steady state value as fragmentation becomes significant and balances coagulation. At steady state, the measurements indicate the extent of flocculation. Increasing the shear rate increases the coagulation and fragmentation rates, resulting in smaller floc sizes at steady state. Increasing the flocculant concentration increases the steady state floc size by strengthening the bonds between primary particles to resist fragmentation. At constant shear rate and flocculant concentration, increasing the solids fraction decreases the steady state floc size indicating formation of weakly bonded flocs. Flocculant mixing was the most important factor for flocculation efficiency at high solids concentrations.     

Investigation of dodecylammonium adsorption on mica,albite and quartz surfaces by QM/MM simulation

The absorption mechanisms of collector and mineral surface structures play important roles in studies of lepidolite flotation. In this work, quantum mechanics (QM) and hybrid quantum mechanics/molecular mechanics (MM) methods were implemented to investigate the flotation mechanisms of lepidolite from muscovite, quartz and albite. The crystal structures, electron density distributions, bonds and the densities of states of lepidolite were calculated and compared with those of muscovite. The adsorption structures and energies of monomer dodecylammonium (DDA) on the three different minerals were also calculated. The headgroup of the DDA cation was found to adsorb on the surface of minerals, with its hydrophobic tail stretching into the vacuum slab, approximately perpendicular to the surface. Simulation results indicate that the purity of fine lepidolite is limited by the existence of muscovite, due to their similarities in surficial structure and properties. Other gangues were found to be removed efficiently with the use of acidic conditions. The results are in good agreement with other experiments. Compared with simple MM simulations, the use of the QM/MM methods to investigate the adsorption on minerals without specific forcefield parameters was concluded to be a more accurate method to attain monomer surfactant–mineral adsorption energies.     

Image Analysis for Off-Line Characterisation of mineral particles and prediction of processing properties

The paper discusses the application of image analysis to multiphase mineral particles. The emphasis is on the development of automatic and routine methods which provide reliable data for the process engineer. Optical systems are discussed briefly, but electron beam instruments are shown to offer many advantages for the identification and discrimination of mineral species. Image capture and analysis procedures are described together with the application of the measured data to aid our understanding of the processing properties of particles of complex structure. Examples are given from studies of beach sands, silver minerals, flyashes, ore characterisation, flotation of base metals, grinding and liberation.     

Energy concentration in electric discharges between particles of semiconducting sulfide minerals under the action of high-power nanosecond pulses

A model for development of electric discharges between particles of sulfide minerals (pyrite) under the action of high-voltage nanosecond pulses is proposed. It is shown that through discharges in a layer of pyrite particles lead to energy concentration in small contact regions between particles; the concentrated energy is sufficiently high for local decomposition (disintegration) of mineral complexes.     

低温热处理刚玉实验中含水矿物包裹体的特征研究

近年来,低温热处理刚玉出现在宝石交易市场,由于其特征容易与天然刚玉混淆,如何鉴定低温热处理刚玉成为宝石实验室的研究热点。在弱氧化氛围,360,610和650 ℃条件下,先后对9粒刚玉进行了热处理实验,并采用显微拉曼定性分析刚玉中的包裹体、显微镜下观察包裹体形貌、显微红外光谱分析含水矿物包裹体中羟基的特征峰等方法,对刚玉低温热处理前后的特征进行了对比研究。热处理实验揭示：600 ℃左右温度、弱氧化氛围已能有效去除刚玉中的蓝色调,并增强红色,可达到热处理改善或改变刚玉颜色的目的。研究结果表明：针铁矿、高岭石、勃姆石等含水矿物包体主要存在于刚玉的开放裂隙中,硬水铝石、磷灰石、云母等含水矿物包体主要存在于刚玉晶体中。针铁矿热处理前红外光谱可显示与羟基相关的3 435 cm-1吸收峰,并伴有以3 185 cm-1为中心的吸收宽带,经360 ℃热处理后相关吸收消失,其颜色由亮黄色变为红色;高岭石热处理前红外光谱在3 620,3 648,3 670和3 698 cm-1附近显示一组与羟基相关的吸收峰,经610 ℃热处理后相关吸收峰消失;勃姆石热处理前红外光谱显示与羟基相关的3 086和3 311 cm-1吸收峰,经610 ℃热处理后相关吸收峰消失。硬水铝石包裹体通常呈针状,热处理前红外光谱显示与羟基相关的1 980和2 110 cm-1吸收峰,经610 ℃热处理后相关吸收峰消失,但仍保持针状晶形假像;磷灰石包体通常呈透明柱状或粒状晶形,由于OH与F相互作用,红外光谱在3 550 cm-1附近显示与羟基相关的吸收峰,610 ℃热处理后相关吸收峰仍然存在,磷灰石包体的形貌未见改变;白云母呈近透明无色片状晶形分布于刚玉中,红外光谱在3 624 cm-1附近显示与云母中羟基相关的吸收峰,650 ℃热处理后这一吸收峰仍然存在,云母的形状未见变化,透明度略微降低。通过实验,证明含水矿物包裹体对于鉴定低温热处理刚玉具有重要作用。     

