Iron redox-equilibria and sulphide capacity of PGM melter-type slags

New measurements have been made on the ferric to ferrous ratio as well as the sulphide capacity for platinum group metals (PGM) melter-type slags. In South Africa, these slags are produced from the smelting of low-grade copper–nickel sulphide ores, Nell [Nell, J., 2004. Melting of platinum group metal concentrates in South Africa. The South African institute of Mining and Metallurgy 104 (7), 423–428]. The typical mass compositions are 5–10% Al₂O₃, 2–15% CaO, 5–30% FeO_x, 15–25% MgO and 40–60% SiO₂ with a molar basicity defined as (CaO + MgO)/SiO₂ of 0.6–1. The industrial furnaces operate at temperatures ranging from 1450 to 1600 °C under fairly reducing conditions (typically a pO₂ close to 10⁻⁸ atm at 1500 °C). The gas–slag equilibrium was studied by subjecting a synthetic slag to controlled atmospheres in a vertical tube-furnace using Ar–CO–CO₂ (–SO₂) gas mixtures. The ratio of ferric to ferrous was determined at 1450 °C for oxygen activities, defined as pCO₂/pCO, ranging from 0.11 to 1.75 by analysing the quenched slags using the standard titration and XRF techniques. The measured Fe³⁺/Fe²⁺ ratio increased from 0.029 to 0.110 with the increasing oxygen activity. Slight non-ideal iron redox behaviour was observed, as has been reported for low alumina and low iron-containing slags. The present results are in good agreement with the trends found in the literature for similar multi-component slag systems (mostly iron bath smelting slags). Sulphide capacity was measured at partial pressures of oxygen and sulphur of approximately 10⁻⁹ and 10⁻³ atm respectively, with total-iron contents of 8.2 and 15.6 wt%, and temperature ranging from 1450 to 1525 °C. The present sulphide capacity data ranged from 10^−4.43 to 10^−3.71. The expected increase in sulphide capacity with increasing temperature was observed, and at a given temperature, the sulphide capacity increased with an increase in iron oxide content.     

Understanding the influence of acidic components (Si,Al, and Ti) on ash flow temperature of South African coal sources

Ash flow temperature is one property that specifically gives more information on the suitability of a coal source for combustion or gasification purposes. Therefore the chemistry and mineral interaction have to be understood in order to determine the suitability for fixed bed gasification purposes with regards to ash flow properties. Various authors ([Seggiani, M., 1999. Empirical correlations of the ash flow temperatures and temperature of critical viscosity for coal and biomass ashes. Fuel 78, 1121; Alpern, B., Nahuys, J., Martinez, L., 1984. Mineral matter in ashy and non-washable coals—its influence on chemical properties. Commun. Serv. Geol. Portugal 70 (2), 299]) have expressed the fusibility of coal ash as a function of the content of the principal oxides frequently found in coal ash, i.e. SiO₂, Al₂O₃, TiO₂, Fe₂O₃, CaO, MgO, Na₂O and K₂O. However, coal ash fusibility characteristics are difficult to determine precisely, partly because coal ash contains many components with different chemical behaviours, and may very from coal source to coal source.The purpose of this study is primarily to understand the effect and chemistry of the acidic components (Si, Al and Ti) of South African coal sources, as well as the manipulation or addition of these components to the coal sources, with the view to understand their effect on the ash flow properties.A representative coal blend as it is currently used for gasification purposes, as well as coal mixtures with the addition of pure SiO₂, Al₂O₃ and TiO₂, respectively, were prepared. The variation of the acidic components SiO₂, Al₂O₃ and TiO₂ varied from 1 mass% to 50 mass% to the coal blend. The particle size of the samples were representatively prepared to <1 mm and analyzed for ash flow temperature and ash composition as dependant variables according to ASTM D1857-87 and ASTM D2795-95, respectively. The raw data was then statistically evaluated by means of regression models.Results of the statistical evaluation of ash flow temperature and the ash elemental composition indicated that based on the 95% confidence interval Al₂O₃, Fe₂O₃, CaO, MgO, P₂O₅, as well as the SiO₂–Al₂O₃ ratio have a statistical significant effect on ash flow temperature. Regression trends of the coal and Al₂O₃, SiO₂ and TiO₂ mixtures indicated that Al₂O₃ has the biggest effect on the ash flow temperature. A shift towards increasing the Al₂O₃ concentration has a significant increasing effect on the ash flow temperature in the three-component system Al₂O₃–SiO₂–TiO₂ phase diagram. The ash flow temperature is the highest at the point where the Al₂O₃ concentration is maximized. The shifts in frequency of the absorption band associated with the 6s–6p electron transaction which relates to the basicity of a glass or slag also relates to the different effect of the individual acidic components on ash flow temperature. The shift can be considered as a measure of the electron donor power and is usually expressed in terms of the optical (Λ) basicity. The ion–oxygen attraction and the stronger (more positive) value obtained for Al₂O₃ in comparison with TiO₂ and SiO₂ could be seen; and possibly explain why Al₂O₃ has a bigger influence and effect on increasing the ash flow temperature.It can be concluded from this experimental work with the emphasis on flow properties, that the acidic components Al₂O₃, SiO₂ and TiO₂ all have an increasing effect on ash flow temperature when added to the coal blends currently used for gasification. In addition to this general conclusion, it has also been confirmed that Al₂O₃ addition to the coal blend has the most significant effect towards increasing the ash flow temperature when compared to SiO₂ and TiO₂.     