Elevated radionuclide concentrations in heavy mineral-rich beach sands in the Cox's Bazar region, Bangladesh and related possible radiological effects

The study focuses on elevated levels of environmental radioactivity present in heavy mineral deposits located along a 120-km coastal section of Cox's Bazar on the eastern panhandle of Bangladesh. The deposits are situated in or at sand dunes located on the recent beach (foredune area) or in attached paleo-beach areas (backdune area). This study investigates activity concentrations in bulk beach sands (six representative samples) and in five mineral fractions separated from the beach sands in order to assess potential radio-ecological effects and the possible use of the mineral deposits as a source for uranium and thorium. The bulk beach sands and individual mineral fractions were analysed by gamma-ray spectroscopy. The activity concentrations of U-238, U-235, Th-232 and K-40 in the bulk beach sand samples were found to be considerably high and positively correlated to the concentration of heavy minerals in the sand. In the mineral fractions, the highest activity concentrations were found in the zircon fraction followed by garnet, rutile, ilmenite and magnetite. The determination of (i) the radium activity, (ii) several radiation hazard indices and (iii) adsorbed and effective gamma doses allowed to assess the related exposure of the environment and the local population to elevated radioactivity. It becomes evident from the present data that (1) if raw sands or mineral fractions mined in the study area are used for building purposes or industrial use, their activity concentrations have to be considered from a radio-ecological perspective and (2) if mining and processing of the minerals is being considered, uranium and thorium may become strategically significant by-products.     

Wetting behavior of magnesite and dolomite surfaces

Magnesite and dolomite are salt-type minerals that show similar chemical composition and flotation behavior due to same crystal structure, and sparingly soluble nature. The surface properties of minerals play a major role in determining their separation from each other in processes such as flotation. During flotation process, selectivity problem arises between magnesite and associated gangue minerals such as dolomite. There is a close relationship between floatability of minerals and their contact angles. Therefore, surface hydrophobicity of magnesite and dolomite minerals was investigated by contact angle measurements in the absence and presence of flotation reagents.Magnesite and dolomite show hydrophilic properties and they have got a small contact angle (magnesite ∼10.4° and dolomite ∼6.6°) in distilled water in the absence of any surfactant. The contact angle values at the magnesite and dolomite surfaces remained at 9.7°-10.9° in the presence of petroleum sulphonates (R825 and R840) while sodium oleate affected hydrophobicity of magnesite, and the contact angle value increased up to 79°. The contact angle value of 39° at dolomite surface was obtained in the solution of sodium oleate, respectively.     

A novel flotation technique combining carrier flotation and cavitation bubbles to enhance separation efficiency of ultra-fine particles

In this paper, a novel flotation technique that combines nano-scale bubbles generated by hydrodynamic cavitation (HC) and carrier flotation is proposed to promote the flotation efficiency of a high-ash (43%) ultra-fine coal sample (<45 µm). We investigated the mechanism by which cavitation bubbles enhance the separation efficiency of carrier flotation using focused beam reflectance measurements, polarizing microscopy, and extended Derjaguin–Landau–Verwey–Overbeek theory. The carrier particles (polystyrene (PS)) and fine coal were pre-treated in a venturi tube and then floated in a laboratory mechanical flotation cell. The flotation results indicate that the presence of cavitation bubbles significantly improved the carrier flotation performance of high-ash ultra-fine coal. This improvement was attributed to the presence of highly hydrophobic PS, which creates additional gas nuclei in the flotation system. The nano-bubbles, which were produced by the venturi tube and adhered to the fine coal particle surfaces, were conducive to the agglomeration of fine coal particles into large aggregates. Moreover, the nano-bubbles functioned as “bridges” of interaction between the carrier particles and large aggregates of fine coal particles. This paper mainly focused on the effect of carrier (PS) and HC on high-ash fine coal. The influence of different HC intensities on carrier (PS) flotation was discussed. Two models for the interactions between the coal particles, nano-bubbles, and PS during cavitation were proposed and were proved using the E-DLVO theory.     