含硼炉渣脱硫性能研究

用静态平衡法研究了含有 Ｂ２Ｏ３的 ＭｇＯ－ＣａＯ－ＳｉＯ２－Ｂ２Ｏ３－Ａｌ２Ｏ３五元渣系的脱硫率与炉渣组成变化的关系．当三元碱度Ｒ３小于２．２时,脱硫率随Ｒ３增大而增大,随Ｂ２Ｏ２含量的增加而减小; Ｒ３较大时,其增大对脱硫率影响不大,这时 Ｂ２Ｏ３含量的增加有利于改善动力学因素,提高脱硫率．     

Paste backfill of high-sulphide mill tailings using alkali-activated blast furnace slag: Effect of activator nature,concentration and slag properties

The effect of activator type, concentration and slag composition on the strength and stability properties of paste backfill (CPB) of high-sulphide tailings using alkali-activated slag (AAS) as binder (7 wt.%) were investigated in this study. Acidic and neutral (AS–NS) slags were activated with liquid sodium silicate (LSS) and sodium hydroxide (SH) at 6–10 wt.% concentrations. Ordinary Portland cement (OPC) results were used for comparison. The strength development was found to remarkably improve with increasing the concentration from 6 to 8 wt.%. Further increase in concentration did not enhance the strength. SH was determined to produce higher early-age strength whilst LSS produced higher long-term strengths as an indication of slag selectivity for activators. More extensive gypsum formation was observed at lower concentrations in SEM/EDS studies. An increase in Na₂O concentration raised the activator consumption. High concentrations also led to poorly crystallized C–S–H gel, loose structure and drying shrinkage cracks especially in NS–SH samples. A reduction in total porosity up to 20% was obtained in AAS samples compared to OPC. Amorphous structure, chemical modulus ratio and/or basicity index (BI) values were seen to control the pozzolanic reactivity, and therefore, the alkali-activation and hardening process.     

Gold and arsenic recovery from calcinates of rebellious pyrite–arsenopyrite concentrates

The products of stepped calcination of pyrite–arsenopyrite concentrates contain ferric arsenate phases FeAsO₄, Fe₄As₂O₁₁, Fe₃(AsO₄)₂. The article reports the research data on leaching of calcines in alkaline medium including caustic soda and hydrogen peroxide used as an oxidizer. The experiments prove the efficiency of alkaline leaching with H₂O₂ for dissociation of gold associated with ferric arsenates (II) and (III) and for reduction of arsenic content from 1.2–1.4 to 0.006–0.15%. Preliminary leaching of calcinates enhances gold cyanidation yield from 91–92.9 to 97.3–97.9%.     

影响江西某闪速炼铜渣在选矿过程中铜、砷分离的矿物学因素探讨

为查清江西某闪速炉渣浮选铜精矿中砷含量较高的原因,对该闪速炉渣进行了系统的工艺矿物学研究。结果表明:闪速炉中的砷主要以砷化铜、砷化铁等金属砷化物的形式存在,这些含砷矿物粒度微细,大部分都是以微细粒形式包裹于冰铜中,在磨矿过程中很难解离,而且砷化铜与冰铜的浮游性能较为相似,在选矿过程中不易将两者分离,将最终导致铜精矿中砷含量过高。     

Das Auflösungsverhalten von Al2O3 und MgO*Al2O3 Partikeln mit definierter Oberfläche in hoch MgO-hältigen sekundärmetallurgischen Pfannenschlacken

The importance of enhanced knowledge concerning the dissolution behavior of non-metallic inclusions in secondary metallurgical ladle slag is rising. This is mainly caused by increasing demands on steel cleanness. To clarify this behavior, an experimental investigation campaign was carried out by In-situ Laser-Scanning-Confocal-Microscopy investigations. The dissolution kinetics of Al₂O₃ and MgO*Al₂O₃ spherical particles were studied for various CaO-Al₂O₃-SiO₂-MgO slag compositions at 1600 °C.     

矿用环保型防灭火材料—电石渣泡沫的实验研究

实验研制电石渣泡沫是一种多功能三相凝胶泡沫,利用泡沫的高含水性、窒息性以及封堵特性实现了对采空区煤火灾害的防治;利用泡沫的强碱性可以吸收CO2等酸性有毒有害气体。本实验在强碱性环境下测试了3种发泡剂α-烯烃磺酸钠(AOS)、十二烷基硫酸钠(SDS)、脂肪醇聚氧乙烯醚硫酸钠(AES)及其复配对泡沫发泡性的影响,得出了复配的最优配比;同时研究了不同稳泡剂聚乙烯醇(PVA)、海藻酸钠(SA)对泡沫稳泡性的影响;此外,综合分析了不同水灰比对泡沫性能的影响。最后通过煤自燃特性综合测试系统和X-射线衍射实验验证了电石渣泡沫对煤样有一定的阻化效果,对CO2有明显的吸收效果。     

Calcium leaching from waste steelmaking slag: Significance of leachate chemistry and effects on slag grain mineralogy

Accelerated carbonation of alkaline wastes such as steelmaking slag offers the potential to combine waste valorisation with climate change mitigation by utilising carbon dioxide (CO₂). One method of achieving this is through an indirect carbonation process to produce a marketable precipitated calcium carbonate (PCC), using ammonium salts to selectively extract calcium from steelmaking slag. Two unaddressed design parameters for a slag based plant differing from that of a traditional PCC plant are the effect of mineralogy on extraction efficiency when using a multicomponent, heterogeneous feed such as slag and the challenges raised by the resulting leachate chemistry. This paper presents petrographic textural observations on the effect of calcium leaching via ammonium chloride on individual grains of dicalcium silicate in three different widely unutilised steelmaking slags. These observations are then interpreted in conjunction with measured changes in solution leachate chemistry. The results indicate that although silica enriched regions form at the reaction front, the reaction continues into the core of the particle due to fracture propagation caused by volume reduction as calcium is extracted. Co-leaching of sulfur alongside calcium and the formation of precipitate in the leachate highlights potential engineering challenges when the process is scaled up due to fouling of process equipment. The main mineral phases in all untreated slags were found to be calcium silicates, predominantly dicalcium silicate (Ca₂SiO₄). This was followed by a complex mixture of calcium/magnesium-wustite (CaFeMnMg)O type phases and srebrodolskite (Ca₂Fe₂O₅(Ti, V)). Results indicate that calcium silicate is the more reactive component of BOS slag, while lime bound as (CaFeMnMg)O is most reactive in HMD and SS slags. Selectivity of the ammonium chloride solvent was high at 95–97% and efficiency of calcium extraction ranged between 25% and 39%.     