漫反射光谱在“老挝石”颜色成因上的应用

近来,一种产自老挝的新型印章石(俗称“老挝石”)涌进国内市场,对我国印章石市场造成一定影响,“老挝石”的研究尚处于起步阶段,对其颜色成因的研究更为缺乏。采用漫反射光谱(DRS)结合X射线粉晶衍射(XRD)、红外光谱(FTIR)、X射线荧光光谱(EDXRF)等测试对红色“老挝石”的矿物成分和致色机理进行深入研究。结果显示,“老挝石”的主要矿物成分为地开石,并含有少量高岭石,化学成分中的Fe含量和“老挝石”红色色调呈正相关关系,即颜色越深Fe的含量越高。铁质矿物呈微晶集合体浸染分布于地开石的颗粒间,由于其含量低、粒度细小,常规的微区测试方法无法确认其种属。相比之下,漫反射光谱对微晶铁矿物的鉴定十分有效,对可见光波段漫反射光谱处理得到导数等,在土壤沉积物中已经被用来定量测定针铁矿和赤铁矿。该研究中“老挝石”基体与土壤沉积物均为粘土矿物,可以用漫反射光谱来判定“老挝石”中铁矿物种属。漫反射光谱一阶导数法显示,其谱峰位于565～570 nm,由此确认铁矿物的种属为赤铁矿。微晶赤铁矿分布于“老挝石”矿物颗粒间,使样品产生红色,赤铁矿含量越高,红色调越深。     

显微-反射傅里叶变换红外光谱研究油酸钠与胶磷矿吸附机理

红外光谱已经成为浮选药剂作用机理研究的最重要手段之一。由于矿物本身具有较强的红外吸收,传统溴化钾压片透射光谱很难检测到矿物表面吸附药剂的微弱红外信号。采用显微-傅里叶变换红外光谱仪的反射模式,测定了不同浓度油酸钠在胶磷矿表面的吸附形式,并观察了吸附形貌。结果表明,与透射红外光谱相比,反射红外光谱对表面有更高的灵敏度,能更好地揭示实际浮选药剂浓度下的吸附机理。碱性条件下当油酸钠浓度较低时,油酸离子与表面晶格钙离子发生化学吸附,吸收峰在1 552 cm-1,同时也存在油酸钙沉淀的物理吸附,吸收峰在1 570和1 535 cm-1;当油酸钠浓度超过临界胶束浓度时,胶束使得胶磷矿表面亲水,导致油酸钠溶液残留在表面,吸收峰在1 560 cm-1,掩盖了其他吸收峰;表面经水洗涤后药剂吸收峰强度大幅减弱,是由于残留的油酸钠和物理吸附的油酸钙被洗掉。另外,随着油酸钠浓度增大,药剂二维形貌由点状吸附聚集为片状吸附,覆盖面积增大,但并不是完全覆盖,这与矿物表面异质性有关。以上研究结果有利于理解磷矿石提磷或铁矿石脱磷浮选体系中捕收剂与胶磷矿的作用机理。     

Mössbauer spectroscopy description of limonite from Taraco, in the Huancane Province of the Puno Region, Peru

Natural iron oxides are very common in nature and are the main components of many minerals, rocks and soils. There are a great variety of these minerals in Peru, especially in the Andes region. The mineral studied was extracted from the Taraco District in the Huancané Province of the Puno Region. The extracted sample is a yellowish mineral with very small particles which is called limonite. X-ray diffraction indicates the presence of goethite as the principal mineralogical phase and quartz as the secondary phase. The ⁵⁷Fe Mössbauer spectra at room temperature show broadened spectra that were fitted using a distribution model. The most probable field of the magnetic component is 21T, corresponding to the presence of small particles of goethite, confirmed by the 4.2 K spectrum. MS of the calcinated sample in air at 900°C show the presence of two hematite sextets, one related to bulk particles and another to surface particles. Chemical analysis using Scanning Electron Microscopy and Energy Dispersive X-ray Spectrometer indicates that O and Fe are the major components; other elements such as Al, Si, Mg and Ca are also present.     

Design of a flotation cell equipped with ultrasound transducers to enhance coal flotation

Ultrasonic treatment is widely used for surface cleaning during physical, chemical and physico-chemical processes in mineral processing. Several research papers and a few industrial applications about the subject suggest that the mechanism behind the positive effect of ultrasound for mineral processing and especially flotation is due to formation of cavitation by ultrasonic energy. Within this study, coal floatability is investigated by use of a specially designed flotation cell equipped with ultrasound transducers with different power, frequency and geometry. The results indicate that ultrasonic treatment during coal flotation positively affects the quality and quantity of the properties of floated coals while using of lesser amounts of reagent than a conventional flotation system.     

拉曼Mapping研究白云鄂博萤石型稀土矿物赋存特征及分布规律

白云鄂博矿以资源丰富、储量巨大而闻名。其中独居石矿物是主要稀土原料之一,在冶金、军事、化工材料等领域都有广泛的应用。前人已经对白云鄂博矿物学特征进行了充分的研究,随着开采深度的增加,原生矿物增多,对现阶段稀土矿物赋存状态有待深入了解。利用拉曼Mapping成像技术结合扫描电子显微镜(scanning electron microscope, SEM)与能谱议（energy dispersive spectrometer, EDS）方法,能够对白云鄂博共伴生矿物赋存特征进行更深的研究。EDS与能谱结果显示：矿物扫描区由萤石、重晶石、独居石、磷灰石和铁矿物构成。拉曼Mapping分析显示：显微共聚焦图下扫描基底为萤石矿物（CaF₂）,拉曼特征峰普遍出现在220～650 cm-1,与已知文献报道的萤石拉曼峰略有不同。较大颗粒为重晶石矿物（BaSO₄）,为典型的硫酸盐矿物。中等颗粒大小为独居石矿物（Ce,La,Nd）PO₄,细小颗粒集中区为磷灰石矿物（Ca₅[PO₄]₃F）。虽然独居石与磷灰石都为典型的磷酸盐矿物且具有相同磷酸根结构,但由于外部金属阳离子的结合种类不同,其拉曼峰位也不相同。拉曼Mapping结合EDS分析矿物的赋存特征及分布规律关系为：独居石呈板状或块状分布在重晶石与磷灰石中间或磷灰石与萤石矿物之间,粒度约为50～120 μm。重晶石矿物颗粒较粗呈块状集合体分布,颗粒大小为50～200 μm,常与独居石共生,矿物颗粒紧密生长。磷灰石呈细粒状或块状,星散分布在独居石与重晶石周围,类似侵染分布在萤石中。少量磷灰石颗粒与独居石相互交代成不规则共生体,大部分磷灰石呈单体分布在矿物之间。萤石矿物中富集最多,占比约55%,与独居石、重晶石、磷灰石、铁矿物伴生。从赋存状态上判断形成时期应早于其他伴生矿物。对矿物成因复杂,共伴生矿物极多白云鄂博矿床。EDS虽能分析矿物学基本关系,但独居石与重晶石矿物中的能谱图部分重合。是由于能谱扫描Ba,S与稀土元素Ce,La,Nd时激发能量线系太相近以及能谱分辨率较低。利用Mapping成像技术对于矿物鉴定上具有简单、可靠的优点,可以弥补EDS分析误判拉曼Mapping为矿物学分析提供一种新的鉴别思路,同时也为白云鄂博矿物的鉴定提供了参考性的拉曼光谱。     

The application of power ultrasound to the surface cleaning of silica and heavy mineral sands

Power ultrasound may be used in the processing of minerals to clean their surfaces of oxidation products and fine coatings, mainly through the large, but very localised, forces produced by cavitation. Results of the application of power ultrasound to remove iron-rich coatings from the surfaces of silica sand used in glass making and to improve the electrostatic separation of mineral sand concentrates through lowering the resistivity of the conducting minerals (ilmenite and rutile) are presented. Parameters affecting ultrasonic cleaning, such as input power and levels of reagent addition, are discussed. In particular, we present data showing the relationship between power input and the particle size of surface coatings removed. This can be explained by the Derjaguin approximation for the energy of interaction between a sphere and a flat surface.     

褐煤热解与燃烧时矿物转化和细灰形成的CCSEM研究

在沉降炉中进行了一种典型中国褐煤的热解与燃烧实验,热解气氛为N2,燃烧气氛为O₂/N₂=21:79,采用CCSEM分析原煤、煤焦与煤灰。CCSEM分析结果表明,铁氧化物、石英、黄铁矿、伊利石和高岭土是煤中主要的矿物成分,同时也是主要的外在矿成分,褐煤中57.26%的矿物粒径小于10μm。在热解与燃烧过程中,煤中主要矿物发生了明显转化。富Si矿物和硅铝酸盐在热解和燃烧过程中可能发生了破碎;而富Fe矿物部分明显破碎生成细小矿物,部分外在矿直接转化,未发生明显破碎。细灰少量来自于细小富硅矿、石英和铁氧化物等矿物的直接转化,70%以上的细灰由Ca、Fe含量很高的混合硅铝酸盐组成。