A mechanistic model to predict matte temperatures during the smelting of UG2-rich blends of platinum group metal concentrates

High matte temperatures can be related to numerous catastrophic furnace failures in the platinum group metal (PGM) industry where chromite-rich upper group 2 (UG2) concentrates are smelted. Chromite rich concentrates require high slag temperatures as well as sufficient mixing to suspend the chromite spinel particles in the slag and prevent settling in a so-called “mushy” layer consisting of a three phase emulsion of slag, matte and chromite particles. To achieve sufficient bath mixing and to melt and suspend chromite spinel build-up, high hearth power densities are utilised. However, high hearth power densities in conjunction with a heat-isolating concentrate layer, leads to high side wall heat fluxes which motivated the use of intensive cooling in the furnace side wall so that a slag freeze lining can be formed. If matte temperatures are above the slag liquidus temperature, any matte that comes into contact with the freeze lining can destroy the freeze lining. Moreover, if the matte temperature exceeds ca. 1500 °C, chemical thermodynamics indicate that matte has the ability to sulfidise MgO-Fe_xO-Cr₂O₃ refractories, leading to rapid wear of refractories exposed to high temperature flowing matte. Models are derived for the concentrate-to-matte and slag-to-matte droplet heat transfer. Calculations using the derived models, physical properties and furnace operating conditions give realistic matte temperatures and show that matte temperatures rapidly increase as the concentrate bed becomes matte drainage rate limiting. It is shown that for each concentrate blend mean particle size and mineralogy, there is a maximum smelting rate above which the concentrate bed becomes rate limiting with regards matte drainage, thereby significantly contributing to matte preheating, prior to further heat absorption from the slag layer.     

TiO2 对黄金尾砂微晶泡沫玻璃非等温析晶活化能的影响

以黄金尾砂为主要原料,改变原料中晶核剂TiO2的掺量,制备微晶泡沫玻璃.运用差热分析(DSC)、X射线衍射仪(XRD)等分析手段,研究TiO2掺量对微晶泡沫玻璃析晶与发泡的影响.结果表明,随着TiO2含量的增加,析晶活化能呈现出先减小后增大的规律,当TiO2添加量为3.5％时,析晶活化能较小,为95kJ/mol;同时微晶泡沫玻璃析出的主晶相为硅灰石(CaSiO3),次晶相为钙长石(CaAl2Si2O8);当TiO2添加量为3％～4％时,制备得到的微晶泡沫玻璃具有良好的物理性能;主晶相硅灰石(CaSiO3)不随TiO2的添加改变,并且TiO2能促讲晶相牛长.     

Use of oxidation roasting to control NiO reduction in Ni-bearing limonitic laterite

Use of limonitic laterite as an iron source in conventional ironmaking is restricted due to its gangue composition and small particle size. Even direct reduction cannot effectively produce direct reduced iron (DRI) because NiO would be reduced together with iron oxide to form Fe–Ni. A small amount of Ni (about 2 wt.%) in DRI degrades the physical properties of final steel products. The current study investigated how oxidation roasting of limonitic laterite ores affected NiO reduction, with the goal of producing Ni-free DRI and Ni-bearing slag. Ni-bearing slag can be a good secondary Ni resource. Oxidation roasting made NiO inert under H₂ reduction at 900 °C by forming Ni-olivine. Optimum roasting temperature was proposed by examining phase transformation of limonitic laterite ores during heating and by FactSage calculation of the equilibrium Ni fraction in Ni-bearing phases. Furthermore, the effect of Mg–silicate forming additives on the control of NiO reducibility was clarified to maximize the suppression of NiO reduction. Among various additives such as MgSiO₃, Mg₂SiO₄ and Fe–Ni smelting slag, Ni-free olivine-typed flux was found to be the most effective form of Ni-olivine because Ni–Mg ion exchange between Ni-bearing phase and Ni-free olivine occurs more readily than other Ni-olivine formation schemes. Finally, the mechanism of Ni-olivine formation during roasting was studied using a diffusion couple test. Calculated diffusivity values of Ni in Mg₂SiO₄ indicated that the two major routes of Ni-olivine formation while roasting limonitic laterite ore are (1) Ni partitioning within Mg–Ni silicate before crystallization and (2) Ni diffusion from spinel to Ni free olivine after crystallization.     

特殊钢尾渣泡沫混凝土的制备与性能研究

以特殊钢尾渣为主要原料制备泡沫混凝土,利用SEM、MIP、FT-IR、XRD对其表征,研究了特殊钢尾渣用量和发泡剂用量对特殊钢尾渣泡沫混凝土性能的影响。结果表明,特殊钢尾渣泡沫混凝土中特殊钢尾渣作为非活性掺合材料,主要起到填充作用;当发泡剂用量为340 g时,特殊钢尾渣泡沫混凝土发泡效果较好、结构较为均匀,28 d干密度达到设计要求;特殊钢尾渣被包裹,不仅提高了特殊钢尾渣泡沫混凝土力学性能,而且增强了特殊钢尾渣泡沫混凝土应用性和安全性。     

熔融钒渣钙化及酸浸过程动力学研究

针对现有转炉钒渣钙化工艺中存在流程长和能耗高的弊端,本研究直接利用转炉中熔融钒渣的热量,在分离出半钢后,向熔融钒渣中加入氧化钙,使含钒物相发生钙化转型生成易溶于酸的钒酸钙。熔融钒渣可能发生的化学反应的热力学结果由Factsage8.1软件计算得到。研究过程中采用XRF、ICP、XRD和SEM/EDS等技术进行表征。XRD结果表明,随着CaO添加量的增加,熔融钒渣中逐渐形成CaV₂O₅、Ca₇V₄O₁₇、CaVO₃和Ca₃V₂O₈。当CaO添加过多后,也会形成Ca₂SiO₄和CaTiO₃,这些物相会包裹部分钒,降低钒的浸出率。而后对钙化钒渣进行了酸浸提钒试验,考察了钒渣粒度、浸出温度、酸浓度和液固比对钒浸出率的影响,动力学计算结果可知酸浸过程的表观活化能为11.56 kJ.mol_-1^,表明钙化钒渣的酸浸反应为内扩散控制。     

Recovery of titanium compounds from molten Ti-bearing blast furnace slag under the dynamic oxidation condition

A novel technique to recover Titanium compounds from Ti-bearing blast furnace slag under the dynamic oxidation condition was developed and tested. Air was blown into the molten slag as oxygen resource through a lance during the dynamic oxidation process, in which six important results were found: (1) The TiC, (Ti₂O₃), Fe and (FeO) in the slag were oxidized; (2) The temperature of slag temperature rapidly increased; (3) The viscosity of slag decreased; (4) The coalescence, growth and drop of the metallic Fe droplets in the molten slag were carried out under an air agitation condition; (5) The dispersed Ti components were selectively enriched into the perovskite phase, and the perovskite phase could be selectively precipitate and grow; (6) The perovskite phase can be separated by the dressing method, and also these concentrates can be used as the production of the titania enriched material by hydro-metallurgy method. The oxidation of molten slag gives off a large amount of heat, which helps chemical reactions proceed, improve the rate of chemical reactions, and promote the precipitation and growth of the perovskite phase. The features of the technique are clean, low cost and a great capacity to deal with a large quantity of slag. It was confirmed by the experiments of 200 g and pilot experiments of 30 and 1200 kg slag that the precipitation of the perovskite (CaTiO₃) in molten slag is obviously affected by operation factors such as temperature, chemical composition, heat-treatment, additives and so on. The precipitating kinetics and mechanism of the perovskite phase from molten slag during the dynamic oxidation processes were also investigated.     

Manipulate an air–cathode fuel cell toward recovering highly active heterogeneous electro-Fenton catalyst from the Fe(II) in acid mine drainage

The recovery of iron oxides from acid mine drainage (AMD) has attracted extensive research attention due to the double advantage of waste minimization and resource recovery. Recently a novel air–cathode fuel cell approach was proposed to in-situ utilize ferrous iron (Fe(II)) in the AMD for the fabrication of Fe₃O₄/graphite felt (GF) composite as the cathode of electro-Fenton process. In the present work, the influence of fuel cell operating parameters, including solution pH, carbonate concentration and Fe(II) concentration, on the catalytic activity of prepared Fe₃O₄/GF composite is adequately elucidated. The highest activity is observed on the composite obtained from the fuel cell operated with 30 mM Fe(II) and 50 mM carbonate at pH 7.5. The activity of Fe₃O₄/GF is strongly dependent upon iron loading and Fe₃O₄ morphology in the composite. Higher iron loading generally induces higher catalytic activity, and the Fe₃O₄ aggregate is catalytically less reactive relative to the well-dispersed one. The precipitation of Fe(III) oxides on the GF through electrochemical oxidation of Fe(II) plays a key role in determining the structure of Fe₃O₄/GF composite. Solution pH and composition in the fuel cell affect such a process by manipulating the distribution of Fe(II) species in aqueous solution and on the GF.     

官能团对起泡性能和泡沫稳定性影响的研究

浮选是分离微细物料的重要方法,起泡剂类型和泡沫稳定性显著影响浮选效果.本文选取醇类(MIBC)、酯类(DEP)和醚醇类(DGBE)三种起泡剂,通过实验研究官能团对起泡性能和泡沫稳定性的影响.实验用Foamscan测定起泡剂溶液的起泡性能和泡沫稳定性,用Tracker流变仪测定表面张力和气液界面黏弹模量.研究结果表明:起...     

Role of silicate phases during comminution of titania slag

Titania slag is the primary product of ilmenite smelting, and serves as a feedstock to the TiO₂ pigment industry. The fine material (smaller than 106 μm in diameter) which is produced during milling of titania slag is enriched in some impurities, notably SiO₂, Al₂O₃, K₂O and CaO. Investigation of microstructures of solidified slags confirmed that these oxides partition to the silicate phases which form during final solidification. The presence of silicates on the surfaces of particles in milled slag supports the suggestion that the silicates contribute to fracture during crushing and milling. No significant macro-segregation was found in the slag ingots.     

复杂铌矿高温还原熔炼-炉渣冷却结晶富集铌试验

针对白云鄂博铁铌稀土复杂多金属矿中铌矿相种类多、性质差异大、难以利用的难题,提出了复杂铌矿高温还原熔炼-炉渣控温冷却定向结晶富集铌新工艺,考察了碱度(CaO/SiO₂比值)、铁还原率、冷却速度对渣中富铌矿相粒度、形貌与组成的影响。结果表明,铌主要富集于铈铌钙钛矿相,碱度是影响结晶矿相组成的关键因素,而铁还原程度不影响结晶矿相组成。降低冷却速度可以有效提高富铌矿相粒度。     

川西坳陷雷口坡组常量元素特征及其意义

通过对川西坳陷丰卤1井雷口坡组岩屑样品的常量元素分析,研究K含量,w(FeO)/w(Fe₂O₃)值特征以及w(MnO)/w(FeO+ Fe₂O₃)值特征,发现雷口坡组K含量变化与深度成正比关系,K含量整体偏小,未能达到钾盐沉积的标志线;w(FeO)/w(Fe₂O₃)值整体小于1,反映出沉积环境为氧化环境,有着干燥、炎热的气候条件;极小的w(MnO)/w(FeO+ Fe₂O₃)值（<1）不仅反映了氧化的沉积环境和干热的气候条件,还反映了较浅的水体环境。干燥炎热的气候条件以及浅水的次级构造条件都指示着川西坳陷雷口坡组具备良好的钾盐沉积条件,最后建立w(FeO)-w(Fe₂O₃)-w(MnO)判别图,判别图包含3个区域,分别为湿冷深水区、干热浅水区以及湿冷浅水区,发现雷口坡组属于干热浅水区。